Prevalence and Tetracycline Susceptibility of Chlamydia suis in Different Intestinal Sections of Pigs from Commercial Farms

Chlamydia suis, a close relative of the human pathogen C. trachomatis, can be detected in the porcine gut, yet its prevalence and viability across intestinal segments remain poorly defined. This study aimed to assess the segment-specific prevalence, isolation success, and tetracycline susceptibility of C. suis in grower-finisher pigs. Jejunal, ileal, and colonic samples (n = 200 per intestinal segment) were collected from 600 pigs at slaughter and analyzed using C. suis-specific real-time PCR and culture. PCR revealed significantly higher detection rates in the colon (40%) than in the jejunum or ileum (both 4.5%), accompanied by significantly higher calculated bacterial loads in colonic samples. In contrast, viable C. suis was most frequently isolated from ileal material, indicating that the ileum may provide a more favorable condition for active bacterial replication. Among 24 culture-confirmed isolates, 75% were susceptible to tetracycline (MIC/MBC < 2 µg/mL), 12.5% exhibited an intermediate phenotype (2 µg/mL < MIC/MBC < 4 µg/mL) and another 12.5% were resistant (MIC/MBC > 4 µg/mL). Intermediate phenotypes were recovered from the jejunum and ileum, whereas resistant isolates were found in the ileum and colon. These findings suggest that the porcine colon may serve as an intestinal reservoir for C. suis, while the ileum supports more robust bacterial replication. Overall, these data contribute to our understanding of the intestinal ecology of C. suis under field conditions and its tetracycline susceptible patterns.