Low-level antimicrobial resistance of Enterobacteriaceae isolated from the nares of pig-exposed persons

Extended-spectrum beta-lactamase (ESBL)-producing Enterobacteriaceae (ESBL-E) have recently emerged in livestock and humans. Therefore, this study assessed the carriage of Enterobacteriaceae in the anterior nares and associated antimicrobial resistance in pig-exposed persons. Nasal swabs were enriched in non-selective broth and then plated on MacConkey and ESBL-selective agars. Species was confirmed by matrix-assisted laser-desorption ionization-time-of-flight mass spectrometry (MALDI-ToF MS). Antimicrobial susceptibility testing was performed according to European Committee on Antimicrobial Susceptibility Testing (EUCAST) guidelines. Of 114 pig-exposed persons tested, Enterobacteriaceae were detected in the nares of 76 (66.7%) participants. The predominant species were Proteus mirabilis (n = 17, 14.9%), Pantoea agglomerans (n = 13, 11.4%), Morganella morganii (n = 9, 7.9%), Citrobacter koseri (n = 9, 7.9%), Klebsiella pneumoniae, Escherichia coli and Proteus vulgaris (each n = 8, 7.0%). ESBL-E were not detected. Of all isolates tested, 3.4% were resistant against ciprofloxacin, 2.3% against gentamicin, 23.9% against trimethoprim-sulfamethoxazole and 44.3% against tigecycline. Despite the high prevalence of ESBL-E in livestock, pig-exposed persons did not carry ESBL-E in their nares. This finding is important, because colonization of the nasal reservoir might cause endogenous infections or facilitate transmission of ESBL-E in the general population.