Abstract
The viability of Escherichia coli O157:H7 in frozen chicken meat (CM) containing sodium chloride (NaCl), sodium lactate, or polyphosphate over an 18 month period was determined. Additionally, several recovery media were evaluated. Ground CM (10 g) was inoculated (10 6 cfu g -1) with E. coli O157:H7, then held at -20°C. Surviving cells were enumerated monthly using a nonselective medium, tryptic soy agar (TSA). After 11 months, seven additional recovery media were also used to evaluate the ability to recover freeze/NaCl-injured cells. In all treatments, the initial population decreased (P < 0·05) during storage. In CM with no additives, E. coli O157:H7 decreased by 0·6 log 10 cfu g -1 in 18 months. Addition of NaCl and sodium lactate resulted in reductions (P < 0·05) ranging from 1·4-2·4 log 10 cfu g -1 over the same period. Addition of polyphosphate did not affect recovery (P < 0·05). Recovery of E. coli O157:H7 was least (P < 0·05) from CM containing 8% NaCl, and recovery was least efficient (P < 0·05) on selective media (i.e. MacConkey sorbitol agar, MSA). The addition of Mg 2+ to MSA did not enhance recovery. Highest recoveries (P < 0·05) occurred on TSA, TSA plus 1% pyruvic acid and phenol red sorbitol agar (PRSA). E. coli O157:H7 survived (≥18 months) well in frozen poultry, and selective media such as MSA were inadequate for recovering freeze/NaCl-injured cells.
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