Extended-spectrum β-lactamase (ESBL) and AmpC β-lactamase-producing Enterobacteriaceae are no longer restricted to the health care system, but represent increased risks related to environmental integrity and food safety. Fresh produce has been increasingly reported to constitute a reservoir of multidrug-resistant (MDR) potential human pathogenic Enterobacteriaceae. This study aimed to detect, identify, and characterize the antimicrobial resistance of ESBL/AmpC-producing Enterobacteriaceae isolates from fresh vegetables at point of sale. Vegetable samples (spinach, tomatoes, lettuce, cucumber, and green beans; n = 545) were purchased from retailers in Gauteng, the most densely populated province in South Africa. These included street vendors, trolley vendors, farmers' market stalls, and supermarket chain stores. Selective enrichment, plating onto chromogenic media, and matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF MS) confirmation of isolate identities showed that 17.4% (95/545) vegetable samples analyzed were contaminated with presumptive ESBL/AmpC-producing Enterobacteriaceae. Dominant species identified included Escherichia coli, Enterobacter cloacae, Enterobacter asburiae, and Klebsiella pneumoniae. Phenotypic antibiotic resistance analysis showed that 96.1% of 77 selected isolates were MDR, while resistance to aminoglycoside (94.8%), chloramphenicol (85.7%), and tetracycline (53.2%) antibiotic classes was most prevalent. Positive phenotypic analysis for ESBL production was shown in 61 (79.2%) of the 77 isolates, and AmpC production in 41.6% of the isolates. PCR and sequencing confirmed the presence of β-lactamase genes in 75.3% isolates from all vegetable types analyzed, mainly in E. coli, Enterobacter spp., and Serratia spp. isolates. CTX-M group 9 (32.8%) was the dominant ESBL type, while EBC (24.1%) was the most prevalent plasmidic type AmpC β-lactamase. Our findings document for the first time the presence of MDR ESBL/AmpC-producing Enterobacteriaceae in raw vegetables sold at selected retailers in Gauteng Province, South Africa.
Keywords: antibiotic resistance; food safety; fresh produce.