Bacterial Escherichia coli bacteria (coliform bacteria and coliform bacteria) - conditionally isolated by morphological and cultural characteristics group of bacteria of the enterobacteria family, used by sanitary microbiology as a marker of fecal contamination, belong to the group of so-called sanitary-indicative microorganisms [1] [2 ] ] . The bacteria of the Escherichia coli group include [3] representatives of the genera Escherichia (including E. coli ), Citrobacter (a typical representative of C. coli citrovorum ), Enterobacter (a typical representative of E. aerogenes ), which are combined into one Enterobacteriaceae family due to the common morphological and cultural properties. Colymorphic bacteria differ in enzymatic properties and antigenic structure.
Content
- 1 Morphology
- 2 Cultural properties.
- 3 Biochemical properties
- 4 Sustainability
- 5 Sanitary value
- 6 Sources
- 7 Notes
Morphology
Bacteria of the group of Escherichia coli - short (length 1-3 microns, width 0.5-0.8 microns) polymorphic motile and motionless gram-negative sticks that do not form spores .
Cultural properties.
Bacteria grow well on simple nutrient media: meat and peptone broth (MPB), meat and peptone agar (MPA). On the BCH they give abundant growth with a significant turbidity of the environment; the precipitate is small, grayish in color, easily broken. They form a parietal ring, the film on the surface of the broth is usually absent. On MPA, colonies are transparent with a grayish-blue tint, easily merging with each other. On medium Endo form flat red colonies of medium size. Red colonies can be with dark metallic luster ( E. coli ) or without luster ( E. aerogenes ). Colorless colonies are characteristic of lactose-negative variants of E. coli ( B. paracoli ).
They are characterized by wide adaptive variability, as a result of which various options arise, which complicates their classification.
Biochemical properties
Most bacteria of the group of Escherichia coli (BHLC) do not dilute gelatin , clot milk, break down peptones to form amines , ammonia , hydrogen sulfide , and have high enzymatic activity against lactose, glucose, and other sugars , as well as alcohols . Do not have oxidase activity. By their ability to cleave lactose at a temperature of 37 ° C, BGKP are divided into lactose-negative and lactose-positive Escherichia coli (LCP), or coliform, which are formed according to international standards. Fecal Escherichia coli (PCF), capable of fermenting lactose at a temperature of 44.5 ° C, are distinguished from the LCP group. These include E. coli , not growing on citrate medium.
Sustainability
Bacteria of the group of Escherichia coli are neutralized by conventional pasteurization methods (65–75 ° C). At 60 ° C, E. coli dies after 15 minutes. A 1% solution of phenol causes the death of the microbe after 5-15 minutes, mercuric chloride at a dilution of 1: 1000 - after 2 minutes, resistant to many aniline dyes.
Sanitary value
The sanitary-indicative value of individual genera of bacteria of the group of Escherichia coli is not the same. Detection of bacteria of the genus Escherichia in food, water, soil, equipment indicates fresh fecal contamination, which is of great sanitary and epidemiological importance.
It is believed that the bacteria of the genera Citrobacter and Enterobacter are indicators of older (several weeks) fecal contamination and therefore they have a lower sanitary-indicative value in comparison with bacteria of the genus Escherichia .
With prolonged use of antibiotics, various variants of E. coli are also found in the human intestines. Of particular interest are lactose-negative variants of E. coli. These are altered Escherichia, which have lost the ability to ferment lactose. They are excreted in human intestinal infections ( typhoid fever , dysentery , etc.) during the recovery period.
Of the greatest sanitary-indicative value are E. coli, which do not grow on the Coser medium ( citrate medium ) and fermenting carbohydrates at 43–45 ° С ( E. coli ). They are an indicator of fresh fecal contamination.
In connection with the unequal sanitary and indicative value of individual genera of bacteria, groups of Escherichia coli differentiate them on the basis of the signs that form the TIMAC complex.
Sources
- Kornelaeva R.P., Stepanenko P.P., Pavlova E.V. Sanitary microbiology of raw materials and animal products. - M .: Poligrafservis LLC, 2006. - p. 15-18
Notes
- ↑ Litusov N.V., Sergeev A.V., Grgoryeva Yu. V., Ishutinova V.G. Microflora of the environment and the human body. Study guide . - Ekaterinburg, 2008. - S. 22. (unavailable link)
- ↑ Archived copy (inaccessible link) . Date of treatment November 24, 2010. Archived June 15, 2015.
- ↑ Bacteriological Analytical Manual Chapter 4 Enumeration of Escherichia coli and the Coliform Bacteria