Survival of coliforms and bacterial pathogens within protozoa during chlorination

Abstract

The susceptibility of coliform bacteria and bacterial pathogens to free chlorine residuals was determined before and after incubation with amoebae and ciliate protozoa. Viability of bacteria was quantified to determine their resistance to free chlorine residuals when ingested by laboratory strains of Acanthamoeba castellanii and Tetrahymena pyriformis. Cocultures of bacteria and protozoa were incubated to facilitate ingestion of the bacteria and then were chlorinated, neutralized, and sonicated to release intracellular bacteria. Qualitative susceptibility of protozoan strains to free chlorine was also assessed. Protozoa were shown to survive and grow after exposure to levels of free chlorine residuals that killed free-living bacteria. Ingested coliforms Escherichia coli, Citrobacter freundii, Enterobacter agglomerans, Enterobacter cloacae, Klebsiella pneumoniae, and Klebsiella oxytoca and bacterial pathogens Salmonella typhimurium, Yersinia enterocolitica, Shigella sonnei, Legionella gormanii, and Campylobacter jejuni had increased resistance to free chlorine residuals. Bacteria could be cultured from within treated protozoans well after the time required for 99% inactivation of free-living cells. All bacterial pathogens were >50-fold more resistant to free chlorinc when ingested by T. pyriformis. Escherichia coli ingested by a Cyclidium sp., a ciliate isolated from a drinking water reservoir, were also shown to be more resistant to free chlorine. The mechanism that increased resistance appeared to be survival within protozoan cells. This study indicates that bacteria can survive ingestion by protozoa. This bacterium-protozoan association provides bacteria with increased resistance to free chlorine residuals which can lead to persistence of bacteria in chlorine-treated water. We propose that resistance to digestion by predatory protozoa was an evolutionary precursor of pathogenicity in bacteria and that today it is a mechanism for survival of fastidious bacteria in dilute and inhospitable aquatic environments.

The ecological habitat and transmission ofEscherichia coliO157:H7

“…They are likely to constitute an important environmental reservoir for transmission of E. coli O157:H7 and other pathogens. Bacterial pathogens including Vibrio, Legionella, Mycobacteria, enteropathogenic E. coli, and the meningitis-causing E. coli strain K1 multiply and/or survive within protozoa (King et al, 1988;Werner et al, 1990;Barker & Brown, 1994;Fields, 1996;Steinert et al, 1998;Alsam et al, 2006;Huws et al, 2008). Escherichia coli O157 and non-O157 strains have been shown to survive within the environmental protozoa Acanthamoeba polyphaga and Acanthamoeba castellanii (King et al, 1988;Barker et al, 1999;Carruthers et al, 2010).…”

“…In addition to enhanced environmental survival, bacterial co-habitation with protozoa could induce adaptative changes in bacteria (King et al, 1988;Barker et al, 1993). Furthermore, we recently observed that the coculture of E. coli O157:H7 with A. castellanii increased bacterial persistence over 3 weeks (Chekabab et al, 2012).…”

Legionella: from environmental habitats to disease pathology, detection and control

“…This compartment may constitute a rich source of nutrients for the bacteria and is probably recognized as a cellular compartment. King et al (1988) proposed that resistance to digestion by predatory protozoa was an evolutionary precursor of pathogenicity in bacteria and that today it is a mechanism for the survival of fastidious bacteria in dilute and inhospitable aquatic environments. L. pneumophila proliferates intracellularly in various species of protozoa, surviving at some temperatures and proliferating at others within vacuoles studded with ribosomes (Kikuhara et al, 1994).…”

Influence of temperature, oxygen and bacterial strain identity on the association of Campylobacter jejuni with Acanthamoeba castellanii

“…Baré et al, unpublished data). Although some data are available on Campylobacter-protozoan interactions (King et al, 1988;Axelsson-Olsson et al, 2005;Snelling et al, 2005), more information is needed about the effect of environmental factors and bacteria-specific characteristics on, and the nature of their association with protozoa.…”