Extended-spectrum ß-lactamase (ESBL)- and Carbapenemase-producing Enterobacterales Isolated from Fresh Herbs and Salads at Retail Level in Switzerland

Abstract

Fresh produce is usually consumed raw or minimally processed, making it a potential vehicle for the transmission of antimicrobial-resistant (AMR) microorganisms to humans. The objective of the study was to assess the occurrence of extended-spectrum ß-lactamase (ESBL)- and carbapenemase-producing Enterobacterales (ESBL-E and CPE), respectively, in 118 fresh herbs and 101 bagged salads collected at retail level in Switzerland and to characterize the isolates’ phenotypic and genotypic properties using culture-based methods and whole genome sequencing (WGS).Of the fresh herbs, 6/118 contained ESBL-E and 7/118 yielded CPE. Of the salads, 13/101 contained ESBL-E and 1/101 CPE. Antimicrobial susceptibility testing (AST) identified 9/29 isolates as multidrug-resistant (MDR).ESBL-E were Escherichia coli (n = 6), Klebsiella pneumoniae (n = 4) Enterobacter chuandaensis (n = 1), and Kluyvera spp. (n = 1) carrying ß-lactamase (bla) genes belonging to the cefotaximase-München (blaCTX-M)-groups, Proteus spp. (n = 1) containing Hôpital-Universitaire-de-Genève-bla (blahugA), Raoultella ornithinolytica (n = 1) carrying sulfhydryl reagent variable bla (blaSHV), and Serratia fonticola (n = 7) carrying S. fonticula bla (blaFONA) genes. CPE were Enterobacter asburiae (n = 1) E. cloacae (n = 6) and E. vonholyi (n = 1) carrying imipenemase bla (blaIMI) genes.Several K. pneumoniae sequence types (STs) were identified (ST967, ST628, ST219, and ST1823), which have been linked to human disease and nosocomial outbreaks. They carried blaCTX-M-15 on plasmids detected globally in environmental and clinical samples. E. coli (ST10, ST48, ST609, ST2040, ST6215 and ST3580) and enterotoxigenic E. coli (ETEC) ST2040 carrying blaCTX-M-15 were found. E. cloacae (ST820 and ST1516) with blaIMI-1 have been found previously in clinical settings and community outbreaks.The occurrence and consumption of fresh produce containing MDR ESBL-E and CPE pose substantial public health risks and raise significant food safety concerns.

Keywords

• Carbapenemases
• Enterobacterales
• Extended-spectrum ß-lactamases
• Fresh herbs
• Pathogens
• Salads