First Finding of a Methicillin-Resistant Staphylococcus aureus (MRSA) t304/ST6 from Bovine Clinical Mastitis

Area of Science:

• Veterinary Microbiology
• Antimicrobial Resistance
• One Health

Background:

• Methicillin-resistant Staphylococcus aureus (MRSA) poses a significant global health threat to both humans and animals.
• The MRSA t304/ST6 variant is commonly found in human infections but rarely reported in livestock.

Purpose of the Study:

• To report and characterize the first occurrence of the MRSA t304/ST6 variant in a bovine clinical mastitis case.
• To investigate the genetic and phenotypic characteristics of this bovine MRSA isolate.

Main Methods:

• Phenotypic and genotypic resistance profiling of the bovine MRSA isolate.
• Analysis of the isolate's genetic makeup, including SCCmec type, plasmid content, and prophage presence.
• Comparison of genetic elements with known human MRSA strains.

Main Results:

• The bovine MRSA t304/ST6 isolate exhibited low susceptibility to cefoxitin (MIC=16 µg/mL) and possessed the mecA gene within SCCmec IVa.
• The isolate harbored a plasmid similar to those found in human MRSA t304/ST6 strains and a Staphylococcus prophage 3 (ϕSA3) encoding an immune evasion cluster (IEC).
• The presence of human-associated virulence genes (sea, sak, scn) suggests a recent human-to-cow host jump.

Conclusions:

• The findings indicate a likely recent transmission of MRSA t304/ST6 from humans to cattle.
• This study underscores the critical need for robust antimicrobial resistance surveillance programs targeting bovine mastitis pathogens like Staphylococcus aureus and MRSA.