Everything is so harmoniously arranged by nature that in this world everyone has his own place and is engaged in those functions that are entrusted to him, be it the crown of nature - an incredibly complex human or the most microscopic organism. Everyone plays their part to make our world a better place. This also applies to various bacteria, which, according to the great plan of the creator of the world, bring people not only benefit, but also certain harm. Let's consider what thermophilic lactic acid bacteria are and what their place is in our life. Are they good or bad?

Features and essence

A whole army of various microorganisms lives on our planet, which are invisible to the eye, but very active and not always useful. One of these useful micro-formations is the thermophilic bacterium. The bacterium lives in hot springs and multiplies at rather high temperatures - above 45 degrees. Whole colonies of these microorganisms have been identified in different geothermal zones of our planet, such as the waters of natural hot springs. Thermophilic bacteria survive due to the presence of special enzymes in them that can function at high temperatures. For them, the most favorable temperature regime is a corridor of 50-65 degrees. Under these conditions, bacteria can feel comfortable and multiply freely.

Many would like to know at what temperature thermophilic bacteria die in order to control their number. In this regard, I would like to note that scientists have not yet been able to obtain accurate data on this. At the present stage of the development of science, it is only known that the maximum temperature for thermophiles is 68-75 degrees. However, this does not mean that bacteria die with such heating - a deviation from the optimal regime makes their life less comfortable and intense, slows down cell growth and reduces the rate of metabolic processes.

Is it possible to kill bacteria? What is detrimental to them?

For thermophilic bacteria to die, a much higher upper threshold must be exceeded. Today, scientists have established that the highest currently known temperature at which these microorganisms can live is 122 degrees Celsius. It is not possible to create higher heating under laboratory conditions. Therefore, it is not yet possible to establish at what temperature the thermophilic bacteria will die. It is only known that sharp temperature fluctuations have a very detrimental effect on the life of bacteria: the development of a culture may stop, but whether it dies is a question.

Varieties and their description

Evaluating the temperature preferences of microorganisms, they can be divided into three main groups: psychrophilic, mesophilic, and, in fact, thermophilic. All of them are dependent on heat, but differ in terms of temperature conditions.

So, psychrophilic bacteria are the least thermally dependent and prefer the temperature range from zero to +10 degrees. This is the optimal development corridor for them, but they can reproduce both at -5 degrees and at +15.

Next - mesophilic thermophilic bacteria, the comfort zone for which is located between 30 and 40 degrees Celsius. Bacteria may well grow and multiply when the temperature drops to 10 degrees or rises to 50 degrees. The optimum growth rate for these organisms is 37 degrees.

And finally, thermophilic bacteria - their active growth is observed when the temperature reaches above 50 degrees. Their main distinguishing feature is the accelerated metabolic rate. In accordance with recent studies, it has been established that under the influence of temperature, significant changes occur in proteins and lipids, which play a major role in all life processes.

Subgroups of thermophilic

This is clearly illustrated by examples of thermophilic bacteria, which are also divided into several independent subgroups:

• Extreme thermophiles with an optimal temperature of 80 degrees with a minimum of 60 and a maximum of 105 degrees.
• Stenothermophiles, or optional, with a range of 55-65 degrees, but show the ability to reproduce even when the temperature drops to 20 degrees. The highest growth ability is observed at 20-40 degrees.
• Eurythermophiles prefer 37-48 degrees. The peculiarity of obligate thermophiles is that they do not lose the ability to grow at 70 degrees, but do not grow below 40 degrees.
• Thermotolerants with an optimal indicator not higher than 48 degrees, the minimum temperature at which they can grow is 10 degrees, and the maximum is 55-60. They differ from mesophiles at the same optimum temperatures in that when the temperature threshold rises, bacteria continue to grow.

Anaerobic thermophiles

The ability of thermophilic organisms to grow rapidly gives them an excellent opportunity to be used in various spheres of life - in industry or agriculture, and even at the household level. At the same time, mesophilic and thermophilic lactic acid bacteria have similar methods of isolation. The difference is only observed in growing temperatures. To establish the exact optimum temperature level, the culture must be passaged for one to two months, or, in other words, re-sowed in a certain temperature range.

In nature, they are widespread and in different conditions many types of thermophilic bacteria live. They love warmth and feel very comfortable in the human stomach, and can also be found in animals, plants, soil, water and various other environments that provide favorable temperature conditions for development. Some bacteria require the presence of air for development, while others do not need oxygen at all. On this basis of dependence on oxygen, thermophilic organisms are divided into aerobic and anaerobic.

