MICROBIOLOGY Study Guide - 2012

CHAPTER 14. SANITARY INDICATOR MICROORGANISMS

The primary sources of infectious disease spread are sick individuals and warm-blooded animals. Pathogenic microorganisms are most massively released via airborne droplets or feces. Direct detection of infection agents in the environment presents certain difficulties. First, they are not constantly present in the environment; second, their numbers are significantly lower than those of saprophytic microorganisms; and third, their cultivation requires rather complex nutrient media.

Along with the release of pathogenic microbes into the environment, Representatives of the normal Human and Animal microflora also enter it. As a rule, this microflora is constant in composition and changes very little during infectious diseases. The saprophytic microbes released in this process serve as indicators of poor sanitary conditions and potential hazard, which is why they are called sanitary indicator microorganisms (SIMs).

Only microorganisms that meet the following criteria can be recognized as sanitary indicators:

✵ they must be constantly present in the excreta of humans and warm-blooded animals and released into the environment in large quantities;

✵ after release, they must remain viable for a period close to the survival time of pathogenic microbes;

✵ they must not multiply in the environment or alter their biological properties;

✵ they must be sufficiently typical so that their Differential Diagnosis presents no difficulties.

SIMs are conventionally divided into three groups.

The first group consists of inhabitants of the human and animal intestine (indicators of fecal contamination). This group includes coliform Bacteria (coliforms), enterococci, sulfite-reducing bacteria (Clostridium perfringens), and coliphages.

The second group comprises inhabitants of the Upper Respiratory Tract and nasopharynx (indicators of airborne droplet contamination). Hemolytic streptococci and staphylococci were traditionally included in this group; however, currently only staphylococci are classified as SIMs.

The third group includes environmental inhabitants (indicators of self-purification processes). It comprises ammonifying, nitrifying, and certain spore-forming bacteria, actinomycetes, and Fungi.

Table 9 shows environmental objects in which sanitary indicator microorganisms are determined.

Class="center">Table 9. Sanitary indicator microorganisms determined in environmental objects

14.1. COLIFORM BACTERIA

Bacteria of this group belong to the phylum Gracilicutes and are grouped in the family Enterobacteriaceae. According to international standards, METABOLISM/2.html">THE CONCEPT OF coliform bacteria is identical to "coliforms".

Currently, this group includes gram-negative, non-spore-forming rods lacking oxidase activity that are capable of fermenting lactose with The production of acid and gas. Coliform bacteria are subdivided into two subgroups:

1) total coliform bacteria, which break down glucose, lactose, and mannitol with the production of acid and gas at 37 °C within 24 h;

2) thermotolerant coliform bacteria, which break down glucose and lactose with the production of acid and gas at 43–44.5 °C.

The coliform group includes the genera: Escherichia, Enterobacter, Citrobacter, Klebsiella.

Representatives of coliform bacteria are small, gram-negative, non-spore-forming rods, mostly motile by means of peritrichously arranged flagella, and do not form capsules. An exception is made by bacteria of the genus Klebsiella, which possess a classical polysaccharide capsule and lack flagella.

Facultative anaerobes obtain energy both through Respiration and Fermentation. During carbohydrate fermentation, they produce gases — СО₂ and Н₂.

Enterobacteria are catalase-positive and oxidase-negative.

The genus Escherichia encompasses coliform bacteria that inhabit the intestines of humans and warm-blooded animals as Saprophytes. This genus also includes enteropathogenic E. coli strains responsible for various gastrointestinal disorders, such as colitis, enterocolitis, and escherichiosis. In individuals with compromised Immunity, coliform strains residing in the Large Intestine can cause purulent-Inflammatory Diseases outside the digestive tract, including cystitis, otitis, and coli-Sepsis. The type species is Escherichia coli.

The genus Enterobacter. Representatives of this genus are found not only in the intestines of humans and animals but also in environmental reservoirs such as fresh water, soil, and plants. In recent years, various Enterobacter species have been isolated in cases of acute gastrointestinal diseases, biliary and Urinary Tract infections, Purulent meningitis, and sepsis in humans and animals. The type species is E. cloacae.

The optimal growth Temperature ranges from 25 to 37 °C. Characteristic biochemical features of bacteria in this genus include acetoin production (positive Voges—Proskauer test) and the utilization of sodium citrate in Simmons' citrate medium.

The genus Citrobacter derives its name from citrus (lemon) due to its ability to grow on Simmons' citrate medium. Members of this genus are present in human and animal feces, soil, sewage, and food products. Classified as opportunistic pathogens, they frequently cause diarrheal diseases (especially Citrobacter freundii) and pyogenic-septic infections. The type species is C. freundii. A distinctive feature of C. freundii is its ability to produce hydrogen sulfide.

The genus Klebsiella was named in 1975 in honor of the German bacteriologist Edwin Klebs, who isolated klebsiellae from patients who died of lobar Pneumonia. Bacteria of this genus are widespread in the environment and are frequently isolated from water, soil, and food products. They may also be present in the biocenoses of the nasopharynx and intestines. Members of this genus can cause a disease known as klebsiellosis. The highest incidence of klebsiellosis is observed in infants under 1 year of age. The clinical manifestations include diarrhea, meningitis, bronchopneumonia, and purulent-septic inflammation. The genus includes opportunistic species such as K. pneumoniae and K. mobilis, as well as saprophytic species like K. planticola and K. terrigena.

Currently, the detection and identification of coliform bacteria (CB) rely on the following differential diagnostic criteria:

✵ character of growth on Endo Agar (the so-called lactose test), taking into account dark red colonies, with or without a metallic sheen;

✵ oxidase test. Colonies on Endo agar are examined for the presence of oxidase. Oxidase-negative colonies are selected for further identification, whereas colonies with a positive oxidase test, belonging to Gram-negative bacteria of the genera Pseudomonas, Aeromonas, and Vibrio, are excluded;

✵ Gram-negative status. Smears prepared from characteristic colonies are Gram-stained and examined microscopically;

✵ fermentation test in Hiss's glucose medium to assess the ability of bacteria to ferment glucose with the production of acid and gas.

It should be noted that coliform bacteria are not ideal sanitary-indicator microorganisms (SIMs). This is because they have many environmental counterparts, are capable of adapting to environmental changes, can multiply in water even at low organic matter concentrations, and are vulnerable to adverse environmental factors. All these limitations necessitate the search for alternative indicators. In 1910, enterococci were proposed as sanitary-indicator microorganisms.