MICROBIOLOGY Study Guide - 2012

CHAPTER 10. MICROBIAL ECOLOGY

10.4. MICROFLORA OF THE HUMAN BODY

✵ permanent (resident or autochthonous);

✵ transient (allochthonous).

The first group comprises microorganisms that are maximally adapted to life within the host Organism and naturally reside there. These are typically Saprophytes and opportunistic pathogens. Resident microbiota is, in turn, subdivided into obligate and facultative. Obligate microbiota forms the foundation of the microbiocenosis and includes bifidobacteria, lactobacilli, E. coli, and others, whereas facultative microbiota accounts for only a minor fraction of the permanent microflora.

Transient microflora is temporary and non-essential. Its presence is determined by the influx of microbes from the environment and the state of the human immune system.

Skin microflora. A negligible number of various microorganisms can be found On the surface of clean skin. There are fewer than 80,000 microbes per 1 cm² of skin. Normally, this number does not increase due to the bactericidal action of skin factors. Sweat Glands secrete IMMUNOGLOBULINS A, G, Lysozyme, lactoferrin, Fatty acids, and other antimicrobial substances. The substrates that nourish skin-dwelling microbes include excretions from sweat and Sebaceous Glands, as well as epithelial Cells. The skin harbors non-pathogenic staphylococci (Staphilococcus epidermidis, S. saprophyticus), corynebacteria (Corynebacterium xerosis), bacilli (Bacillus subtilis), peptococci, mycobacteria (Mycobacterium fortuitum), as well as Yeast-like Fungi (Candida albicans), and occasionally micrococci; pathogenic and opportunistic S. aureus (in approximately 5% of cases), E. coli, hemolytic and non-hemolytic streptococci, tetanus clostridia, Yeasts, and spores of aerobic and anaerobic bacilli. The skin of the hands is most frequently contaminated with microorganisms. Pathogenic microflora can cause pustular and fungal skin infections.

At food Processing and public catering establishments, SANITARY AND BACTERIOLOGICAL studies of hand washings from service personnel are conducted to test for the presence of coliform Bacteria. The detection of coliforms on hands or other body parts indicates fecal contamination.

Oral microflora. More than 100 species of bacteria inhabit the Oral Cavity. Lactobacilli, streptococci, peptococci, staphylococci, bacteroides, neisseriae, veillonellae, fusobacteria, and corynebacteria are constantly found in the Mouth. In addition, Haemophilus influenzae and spirochetes of the genera Leptospira, Borrelia, Treponema are typically present. Conditions for their development in the oral cavity are highly favorable: the presence of nutrients, appropriate humidity, optimal Temperature, and an alkaline salivary reaction.

The dominant representatives of oral microflora are streptococci: S. salivarius, S. mutans, S. sanguis, as well as hemolytic streptococci. Streptococcal species S. salivarius and S. mutans, which cause dental caries, secrete an enzyme that converts sucrose into a polysaccharide called levan. This polysaccharide deposits on the tooth surface as dental plaque, where acidic products of streptococcal Fermentation—primarily lactic acid—accumulate.

The bulk of microorganisms is localized within dental plaque. Microbes account for up to 70% of dental plaque volume. Saliva plays a major role in regulating the Qualitative and quantitative Stability of the oral microflora. It contains antibacterial substances: lysozyme, lactoferrin, peroxidase, and nuclease. Furthermore, it contains specific secretory immunoglobulins.

Microflora of the respiratory tract. During breathing, A large number of microorganisms enter the human body from the environment. Most of them are trapped in the Nasal cavity thanks to the protective function of the epithelium, The activity of micro- and macrophages, and the bactericidal action of mucin and lysozyme present in nasopharyngeal mucus.

Non-pathogenic staphylococci (S. epidermidis, S. saprophyticus), viridans streptococci (Streptococcus viridans), non-hemolytic (S. pyogenes) and α-hemolytic streptococci, corynebacteria, and many Viruses, including Adenoviruses, are present as permanent residents in the nasal cavity. Transient microflora may include Staphylococcus aureus, streptococci (Streptococcus pyogenes, S. pneumoniae), neisseriae (Moraxella lacunata), and others.