Several separate groups belong to anaerobic:

• Butyric acid - during fermentation, they produce butyric acid, feed on sugar, pectins, dextrins, and produce acids - acetic and butyric, as well as hydrogen and carbon dioxide. From useful properties the production of acetone, ethyl, butyl and isopropyl alcohols can be distinguished. It occurs in thermophilic and mesophilic forms.
• Cellulosic ones live in river silt, compost, plant residues. These thermophilic compost bacteria are ideal and widely used in the agricultural field. Being in soil or humus, these bacteria gain activity at 60-65 degrees. There is also a mesophilic form - Omelyansky's stick. These bacteria, with the help of a special enzyme, decompose cellulose, while releasing carbon dioxide, hydrogen, ethyl alcohol, and a number of acids - formic, acetic, fumaric, lactic and other organic acids.
• Methane-forming ones live in the same place as cellulosic ones, and are cultivated in the same place. In this group, the most studied species are methanobacterium and methanobacillus. They are not capable of sporulation, and their use lies in the ability to produce antibiotics, vitamins, enzymes, using wastewater and household waste for nutrition.
• Desulfurizers are most often found next to cellulosic ones and live by reducing sulfates. They have oval spores, which are located closer to one of the ends of the bacillus bacillus, - terminal or subterminal.
• Lactic acid - a special large group of bacteria that live in milk. These thermophilic lactic acid bacteria can be both useful to humans and very harmful. Some of their types can synthesize special aromatic substances. It is they who, after exposure to milk, give pleasant taste and the flavor of curd or cream. Such thermophilic lactic acid bacteria are facultative anaerobic bacteria, therefore, they can optimally multiply in the absence of oxygen or in an environment where it is very deficient.

Lactic acid

Lactic acid bacteria are divided into cocci and rods. The first ones consist of several cells connected in a chain - streptococci and have homo- and heterogeneous fermentation. Homofermented streptococci ferment the sugar in milk, making it live yogurt. In parallel, heterofermentals also release such aromatic substances as diacetin and cytoin. Their cells are round or oval in shape, stain well according to Gram and do not form spores and capsules. They are classified as aerotolerant and can exist in the presence of air. However, they lack the ability to carry out aerobic respiration, and they prefer to continue the process of lactic acid fermentation they are used to. In order to eat, they need a lot of vitamins, proteins, organic acids. In milk, bacteria cause it to coagulate, forming a dense, even clot with a small amount of whey. It is thanks to the aromatics in the cheese that seductive bubbles with a characteristic odor and a low ability to form acids appear. Cocci are highly alcohol-resistant and require high acidity.

Lactic acid sticks

Lactic acid sticks - they are otherwise called lactobacilli - can be either single or paired. Most often, acidophilic lactobacilli are used, especially which is a part of starter cultures and makes it possible to produce tasty and healthy yogurt. Streptobacteria and beta bacteria are also popular in the dairy industry. These organisms are completely immobile and do not form spores or capsules, they are stained according to Gram well.

Lactic thermophiles are facultative anaerobes. They can become monoenzymatic, with a high rate of acidification, or heteroenzyme with the ability to process fructose in parallel, resulting in the formation of six-alcohol mannitol alcohol, acetates, lactates and carbon dioxide gas. They process proteins rather poorly, therefore, in order to grow, they require the presence of amino acids in the environment. Some sticks have the ability to produce catalase, an enzyme that breaks down hydrogen peroxide, or acetaldehyde, which gives the cheese smell and taste.

Heat-resistant lactic acid sticks can survive in milk when pasteurized at a temperature of 85-90 degrees. They are very resistant to disinfecting agents and thus bring considerable harm to the food industry. They are antagonists of Escherichia coli. Found in starter cultures or low-pasteurized milk.

Thermophiles who can't breathe without oxygen

Aerobic thermophiles, which cannot breathe without oxygen, are also divided into two distinct groups:

• Extreme thermophilic are gram-negative bacilli that cannot move, which are obligate bacteria that grow at an optimum temperature of 70 degrees. When the temperature rises higher, the sticks are transformed into thin strands. They live in large quantities in hot water springs and nearby soil.
• Spore-forming ones have forms similar to mesophilic ones. They live and spread in well-loosened soil or aerated waters.

Having considered all these types of microorganisms, it should be noted that the appearance of thermophilic bacteria is their aromorphosis into the habitat. Like other living organisms, bacteria can also perfectly adapt to changes in environmental conditions during their evolution. At the same time, they significantly increase the level of their organization and acquire new abilities.

Benefit and harm

What are the Harm and Benefits of Thermophilic Bacteria? Lactic acid sticks used in the food industry bring undoubted benefits to humans. As a part of various ferments, they produce tasty and healthy lactic acid products that have a very positive effect on all systems of the human body, help to regulate metabolic processes, normalize the digestive tract and in every way help to protect the body from various putrefactive bacteria, cleansing it in parallel from accumulated toxins and slags. In addition to improving the composition of microflora, thermophilic bacteria calm the nervous system, suppress the effect of antibiotics and increase immunity.

