Prevalence of vancomycin- and aminoglycoside-resistant pathogenic enterococci in municipal wastewater: A study in northwest Iran

ABSTRACT The extensive use of antimicrobials has contributed to the emergence of multidrug-resistant (MDR) microorganisms in municipal wastewater. The prevalence, resistance patterns, and virulence factors of Enterococcus species were studied in 25 untreated municipal wastewater samples collected from Ardabil, Iran (2017–2018). We identified 87 Enterococcus isolates using biochemical and PCR assays, of which 59.8% were E. faecium, 33.3% E. faecalis, and 6.9% other species. Susceptibility testing showed considerable resistance to rifampicin (61%) and tetracycline (57.5%), while all isolates were sensitive to teicoplanin. Vancomycin resistance was identified in 3.8% of E. faecium isolates (all vanA positive). Resistance to ampicillin (8%) was exclusively associated with an MDR phenotype. High-level resistance to gentamicin (23%) and streptomycin (27.6%) was associated with PCR-validated aminoglycoside modifying enzyme genes. Moreover, 89.6% of E. faecalis and 71.1% of E. faecium carried at least one virulence gene, with gelE and asa1 being the most prevalent. These findings suggest that municipal wastewater is a major reservoir of virulent MDR enterococci and underscore the urgent need to enhance solutions for wastewater treatment to reduce public health hazards.