Objectives: Staphylococcus bacterium has a global spread and species of this genus are the natural flora of human and animal’s skin. These bacteria are found in the upper part of the respiratory tract and the lower part of the genitourinary tract. Staphylococcus is one of the most important human and animal pathogens that causes various infectious diseases. In animals, staphylococci are the main pathogens causing mastitis, which leads to the contamination of milk and dairy products. Staphylococcus quickly becomes resistant to many types of antibiotics through various mechanisms such as enzyme inactivation, biofilm formation, etc. This bacterium becomes resistant to beta-lactam drugs such as penicillin and methicillin by producing penicillinase and PBP2a protein. Heavy metals with a density of more than 5gr/cm3 are classified into three groups: essential, possibly essential, and toxic. Essential heavy metals in very small amounts are necessary in plants and animals by performing physiological and biochemical actions for the continued growth and survival of living organisms, but in large amounts, they cause cell and tissue damage in humans and animals. Zinc (Zn) is an essential heavy metal that is used in the production of dishes and brass alloys, automobile manufacturing, shipbuilding, battery manufacturing, and military industries. Its compounds are used as food supplements, disinfectants, or to prevent digestive diseases in animals. Zinc plays a role in the development and functioning of the brain, immune system and endocrine system. This element balances the amount of copper in the body and its deficiency causes anemia and delays in growth and development. Cadmium (Cd) is an unnecessary or toxic heavy metal used in the production of alloys, paints and pigments, and mainly nickel-cadmium rechargeable batteries. The entry of this element into the body of animals and consequently humans causes problems such as shortness of breath, destruction of the memory system, osteoporosis, bone fractures, increased blood pressure, diabetes, breast and prostate cancer. It is believed that during environmental pollution, heavy metals cause antibiotic resistance through the co-localization of genes involved in resistance to heavy metals and antibiotics. The aim of our study was to investigate the emergence of heavy metal-resistant Staphylococci among methicillin-resistant Staphylococci species for the first time in Iran. Methodology: In this study, a total of 300 Staphylococcal isolates from humans and domestic animals were studied in order to identify phenotypic resistance to methicillin by cefoxitin disc diffusion method. The isolates that were phenotypically resistant to methicillin (MRS) were tested to evaluate the phenotypic resistance to zinc chloride and cadmium acetate salts using Muller Hinton metal agar medium. Finally, mecA gene was evaluated to evaluate genotypic resistance to methicillin and czrC gene to evaluate genotypic resistance to heavy metals. Findings: The results showed that 17% of Staphylococci isolated from humans and domestic animals were resistant to methicillin. In general, using nucA gene PCR, it was determined that 49% of methicillin-resistant (MRS) isolates are methicillin-resistant Staphylococcus aureus (MRSA). Specific PCR of mecA gene showed that 49% of the isolates were positive for the presence of mecA gene. Heavy metal sensitivity test showed that 49% of MRS isolates were resistant to chloride and 8% to cadmium acetate. PCR of the czrC gene showed that among all the isolates that were phenotypically resistant to these heavy metals, only 66.7% of dog MRS isolates had the czrC gene. Conclusion: In the present study, phenotypic resistance to methicillin was significantly related to the presence of mecA gene in all MRS strains. Interestingly, in dog MRS strains, phenotypic resistance to heavy metals was significantly related to the presence of the czrC gene, and there was also a high correlation between mecA and czrC genes. Environmental pollution of zinc and cadmium and exposure to these heavy metals, as well as the use of high concentrations of zinc, may cause the emergence and spread of methicillin-resistant Staphylococcus in animals; because it is thought that czrC (responsible for resistance to zinc and cadmium salts) and mecA (responsible for methicillin resistance) genes are the same loci. These two genes are both located inside type V of the SCCmec element, so the heavy metals zinc and cadmium probably not only cause the expression of the czrC gene but also the expression of the mecA gene in Staphylococcus spp.

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