Bacteriophages infecting various bacteroides fragilis strains differ in their capacity to distinguish human from animal faecal pollution

Strain HSP40 of Bacteroides fragilis (ATCC 51477) selectively detects bacteriophages excreted by humans. We have tested 115 strains of B. fragilis, isolated from humans, as hosts for the detection of bacteriophages in urban sewage. Only 10% of the strains examined gave counts that were similar to or higher than those given by B. fragilis HSP40. To determine their specificity, some of these were examined for their ability to detect phages in faeces from various animal species and in slaughterhouse wastewater. Two groups of strains were distinguished. The first allowed the recovery of phages in samples with human and animal faecal pollution. The second, which included HSP40, detected phages preferentially in samples with human faecal pollution.