Antibiotic resistance of Enterobacteriaceae isolated from fresh fruits and vegetables and characterization of their AmpC b-lactamases

Enterobacteria may gain antibiotic resistance and be potent pathogens wherever they are present, including in fresh fruits and vegetables. This study tested the antibiotic resistance of enterobacteria isolated from 13 types of local and imported fresh fruits and vegetables (n ¼ 105), using the standard Kirby-Bauer disk diffusion method. Phenotypic and genotypic characterizations of AmpC b-lactamases were determined in cefoxitin-resistant isolates. Ten percent of the enterobacteria tested (n ¼ 88) were pansusceptible, 74% were resistant to at least one antibiotic, and 16% were multidrug resistant. Enterobacteria isolates showed the highest antibiotic resistance against ampicillin (66%), cephalothin (57%), amoxicillin–clavulanic acid (33%), cefoxitin (31%), tetracycline (9%), nalidixic acid (7%), trimethoprim (6%), and kanamycin (5%). Three isolates showed intermediate resistance to the clinically important antibiotic imipenem. Escherichia coli isolated from lettuce exhibited multidrug resistance against five antibiotics. Fifteen isolates were confirmed to have AmpC b-lactamase, using the inhibitor-based test and the antagonism test; the latter test confirmed that the enzyme was an inducible type. Four types of ampC b-lactamase genes (CIT, EBC, FOX, and MOX) were detected in eight isolates: four Enterobacter cloacae isolates and one isolate each of Citrobacter freundii, Enterobacter asburiae, Enterobacter hormaechei, and Enterobacter ludwigii. It was concluded that fresh fruits and vegetables might play a role as a source or vehicle for transferring antibiotic-resistant bacteria that might spread to other countries through exportation. The clinically significant AmpC b-lactamase was rarely documented in the literature on bacteria isolated from fruits and vegetables, and to our knowledge, this is the first report on the detection of an inducible type in such commodities.