Virulence factors, antimicrobial susceptibility, and genotyping of Corynebacterium pseudotuberculosis isolates from sheep abscesses in Western Türkiye

Abstract

Caseous lymphadenitis, a persistent infection in small ruminants associated with a major global economic impact, is caused by the bacterium Corynebacterium pseudotuberculosis. This study aimed to determine the occurrence of caseous lymphadenitis in subcutaneous abscesses of sheep in western Türkiye, and to characterize the isolates in terms of virulence factors, antimicrobial susceptibility, and genetic relatedness. One hundred abscess samples were examined, and 15 isolates were identified as C. pseudotuberculosis using the VITEK 2 system and confirmed by polymerase chain reaction targeting the species-specific pip gene. Four virulence genes related to the iron acquisition system (fagA, fagB, fagC, and fagD) were detected in all isolates. The highest susceptibility was observed to enrofloxacin and gentamicin, while resistance was most common to trimethoprim–sulfamethoxazole and tetracycline. Phylogenetic analysis based on the 16S rRNA gene revealed close genetic similarity among field and reference strains. These findings indicate that conservation of the fag operon may contribute to the pathogenic potential of C. pseudotuberculosis isolates in Türkiye. High antimicrobial resistance rates emphasize the need for rational antibiotic use and preventive measures, including vaccine development targeting iron acquisition systems. This study provides the first molecular characterization of C. pseudotuberculosis from sheep in Türkiye.