Recovery and Growth of Bacteria Following Heat Stress
Abstract:Heat stress has been used as a method of killing bacteria for many years, and is the basis for federal regulations promulgated to reduce pathogens in biosolids (40 CFR 503). However, recent studies have shown heat stressed organisms able to reactivate and regrow .The purpose of this study was to examine bacterial response to heat stress over time and to evaluate the ability of bacteria to recover and grow. Washed Cultures of E.coli were placed into bottles containing sterile buffer and buffer amended with 1% nutrient broth. The bottles were then subjected to heat at 55°C for 4, 6, and 24hours. Contents of bottles were assayed over 10days for growth on non-selective agar plates using the spread plate method. All plates were negative for growth immediately after heat stress, however in the samples heated for 4hrs and 6hrs, recovery of E. coli was seen in buffer with nutrient broth after 24hrs. Recovery was also seen in buffer alone after 72hrs. Samples heated for 24hrs did not show the ability to recover. Further work is being conducted using lower initial densities of E. coli to assess the difference between recovery and re-growth. This research also is evaluating similar responses in Salmonella, Enterococci, and Klebsiella spp.
Document Type: Research Article
Publication date: January 1, 2009
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