Evaluation of the affinity of various species and strains of Staphylococcus to adhere to equine corneocytes.

The study seeks to evaluate how different Staphylococcus strains, including Meticillin-resistant Staphylococcus aureus (MRSA) and a meticillin-susceptible Staphylococcus pseudintermedius (MSSP) attach to horse skin cells, or corneocytes. Contrary to what was hypothesized, results showed that all MRSA strains, other than strain USA 500, and MSSP strain attached more significantly to horse corneocytes than did MSSA strains.

Objective

• The primary objective of the study was to determine the affinities of different strains of Staphylococcus, specifically various MRSA strains, MSSA strains, and one MSSP strain, for horse corneocytes.
• The research hypothesized that the MRSA strain, USA 500, known for predominantly colonizing horses and their handlers, would exhibit greater adhesion to horse corneocytes compared to the other staphylococcal strains tested.

Methodology

• The strains of MRSA tested in the study included epidemic strains (USA 100, USA 300, USA 500, and USA 800), two control strains of MSSA, and one MSSP field strain obtained.
• The adhesion tests were conducted on corneocytes extracted from 15 client-owned horses. These corneocytes were incubated with the studied strains under conditions aimed at maximizing S. aureus adhesion without any competitive interference. The bacterial concentration during these tests was maintained at a level of 10(8) colony-forming units/mL for a duration of 45 minutes.
• The density of bacterial adhesion on the cell surface was quantified using a validated image-analysis system.

Results

• The MSSP strain adhered to the horse corneocytes with significantly higher affinity than the MSSA strains.
• All MRSA strains tested had a significantly higher affinity for horse corneocytes than did MSSA strains. However, no statistically significant difference was detected in the adhesion capacity between the USA 500 MRSA strain and the other MRSA strains included in the test.

Conclusion

• The conclusion drawn from the study results was that MRSA strain USA 500, despite being the predominant colonizer of horses, did not exhibit higher adhesion to horse corneocytes than the other Staphylococcus strains under testing.
• As such, the high frequency of horse colonization by the MRSA strain USA 500 may not be solely due to its greater adhesion to corneocytes, indicating the need for further studies to better understand the epidemiological role of this strain in the colonization and infection of horses in North America.