Microflora of the gastrointestinal tract (GIT). The quantitative and qualitative COMPOSITION OF THE GIT microbiota varies significantly depending on the specific section. In The Stomach, due to the acidic reaction of the environment and the high activity of hydrolase-Class Enzymes, conditions for Microbial growth are unfavorable, and their count does not exceed 10³—10⁴ cells per 1 cm³ of content. These are primarily acid-tolerant lactobacilli, Helicobacter pylori, and yeasts. The bactericidal properties of gastric juice create a unique barrier against the penetration of microbes into the intestine. When the pH shifts toward neutrality due to various factors, other bacteria may be present in the stomach in small quantities (Sarcina ventriculi, B. subtilis).

In the Small Intestine, particularly in its upper sections, a small number of microorganisms reside—10⁴—10⁵ per 1 g. The majority (up to 70% in the small intestine) consist of anaerobes. Among them, eubacteria and clostridia predominate. The latter are regarded today as a very important digestive group exhibiting peptolytic and cellulolytic activity.

The second most prevalent group in the small intestine consists of aerobic actinomycetes, making up 17%. The Biological Role of actinomycetes is immense: they surpass all other microorganisms in their ability to produce Antibiotics and Vitamins and possess a powerful enzymatic apparatus. Bifidobacteria are also closely associated with the actinomycete group. Staphylococci, streptococci, enterococci, and coryneform bacteria account for about 5% of small intestine colonization.

The bulk of microorganisms resides in the Large Intestine, where the microbial count reaches 10¹⁰—10¹² per 1 g. At the same time, about 90% of the fecal microflora consists of anaerobic bacteria: bifidobacteria (up to 10⁸—10⁹ per 1 g), bacteroides, clostridia, veillonellae, peptococci (from 10⁵ to 10¹¹ per 1 g), and facultatively anaerobic bacteria primarily represented by Escherichia coli (from 10⁶ to 10⁹ per 1 g of feces), fecal streptococci (Enterococcus faecalis), and lactic acid bacteria (Lactobacillus L. casei, L. salivarius — up to 10¹⁰ per 1 g). Over the course of a day, a person excretes about 17 x 10¹² microbes with feces, which make up approximately 1/3 of the dry mass of feces.

Transient microflora is found in the large intestine in much smaller numbers. It includes bacteria of the genera Proteus, Klebsiella, Clostridium, Pseudomonas aeruginosa, yeast-like fungi, Protozoa, and A number of other microorganisms.

Microflora of the Urogenital System. The quantitative and species composition of the microbiota in these biotopes depends on sex, age, and organ. The lower Urethra harbors peptococci, peptostreptococci, corynebacteria, mycobacteria, bacteroides, enterobacteria, and fungi of the genera Candida, Torulopsis, Geotrichum.

Vaginal microflora depends on various factors and becomes established with the onset of Puberty. During this period, lactobacilli (L. acidophilus, L. fermentum) dominate the Vagina. Subsequently, enterococci, staphylococci (S. saprophyticus), streptococci (Str. faecalis), corynebacteria (Corynebacterium xerosis), yeast-like fungi, and protozoa join the microbiocenosis.

Microbial biocenoses that have evolved across various systems of the macroorganism support their normal physiological Functions and play a specific role in Immunity. Obligate microflora exhibits a pronounced antagonistic effect against many pathogenic microorganisms, which is associated with The production of bacteriocins, antibiotic substances, and metabolic products such as lactic and acetic acids, hydrogen peroxide, alcohols, and others. These substances inhibit the growth of putrefactive microorganisms that inhabit the intestine and produce protein breakdown products toxic to humans. When xenobiotics enter the body from the external environment, intestinal microorganisms participate in their detoxification through biosorption or conversion into non-toxic products.

Alterations in microbial biocenoses frequently lead to pathological conditions, severe functional Disorders of the organism (dysbiosis), and a weakened resistance to various diseases.

The onset of dysbiosis can be triggered by diverse factors: the irrational use of broad-spectrum antibiotics, chronic infections, radiation exposure, surgical interventions, stress, or prolonged stays by individuals in extreme environments and weightlessness.

Currently, to normalize intestinal microflora in dysbiosis, preparations are used that consist of dried cultures of microorganisms belonging to the normal microflora of the human gut—the so-called Probiotics.

For therapeutic and preventive purposes, it is also recommended to consume food products enriched with probiotics—specially selected strains of lactobacilli and bifidobacteria—and prebiotics, which are substances that stimulate the growth of probiotics in the intestine. Such substances include lactulose, fructooligosaccharides, and others.