Thermal resistance of wild-type and antibiotic-resistant Listeria monocytogenes in meat and potato substrates.
OBJECTIVE
This study aimed to elucidate the relationship, if any, between the acquisition/possession of antibiotic resistance in strains of Listeria monocytogenes and the resistance of such strains to heat stress.


RESULTS
D-values calculated using a linear survival model were used to compare the heat resistance of two wild-type (WT) and two antibiotic (streptomycin)-resistant (AR) mutant strains of L. monocytogenes measured in minced beef and potato substrates at 55 degrees C, with and without prior heat shock at 48 degrees C. In both minced beef and potato, no significant 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 significantly higher in samples which had received heat-shock treatment. In minced 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.


CONCLUSIONS
The study demonstrated that heat shock, and the type of media used to determine bacterial numbers during heat processing, can significantly affect the D-values obtained.
Walsh
D
D
The National Food Centre, Teagasc, Dunsinea, Castleknock, Dublin 15, Ireland. D.WALSH@nfc.teagasc.ie
Sheridan
J J
JJ
Duffy
G
G
Blair
I S
IS
McDowell
D A
DA
Harrington
D
D
D004352:Drug Resistance, Microbial / Q000235:genetics / Q000502:physiology*; D005516:Food Microbiology; D006358:Hot Temperature; D008089:Listeria monocytogenes / Q000502:physiology*; D008460:Meat / Q000382:microbiology*; D011198:Solanum tuberosum / Q000382:microbiology*