Survival of Human Enteric and Other Sewage Microorganisms Under Simulated Deep-Sea Conditions

Abstract

The survival of pure cultures of Escherichia coli, Streptococcus faecalis, Clostridium perfringens , and Vibrio parahaemolyticus under simulated deep-sea conditions of low temperature (4 C), seawater, and hydrostatic pressures ranging from 1 to 1,000 atm was determined over a period exceeding 300 h. The viability of E. coli and total aerobic bacteria in seawater-diluted raw sewage subjected to these deep-sea conditions was also measured. There was a greater survival of both E. coli and S. faecalis at 250 and 500 atm than at 1 atm at 4 C. S. faecalis was quite insensitive to 1,000 atm, whereas with E. coli there was a 10-fold die-off per 50-h exposure to 1,000 atm. In contrast, V. parahaemolyticus and C. perfringens were quite sensitive to pressures exceeding 250 atm, and with both of these species there was a total loss of viability of approximately 10 8 cells per ml within 100 h at 1,000 atm and within 200 h at 500 atm. The viability of the naturally occurring fecal coliforms in sewage exposed to moderate pressures at 4 C was found to be similar to the survival patterns demonstrated with pure cultures of E. coli . The total numbers of aerobic bacteria in these sewage samples, however, stabilized at 500 and 1,000 atm after 100 h, and at 1 and 250 atm there was significant growth of sewage-associated bacteria, which apparently utilized the organic compounds in the seawater-diluted sewage samples. A preliminary classification of some of these bacteria indicated that approximately 90% (160 isolates) of the organisms that survived over a 400-h exposure to 500 and 1,000 atm were Arthrobacter/Corynebacterium species, and the representative organisms capable of growing at 1 and 250 atm in seawater at 4 C were gram-positive cellulose digesters and an unidentified gram-negative coccus. The significance of these results with respect to the contamination of the deep ocean with human pathogens and the possibility of sewage-associated microorganisms growing and competing with indigenous marine microbial flora in situ is discussed.