A comprehensive One Health investigation of erythromycin and quinupristin/dalfopristin resistant <i>Enterococcus</i> spp. in Iran

Enterococci, flagged by the WHO as a rising cause of antibiotic-resistant infections, make surveillance crucial to control resistant strains. We investigated the resistance to linezolid, quinupristin/dalfopristin (Q/D), and erythromycin in <i>Enterococcus faecalis</i> (<i>n</i> = 251) and <i>Enterococcus faecium</i> (<i>n</i> = 434) isolates collected from patients, healthy carriers, hospitals, poultry, livestock, and municipal wastewater in Ardabil, Iran. The isolates were tested for resistance using phenotypic and genotypic methods. Although none of the isolates were resistant to linezolid, 24.9% of <i>E. faecium</i> isolates were resistant to Q/D, particularly those from patients and poultry slaughterhouse wastewater effluent (<i>P</i> < 0.05). The Q/D resistance genes <i>msrC</i> and <i>ermB</i> were detected in 76.85 and 20.37% of <i>E. faecium</i> isolates, respectively. Erythromycin resistance was common in <i>E. faecalis</i> (51.8%) and <i>E. faecium</i> (37.5%), with no significant difference between sources. However, isolates from patients and livestock wastewater had higher erythromycin MICs. Erythromycin resistance genes, such as <i>ermB</i>, <i>ermC</i>, <i>ermTR</i>, and <i>ermA</i>, were found in 80.7, 41.2, 26.5, and 19% of <i>E. faecium</i> and 80.3, 51.6, 22.4, and 25.8% of <i>E. faecalis</i> isolates, respectively. In conclusion, linezolid is a viable treatment for enterococcal infections in Ardabil, but widespread erythromycin- and Q/D-resistant enterococci pose a public health risk.