Ecological relationships in the microbiocenosis
The normal microflora, including lactobacilli and various species of yeast, maintains complex ecological relationships with the macroorganism and other microbes. Several forms of such contacts are distinguished:
- Commensalism (+/0): commensal bacteria benefit from living in the intestine without harming the human host.
- Mutualism (+/+): mutually beneficial coexistence essential for survival (e.g., intestinal microflora and the host organism).
- Metabiosis: some microorganisms use the metabolic products of others for survival.
- Satelitism: yeast colonies release metabolites that stimulate the development of neighboring colonies, activate their functions, and accelerate substrate processing.
Lactobacilli (Lactobacillus) provide colonization resistance of the large intestine. They enter into antagonistic relationships with putrefactive and extraneous flora. The mechanism of competitor suppression includes a high reproduction rate, the production of specific antimicrobial substances, and alteration of the physicochemical properties of the medium (secretion of organic acids that shift the pH in a direction unfavorable for pathogens).
Use as part of probiotics
To correct dysbiosis, probiotics are used — preparations containing live microorganisms with antagonistic activity against pathogens and opportunistic microflora.
Preparations containing lactobacilli are divided into:
- Monocomponent: lactobacterin, biobacton, gastropharm.
- Polycomponent: acilact.
- Combined: acipol (contains L. acidophilus and heated kefir grains), kipacid.
Lactobacilli are also part of associated preparations (bifilakt, linex) and synbiotics — complexes of probiotics and prebiotics (maxilak, biovestin-lacto).
Yeasts are also actively used in therapy. For example, enterol is a single-ingredient preparation based on Saccharomyces yeasts. In addition, metabolic products of lactobacilli are used to create metabiotics (hilak) — chemical substances of known structure that directly stimulate the normal microbiota, bypassing the stage of live bacteria engraftment.
Laboratory diagnostics and cultivation
To assess the qualitative and quantitative composition of microflora, bacteriological stool examination is used. Despite its high specificity, the method has drawbacks: duration (at least 7 days), the use of expensive media, and the predominant detection of lumen or transient flora only.
Selective nutrient media are used to isolate specific groups of microorganisms:
- Lactobacilli are cultivated on MRS-4 (MRS) and Blikfeldt media. The latter contains pancreatic casein hydrolyzate, baker's yeast autolysate, glucose, and magnesium and manganese sulfates.
- Fungi of the genus Candida are grown on Sabouraud medium (peptone, glucose, agar). To suppress the growth of accompanying bacteria, a 2% potassium tellurite solution or antibiotics (tetracycline, benzylpenicillin) are added to it.
Before inoculation, the material is prepared: a 1 g sample of freshly passed stool is taken, 9 ml of saline is added (10⁻¹ dilution), and mixed thoroughly.
An alternative rapid method is gas-liquid chromatography. It detects volatile fatty acids (metabolic products), but does not evaluate the sensitivity of bacteria to antibiotics and phages.
For quick memorization of monocomponent probiotics with lactobacilli, use the mnemonic: "Summer Will Be Gastronomic" (Lactobacterin, Biobacton, Gastropharm).
Class and exam questions
How do yeasts affect the growth of other microorganisms?
Yeasts are capable of satelitism — they release specific metabolites into the environment that stimulate the development of neighboring colonies and accelerate the processing of the nutrient substrate.
How do lactobacilli ensure colonization resistance?
They exhibit microbial antagonism: they multiply rapidly, secrete antimicrobial substances, and produce organic acids that shift the pH of the medium, making it unsuitable for pathogens.
What nutrient media are needed for the cultivation of lactobacilli and fungi?
Lactobacilli are grown on Blikfeldt and MRS-4 media. For fungi (e.g., Candida), Sabouraud medium is used, supplemented with antibiotics or potassium tellurite to suppress extraneous flora.
What is the disadvantage of rapid diagnostics of bacterial metabolites?
Gas-liquid chromatography rapidly detects volatile fatty acids, but does not reveal important biological properties of bacteria, such as sensitivity to antibiotics and bacteriophages.
What else to study on this topic
- Classification and composition of modern probiotics and synbiotics
- Metabiotics: mechanism of action of bacterial metabolites
- Rules for collecting and preparing material for the diagnosis of dysbiosis
- Forms of microbial antagonism and competitor advantage factors
- True and false parasitism in medical microbiology
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