Food Safety - E. coli and Coliform

The Coliform Family

Food Safety

E. coli and Coliform

Coliforms are gram negative, facultative anaerobic rod shaped bacteria commonly found in feces of warm blooded animals, in soil and aquatic environments. These bacteria are mostly harmless but they are used as a hygiene indicator of fecal contamination. High levels indicate unsanitary food processing conditions or poor hygiene practices. For factories that have effective kill steps, they indicate post processing contamination. E. coil/ coliforms do not form spores and they can be motile or non-motile. Coliforms are still used as a fecal contamination in food and especially water, although it includes bacteria of non-fecal origin, as it represents a conservative risk management tool and a bigger safety net.

01 Fecal Coliforms

Fecal Coliforms and Non Fecal Coliforms are two types of coliform bacteria, the main difference lies in its origin, fecal having its origin in the intestinal tract of warm-blooded animals and non-fecal is not. Therefore fecal coliform is used to indicate the presence of pathogenic microorganism in food and water and possible fecal contamination to the product. The importance of fecal coliform is diminished after it was found in insects.

02 Non Fecal Coliforms

03 E. coli

E. coli is part of the fecal coliform group that is deemed to be a more specific indicator of fecal contamination. It is a gram negative facultative anaerobe and are typically rod shaped. In 1986, the USEPA recommended e coli in place of fecal coliform as a water quality fecal contamination indicator. This is also generally accepted as such in the food industry. A common subdivision of coli strains is by serotype based on the major surface antigen being O type (part of the liposaccharide layer) and the H antigen (on the flagella). Many sub species of E coli are pathogenic e.g. O157H7. Another example is O104:H4 which is called Enteroaggressive E. coli (EAEC). These bacteria has acquired the Shiga Toxin genes characterized by the genetic markers Shiga Toxin stx2. They are often called E coli (STEC). E. coli is differentiated by culture at elevated temperature and the presence of an enzyme MUG which is specific to E. coli.

04 Shiga Toxins – Top 6 STEC

The verotoxin producing E coli (VTEC group) is called because it produces a toxin cytotoxic to a cultured cell line called vero cells. These group are also known as Shiga like toxin producing E coli (STEC) especially in the USA. Some VTEC strains are able to cause hemorrhagic colitis in humans and are usually referred to as Enterohaemorrhagic E coli (EHEC). In the VTEC group serogroup 0157 is the most important but others such as O26, O145, O45, O103, O111, O121 are also important. Some toxins may cause a syndrome called hemolytic uremic syndrome (HUS) which can lead to kidney failure. There are two major forms of shiga toxins; Stx1 and Stx2. These toxins are encoded by the Stx1 and Stx2 genes in STEC. Variants of Stx1 consists pf Stx1a, Stx1c and Stx1d and of Stx2 are Stx1a, Stxb, Stxc, Stxd, Stxe and Stxg. STEC often posess other virulence factors such as intimin and entero hemalysin and are encoded by eae and ehxA genes. Intimin is a virulence factor of EPEC (eg Ecoli O127:H6) and EHEC (eg Ecoli O157:H7.

Together these bacteria are also known as the Top 6 Shiga toxin producing E coli (Top 6 STEC) If it includes O157:H7 then is also referred as Top7 STEC. A major German outbreak in 2011 was caused by O104.

Methods to detect non O157 VTEC are not widely available and very tedious involving many steps. GDS MP ID Top six is a simple PCR method for detection.

E. coli and Coliform Detection Methods

BioControl SimPlate Total Coliform & E. coli IDEXX Water TRANSIA PLATE EHEC Biocontrol GDS PCR System for E. coli O157:H7 and E. coli O104:H4 VIP Gold Chromogenic Coliform Agar Chromogenic E.coil O 157 Agar EC X-GLUC Agar ENDO AGAR Video

BioControl SimPlate Total Coliform & E. coli

SimPlate is a rapid method made for accurate counting. Where enumeration is needed this is the method of choice. It grows bacteria in wells to prevent super spreaders like proteus from masking other colonies. Color differentiation and fluorescence makes reading easy.

IDEXX Water

IDEXX Water provides a rapid 24 hours test for E. coli and Coliform in water that uses prepared media. Simply collect 100 ml of sample and pour the prepared media into the bottle and incubate. The results are as shown above. No confirmation is needed. The test has the highest degree of accuracy for water testing and is good for resuscitating stressed bacteria as is found in all potable water. Quantification can be done with an additional device called Quanti-tray. For faster results use Colilert-18, a test that completes in 18 hours. This method is EPA and APHA approved.

TRANSIA PLATE EHEC

Biocontrol GDS PCR System for E. coli O157:H7 and E. coli O104:H4

VIP Gold

Chromogenic Coliform Agar

Chromogenic E.coil O 157 Agar

EC X-GLUC Agar

Biolife EC X-GLUC Agar Culture Media detects E. coli using the presence of the enzyme β-glucuronidase. Some species of salmonella and shigella also appear as blue green colonies. Bile salts inhibit gram positive bacteria. It performs well with water samples. Non β-glucuronidase bacteria grows as colorless colonies. Rapid Indole Test can be made by putting drop of Kovacs reagent onto the medium and observing the reagent turn red.

ENDO AGAR