Enteroviruses and bacteriophages in bathing waters

Abstract

A new procedure for detecting and counting enteroviruses based on the VIRADEN method applied to 10 liters of seawater was examined. It improved the efficiency of detection by taking into account both the number of positive isolations and numbers found with traditional methods. It was then used to quantify viruses in bathing waters. A number of bacterial indicators and bacteriophages were also tested. Cultivable enteroviruses were detected in 55% of the samples, most of which complied with bacteriological criteria. In contrast, viral genomes were only detected in 20% of the samples by reverse transcription-PCR. Somatic coliphages outnumbered all other indicators. F-specific RNA phages were detected in only 15% of the samples, whereas phages infecting Bacteroides thetaiotaomicron were detected in 70% of samples. A numerical relationship between the numbers of enteroviruses and the numbers of enterococci and somatic coliphages was observed. In situ inactivation experiments showed that viruses persisted significantly longer than the bacterial indicators. Only somatic coliphages and bacteriophages infecting Bacteroides persisted longer than the viruses. These results explain the numbers of enteroviruses and indicators in bathing waters attending the numbers usually found in sewage in the area. Somatic coliphages show a very good potential to predict the risk of viruses being present in bathing waters.

FIG. 1.

Survival of the various indicators studied in the in situ inactivation experiments. E. coli was below the detection limit at 48 h. F-specific phages with RNA genome (FRNAPH) were below the detection limit at 72 h. Fecal coliforms (FC) and fecal enterococci (FE) were below the detection limit at 168 h. Also shown are values for somatic coliphages (SOMCPH), phages infecting Bacteroides thetaiotaomicron GA-17 (BTPH), echovirus 6 (EV6), and coxsackievirus B5 (CVB5). N_t, number of microorganisms at time t; N₀, number of microorganisms at time zero.