Pathways of Methicillin-Resistant Staphylococcus aureus in Animal Model: New Insights Regarding Public Health

BACKGROUND: Staphylococcus aureus is considered one of the major threats regarding food safety worldwide. Methicillin-resistant S. aureus (MRSA) strains in livestock, companion animals, and wild animals continue to be a potential risk to people working with them. AIM: The current research aims to investigate the potential pathways of livestock-associated methicillin-resistant Staphylococcus aureus (LA-MRSA) strains in the body after oral infection using the experimental mouse model. METHODS: Seven groups of SPF male mice were purchased and housed. On day 1, six groups of mice were infected orally by the sterile gastric probe using 100 μL/mice of LA-MRSA bacterial suspension (1 × 10(8) colony-forming units (CFU)/mL). The remaining group was kept as negative controls. Over 15 days, these animals have been monitored. Fresh fecal samples were screened for LA-MRSA at day 0, day 7 and day 14 following oral administration of MRSA strains. All animals were sacrificed at day 15, and internal organs (liver, lung, kidney, and intestine) were harvested aseptically and divided into two sections. The first part was histopathologically investigated, while the other half has been tested for LA-MRSA re-isolation. RESULT: The oral challenge of mice by MRSA strains showed that MRSA was re-isolated from feces and intestines of all inoculated mice groups and from internal organs (liver, lung, kidney and intestine) of most mice. Results were confirmed by the detection of the bacteria in gram-stained tissue sections and changes in H&E-stained histopathological tissue sections from these organs. CONCLUSION: Data from the present study indicate the possible colonization of livestock-associated methicillin-resistant Staphylococcus aureus (LA-MRSA) in internal organs following oral infection and thus posing a risk for food-borne infection of MRSA. Infected animals could pass LA-MRSA through feces again, resulting in increased dispersion and environmental contamination.