Question

On the indicators of faecal contamination in the waters:

A. Define what is an indicator of faecal contamination and the characteristics of an ideal indicator. Differentiate between a fecal and a process indicator.

b. Select four indicators of fecal contamination and discuss them. Mention advantages and disadvantages of these methods.

c. If you want to determine if a water sample related to a lentic system is contaminated with human fecal material what indicators would you use, explain.

Answer 1

A. An indicator of faecal contamination can be defined as an organism used in the detection and estimation of fecal contamination in water. They are not serious human pathogens but can indicate fecal contamination and serious enteric pathogens in water.  The characteristics of an ideal indicator organism are

1. The indicator is present whenever enteric pathogens are present.
2. The organism is present in more numbers than the serious pathogens.
3. The organism has a higher resistance to antimicrobial agents than the hardiest enteric pathogen.
4. The organism does not proliferate in water.
5. The organism is easily culturable and detectable than the pathogens.
6. The indicator grows independent of other organisms.

The process indicator is different from a fecal indicator. The fecal indicator indicates the fecal contamination and presence of enteric pathogens in water, whereas the process indicator indicates the progress and efficacy of a wastewater treatment process. For example, Coliforms are used as process indicators to check efficacy of chlorination process.

B. Total coliforms, or a subset of this group, the Fecal coliforms were the most used organisms as indicators of fecal contamination. Total coliforms were the first bacteria used as indicators. Fecal coliforms are more useful than Total coliforms as the former include some bacteria which are the normal inhabitants of soil and water. One disadvantage in using Coliforms is that they can proliferate in water under some circumstances. E. coli and F+RNA Coliphage are another examples of indicator organisms. Repeated and frequent screening for E. coli in water is an effective method for predicting pathogens in it. A qPCR-based E. coli assay is very efficient in this regard. Screening for F+RNA coliphage is also effective in predicting bacterial pathogens, but not very sensitive for pathogens like Rotavirus.

C. The traditional fecal indicators mainly include Coliforms. But they are not specific to human fecal material and can grow outside the host body. To overcome these disadvantages, anaerobic enteric bacteria like Bacteroidales could be used. Quantitative real time PCR can be used to detect these host specific Bacteroidales. Species Prevotella and Bacteroides are examples of Bacteroidales in human gut. Fecal anaerobes are more effective as indicators because they will not grow once released from their host into the environment, in contrast to E. coli and Enterococci, which have been shown to persist and even grow in beach sand.