Factors affecting the survival of pathogenic bacteria in subtropical river water

The present study was carried out to determine the factors causing the disappearance of introduced Salmonella enteritidis, Staphylococcus aureus, and Vibrio cholerae in natural river water. When large numbers of the above organisms (final level 10(7)-10(8) CFU per ml) were added to river water, the decline of their numbers coincided with increasing numbers of protozoa. Furthermore, their survival was improved dramatically if the river water was amended with a eucaryote inhibitor. After comparing the survivals of the test organisms in physiological saline, filtered river water, and in dialysis tubes immersed in river water, the results suggested that for Salmonella, predation was the most significant factor which caused the decline of its population in natural river water; starvation and toxic materials played lesser roles. Staphylococcus and Vibrio were also vulnerable to predation and toxic materials have molecular weights larger than 12,000. In the natural environment, these three factors together could cause rapid disappearance of the introduced microorganisms.