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 impact of therapeutic zinc oxide (ZnO) supplementation in pig feed on the prevalence and persistence of methicillin-resistant Staphylococcus aureus (MRSA) in nursery pigs. The focus keyphrase, “zinc oxide therapy and MRSA in pigs,” is central to the research. The study was prompted by concerns that the use of high-dose ZnO, a common alternative to antibiotics in pig farming, may select for MRSA due to the genetic linkage between the zinc resistance gene (czrC) and the methicillin resistance gene (mecA) within the SCCmec element of MRSA. The randomized controlled trial compared a therapeutic ZnO dose (3000 mg/kg) to the recommended dietary dose (100 mg/kg), monitoring pigs from birth through four weeks post-weaning for MRSA carriage, growth performance, and serum zinc levels.
Who was studied?
The study population comprised 110 nursery pigs, all naturally colonized with czrC-positive MRSA, sourced from 23 sows at the University of Guelph’s swine research station. Upon weaning at 21 days, pigs were randomized to receive either control feed (100 mg ZnO/kg; n=49) or treatment feed (3000 mg ZnO/kg; n=50), with neither group receiving additional antimicrobials. Pigs were monitored throughout a 49-day period, with nasal swabs for MRSA detection collected at multiple intervals. The design allowed assessment of MRSA prevalence and persistence in relation to zinc oxide therapy, while controlling for variables such as birthweight, parity, and sow MRSA status.
Most important findings
| Critical Point | Detail |
|---|---|
| MRSA Prevalence & Persistence | Therapeutic ZnO supplementation (3000 mg/kg) significantly increased MRSA prevalence in pigs at 1 week (OR=18.1, P<0.01) and 2 weeks (OR=3.01, P=0.01) post-weaning compared to the control group, with a sharp rise immediately after weaning and a subsequent decline by week 4. Persistent MRSA carriage (≥2 positive tests post-weaning) was observed in 22% of treated pigs versus only 2% of controls (P<0.01). |
| Resistance Genetics | All MRSA isolates harbored the czrC gene and demonstrated uniform resistance to zinc, regardless of treatment group, indicating pre-existing genetic capacity for zinc and methicillin resistance in the herd. |
| Growth and Health Outcomes | No significant differences in growth performance, feed intake, or health status were observed between groups. Notably, pigs not receiving therapeutic ZnO experienced neither health nor productivity issues, questioning the necessity of prophylactic ZnO use in healthy herds. |
| Serum Zinc Levels | Serum zinc was significantly higher at 4 weeks post-weaning in treated pigs (P=0.02), confirming effective systemic absorption of dietary zinc. However, this did not correlate with improved growth. |
| Human Health Implications | The findings underscore the risk that non-antibiotic interventions like high-dose ZnO can maintain or increase MRSA prevalence in livestock, with potential for zoonotic transmission and broader public health impact. |
Key implications
The study demonstrates that therapeutic zinc oxide therapy in pig farming can inadvertently drive the prevalence and persistence of MRSA, even in the absence of antibiotics. For heavy metal certification programs, these findings highlight the need for stringent regulation of ZnO use to limit co-selection of antimicrobial resistance. Furthermore, the lack of observed health benefits in pigs not receiving high-dose ZnO suggests that routine prophylactic use of zinc oxide should be reevaluated, supporting the adoption of responsible, evidence-based supplementation policies to mitigate resistance risks in both animal and human populations.
Citation
Slifierz MJ, Friendship R, Weese JS. Zinc Oxide Therapy Increases Prevalence and Persistence of Methicillin-Resistant Staphylococcus aureus in Pigs: A Randomized Controlled Trial. Zoonoses and Public Health. 2015;62:301-308. doi:10.1111/zph.12150
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.
