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 env ironments. In other respects, these bacteria share an oral route of in fection and have to cross the gastric barrier to cause disease in huma n 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 acqu ire 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 typhimu rium was enhanced by a hundred to a hundred millions limes after 100 m in in seawater. This effect was also observed when cells were incubate d in distilled water and phosphate buffers with low or high osmolarity . It is therefore not specific to seawater. Acid resistance was, howev er, 2 to 4 times higher in seawater. Acquired resistance depended on t he growth phase of the cells. It was lost by subculturing the cells an d 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-re sistant, enteric pathogens in natural waters may have sanitary and epi demiological implications.