Population Genetics and Immune Response to Staphylococcus pseudintermedius

Staphylococcus pseudintermedius is an opportunistic bacterium affecting canines that has recently developed a high prevalence of methicillin resistance and corresponding multi-drug resistance. Developments of alternatives to antibiotics such as vaccines are important strategies for control of this organism.Multilocus sequence typing is based on the sequence variations of slowly evolving genes and usually uses a minimum of seven genes. Population genetic studies of S. pseudintermedius have been based on sequencing four genes (MLST-4). Forty-five genes were selected from available genomic data and tested as MLST candidates. Four genes were amplified from all isolates and showed the highest number of alleles. By adding four new genes to the existing ones, an MLST scheme based on 8 genes (MLST-8) was developed for S. pseudintermedius. MLST-8 was applied to 176 isolates of previously characterized S. pseudintermedius from dogs (165 isolates), cats (5 isolates) and humans (6 isolates). They were contained in 83 sequence types (STs). MLST-8 identified 106 STs which indicated a high level of diversity of the species but also verified the clonal nature of methicillin resistant isolates.Five different STs of S. pseudintermedius were selected and reacted with serum samples from dogs with pyoderma and healthy control dogs to measure their immune reactivity. Significant differences in the IgG reactivity between the different genetic backgrounds of S. pseudintermedius were found, this variation should be considered in designing a vaccine for S. pseudintermedius. The reactivity of other staphylococcal species with canine pyoderma and healthy control sera showed that minor genetic differences may be associated with significant variations in IgG reactivity.