In addition to the food industry, this type of bacteria is used quite widely in the pharmacological and cosmetic fields. On their basis, various probiotics are made, as well as cosmetic products that give the skin well-groomed and elasticity, and are also used to whiten and restore it. Live yogurt masks can work wonders.

Thermophilic and mesophilic bacteria that live in soil and compost help recycle organic matter, fertilizing the soil for good plant growth. The released methane can be successfully used for heating residential buildings and industrial facilities. With such a huge scale of benefits, the small harm that thermophilic sticks deliver to food industry enterprises is leveled by the effect of bactericidal drugs and constant monitoring of food production equipment.

Conclusion

In this article, we have given the basic concepts of such a large and poorly understood class of bacteria. It follows from the above material that thermophilic bacteria are already widely used by humans for their own good. But this process is far from complete, and many more pleasant and useful discoveries await us.

Mesophils are representatives of various groups of bacteria: spore-forming bacteria of the genera Bacillus and Clostridium, non-spore-forming bacteria of the genus Proteus, many staphylococci, etc.

Mesophiles are the main part of bacteria that colonize food and pose the greatest danger. These bacteria are widespread in soil, dust, food processing air, processed foods and food products... The danger is compounded by the fact that many mesophils form heat-resistant spores.

Clostridium bacteria. Movable rods (peritrichs), anaerobes, form spores. Some are non-strict anaerobes and can grow not only inside but also on the surface of food. Of the 60 known species of this genus, about 30 can reproduce in food products. According to their biochemical properties, all clostridia are divided into putrefactive (possess proteolytic enzymes) and fermentative. Two types can cause food poisoning.

Putrid (proteolytic) clostridia decompose gelatin, proteins of milk and dairy products, meat, fish, loosen them, sometimes form a black pigment. The breakdown of proteins is called proteolysis, hence the name of these bacteria. Clostridial spores are extremely heat-resistant. Thanks to a large set of enzymes, Clostridia can ferment carbohydrates. Under their influence, milk coagulates, gelatin liquefies. Proteolytic clostridia can develop in a wide temperature range - from 16 to 50 ° C. When they multiply, volatile substances accumulate in the products, giving a putrid smell.

Clostridia of the Perfringens species are also causative agents of food spoilage. The consistency of the product becomes loose, crumbling, its color changes, a sour smell appears, swelling and bombardment of canned food is observed. These bacteria seed meat, milk (in fermented milk products they are not), flour, cereals, fish, cause food poisoning when toxins of bacteria enter the human digestive tract with food or gas gangrene when bacteria penetrate into muscle tissue as a result of injuries and wounds.

Saccharolytic clostridia include butyric spore-forming bacteria with spores located at the end of the cell. They are able to ferment carbohydrates, and during their development, oil and acetic acid products that have an unpleasant odor turn sour, gases accumulate in them. These bacteria are widespread in plant materials and dairy products. Their spores are less heat-resistant than proteolytic clostridia, but more acid-resistant. They are also found in canned vegetables and products processed at temperatures of 105 ° C and below, and cause spoilage. Food poisoning is caused by eating fish and canned meat, smoked and salted foods containing living bacterial cells or their toxins. Clostridial spores can be kept alive in tomato products, canned vegetables and fruit, which are pasteurized or sterilized at temperatures of 105 ° C and below.

Bacillus bacteria. Mesophilic spore-forming bacteria live in the soil, spread with dust and get onto raw materials, equipment and products. According to their physiological properties, bacteria of the genus Bacillus can be divided into two groups:

bacteria that form gaseous products during the decomposition of carbohydrates. They can ferment carbohydrates, organic acids and alcohols to form acetic and formic acids, alcohol, carbon dioxide and hydrogen. This group includes Bacillus polymix and Bacillus macerans, resistant to high acidity and high sugar concentrations.

Thanks to these properties, they can multiply in products with a pH of 3.6 and higher, containing up to 25% sugar. In some cases, Bacillus polymix develops in fruit syrups with a sugar content of 25-40%;

bacteria that do not produce noticeable amounts of gas during the fermentation of carbohydrates, but accumulate acids. These bacteria are found in a variety of foods. They belong to the group Bacillus subtilis (hay bacillus), which is widespread in nature and produces mainly lactic acid. Rods develop in a wide temperature range - from 5 to 55 ° C. Many are resistant to high temperatures. Bacillus subtilis is often found in residual microflora after food canning (about 60% of this microflora is mesophilic).

