Extended-spectrum ß-lactamase (ESBL)- and Carbapenemase-producing Enterobacterales Isolated from Fresh Herbs and Salads at Retail Level in Switzerland
Silvan Tresch, Michael Biggel, Manuela Schnyder, Magdalena Nüesch‐Inderbinen, Roger Stephan
Abstract
• Fresh herbs and salads are reservoirs of bacteria with antibiotic-resistant genes. • 13% of the salads contained extended-spectrum ß-lactamase-producing bacteria. • 85% of the contaminated salads were prewashed bagged salads. • 5% of fresh herbs contained extended-spectrum ß-lactamase-producing bacteria. • 6% of the fresh herbs contained carbapenemase-producing Enterobacter spp. 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 ( bla CTX-M )-groups, Proteus spp. ( n = 1) containing Hôpital-Universitaire-de-Genève- bla ( bla hugA ), Raoultella ornithinolytica ( n = 1) carrying sulfhydryl reagent variable bla (bla SHV ), and Serratia fonticola ( n = 7) carrying S. fonticula bla ( bla FONA ) genes. CPE were Enterobacter asburiae ( n = 1) E. cloacae ( n = 6) and E. vonholyi ( n = 1) carrying imipenemase bla ( bla IMI ) 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 bla CTX-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 bla CTX-M-15 were found. E. cloacae (ST820 and ST1516) with bla IMI-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.