Potential spread of multidrug-resistant coagulase-negative staphylococci through healthcare waste

Healthcare waste (HCW) might potentially harbor infective viable microorganisms in sanitary landfills. We investigated the antimicrobial susceptibility patterns and the occurrence of the mecA gene in coagulase-negative Staphylococcus strains (CoNS) recovered from the leachate of the HCW in an untreated sanitary landfill.

Bacterial identification was performed by physiological and molecular approaches, and minimum inhibitory concentrations (MICs) of antimicrobial drugs were determined by the agar dilution method according to CLSI guidelines. All oxacillin-resistant bacteria were screened for the mecA gene.

Out of 73 CoNS, seven different species were identified by 16S rDNA sequencing: Staphylococcus felis (64.4%; n = 47), Staphylococcus sciuri (26.0%; n = 19), Staphylococcus epidermidis (2.7%; n = 2), Staphylococcus warneri (2.7%; n = 2), Staphylococcus lentus (1.4%; n = 1), Staphylococcus saprophyticus (1.4%; n = 1), and Staphylococcus haemolyticus (1.4%; n = 1). Penicillin was the least effective antimicrobial (60.3% of resistance; n = 44) followed by erythromycin (39.8%; n = 29), azithromycin (28.8%; n = 21), and oxacillin (16.5%; n = 12). The most effective drug was vancomycin, for which no resistance was observed, followed by gentamicin and levofloxacin, for which only intermediate resistance was observed (22%, n = 16 and 1.4%, n = 1, respectively). Among the oxacillin-resistant strains, the mecA gene was detected in two isolates.

Considering the high antimicrobial resistance observed, our results raise concerns about the survival of putative bacterial pathogens carrying important resistance markers in HCW and their environmental spread through untreated residues discharged in sanitary landfills.