Bovine mastitis outbreak in Japan caused by methicillin-resistant Staphylococcus aureus New York/Japan clone

Area of Science:

• Veterinary Medicine
• Microbiology
• Infectious Diseases

Background:

• Methicillin-resistant Staphylococcus aureus (MRSA) poses significant challenges in both human and animal healthcare due to multidrug resistance.
• The New York/Japan clone (NJC) of MRSA, typically associated with hospital-acquired infections in humans, was identified in a Japanese dairy herd, differing genetically from common bovine-associated strains.

Purpose of the Study:

• To monitor and describe a bovine mastitis outbreak caused by the NJC MRSA clone in Japan.
• To investigate the transmission dynamics and effective eradication strategies for MRSA in a dairy herd setting.

Main Methods:

• Monitoring of a bovine mastitis case caused by MRSA NJC isolates over a 5-month period.
• Regular milk testing of lactating cows to identify MRSA carriers.
• Implementation of culling and dry-off procedures for infected cows.
• Genotyping to analyze the genetic exchange of the staphylococcal cassette chromosome mec.

Main Results:

• MRSA NJC isolates in the dairy herd possessed human-associated virulence factors (β-hemolysin-converting bacteriophage, immune evasion cluster), suggesting human-to-bovine transmission.
• Most intramammary infections (IMIs) were asymptomatic, with only 3 initial clinical cases observed out of 78 cows.
• 31 cows were identified as MRSA carriers, and eradication was achieved within 5 months through targeted interventions.
• Genotyping indicated facile exchange of the staphylococcal cassette chromosome mec between MRSA and methicillin-sensitive S. aureus in infected udders.

Conclusions:

• A combination of culling and drying off infected quarters proved effective in eradicating MRSA from the dairy herd.
• The study underscores the potential for MRSA clones, like NJC, to emerge in animal populations, possibly through human carriers.
• Effective surveillance and intervention protocols are crucial for managing MRSA in livestock to prevent further spread and potential zoonotic implications.