Survival of host-associated Bacteroidales cells and their relationship with Enterococcus spp., Campylobacter jejuni, Salmonella enterica serovar typhimurium, and adenovirus in freshwater microcosms as measured by propidium monoazide-quantitative PCR

Abstract

The ideal host-associated genetic fecal marker would be capable of predicting the presence of specific pathogens of concern. Flowthrough freshwater microcosms containing mixed feces and inocula of the pathogens Campylobacter jejuni, Salmonella enterica serovar Typhimurium, and adenovirus were placed at ambient temperature in the presence and absence of diurnal sunlight. The total Enterococcus DNA increased during the early periods (23 h) under sunlight exposure, even though cultivable Enterococcus and DNA in intact cells, as measured by propidium monoazide (PMA), decreased with first-order kinetics during the entire period. We found a significant difference in the decay of host-associated Bacteroidales cells between sunlight exposure and dark conditions (P value < 0.05), whereas the persistence of host-associated Bacteroidales DNA was comparable. The 2-log reduction times of adenovirus were 72 h for sunlight exposure and 99 h for dark conditions with similar decay rate constants (P value = 0.13). The persistences of fecal Bacteroidales cells and Campylobacter cells exposed to sunlight were similar, and host-associated Bacteroidales DNA and waterborne pathogen DNA were degraded at comparable rates (P values > 0.05). Overall, the ratio of quantitative PCR (qPCR) cycle threshold (CT) values with and without PMA treatment was indicative of the time elapsed since inoculation of the microcosm with (i) fecal material from different animal sources based on host-associated Bacteroidales and (ii) pure cultures of bacterial pathogens. The use of both PMA-qPCR and qPCR may yield more realistic information about recent sources of fecal contamination and result in improved prediction of waterborne pathogens and assessment of health risk.