Abstract
Salmonella enterica serovar Infantis is the fifth most common Salmonella serovar isolated in England and Wales. Epidemiological, genotyping and antimicrobial-resistance data for S . enterica Infantis isolates were used to analyse English and Welsh demographics over a 5 year period. Travel cases associated with S . enterica Infantis were mainly from Asia, followed by cases from Europe and North America. Since 2000, increasing numbers of S . enterica Infantis had multidrug resistance determinants harboured on a large plasmid termed ‘plasmid of emerging S . enterica Infantis’ (pESI). Between 2013 and 2018, 42 S . enterica Infantis isolates were isolated from humans and food that harboured resistance determinants to multiple antimicrobial classes present on a pESI-like plasmid, including extended-spectrum β-lactamases (ESBLs; bla CTX-M-65). Nanopore sequencing of an ESBL-producing human S . enterica Infantis isolate indicated the presence of two regions on an IncFIB pESI-like plasmid harbouring multiple resistance genes. Phylogenetic analysis of the English and Welsh S . enterica Infantis population indicated that the majority of multidrug-resistant isolates harbouring the pESI-like plasmid belonged to a single clade maintained within the population. The bla CTX-M-65 ESBL isolates first isolated in 2013 comprise a lineage within this clade, which was mainly associated with South America. Our data, therefore, show the emergence of a stable resistant clone that has been in circulation for some time in the human population in England and Wales, highlighting the necessity of monitoring resistance in this serovar.
Highlights
Non-typhoidal Salmonella infections are generally self- limiting, cause an estimated 93.8 million global cases per annum, with approximately 86 % of these being foodborne gastroenteritis cases [1]
Out of the 943 S. enterica Infantis isolates analysed for the demographic study, 917 were from eBG31 and 26 belonged to eBG297 (Table S2)
S. enterica Infantis has been the most prevalent serovar isolated from fresh poultry meat and broiler flocks from across Europe [6, 54] and human S. enterica Infantis infections are often associated with poultry meat [2, 6, 55,56,57,58]
Summary
Non-typhoidal Salmonella infections are generally self- limiting (but may cause disease requiring antimicrobial treatment), cause an estimated 93.8 million global cases per annum, with approximately 86 % of these being foodborne gastroenteritis cases [1]. The population structure of S. enterica Infantis isolates in England and Wales consists of two eBurst groups (eBGs), eBG31 and eBG297, with eBG31 being the predominant group [3] This serovar is dominant in animal reservoirs, especially in poultry where it accounted for 36.7 % of isolates in Europe in 2018 [4,5,6]. The plasmid described, ∼280 kbp in size, contained genes conferring resistance to tetracycline, trimethoprim, sulfamethoxazole, antiseptics and heavy metals, and was termed 'plasmid of emerging S. enterica Infantis' (pESI). This plasmid contained genes associated with virulence, including those encoding yersiniabactin (ybt operon) and fimbriae (fea and ipf operons), which enhance the colonization capability and fitness of the bacterium [9]. Similar pESI-like plasmids that have evolved to confer resistance to extended-spectrum β-lactams via the acquisition of blaCTX-M-1 and blaCTX-M-65 genes have been reported across the globe, including the United States, South America and Europe [4,5,6,7,8,9,10,11]
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