INVESTIGATION OF ANTIMICROBIAL RESISTANCE IN Staphylococcus pseudintermedius

Abstract

Staphylococcus pseudintermedius is a coagulase positive bacterium and found on the mucous membranes of approximately 90% of healthy dogs. This organism is an opportunistic pathogen in dogs and an increasingly recognized zoonoses. As in human medicine, the emergence of antimicrobial resistance is a growing problem in companion animal practice. In the current investigation, we saught to 1. Identify the emergence of resistance among S. pseudintermedius colonizing healthy dogs, 2. Determine whether there are strain specific tissue tropisms among isolates causing dermatological and urinary tract infections, 3. Perform a clinical and bacteriological description of human S. pseudintermedius infections and 4. To describe the correlation of susceptibility of isolates to tetracycline, doxycycline and minocycline, and to describe the mechanisms of tetracycline resistance. We found that methicillin-resistant S. pseudintermedius colonizes 7% of healthy dogs and that since a previous surveillance study conducted in 2008, resistance has emerged in our region. S. pseudintermedius isolates from dermatological and urinary tract infections were genetically heterogeneous, suggesting that these organisms are true opportunists and do not possess a strain specific tissue tropism. Despite this genetic heterogeneity, antimicrobial resistance was found to be significantly higher in isolates from dermatological infections compared to those from the urinary tract. Human infections with S. pseudintermedius were relatively rare, comprising 0.05% of skin and soft tissue infections in a large Canadian health region. Among these human isolates, we found that all methicillin resistant isolates were the European pandemic clones ST71 and ST181. We found that tetracycline is not a satisfactory indicator for doxycycline and minocycline resistance, and that these phenotypic discrepancies could not be explained by the presence or absence of particular resistance genes. Furthermore, factors related to tetM (which was the most commonly identified resistance gene including copy number, predicted amino acid sequence or expression level, were not significantly associated with the phenotypic diversity observed. Although numerically high association were found in high MIC category on tetM expression comparing to low MIC category, larger studies required for further conclusions. The genotypic evidence on MICs for tetracycline and doxycycline is largely unknown and more studies are required.