phenotypic and genotypic study of resistance to zinc and cadmium salts in methicillin-resistant staphylococci isolated from humans and domestic animals

The aim of this study was to investigate the emergence of staphylococci resistant to heavy metals among methicillin-resistant staphylococcus spp. (mrs) for the first time in iran. in the present study, in the first step, 300 staphylococcus isolates from humans and domestic animals (cows, horses, dogs, and cats) were studied by disk diffusion method to identify resistance to methicillin. then among the resistant isolates, staphylococcus aureus (s. aureus) was confirmed by detecting the nuca gene using pcr. after identifying the mrs and methicillin-resistant s. aureus (mrsa) strains, these isolates were phenotypically tested to evaluate the resistance to zinc chloride and cadmium acetate using muller hinton agar (mha) culture medium supplemented with metal. finally, meca and czrc genes were examined using the pcr method to evaluate the genotypic resistance to methicillin and heavy metals, respectively. the frequency of phenotypic mrs isolates in the phenotypic evaluation was 51 (17%), and almost half of the mrs isolates (n = 25 or 49%) were confirmed to be mrsa using the s. aureus -specific pcr assay for the meca gene. heavy metal susceptibility testing using mueller hinton agar plates (becton dickinson) supplemented with either zinc chloride or cadmium acetate revealed that 49% and 8% of mrs isolates were resistant to zinc chloride and cadmium acetate, respectively. pcr of the czrc gene showed that only 66.7% of dog mrs isolates phenotypically resistant to these heavy metals harbored the czrc gene. here, phenotypic resistance to methicillin had a significant relationship with the existence of the meca gene in all mrs strains. interestingly, in dog mrs strains the phenotypic resistance to heavy metals had a significant relationship to the harboring of the czrc gene, and also there was a high correlation between meca and czrc genes. therefore, the presence of heavy metals (zinc and cadmium) in the living environment of staphylococci makes these bacteria resistant to methicillin.