10.04.2020

Alba et al., Microbial Genomics 2020

Salmonella enterica serovar Infantis (S. Infantis) was reported as the most frequent serovar in broilers flocks (45.6%) and broiler meat (50.6%) in Europe and its prevalence is increasing in breeding hens in some European Member States.
In humans, S. Infantis has been classified as the fourth most prevalent serovar in non-typhoidal Salmonella (NTS) human infections in Europe. 
A clone harbouring a conjugative plasmid of emerging S. Infantis (pESI)-like megaplasmid, carrying multidrug resistant (MDR) and extended-spectrum beta-lactamases (ESBL) genes, has spread in the Italian broiler chicken industry also causing human illness. The European S. Infantis population appeared heterogeneous, with different genetic clusters defined at core-genome level. However, pESI-like variants present in 64.1% of the isolates were more genetically homogeneous and capable of infecting different clonal lineages in most of the countries. Two different pESI-like with ESBL genes (n=82) were observed: blaCTX-M-1-positive in European isolates and blaCTX-M-65-positive in American isolates (study outgroup). Both variants had toxin-antitoxin systems, resistance genes towards tetracyclines, trimethoprim, sulphonamides and aminoglycosides, heavy metals (merA) and disinfectants (qacEΔ). Worryingly, 66% of the total isolates studied presented different gyrA chromosomal point mutations associated with (fluoro)quinolone resistance (MIC range 0.125–0.5mg/L), while 18% displayed transferable macrolide resistance mediated by mph, mef and erm(B) genes. Proper intervention strategies are needed to prevent further dissemination/transmission of MDR S. Infantis and pESI-like along the food chain in Europe.