Lecture 21

Question 1

What are the main indicator organisms routinely used in microbiological analysis, and why are they used?

Answer 1

Total coliforms
Faecal (thermotolerant) coliforms
E. coli type 1
Enterococci
Clostridium perfringens
These organisms are used because they are always present in large numbers in the faeces of humans, warm-blooded animals, and in sewage. Testing for these indicators is more practical than testing for pathogens directly.

Question 2

What are the desirable features of faecal indicator microorganisms?

Answer 2

Should be naturally present in the faeces of humans, animals, and poultry
Should be present in large numbers in faeces for easy detection in dilute samples
Should be specific to the intestine
Should survive in water as long as or longer than pathogens
Should be easily and reliably detectable, even in low numbers
Test methods should be applicable to all water types
Should be non-pathogenic for the safety of analysts