Resistance to Zinc and Cadmium inStaphylococcus aureusof Human and Animal Origin

Abstract

Objective.Studies conducted in Europe have observed resistance to trace metals such as zinc chloride and copper sulfate in livestock-associatedStaphylococcus aureus. This study was conducted to determine the prevalence of zinc and cadmium resistance inS. aureusisolated in the United States.Design.Cross-sectional study of convenience sample ofS. aureusisolates.Participants.Three hundred forty-nineS. aureusisolates, including methicillin-resistantS. aureus(MRSA) and methicillin-susceptibleS. aureus(MSSA) obtained from human, swine, and retail meat were included in the sample set.Methods.Polymerase chain reaction was used to test for the presence of genes for zinc and cadmium resistance (czrC), methicillin resistance (mecA), and staphylococcal complement inhibitor (scn). Antibiotic susceptibility of isolates was tested using the broth microdilution method. Data were analyzed using the multivariable logistic regression method.Results.Twenty-nine percent (102/349) ofS. aureusisolates wereczrCpositive. MRSA isolates were more likely to beczrCpositive compared to MSSA (MRSAczrCpositive: 12/61, 19.6%; MSSAczrCpositive: 12/183, 6.6%). After adjustment for oxacillin and clindamycin susceptibility in analysis, multidrug-resistantS. aureuswas observed to have low odds of beingczrCpositive (P= .03). The odds of beingczrCpositive were observed to be significantly high in tetracycline-resistantS. aureusisolated from noninfection samples (P = .009) and swine (P< .0001).Conclusions.Resistance to zinc and cadmium was observed to be associated with MRSA, a finding consistently observed in European studies. Prolonged exposure to zinc in livestock feeds and fertilizers could propagate resistance to the metal ion, thereby hindering use of zinc-based topical agents in treatingS. aureusinfections.