Bacillus cereus is a mobile bacillus, widespread in the external environment; the optimum for bacterial growth is 30 ° C. The main habitat is soil, from where they enter the air and water bodies. Upon contact with food, they develop rapidly and their number can be hundreds and thousands of cells per 100 cm 2 of the surface. Seeds culinary products, starch, raw milk, confectionery, dairy products, nutritional supplements, canned food, fruits. The most contaminated with bacteria are vegetables that are in close contact with the soil. In food, spores begin to germinate at pH 5.5 and above. Some types of bacteria can thrive in an environment containing 8-15% sodium chloride.

Eating products containing 1 g of 10 6 cells of Bacillus Cereus poses a danger to human health, as it causes food poisoning.

Mesophilic bacteria can also spoil food in refrigerated storage.

Proteus bacteria. Representatives of the Proteus genus are small cells that can change shape from rods to cocci, and under certain conditions they form threads and other forms. These bacteria are mesophiles, facultative anaerobes, are mobile (peritrichous), do not form spores. The temperature range of development is 10-43 ° C.

In environments with carbohydrates, they form gases and acids, in protein environments they cause putrefaction (proteolysis).

Non-spore-forming bacteria. Among the mesophilic microbes, there are also non-spore-forming bacteria from the lactobacillus family, which are widespread in nature and play a role in the food industry. They develop in the temperature range from 8 to 42 ° C with an optimum of 25 to 30 ° C. Found in dairy, grain and meat products, on equipment of dairies, in water, waste water, beer, wine, fruits and fruit juices, pickles, starter cultures for dough, etc. The spoilage of fruit juices, canned food, wines and other products is caused by bacteria that develop at a temperature of 12 ° C and above.

To obtain high-quality and stable fermented milk products, starter cultures are added to milk. Starter cultures- pure cultures or a mixture of pure cultures of lactic acid bacteria.

Classification of fermented milk products

Depending on the composition of the microflora of the starter cultures, fermented milk products are divided into 5 groups:

1. Products prepared using multi-component starter cultures

These products include kefir and koumiss, which are prepared using a natural symbiotic starter culture - kefir fungus... Kefir fungi are a strong symbiotic formation. They always have a definite structure and pass on their properties and structure to subsequent generations. They have an irregular shape, strongly folded or bumpy surface, their consistency is elastic, soft-cartilaginous, sizes from 1-2 mm to 3-6 cm and more. The kefir fungus contains a number of lactic acid bacteria: mesophilic lactic acid streptococci of Streptococcus lactis, Streptococcus cremoris species; aroma-forming bacteria of the species Streptococcus diacetylactis, Leuconostoc dextranicum; lactic acid sticks of the genus Lactobacillus; acetic acid bacteria; yeast. Microscopic examination of sections of kefir fungus reveals close interlacing of rod-shaped filaments that form the stroma of the fungus, which holds the rest of the microorganisms.

Mesophilic lactic acid streptococci provide active acidification and clot formation. Their number in the finished product reaches 10 9 in 1 cm 3.

Aroma-forming bacteria develop more slowly than milk and creamy streptococci. They form aromas and gases. Their number in kefir is 10 7 -10 8 in 1 cm 3.

The number of lactic acid sticks in kefir reaches 10 7 -10 8 in 1 cm 3. With an increase in the duration of the fermentation process and at elevated temperatures, the number of these bacteria increases to 10 9 per 1 cm 3, which leads to peroxidation of the product.

Yeast develops much more slowly than lactic acid bacteria, therefore, an increase in their number is noted during the ripening of the product and is 10 6 in 1 cm 3. Excessive yeast development can occur at elevated fermentation temperatures and prolonged exposure of the product at these temperatures.

Acetic acid bacteria, which are contained in kefir in an amount of 10 4 -10 5 in 1 cm 3, develop even more slowly. Excessive development of acetic acid bacteria in kefir can lead to the appearance of a slimy viscous consistency.

The process of fermentation and maturation of kefir is carried out at a temperature of 20-22 0 С for 10-12 hours.

2. Products prepared using mesophilic lactic acid streptococci

These products include cottage cheese and sour cream. When preparing these products, the milk fermentation process is carried out at a temperature of 30 0 C for 6-8 hours. The microflora of these products includes homofermentative streptococci: Streptococcus lactis, Streptococcus cremoris; heteroenzymatic aroma-forming streptococci: Streptococcus diacetylactis, Streptococcus acetoinicus and aroma-forming leukonostoks of the species Leuconostoc dextranicum. Their number in the finished cottage cheese is 10 8 -10 9 cells per 1 g, in sour cream - 10 7 cells per 1 g.

3. Products prepared using thermophilic lactic acid bacteria

Using thermophilic lactic acid bacteria, yoghurt, yogurt, fermented baked milk and varenets are prepared. The fermentation process is carried out at a temperature of 40-45 0 С for 3-5 hours.

