Identification of fusidic acid resistance in clinical isolates of <i>Staphylococcus pseudintermedius</i> from dogs in Korea

Abstract

BACKGROUND: Staphylococcus pseudintermedius is a major bacterial species associated with canine pyoderma and otitis. Fusidic acid is used to treat skin infections caused by Gram-positive bacteria. The incidence of resistance to fusidic acid in S. pseudintermedius has importance in terms of limiting treatment options for bacterial infections. HYPOTHESIS/OBJECTIVES: To evaluate the occurrence and mechanisms of fusidic acid resistance in clinical isolates of S. pseudintermedius. ANIMALS: Fifty-two S. pseudintermedius isolates were collected from dogs with pyoderma (n = 36) or otitis (n = 16). METHODS AND MATERIALS: The disk diffusion method determined that isolates <24 mm were resistant to fusidic acid. Minimum inhibitory concentrations (MICs) were measured by the E-test in those with confirmed resistance to fusidic acid by the disk diffusion method. Phenotypically fusidic acid resistant isolates were subjected to PCR to detect the presence of resistance-related genes (fusA, fusB, fusC and fusD) and fusA was further sequenced to identify point mutations. RESULTS: Fourteen of 52 (27%) S. pseudintermedius isolates were resistant to fusidic acid and all of these showed low-level resistance. Among fusidic acid resistant isolates, fusA point mutations were confirmed in 11 isolates and amino acid substitutions were found in five. fusC was detected in seven isolates, but neither fusB nor fusD was detected. CONCLUSIONS AND CLINICAL IMPORTANCE: This study demonstrates the occurrence and resistance mechanisms to fusidic acid in clinical isolates of S. pseudintermedius. Continuous monitoring for fusidic acid resistance is recommended.