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

Abstract

This study aimed at determining the genetic and virulence characteristics of the <i>Listeria monocytogenes</i> from smoked ducks. <i>L. monocytogenes</i> was isolated by plating, and the isolated colonies were identified by PCR. All the obtained seven <i>L. monocytogenes</i> isolates possessed the virulence genes (<i>inl</i>A, <i>inl</i>B, <i>plc</i>B, and <i>hly</i>A) and a 385 bp <i>act</i>A amplicon. The <i>L. monocytogenes</i> 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 (<i>L. monocytogenes</i> 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 (<i>inl</i>A, <i>inl</i>B, <i>plc</i>B, and <i>hly</i>A) and the 385-bp <i>act</i>A amplicon, moreover, three isolates showed clindamycin resistance. In conclusion, this study allowed us to characterize <i>L. monocytogenes</i> isolates from smoked ducks, exhibiting clindamycin and penicillin G resistance, along with the 385-bp <i>act</i>A amplicon, representing higher invasion efficiency than the 268-bp <i>act</i>A, and the higher heat resistance serotype 1/2b.