Infectious Diseases 2020

Infectious Diseases 2020

Molecular epidemiology of Salmonella Infantis in Europe

Alba et al., Microbial Genomics 2020 10 April, 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.