The composition of microflora yoghurt and curdled milk includes thermophilic streptococcus (Streptococcus thermophilus) and bulgarian bacillus (Lactobacillus bulgaricus) in a ratio of 4: 1 ... 5: 1. A symbiotic culture of these microorganisms is also used. The content of thermophilic streptococci and Bulgarian bacillus in 1 cm 3 of the product is 10 7 -10 8.

In production ryazhenka and varenza use a ferment of thermophilic lactic acid streptococcus in the amount of 3-5%. Sometimes a Bulgarian stick is added. The content of thermophilic streptococcus in 1 cm 3 of the product is 10 7 -10 8 cells.

4. Products prepared using mesophilic and thermophilic lactic acid streptococci

These products include sour cream, milk-protein paste, cottage cheese produced by the accelerated method, as well as low-fat drinks with fruit and berry fillers. Milk fermentation is carried out at temperatures of 35-38 0 С for 6-7 hours.

Microorganisms leading lactic acid processes are mesophilic and thermophilic streptococci. Mesophilic streptococci carry out the active course of the lactic acid process and are involved in ensuring the water-holding capacity of the clot. Their number in 1 cm 3 of the product is 10 6 -10 8 cells. The main function of thermophilic streptococci is to provide the necessary viscosity of the clot, its ability to retain serum and restore the structure after mixing. Their content in the product is 10 6 -10 8 cells per 1 cm 3.

5. Products prepared using acidophilus sticks and bifidobacteria

These are products for therapeutic and prophylactic purposes. These include: acidophilic milk, acidophilus, acidophilus-yeast milk, acidophilic paste, acidophilic infant formula, fermented milk products using bifidobacteria.

Use of bacteria of the genus Lactobacillus acidophilus in the production of products for children and diet food due to the ability of these bacteria to secrete in the process of vital activity specific antibiotic substances that suppress the growth of bacteria of the group of E. coli, dysentery bacillus, salmonella, coagulase-positive staphylococci, etc. The bactericidal properties of acidophilus are enhanced in the presence of lactic acid.

Acidophilic milk prepared by fermenting pasteurized milk with pure cultures of acidophilus sticks. Acidophilic the paste is produced from acidophilic milk of a certain acidity (80-90 0 T) by pressing part of the whey. Acidophilus is produced from pasteurized milk, fermenting it with a ferment consisting of acidophilic sticks, lactic acid streptococci and kefir ferment in equal proportions. When preparing acidophilic yeast milk, in addition to acidophilic rods, yeast of the type Saccharomyces lactis is included in the starter culture.

The main defect of fermented milk products using acidophilic sticks is product peroxidation. This occurs when no rapid cooling of the product is carried out.

Foods fortified with bifidobacteria characterized by high dietary properties, as they contain a number of biologically active compounds: free amino acids, volatile fatty acids, enzymes, antibiotic substances, micro- and macroelements

Currently, a wide range of dairy products with bifidobacteria are produced. All these products can be conditionally divided into three groups. To the first group includes products into which viable cells of bifidobacteria, grown on special media, are introduced. The multiplication of these microorganisms in the product is not provided. To the second group include products fermented with pure or mixed cultures of bifidobacteria, in the production of which the activation of the growth of bifidobacteria is achieved by enriching milk with bifidogenic factors of various nature. In addition, you can use mutant strains of bifidobacteria, adapted to milk and capable of growing under aerobic conditions. Third group includes products of mixed fermentation, most often fermented by joint cultures of bifidobacteria and lactic acid bacteria.

Microbiological control of the production of fermented milk products

Microbiological control of the production of fermented milk products consists in monitoring the technological process, sanitary and hygienic control of production conditions and finished products.

When monitoring technology, the effectiveness of milk pasteurization is checked at least once every 10 days.

Particular attention is paid to quality control of the starter cultures for the presence of E. coli bacteria, taking samples from the pipeline when feeding the starter culture into the bath (BGKP is not allowed in 10 cm 3 of the starter culture). Also investigate the mixture after fermentation and fermentation. In the latter case, samples are taken from a bath, reservoir or bottle using a thermostatic production method. Determine the presence of BGKP, which should not be contained in 1 cm 3.

Control technological processes fermented milk products are produced once a month.

Finished products control for the presence of BGKP (bacteria of the Escherichia coli group), and, if necessary, on a microscopic specimen at least once every 5 days. BGKP are not allowed in 0.1 cm 3 of kefir, curdled milk, yogurt, acidophilus-yeast milk and other fermented milk drinks. In sour cream of 20% and 25% fat content, BGKP should not be found in 0.01 cm 3, in cottage cheese - in 0.001 g. In cottage cheese, the content of Staphylococcus aureus is also normalized (not allowed in 0.01 g). Pathogenic microorganisms, including salmonella, are not allowed in 25 cm 3 (g) of all types of fermented milk products.

