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The aim of this study was to investigate the occurrence of Chlamydia suis and tetracycline resistance determinants in conjunctival swabs of Italian wild boars, by PCR. Extracted DNA collected from 50 wild boars from Northern and Central Italy was examined by molecular methods. One sample (2%) from the Central Italy was positive for C. suis. Fragments of tetR(C) and tetR(C)-tet(C) resistance determinants were amplified from the same sample. Further molecular investigations suggested the attribution of these tetracycline resistance determinants to C. suis, such as the truncation oftetR(C) and absence of a intact invasion (inv)-like region. While tetracycline-resistant C. suis is very common in domestic pigs, its occurrence has not been reported in wild boar before. Wild boar might acquire tetracycline resistance determinants through direct or indirect contact with domestic pigs.

The aims of the present study were to assess the prevalence of Chlamydia suis in an Italian pig herd, determine the tetracycline susceptibility of C. suis isolates, and evaluate tet(C) and tetR(C) gene expression. Conjunctival swabs from 20 pigs were tested for C. suis by real-time polymerase chain reaction, and 55% (11) were positive. C. suis was then isolated from 11 conjunctival swabs resampled from the same herd. All positive samples and isolates were positive for the tet(C) resistance gene. The in vitro susceptibility to tetracycline of the C. suis isolates showed MIC values ranging from 0.5 to 4 μg/mL. Tet(C) and tetR(C) transcripts were found in all the isolates, cultured both in the absence and presence of tetracycline. This contrasts with other Gram-negative bacteria in which both genes are repressed in the absence of the drug. Further investigation into tet gene regulation in C. suis is needed.