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Abstract: Two major regional clones of methicillin-resistant Staphylococcus pseudintermedius (MRSP) have been identified in Europe and North America. They are designated multilocus sequence types (ST) 71 and 68 and contain staphylococcal chromosome cassette (SCCmec) types II–III and VT, respectively. One notable difference between the two clones is a deletion in the mecI/mecR1 regulatory apparatus of ST 68 SCCmec VT. This deletion in analogous methicillin-resistant Staphylococcus aureus (MRSA) results in more responsive and greater expression of the mecA encoded penicillin-binding protein 2a, and is associated with SCCmec types occurring in community-acquired MRSA lineages. The aim of this study was to characterize mec and bla regulatory apparatuses in MRSP and determine their effects on expression of mecA. Seventeen S. pseudintermedius isolates representing nine methicillin-resistant ST lineages were screened for the presence of the repressors blaI and mecI and sensors blaR1 and mecR1. The bla and mec operons for each isolate were sequenced and compared for homology between the repressor open-reading frames (ORF), sensor ORFs, and mecA promoter regions. A real-time reverse transcriptase PCR expression assay was developed, validated and applied to nine isolates determining the effect of oxacillin induction on mecA transcription. Significant differences were found in mecA expression between isolates with a full regulatory complement (mecI/mecR1 and blaI/blaR1) and those with truncated and/or absent regulatory elements. Isolates representative of European and North American MRSP ST regional clones have dissimilar mecA responses to oxacillin. [Copyright &y& Elsevier]

Abstract: Methicillin resistance encoded by the mecA gene is increasingly observed in Staphylococcus pseudintermedius. Little is known about the population genetics of veterinary staphylococci bearing methicillin resistance. The aim of this study was to determine the relatedness of resistant bacteria and to compare them with methicillin-susceptible isolates. Multilocus sequence typing (MLST) and pulsed-field gel electrophoresis (PFGE) fragment profiling were performed on methicillin-resistant S. pseudintermedius (MRSP) and methicillin-susceptible S. pseudintermedius (MSSP) isolates obtained from canine samples submitted to the veterinary teaching hospital bacteriology service between 2006 and 2008. Multilocus sequence typing detected 20 different sequence types, 16 of which were not previously described. Methicillin-resistant isolates were predominantly ST 68, possessed the Staphylococcus aureus-associated staphylococcal chromosomal cassette mec (SCCmec) type VT and fell within the largest PFGE cluster; whereas methicillin-susceptible strains were more genetically diverse. This suggests that most methicillin resistance within the population of isolates tested originated from a single source which has persisted and expanded for several years. [Copyright &y& Elsevier]