When the microbiological indicators of the finished product deteriorate, additional control of technological processes is carried out to establish the reasons that affect the quality of the product.

Defects of fermented milk products and the reasons for their occurrence

The defects of fermented milk products are caused by the development of extraneous microflora, which may be associated with both insufficient activity of starter cultures and with the development of residual microflora of pasteurized milk.

Most common vices of fermented milk products are:

Bloating

It occurs when yeast and bacteria of the Escherichia coli group develop in fermented milk products. The presence of BGKP testifies to the low sanitary state of production.

Slow fermentation

It is observed when the activity of the ferment is weakened, due to the use of low quality milk or the development of a bacteriophage. Slow fermentation can lead to the development of foreign microorganisms that cause changes in taste and odor.

Too fast ripening

Most often, this defect is observed in kefir and sour cream in the warm season at enterprises where normal temperature conditions for fermentation are not created. At the same time, the acidity of the product increases intensively, the clot in kefir is flabby, and strong gas formation occurs in the product.

This defect can also be caused by the development of heat-resistant lactic acid sticks, which are the residual microflora of pasteurized milk.

Smell of hydrogen sulfide

Hydrogen sulfide accumulates due to the decomposition of milk proteins. The defect usually occurs in spring or autumn (with a weakening of lactic acid fermentation) and is associated with the development of Escherichia coli and putrefactive bacteria. If this defect occurs, it is necessary to change the leaven.

Slime, viscidity

The stringiness of the clot in fermented milk products can be caused by the development of acetic acid bacteria and the appearance of mucousness in lactic acid bacteria. To prevent this defect, it is necessary to exclude the possibility of kefir starter culture entering milk processed into other types of dairy products.

Mold growth

It occurs during prolonged storage of the product in a refrigerator.

If you are interested in the purchase of starter cultures for the production of fermented milk products in Uzbekistan, you can on our website in the section by clicking on.

Lactobacillus bulgaricus(bulgarian stick)- the bacterium is so named because at one time it was isolated from the Bulgarian sour milk "Yagurt". A non-motile, immobile bacterium, reaching 20 µm in length and often joining in short chains (Fig. 2.2). It is thermophilic and grows best at temperatures from 40 ° C. Milk coagulates quickly, and the lactic acid content in it reaches 32 g / l.

Rice. 2.2.

Streptococcus thermophilus (thermophilic streptococcus) - often found in milking equipment, milk dishes and raw milk. Resistant to short-term pasteurization, but dies during high-temperature pasteurization. Thermophilic streptococcus, like Streptococcus cremoris, is a long chain (Fig. 2.3).

The optimum temperature for its development is 40-45 ° C. He teamed up with Lactobacillus bulgaricus used for the preparation of yoghurt and as a culture component for the preparation of Emmental cheese.

Streptococcus thermophilus is extremely sensitive to penicillin and some antibiotics and therefore is used as a test microbe for the biological determination (detection) of antibiotics in milk.

Rice. 2.3. Thermophilic lactic acid bacteria: Streptococcus thermophilus and Lactobacillus bulgaricus

Lactobacillus acidophilum (acidophilus bacillus)- isolated from the intestines in 1922, ferments milk in 24 hours.

Use of bacteria of the genus Lactobacillus acidophilus in the production of baby food and dietary food due to the ability of these bacteria to secrete in the process of life specific antibiotic substances that suppress the growth of bacteria of the E. coli, dysentery bacillus, salmonella, coagulase-positive staphylococci, etc. The bactericidal properties of acidophilus are enhanced in the presence of lactic acid.

Rice. 2.4.

Propionic acid bacteria (Propionobacteria, Propionibacterium) - non-spore-bearing gram-positive immovable rod-shaped bacteria that reproduce by binary fission, facultative anaerobes, 0.5-0.8 or 1.0-1.5 microns in size (Fig. 2.5).

Rice. 2.5.

Propionic acid bacteria live in the intestinal tract of ruminants and often appear in raw milk. Proionic acid bacteria are used in the food industry (bakery, cheese making), as well as in the microbiological industry as producers of vitamin B12.

Lactobacterium helveticum- long rods, located in the form of separate cells and chains. It grows at 22-50 ° C, the optimum temperature for development is 40 ° C. It grows in the presence of 2 or 5% sodium chloride in the environment. The maximum acidity of milk reaches 300-350 ° T.

Widely distributed in nature. It can be isolated from soil, decaying organic matter and plants (Figure 2.6). Used in production blue cheeses, antifungal drugs, polysaccharides, proteolytic and other enzymes. Mushroom is an integral part of cheeses such as Roquefort, Stilton, Danish blue and other blue cheeses.

Rice. 2.6.

