Survival of pathogenic bacteria in compost with special reference to Escherichia coli
GONG Chun-ming , Koichi Inoue , Shunji Inanaga , Takashi Someya
DOI:
Received ,Revised , Accepted , Available online
Volume 17,2005,Pages 770-774
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Application of compost in agricultural practice could potentially cause contamination of foodstuffs with pathogenic bacteria such as Escherichia coli O157: H7 ( E. Coli O157). We investigated pathogenic bacteria in compost collected from the compost facilities, and evaluated the survival of E. coli K12 and O157 in laboratory experiments. Out of 19 compost product samples, coliform bacteria and salmonella were detected in 7 and 3 samples respectively. The number of coliform bacteria was 1.8 × 102 to 2.5 × 106 CFU/g dw and that of salmonella was 4.2 × 101 to 6.0 × 103 CFU/g dw. Moreover, coliform bacteria, fecal coliform, E. coli and salmonella were detected during composting at 54℃ to 67℃. The results indicated that moisture content was a very important factor to the heat sensitivity of pathogenic bacteria in compost, E. coli in compost of high moisture content was more sensitive than that in compost of low moisture content, cells harvested in logarithmic phase was more sensitive than these in stationary phase, and E. coli K12 was more sensitive than E. coli O157. Based on the D values, the lethal time of E. coli K12 and O157 from 108 to 100 CFU/g dw were 16.3 and 28.8 min, respectively, at 60℃ in compost with 40% moisture content. However, some E. coli cells survived in composting process at 54℃ to 67℃. Water potential (low moisture content) and physiological aspects of bacteria (stationary phase) could explain only in part of the prolonged survival of E. coli in compost, and there should be some other factors that are conducive to bacterial survival in compost.
