Lactose fermentation

Escherichia coli and Klebsiella pneumoniae subsp, aerogenes produce acid from lactose on this medium, altering the colour of the indicator, and also adsorb some of the indicator which may be precipitated around the growing cells. The organisms causing typhoid and paratyphoid fever and bacillary dysentery do not ferment lactose, and colonies of these organisms appear transparent. 

Crow, V. L. and Thomas, T. D. 1984. Properties of a Streptococcus lactis strain that ferments lactose slowly. J. Bacteriol. 157, 28-34. 

The coliform group of microorganisms is defined as all aerobic and anaerobic. Gramnegative, nonspore-forming, rod-shaped bacteria that ferment lactose with gas and acid formation within 48 honrs at 35°C. The group belongs to the genera Escherichia,... 

A further test is done to confirm the presumptive test result this is called the confirmed test. The theory behind this test uses the property of the coliforms to ferment lactose even in the presence of a green dye. Noncoliform organisms cannot ferment lactose in the presence of this dye. The growth medium is called brilliant green lactose bile broth. A wire loop from the positive presumptive test is inoculated into fermentation tubes containing the broth. As in the presumptive test, the tubes are incubated at 35 + 0.5°C. Liberation of gases within 24 to 48 3 hours indicates a positive confirmed test. 

The characteristic features of the coliforms are non-sporing, Gram-negative rods, which are bile tolerant and able to ferment lactose at 37 °C producing acid and gas within 48 hours. The term faecal coliform was used to describe coliforms capable of fermenting lactose to acid and gas within 24 hours at 44 °C. The term thermotolerant coliforms is now used more commonly in the UK, although the term faecal coliform is still widely used elsewhere. It should be pointed out that not all thermotolerant coliforms are faecal in origin. 

There are numerous variations on this medium using mannitol instead of lactose, teepol or sodium lauryl sulfate instead of bile salts, and alternative indicators such as Phenol Red. However, all the tests are based on the ability of coliforms to grow in the presence of some inhibitor, and ferment lactose or mannitol to acid and gas, the acid changing the colour of the indicator. 

Conform bacterium Gram-negative, nonspore-forming, aerobic or facultatively anaerobic bacterium that ferments lactose and produces acid and gas, significant numbers may indicate water pollution. 

Bactericidal activity Lactobacilli ferment lactose to lactic acid, thereby reducing the pH to a level that harmful bacteria cannot tolerate. Hydrogen peroxide is also produced, which inhibits the growth of Gram-negative bacteria, ft has also been reported that lactic acid producing bacteria of the Streptococcus and Lactobacillus species produce antibiotics. 

Total coliforms Gut of warm-blooded animals, soil, plant matter, and water environment Rod-shaped ferment lactose and produce gas at 35°C oxidase negative Gram negative No... 

Fecal coliforms (FC) are a subgroup of total coliforms consisting mainly of E. coli, Enterobacter, and some Klebsiella. They inhabit the intestines of warm-blooded animals. Because they can grow and ferment lactose at a relatively high temperature ( 45.0°C),... 

Confirmation test for total coliforms The LTB and BGLBB are used here to confirm the presence of coliforms in the samples. Colonies that ferment lactose in BGLBB confirm the presence of coliforms. Inoculate growth from each red colony (up to 10 randomly selected colonies) with a golden sheen on the filter into tubes of LTB. Incubate at 35°C for 48 h. Then subculture LTB tubes that are positive (show gas production) to BGLBB and incubate at 35°C for 48 h. A confirmed coliform test is one that shows gas production in BGLBB within 48 h. Other methods of verifying coliforms are available (see Section 4.8.2). 

Carbohydrates are also precursors of carboxylic adds. Bacteria of the genera Clostridium, Butyribacterium and Butyrmbrio ferment sugars primarily to acetic and butyric acids. Bacteria of the genus Propionibacterium (P. freudenreichii subsp. shermanii) ferment lactose to lactic acid, which is reduced to propionic acid, an important add of the most famous Swiss cheese, Emmental (Figure 8.39). The first step of this biosynthesis is the reaction of... 

Lactobacillus rhamnosus (formerly L. delbrueckii) produces high yields of L(+)-lactic acid from sucrose and glucose at 45 °C, making it an excellent commercial production strain (O Table 1.8). But this bacterium will not utilize lactose, so it cannot make use of cheese whey. Lactobacillus delbrueckii subsp. bulgaricus and L. helveticus both ferment lactose from cheese whey, producing high yields of lactic acid. Lactobacillus delbrueckii produces the d(—) enantiomer and L. helveticus a racemic mixture of DL-lactic acid. Because most commercial fermentations are developed for L(+)-lactic add production, strains of L. casei and Lactococcus lactis are being developed for fermentation of lactose sources such as cheese whey. 

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