Molecular Characterization of Methicillin-Resistant Staphylococcus aureus Isolated from Australian Animals and Veterinarians.

This study investigates the presence and types of antibiotic-resistant bacteria known as methicillin-resistant Staphylococcus aureus (MRSA) in Australian animals and veterinarians, highlighting the dominance of one bacterial clone in pets and another in horses. The research also notes the notable absence of MRSA in Australian livestock — a contrast to other countries — which is possibly related to Australia’s geographic isolation, livestock importation restrictions, and controlled use of critical antibiotics.

Presence and Types of MRSA in Australian Animals and Veterinarians

• The researchers collected 1,080 staphylococcus samples from Australian animals in 2013 and found that 4% of the 360 S. aureus samples were MRSA.
• The MRSA isolates were primarily found in pets; there were no findings of MRSA in livestock.
• Whole genome sequencing was then performed on these MRSA to better understand their molecular characteristics.
• The most common form of MRSA found in dogs and cats was ST22-IV (EMRSA-15), while horses mostly had clonal complex (CC) 8.
• Most ST22-IV isolates showed resistance to the antibiotic ciprofloxacin.

Analysis of Host-Specific Genetic Markers

• The MRSA genomes were then assessed for the presence of specific genetic markers that might indicate adaptability to different hosts.
• These markers include genes responsible for producing proteins impacting bacterial infections, such as staphylokinase, chemotaxis-inhibiting proteins, staphylococcal complement inhibitor, enterotoxin A, and Von Willebrand Factor binding protein.
• The researchers also evaluated a selection of MRSA genomes previously obtained from veterinarians in Australia.
• Contrary to expectations, the distribution of these host-specific markers did not show a clear pattern among either the animal or veterinarian isolates.

The Absence of MRSA in Australian Livestock

• The researchers noted that the lack of MRSA in Australian livestock is a unique deviation from the situation in many other countries where MRSA is frequently found in livestock.
• Multiple potential explanations were proposed for this phenomenon, including Australia’s geographical isolation and the country’s strict regulations on live animal imports.
• However, one of the most significant factors attributed to this absence of MRSA in livestock is the restrictions Australia has placed on the use of critically important antibiotics within the livestock industry.