MICROBIOLOGY: A Study Guide - 2012

CHAPTER 10. MICROBIAL ECOLOGY

10.2. AQUATIC MICROFLORA

Natural Water bodies provide a favorable environment for A wide variety of microorganisms, including Bacteria, microscopic Algae, Fungi, Viruses, and Protozoa. The aquatic microflora is divided into indigenous (autochthonous) and transient (allochthonous) populations. The key Factors Determining the species composition and quantitative ratios of microorganisms are the availability of nutrients, Temperature, pH, concentrations of dissolved oxygen and carbon dioxide, and the population density of coastal areas.

Spring and artesian well waters are virtually devoid of microorganisms, with counts typically not exceeding 10 CFU/cm³. Ocean and sea water also harbor specific microbial communities, including luminous and halophilic bacteria. Certain vibrios (Vibrio parahaemolyticus) infect Mollusks and specific fish species, which can cause foodborne toxicoinfections if consumed.

In enclosed water bodies (ponds, lakes), microorganisms are distributed vertically, with the highest concentrations found at a depth of 10–100 cm. Microbial numbers decline significantly in deeper layers. The coastal waters of water bodies, particularly enclosed ones, contain considerably more microorganisms than open offshore areas. Microorganisms are especially abundant in silt, where the surface layer forms a microbial film that drives the natural self-purification processes of the water body.

Driven by contaminated storm runoff, snowmelt, and wastewater, lakes and rivers receive saprophytic microorganisms—Human and Animal commensals such as Escherichia coli, Enterobacter, Citrobacter, enterococci, and clostridia—as well as pathogenic microorganisms, including the causative agents of typhoid fever, paratyphoid, dysentery, cholera, leptospirosis, and enteroviral infections. Although water is not an optimal medium for the proliferation of pathogens, they can survive in it for extended periods. Consequently, water serves as a major transmission vehicle for numerous infectious diseases.

The epidemiological safety of water is assessed using the following parameters (SanPiN 2.1.4.1074–01):

✵ Total microbial count—the number of mesophilic chemoorganotrophic bacteria. For central municipal drinking water supplies, the total microbial count must not exceed 50 colony-forming units (CFU) per 1 cm³ of water;

✵ Thermotolerant and total coliform bacteria (coliforms) must be absent in 100 cm³ of water;

✵ Spores of sulfite-reducing bacteria and Molds must be absent in 20 cm³ of water;

✵ Coliphages (PFU—plaque-forming units) must be absent in 100 cm³ of water.

Water from open reservoirs and wells is considered safe if the total microbial count does not exceed 1000 CFU/cm³ and the coli- titer (the smallest volume of water in which E. coli is detected) is at least 100 cm³.

Food Processing and public catering facilities are subject to stringent water quality standards. Water is a direct ingredient in Many food products and serves as a primary component in beer, kvass, and soft beverages. It is also used for washing raw Materials, equipment, pipelines, tableware, and utensils. Therefore, it must consistently meet established Sanitary and hygienic standards.