TIMAC - A set of tests for differentiating individual genera of bacteria of the group of Escherichia coli
- T - temperature test ( Aikman test );
- And - test indole formation ;
- M - reaction with methyl red ;
- A - reaction to acetylmethylcarbinol ( Voges-Proskauer reaction );
- C - citrate test ;
- L - fermentation of lactose .
In the TIMAC complex, temperature and citrate tests are the main, most stable, allowing to differentiate bacteria of the group of Escherichia coli of fecal origin from bacteria of the group of Escherichia coli living in the environment.
Content
Temperature Test (Aikman Test)
The ability to ferment carbohydrates ( lactose , glucose , mannitol ) at a cultivation temperature exceeding the human body temperature is called the temperature test . For differentiation of Escherichia from Citrobacter and Enterobacter , a cultivation temperature of 43-44 ° C is proposed. For Escherichia, the temperature test is positive, that is, they can ferment carbohydrates at 43-44 ° C, most bacteria of the genera Citrobacter and Enterobacter do not have this ability. The temperature test is determined on special media Aikman , Kessler , Buliz .
Indole Test
The ability to produce indole is inherent in Escherichia ; bacteria from the genera Citrobacter and Enterobacter do not form indole. Strains of E. coli isolated from the human intestine formed indole in 90.1-98.6% of cases.
Methyl Red Reaction
The reaction is to determine the rate of acid production during microbial fermentation of a carbohydrate. The reaction is carried out as follows. A few drops of methyl red are added to the culture (3-5 days old) grown on Clark's medium. At pH 5.0 and below, the indicator changes its light yellow color to red, which indicates strong acid formation. E. coli and Citr. coli citrovorum gives red color to the medium, Ent aerogenes gives yellow. At pH above 5, the medium remains light yellow.
Acetylmethylcarbinol reaction
Aromatic substance - acetylmethylcarbinol (acetoin) form Ent. aerogenes. E. coli and Citr. coli citrovorum do not have this ability. To set up the reaction, the same volume of a 40% KOH solution is added to 5 ml of a 4-5-day-old culture grown in peptone water with glucose or in Clark medium . In the presence of acetylmethylcarbinol, the medium turns pink.
Citrate Test
The ability of a microorganism to assimilate citric acid or its salts as the sole carbon source is called the citrate test. The studied culture is sown on a citrate synthetic medium (liquid Coser or dense Simmons). Citrobacter and Enterobacter grow on citrate media and are called citrate-positive or citratassimilatory bacteria, while Escherichia do not grow on these media and are called citrate-negative.
Lactose Fermentation
The ability to ferment lactose is inherent in most Enterobacteriaceae families. Representatives of the genus Escherichia (with the exception of lactose-negative E. coli variants) ferment lactose, Citrobacter and Enterobacter ferment lactose intermittently. The signs included in this complex determine the belonging of bacteria of the group of Escherichia coli to one of three genera: Escherichia, Citrobacter and Enterobacter.
Literature
- R.P. Kornelaev, PP. Stepanenko, E. V. Pavlova “Sanitary microbiology of raw materials and animal products” Moscow, 2006