Effect of a short period of starvation in oligotrophic waters on the resistance of enteric bacterial pathogens to gastric pH conditions
Enteric bacterial pathogens may undergo severe stresses in aquatic environments. In other respects, these bacteria share an oral route of infection and have to cross the gastric barrier to cause disease in human hosts. Considering the cross-protection against environmental stress, i.e. heat, acid and oxidation, induced by osmotic shock and nutrient starvation, the ability of various enterobacteria, including species of Escherichia, Shigella, Salmonella, Klebsiella and Yersinia, to acquire resistance to the acidic conditions encountered in the stomach (pH 2.5 for 2 h) after incubation in oligotrophic fresh or seawaters was examined. Acid resistance of E. coli, shigellae and Salmonella typhimurium was enhanced by a hundred to a hundred millions times after 100 min in seawater. This effect was also observed when cells were incubated in distilled water and phosphate buffers with low or high osmolarity. It is therefore not specific to seawater. Acid resistance was, however, 2 to 4 times higher in seawater. Acquired resistance depended on the growth phase of the cells. It was lost by subculturing the cells and proved partly dependent on rpoS and on de novo protein synthesis. A similar induced acid resistance was observed in faecal coliforms from human faeces and wastewater. The increased levels of surviving acid-resistant, enteric pathogens in natural waters may have sanitary and epidemiological implications.