Survival of Salmonella Species in River Water |
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Authors: | Jorge W Santo Domingo Stephen Harmon Jason Bennett |
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Institution: | (1) U.S. Environmental Protection Agency, National Exposure Research Laboratory, 26 W. Martin Luther King Dr., Cincinnati, OH 45268 USA , US;(2) National Risk Management Research Laboratory, 26 W. Martin Luther King Dr., Cincinnati, OH 45268, USA , US |
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Abstract: | The survival of four Salmonella strains in river water microcosms was monitored by culturing techniques, direct counts, whole-cell hybridization, scanning
electron microscopy, and resuscitation techniques via the direct viable count method and flow cytometry. Plate counts of bacteria
resuspended in filtered and untreated river water decreased several orders of magnitude within the first week of incubation,
while they did not decrease as rapidly in autoclaved water. In situ hybridization studies suggested a rapid decrease in ribosomal
content, as determined by the drastic decrease in the number of detectable cells after 72 h. In contrast, direct counts remained
relatively constant during 45 days in all microcosoms. Although the culturable counts of two bacterial strains in filtered
water after 31 days represented approximately 0.001% of the total counts, direct viable counts and resuscitation studies with
a dilution series suggested that the number of viable bacteria was at least four orders of magnitude higher. Additionally,
notable changes in forward scatter and in nucleic acid content were observed only after 4 h of nutrient amendments by flow
cytometry. However, cells from the resuscitation experiments did not grow on solid media unless cell-free supernatant from
viable cultures was added during the resuscitation period. The results in this study suggest the presence of a not immediately
culturable status in Salmonella.
Received: 20 October 1999 / Accepted: 10 January 2000 |
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