Shiga toxin-producing Escherichia coli (STEC) carried by asymptomatic individuals constitute an important reservoir for community transmission, but large-scale analyses of antimicrobial resistance (AMR) in carrier-derived STEC remain limited. In this study, to obtain fundamental information relevant to the eradication of STEC carriage, we analyzed 495 STEC strains isolated from stool-screened asymptomatic carriers in Japan. All the isolates had been previously subjected to whole-genome sequencing and were classified into more than 100 serotypes, predominantly O156:H25 (13.5%), O174:H21 (7.7%), and O105:H7 (6.1%). Genome-based analysis revealed at least one antimicrobial resistance gene (ARG) in 83 isolates (16.8%), with aph(3″)-Ib, aph(6)-Id, sul2, tet(A), and blaTEM-1 being the most prevalent. Most carrier-derived STEC belonged to phylogroup B1, whereas ARGs were identified in isolates from diverse phylogenetic lineages. Comparative analysis revealed that the AMR profiles of carrier-derived STEC were similar to those of human commensal E. coli, whereas cattle commensal isolates exhibited a higher ARG prevalence. Phenotypic susceptibility testing revealed that resistance to ampicillin (n = 33) and tetracycline (n = 50) was the most common, whereas resistance to fluoroquinolones (n = 1) was infrequent and no resistance was observed to fosfomycin (n = 0) or amikacin (n = 0). Together, these findings provide a comprehensive overview of AMR in STEC from asymptomatic carriers in Japan and support the continued effectiveness of several antimicrobial agents while underscoring the importance of ongoing genomic surveillance.
Imai et al. (Thu,) studied this question.