Thermal resistance of wild-type and anti biotic-resistant Listeria monocytogenes in meat and potato substrates

Aims: This study aimed to elucidate the relationship, if any, between the a cquisition/possession of antibiotic resistance in strains of Listeria monoc ytogenes and the resistance of such strains to heat stress. Methods and Results: D-values calculated using a linear survival model were used to comp are the heat resistance of two wild-type (WT) and two antibio tic (streptomycin)-resistant (AR) mutant strains of L. monocytogenes measur ed in minced beef and potato substrates at 55 degreesC, with and without pr ior heat shock at 48 degreesC. In both minced beef and potato, no significa nt differences (P < 0.05) between D-values of AR and WT strains were noted. Heat shock did not significantly increase D-values of WT or AR strains in minced beef, while in potato slices, D-values in almost all cases were sign ificantly higher in samples which had received heat-shock treatment. In min ced beef, the use of a non-selective/overlay recovery medium did not result in higher D-values for any strains, while in potato, significantly higher (P < 0.05) D-values were obtained in most cases. Conclusions: The presence or absence of antibiotic resistance genes did not modulate the heat resistance of the strains examined in this study. Significance and Impact of the Study: The study demonstrated that heat shoc k, and the type of media used to determine bacterial numbers during heat pr ocessing, can significantly affect the D-values obtained.