Bacteroides fragilis and Escherichia coli bacteriophages: excretion by humans and animals

Abstract

The faecal excretion of somatic and male-specific coliphages, and phages of Bacteroides fragilis strain HSP40, by humans and a variety of animals has been investigated as part of research on indicator features of phages. Ninety human stool specimens were obtained from black and white male and female individuals varying in age from 6 months to 85 years. Sixty-five faecal samples from domestic animals including cattle, sheep, pigs, horses, dogs, cats, geese and rabbits, were obtained from various agricultural and domestic sources. The National Zoological Gardens in Pretoria kindly supplied 38 stool specimens from higher primates (gorilla, orangoutang and chimpanzee). Thirty-seven stool specimens from chacma baboons and vervet monkeys were obtained from the Zoological Gardens and our animal research centre. Five specimens of seabird droppings were obtained from the west coast of South Africa. The qualitative presence of phages was determined by an enrichment procedure followed by a plaque spot test. Double agar layer plaque assays were used to titrate phages. Bacteroides fragilis phages were detected in 13% of human stool samples, but not in any animal faeces. Somatic coliphages were detected in 54% of human, 56% of domestic animal, 57% of monkey and baboon, 53% of higher primate, and 60% of seabird specimens. Male-specific coliphages were detected in 26% of human, 90% of domestic animal, 76% of monkey and baboon, 63% of higher primate, and 20% of seagull faecal samples. Titres of phages in selected samples varied from undetectable by direct plaque assay to 4.5 × 106 somatic and 3.2 × 104 male-specific coliphages per gram of seabird droppings. Faecally polluted environments may, therefore, contain substantial numbers of somatic and male-specific coliphages of human and animal origin. The results confirm earlier observations that B fragilis phages can be used to distinguish between faecal pollution of human and animal origin.