Community-associated MRSA SCCmec type IVd in Irish equids.

This study investigates the rise of meticillin-resistant Staphylococcus aureus (MRSA), specifically community-associated MRSA (CA-MRSA) SCCmec type IVd, in horses in Ireland to help better understand these pathogens and their clinical impact on equine health.

Research Context

• The study begins by acknowledging the increased reports of MRSA in animals, particularly horses, in the past five years. This rise has sparked discussions about the potential impact on animal owners and veterinary staff.
• Prior studies have mainly differentiated between meticillin-sensitive and -resistant organisms, but there is limited attention to the further characterization of animal MRSA into health care-associated (HA-MRSA) or community-associated (CA-MRSA) types. The latter, though still S. aureus, exhibits different epidemiological and microbiological characteristics. Notably, CA-MRSA is more likely to produce Panton-Valentine leukocidin (PVL) toxin that causes cell and tissue destruction.
• The researchers aim to further characterize known equine MRSA isolates from culture collections, due to the clinical and epidemiological differences between the two types of MRSA.

Methodology

• For the study, 16 laboratory-confirmed MRSA isolates were obtained from the Irish Equine Centre, collected from horses during 2006 and 2007. These specimens were obtained from pathological samples including wound swabs, joint fluids, nasal swabs, and skin scrapings.
• To categorize the isolates as HA-MRSA or CA-MRSA, the presence of the PVL toxin gene was tested and the SCCmec gene arrangements were analyzed.

Results

• The researchers found that all the 16 MRSA isolates were PVL-negative and exhibited a banding pattern similar to SCCmec IVd. The SCCmec IVd subtype was later confirmed by direct automated sequencing.
• To date, according to the researchers, there has been little mention in the scientific literature of CA-MRSA (PVL-negative, SCCmec IVd subtype) from either humans or animals, suggesting that humans are not the primary source of this type of MRSA for horses.

Conclusion

• The study concludes that the presence of PVL toxin-negative MRSA organisms, belonging to the SCCmec IVd subtype in Irish horses, suggests a community origin rather than a healthcare origin.
• The researchers also call for a rigorous investigation and characterization of all isolated MRSA organisms from animal populations to better understand the potential clinical implications of emerging CA-MRSA in animals.