King C H, Shotts E B, Wooley R E, Porter K G
Department of Medical Microbiology, College of Veterinary Medicine, Athens, Georgia.
Appl Environ Microbiol. 1988 Dec;54(12):3023-33. doi: 10.1128/aem.54.12.3023-3033.1988.
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 greater than 50-fold more resistant to free chlorine 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.
在与变形虫和纤毛原生动物共培养前后，测定了大肠菌群和细菌病原体对游离氯残留的敏感性。对细菌的活力进行定量，以确定当被实验室菌株卡氏棘阿米巴和梨形四膜虫摄取时，它们对游离氯残留的抗性。将细菌和原生动物的共培养物进行孵育，以促进细菌的摄取，然后进行氯化、中和并超声处理，以释放细胞内的细菌。还评估了原生动物菌株对游离氯的定性敏感性。结果表明，原生动物在接触能杀死自由生活细菌的游离氯残留水平后仍能存活和生长。被摄取的大肠埃希氏菌、弗氏柠檬酸杆菌、聚团肠杆菌、阴沟肠杆菌、肺炎克雷伯菌和产酸克雷伯菌以及细菌病原体鼠伤寒沙门氏菌、小肠结肠炎耶尔森菌、宋内志贺菌、戈尔曼军团菌和空肠弯曲菌对游离氯残留的抗性增强。在自由生活细胞99%失活所需时间之后，仍能从经处理的原生动物体内培养出细菌。所有细菌病原体被梨形四膜虫摄取后，对游离氯的抗性提高了50倍以上。从饮用水蓄水池分离出的一种纤毛虫Cyclidium sp.摄取的大肠埃希氏菌对游离氯的抗性也增强。抗性增强的机制似乎是在原生动物细胞内存活。这项研究表明，细菌在被原生动物摄取后仍能存活。这种细菌与原生动物的关联使细菌对游离氯残留的抗性增强，这可能导致细菌在经氯处理的水中持续存在。我们提出，对捕食性原生动物消化的抗性是细菌致病性的进化前身，而如今它是挑剔细菌在稀薄且不适宜生存的水生环境中生存的一种机制。
