High Prevalence of Listeria monocytogenes in Smoked Duck: Antibiotic and Heat Resistance, Virulence, and Genetics of the Isolates

This study aimed at determining the genetic and virulence characteristics of the Listeria monocytogenes from smoked ducks. L. monocytogenes was isolated by plating, and the isolated colonies were identified by PCR. All the obtained seven L. monocytogenes isolates possessed the virulence genes (inlA, inlB, plcB, and hlyA) and a 385 bp actA amplicon. The L. monocytogenes isolates (SMFM2018 SD 1-1, SMFM 2018 SD 4-1, SMFM 2018 SD 4-2, SMFM 2018 SD 5-2, SMFM 2018 SD 5-3, SMFM 2018 SD 6-2, and SMFM 2018 SD 7-1) were inoculated in tryptic soy broth (TSB) containing 0.6% yeast extract at 60°C, followed by cell counting on tryptic soy agar (TSA) containing 0.6% yeast extract at 0, 2, 5, 8, and 10 min. We identified five heat resistant isolates compared to the standard strain (L. monocytogenes ATCC13932), among which three exhibited the serotype 1/2b and D-values of 5.41, 6.48, and 6.71, respectively at 60°C. The optical densities of the cultures were regulated to a 0.5 McFarland standard to assess resistance against nine antibiotics after an incubation at 30°C for 24 h. All isolates were penicillin G resistant, possessing the virulence genes (inlA, inlB, plcB, and hlyA) and the 385-bp actA amplicon, moreover, three isolates showed clindamycin resistance. In conclusion, this study allowed us to characterize L. monocytogenes isolates from smoked ducks, exhibiting clindamycin and penicillin G resistance, along with the 385-bp actA amplicon, representing higher invasion efficiency than the 268-bp actA, and the higher heat resistance serotype 1/2b.