A SIMPLE AND RAPID METHOD FOR THE DETECTION AND ENUMERATION OF PHAGES OF BACTEROIDES FRAGILIS HSP40 IN FOODS AND SEWAGE1

Abstract

ABSTRACTThe phage‐host model of Bacteroides fragilis HSP40 has been documented as a potential index of human sewage and enteroviruses in sewage samples. However, this organism is an obligate anaerobe, which significantly limits the convenience of this model. The objectives of this study were to develop a simple method for the detection and enumeration of phages of B. fragilis HSP40 without using cumbersome anaerobic methods, to compare the novel method to the standard plaque assay (PA), and to enumerate phages naturally occurring in foods and sewage using both methods. Oxyrase enzymeTM (OE) was used at 0.5 U/ml in the growth medium of B. fragilis HSP40 before aerobic incubation. A double tube for phage (DTP) was developed and compared to the standard PA throughout the study. An enrichment procedure for samples was tested using 0.5 U/ml OE. Results indicated that the DTP could detect plaque forming units (PFU) of phages of B. fragilis HSP40 within 12–18h, with a sensitivity of 1 PFU/ml. The need for anaerobic incubation was totally eliminated by using OE and applying the DTP. Phage counts using DTP and PA were highly correlated (R2= 0.99–1.00) in spiked peptone water and ground beef. Enrichment of samples with OE enhanced phage recovery from spiked ground beef. With the DTP and PA, phages of B. fragilis HSP40 were detected from sewage, oysters, mushrooms and chicken. No such phage was detected from fresh ground beef before and after enrichment with either method. The DTP method was simpler than the PA, and it can be recommended for rapid screening of foods for fecal contamination and potential presence of viruses.