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.