Clinical Pharmacist and Master’s student in Clinical Pharmacy with research interests in pharmacovigilance, behavioral interventions in mental health, and AI applications in clinical decision support. Experience includes digital health research with Bloomsbury Health (London) and pharmacovigilance practice in patient support programs. Published work covers drug awareness among healthcare providers, postpartum depression management, and patient safety reporting. 
Clinical Pharmacist and Master’s student in Clinical Pharmacy with research interests in pharmacovigilance, behavioral interventions in mental health, and AI applications in clinical decision support. Experience includes digital health research with Bloomsbury Health (London) and pharmacovigilance practice in patient support programs. Published work covers drug awareness among healthcare providers, postpartum depression management, and patient safety reporting. What was studied?
This original research article investigated the relationship between zinc supplementation in pig diets and the nasal carriage of methicillin-resistant Staphylococcus aureus (MRSA) harboring the mecA gene. The primary aim was to determine whether supplementing pig diets with elevated zinc, specifically as zinc oxide (ZnO), influences the prevalence of MRSA and the czrC gene, which encodes resistance to zinc and cadmium and has been linked to methicillin resistance. By collecting nasal swabs from pigs exposed to different dietary zinc concentrations, the researchers examined both phenotypic and genotypic resistance to zinc and methicillin. This study is especially relevant for the heavy metal certification program, as it explores the potential for zinc supplementation to co-select for antibiotic resistance, thereby highlighting an intersection between heavy metal use in animal feed and antimicrobial resistance.
Who was studied?
The study population consisted of nursery pigs (n=40) and finisher pigs (n=40) from a controlled nutritional study in the United States. These pigs were divided into groups receiving various dietary regimens: nursery pigs were split into control (basal diet with zinc sulfate) and high zinc (basal diet plus 1800 mg/kg ZnO) groups, while finisher pigs were allocated to four groups receiving 0, 75, 150, or 225 mg/kg of supplemental ZnO, in addition to a basal diet. Nasal swabs were taken once from each pig to assess the prevalence of MRSA and the presence of the resistance genes mecA, czrC, and tet(M). The inclusion of both nursery and finisher pigs and the use of multiple zinc supplementation levels allowed the researchers to assess age-related and dose-dependent effects of zinc on the carriage of MRSA.
Most Important Findings
| Critical Points | Details |
|---|---|
| Zinc supplementation increases MRSA prevalence | Pigs fed higher levels of ZnO exhibited a dose-dependent increase in nasal carriage of mecA-positive MRSA. In nursery pigs, 0% of controls and 20% of those fed high zinc were MRSA-positive. Among finisher pigs, MRSA prevalence was 0%, 10%, 20%, and 50% for 0, 75, 150, and 225 mg/kg ZnO groups, respectively. |
| CzrC gene association with MRSA and zinc | 58.3% of mecA-positive S. aureus isolates also carried the czrC gene, whereas none of the mecA-negative isolates did. Presence of both mecA and czrC was significantly associated with higher zinc supplementation (p=0.002 for mecA, p=0.006 for czrC). |
| Zinc resistance phenotype | The median minimum inhibitory concentration (MIC) of zinc for czrC-positive isolates was 12 mM, compared to 2 mM for czrC-negative isolates (p<0.0001), indicating a strong phenotypic resistance in czrC-positive strains. |
| No significant link to tetracycline resistance | Although the tet(M) gene was present in 28.7% of S. aureus isolates, its prevalence did not significantly associate with mecA or czrC, nor did the tetracycline MIC differ significantly between MRSA and MSSA. |
| Implications for heavy metal use in agriculture | The co-location of zinc and methicillin resistance genes suggests that heavy metal supplementation in feed can co-select for antibiotic resistance, which is a concern for food safety and public health. |
Key implications
The study demonstrates that elevated zinc supplementation in pig diets can co-select for both zinc and methicillin resistance, specifically czrC-positive and mecA-positive MRSA. For heavy metal certification programs, this finding underscores the need to monitor and regulate zinc use in animal feeds to prevent the propagation of antibiotic-resistant pathogens, which could have significant repercussions for public health and food safety.
Citation
Amachawadi RG, Scott HM, Nitikanchana S, Vinasco J, Tokach MD, Dritz SS, Nelssen JL, Goodband RD, Nagaraja TG. Nasal Carriage of mecA-Positive Methicillin-Resistant Staphylococcus aureus in Pigs Exhibits Dose–Response to Zinc Supplementation. Foodborne Pathog Dis. 2015;12(2):159-163. doi:10.1089/fpd.2014.1851
Heavy metals are high-density elements that accumulate in the body and environment, disrupting biological processes. Lead, cadmium, arsenic, mercury, nickel, tin, aluminum, and chromium are of greatest concern due to persistence, bioaccumulation, and health risks, making them central to the HMTC program’s safety standards.
