Faecal streptococci

FAECAL STREPTOCOCCI (ENTEROCOCCI)

Enterococci are index organisms which assume the safety of milk and milk products while coliforms are indicator organisms which suggest the quality of product. The importance of enerococci as indicator organisms for the presence of related pathogenic micro-organisms in food materials including milk and milk products is now widely recognized. Since complete reliance can not be placed on faecal coliforms or E.coli, it has been suggested that enterococci provide a better index of food sanitary quality than do coliforms since these organisms are more resistant to adverse processing conditions like low and high temperature (freezing and heating). However, subsequently, the use of both E.coli and enterococci as indicator organisms for reliable and accurate assessment of hygienic quality of food products have been recommended. In view of considerable importance of these organisms in dairy products, their detection in these products is also equally important.

Some of the selective media used for the presumptive isolation of enterococci in milk and milk products are listed below.

  • Citrate azide medium
  • m-Enterococcus agar
  • KF streptococcal agar
  • Packer’s agar
  • Enterococcus selective differential medium
  • Thallus acetate agar

Out of all these media, citrate azide agar appears to be the medium of choice as almost all the types of Enterococcus group can grow on this medium.

Medium

  • Sodium azide citrate agar : To the medium triphenyl tetrazolium chloride at 0.01 % and sodium azide at 0.04% concentration are added. These are added at the time of plating.

Procedure

  • Serial dilutions of milk sample is prepared (1 in 10, 1 in 100)
  • Suitable dilution is transferred to the petridish and approximately 10-15 ml of tempered media also is poured into the plate and mixed.
  • Incubate the plate at 370 for 24 hours.
  • The colonies pink in colour are counted.

Calculation

No.of colonies x dilution factor

Result

 

Comment

 

Questions

  1. As per lancefield and sherman’s classification under which group does the enterococci fall?
  2. Enumerate the bacteria under enterococci group?
  3. Differentiate enterococci from lactic streptococci?
Last modified: Tuesday, 17 April 2012, 11:07 AM