Survival of Escherichia coli O157:H7 during storage of yogurt at different temperatures

The behavior of E. coli O157:117 strains during the storage of plain live yogurt at 4, 8, 17, and 22 degreesC was investigated. Lactic acid bacteria and pH were also studied. Linear regression analysis was carried out to obtain the specific death rate, the death rate and time of death. During the 1st 24 h, the pathogenic strains decreased slightly at 4 and 8 degreesC. This decrease was greater at 17 degreesC, and even greater at 22 degreesC. E. coli O157:117 was not detected after 312, 168, 28, and 16 h at 4, 8, 17, and 22 degreesC, respectively. Counts of Lactobacillus and Streptococcus were about 9 log CFU/g during the study. An increase was detected in the values for time of death from refrigeration to room temperatures. A decrease in the values of both the specific death rate and the death rate related with the increase of temperature was observed. Counts of E. coli O157:117 were higher than those of nonpathogenic E. coli during the storage period at 4 and 8 degreesC, showing a better and a higher adaptation capacity to acid pH environments at refrigeration temperatures. This behavior was not observed at room temperatures.