Fecal coliforms enumeration

The water analysis is incomplete unless the number of coliform bacteria present is determined as well. A multiple-tube fermentation technique can be used to enumerate positive presumptive, confirmed, and fecal coliform tests. Results of the tests are expressed in terms of the most probable number (MPN). That is, the count is based on a statistical analysis of sets of tubes in a series of serial dilutions. MPN is related to a sample volume of 100 ml. Thus, an MPN of 10 means 10 coliforms per 100 ml of water. 

The whole-water sample and the sample obtained from the treated membrane were analyzed identically to determine the growth and enumeration of the fecal coliform. Based on their probable contamination, at least 2 aliquots of 0.1 to 100 mL of the prepared samples were filtered through a 0.45- Lim membrane to filter out all bacteria. The membranes were placed in petri dishes containing TTC + tergitol agar (Diagnostic Pasteur ref 64454). The dishes were incubated, and then the bacteria were enumerated and expressed as colony forming units (CFU)/100 mL. 

Enumeration of Total Coliforms, Fecal Coliforms, and E. coli.116... 

Four methods may be used to detect and enumerate total coliforms, fecal coliforms, and E. coli in water samples. These are grouped as (a) multiple tube fermentation technique also known as the MPN technique, (b) membrane filtration technique, (c) presence/absence test, and (d) use of the enzymatic substrates test also known as the chromogenic-fluorogenic substrate test. 

The methods described below for detection and enumeration of bacteria in water are based on information from various established standard manuals and textbooks (e.g.. Refs. [2,16,69,77,99]). Because of space constraints, descriptions will focus on detection and enumeration of indicator bacteria (heterotrophic microorganisms, coliforms, E. coli, fecal streptococci/enterococci) and Staphylococcus aureus. 

Presumptive test for total coliforms The various types of media for coliform, fecal coli-form, and E. coli detection and enumeration using the MPN method are presented in Table 4.7 along with the incubation conditions and typical reactions obtained. 

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