Usefulness of bacteriophages infecting Bacteroides fragilis as index microorganisms of remote faecal pollution

Levels of faecal bacteria, somatic coliphages and bacteriophages of Bacteroides fragilis were counted in marine sediments and groundwater as representatives of environments with remote faecal pollution. Additionally, enterovirus were measured in the marine sediments. Clear changes of the proportions of the different microorganisms are observed when microbial numbers in groundwater and marine sediments are compared to the numbers found in sewage or water recently polluted by sewage. These changes show that phages of B. fragilis reach sites that receive persistent pollution more successfully than somatic coliphages or indicator bacteria, with the exception of Clostridium perfringens. Multifactorial analysis of marine sediments and groundwater data clustered phages, viruses and C. perfringens in one factor and faecal bacteria in another. These data clearly suggest that Clostridium, phages of B. fragilis and, in some cases enteroviruses, are better index microorganisms of remote faecal pollution than present bacterial indicators.