Whole-Genome Sequencing and Genomic Characterization of a Multi-Drug Resistant Phenotype of Listeria monocytogenes Isolated from Pet Food

Listeria monocytogenes is already a well-known foodborne bacterial pathogen, ubiquitously dispersed not only in the food production environment but also in the primary animal production environment as well. The present study performed whole-genome characterization of the multidrug-resistant (MDR) L. monocytogenes strain BF11, previously isolated from raw pet food and phenotypically described for antimicrobial resistance. To this end, the genomic analysis performed on the isolate confirmed the pathogen’s designation as a serotype 1/2b strain belonging to ST5 and CC5 (Lineage I), carrying multiple MDR genes, stress-related genes, and mobile genetic elements, despite the absence of plasmids. The strain is phylogenetically closely related to Lineage I epidemic strains (e.g., F2365), as it has a full-length inlA and a functional prfA, rendering it capable of invading human cells and marking its high virulence. Overall, this strain may represent a potentially novel genomic profile when core genome multilocus sequence typing (cgMLST) is used, although further data from additional isolates would be required to confirm its classification within a new Complex Type, while displaying a hybrid unique profile. It is an evolved ST5 L. monocytogenes strain that has acquired genetic material conferring a “clinical signature” (Lineage I-like) and an extensive resistance network. Therefore, presence of L. monocytogenes strain BF11 in pet food is alarming, since such hybrid strains often evade surveillance monitoring as they do not fit strictly into classical categories, posing a serious food safety and public health threat in the concept of One Health.