Penicillium camemberti- a special type of cheese mold used for the production of soft, fatty cheese Camembert, made from cow's milk(fig. 2.7).

Rice. 2.7.

The cheese has a color from white to light creamy, the taste is spicy, piquant, a bit like mushroom. Outside, Cammbert is covered with a fluffy white crust formed PenicUlium camemberti or PenicUlium candidum.

It is believed that the first Camembert was made in 1791 by a Norman peasant woman, Marie Harel. According to legend, during the French Revolution, Marie Harel saved from death a monk who was hiding from persecution, who in gratitude revealed to her the secret of making this cheese known only to him.

However, Goth cheese, now called Camembert, did not appear until the late 19th century. In 1890, engineer M. Riedel invented a wooden box that was used to transport this cheese and made it possible to transport it over long distances, especially in the USA, where it became very popular. These boxes are still in use today.

Thermophilic microorganisms are rod-shaped and form spores. The ability of thermophilic microbes to form spores is considered as an adaptation to the conditions of the environment in which they live. This is natural, since during the reproduction of thermophiles, in a number of cases, a temperature is formed that exceeds the maximum required not only for reproduction, but also for the very existence of vegetative forms. Spores of thermophiles easily tolerate heating up to 100 ° C for 10-29 and even 50-60 hours. Thermophiles are described that do not form spores.

So, in milk, micrococcus was found that multiplied at temperatures from 20 to 70 °.
Tsiklinskaya isolated a lactic acid bacterium with an optimal growth temperature of 50 ° C. In addition, thermophilic vibrios, spirochetes, filamentous forms are known.
Thermophilic microorganisms require free access of oxygen (aerobes) for their reproduction, but anaerobic thermophiles are also known. Some thermophiles are mobile.
Microorganisms that are capable of reproduction at high temperatures are divided into three groups depending on the temperature limits of their growth (maximum, optimum and minimum).
1. Stenothermal, or true, thermophiles reproduce at a temperature of 75-80 °. The optimum growth temperature is 50-65 °. Do not develop at 28-30 °.
2. Eurythermal thermophiles reproduce at temperatures from 28 to 75 °. The reproductive optimum is the same, i.e. 50-65 °.
3. Thermotolerant thermophiles are able to develop in conditions of wide temperature limits (from 5-10 to 70 °). The optimum of reproduction is 35-45 °.
The second and third groups of microorganisms are often found in nature, while representatives of the first group are found less often. Many microorganisms of southern soils (mesophiles) are close to thermophiles and can develop at temperatures of 50-55 °.

Thermophilic microorganisms feed on a variety of substances. Some of them use only protein substances as food, others assimilate only fatty and aromatic amino acids.

Mishustin proved that some thermophilic bacteria cause the fermentation of urea. Imshenetsky, Egorova et al. Described thermophiles assimilating ammonium nitrogen. Also known thermophilic bacteria assimilating gaseous nitrogen, as well as autotrophic thermophilic bacteria assimilating mineral nitrogen. The possibility of assimilating atmospheric nitrogen by thermophilic microorganisms has not been studied enough.
On mesopatamia agar, many thermophiles form very large colonies, often spreading over the entire surface of the agar plate. Different kinds thermophiles form colonies of different sizes, shapes and structures. Many types of thermophilic microbes liquefy gelatin and release hydrogen sulfide on protein media. They often form indole. Some species peptonize milk, others curdle it; often milk does not change. Many thermophiles decompose sugar, starch and alcohols with the formation of acids - acetic, formic, lactic, butyric; some assimilate fatty acids and aromatic hydrocarbons. For the cultivation of thermophilic microbes, conventional mesopatamia media are suitable.
For their better growth, liver extracts, cystine, as well as extracts of spinach, peas and herbal decoctions are used.
Thermophiles are found everywhere on the globe. The hot springs of the volcanic areas contain them all the time. Many thermophiles are found in the soil of lakes, ponds, and rivers. A huge number of them are found in wastewater and in the sludge of treatment facilities. Very often they live in the intestines of animals, birds, and humans. Thermophiles are also found in the air and food (milk, cheese, canned food). Cultivated soils contain up to 10% of thermophiles from the total number of microorganisms in them. Self-heating of hay, grain, cotton, peat, manure, animal skins and other things is caused by the activity of thermophiles. Prof. E.N. Mishustin proved that the population of the soil with thermophiles depends on the degree of its cultivation and fertilization with manure.
It used to be believed that the southern soils are richer in thermophiles, that the soils of areas with a hot climate are the place of their origin. In fact, it turned out that virgin soils, regardless of their location, are poorer in thermophiles; it was also established that the manured soils of the northern regions contain an enormous amount of thermophiles.
The abundance of thermophilic microorganisms in nature leads to their contamination of feed and various products. Thermophilic microbes penetrate the intestines of animals and humans and, together with excrement, enter the manure, where they multiply. The characteristics of thermophiles depend on the conditions in which they live. When the temperature of the environment rises to 60-70 ° and more, the living conditions of microorganisms change; at the same time, firstly, the solubility of gases (carbon dioxide, nitrogen, hydrogen, ammonia, methane) decreases; secondly, the viscosity of liquids decreases and their osmotic pressure increases. As the temperature rises, the rate of chemical and enzymatic processes increases, and the effect of the resulting toxic products accelerates and intensifies. These phenomena determine the physiological characteristics of thermophiles. Thermophilic microorganisms grow at elevated temperatures much faster than other microorganisms. The functions of thermophiles, such as movement, respiration and the transformation of nutrients, are performed much faster in them than in other types of microbes. At low temperatures, microbial cells are dormant; as it rises, they begin to share. The division of each microbial cell takes place in a few minutes. The multiplication of microorganisms is accelerated with an increase in the temperature of the environment to the limits of their inherent optimum. However, even after the cessation of growth, continuing enzymatic processes cause a further increase in the temperature of the manure. Their qualitative composition largely depends on the characteristics of the organic matter on which thermophiles live. Thus, cellulosic thermophiles develop in cotton, straw and straw manure, proteolytic ones develop in warming skins, etc.

