title: Resistance to zinc and cadmium in Staphylococcus aureus of 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-associated Staphylococcus aureus. This study was conducted to determine the prevalence of zinc and cadmium resistance in S. aureus isolated in the United States.
  
  
  METHODS
  Cross-sectional study of convenience sample of S. aureus isolates.
  
  
  METHODS
  Three hundred forty-nine S. aureus isolates, including methicillin-resistant S. aureus (MRSA) and methicillin-susceptible S. 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) of S. aureus isolates were czrC positive. MRSA isolates were more likely to be czrC positive compared to MSSA (MRSA czrC positive: 12/61, 19.6%; MSSA czrC positive: 12/183, 6.6%). After adjustment for oxacillin and clindamycin susceptibility in analysis, multidrug-resistant S. aureus was observed to have low odds of being czrC positive (P = .03). The odds of being czrC positive were observed to be significantly high in tetracycline-resistant S. aureus isolated 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 treating S. aureus infections.
authors.affiliation: Center for Emerging Infectious Diseases, College of Public Health, University of Iowa, Iowa City, Iowa.
authors.forename: Rajeshwari
authors.initials: R
authors.lastname: Nair
authors.forename: Dipendra
authors.initials: D
authors.lastname: Thapaliya
authors.forename: Yutao
authors.initials: Y
authors.lastname: Su
authors.forename: Tara C
authors.initials: TC
authors.lastname: Smith
mesh_terms: D000818:Animals; D002104:Cadmium / Q000494:pharmacology*; D024881:Drug Resistance, Bacterial; D006801:Humans; D055624:Methicillin-Resistant Staphylococcus aureus / Q000187:drug effects; D008826:Microbial Sensitivity Tests; D013203:Staphylococcal Infections / Q000188:drug therapy / Q000382:microbiology / Q000662:veterinary; D013211:Staphylococcus aureus / Q000187:drug effects*; D013552:Swine; D015032:Zinc / Q000494:pharmacology*
chemical_list: D002104:Cadmium; D015032:Zinc