Microbiological processes of decomposition of organic substances, depending on temperature conditions, can proceed under the influence of mesophilic microorganisms (at normal temperatures), and at elevated ones, under the influence of thermophiles. Physiologically, thermophiles are forms similar to mesophiles. It is considered likely that the adaptation of mesophiles to reproduction under high temperature conditions changes their species characteristics, as a result of which the similarity with the original form is largely lost. Some well-known bacterial species do not have thermophilic races. There are many transitional forms between mesophilic and thermophilic microorganisms, and some mesophiles have individual properties or traits that are very characteristic of thermophiles (for example, extremely fast reproduction on nutrient media).

Prof. A.A. Imshenetsky believes that thermophilic microorganisms have such characteristic features that this allows them to be distinguished into an independent group, united by the following properties:
1) thermophilic cells are able to assimilate and dissimilate at high temperatures, which is based on the physicochemical characteristics of their proteins;
2) thermophiles have the ability to multiply extremely quickly, but at the same time their cells also rapidly age and die;
3) thermophiles are characterized by high biochemical activity.

There are several hypotheses to explain the origin of thermophilic microorganisms. Microbiologists believe that microorganisms, adapting to environmental conditions, by virtue of the laws of evolution, change their heredity. The adaptation of microorganisms to existence at high temperatures, i.e. the transformation of mesophilic microorganisms into thermophilic ones, occurs constantly in nature. In the same way, the reverse transformation of thermophilic microorganisms into mesophilic microorganisms can take place with a persistent change in the temperature regime of the external environment in the direction of its decrease.
Experimental work of a number of authors is known who succeeded in laboratory conditions to increase to a large extent the limiting temperature of growth of various microbes.
There is a large amount of material collected by microbiologists confirming the correctness of the hypothesis explaining the origin of thermophilic microorganisms from mesophiles by the adaptation of the latter to high temperatures.
This hypothesis, called the adaptation hypothesis, is based on the materialistic teaching of Michurin biology about the influence of external conditions on the change in the hereditary substance. “External conditions, being included, assimilated by a living body, become no longer external conditions, but internal, i.e. they become particles of a living body and for their growth and development already require that food, those conditions of the external environment, which they themselves were in the past ”. Thus, mesophilic microbes, assimilating living conditions at high temperatures, change the type of metabolism, lose their conservative features, change their heredity and turn into thermophiles.
Self-heating of organic residues is closely related to the reproduction and biochemical activity of thermophiles. The number of thermophilic microbes in fresh manure is relatively small. It is equal to approximately 1-4% of the total number of microorganisms in the manure, while 96-99% are mesophilic microbes that can multiply at relatively low temperatures. But with strong heating of organic substances, the number of thermophiles reaches 73% or more, and the number of mesophiles decreases.
According to Tukalevskaya, the number of mesophilic microorganisms in this sample of compost reached 173 million, but this number of mesophiles decreased to 7 million in the very first week after biothermal heating of the compost. According to our observations, a decrease in the number of mesophiles during heating of manure is a completely natural phenomenon. It is most pronounced in the first days after the temperature rises to 60-70 ° (Table 4). Table 4 shows that the number of thermophiles in fresh manure does not exceed, with some exceptions, one, sometimes several thousand per unit of source material; the exceptions are explained by the fact that the starting material was already in the heating stage. At the same time, the number of microbes capable of multiplying at relatively low temperatures (28-37 °) was enormous.