Tetracycline resistance in Italian Chlamydia suis strains.

In the period from 2004 to 2007, 14 chlamydial isolates were collected from swine with conjunctival and/or reproductive disorders and reared in 4 different farms both in Northern and Southern Italy. The sensitivity of these isolates to doxycycline was tested and compared with the susceptibility to the same drug of the urethral Italian isolate GO86 of C. trachomatis serovar D, the reference strain 6BC of C. psittaci and three isolates of C. abortus, C. pecorum and C. felis, respectively. The C. suis tetracycline resistance (Tcr) phenotype is associated with a resistance gene, tet (C), integrated into the chlamydial chromosome. C. suis isolates were tested for the presence of the tet (C) resistance gene by a PCR assay amplifying a 525 base pair product of the tet (C) gene-coding region. As far as sensitivity to doxycycline is concerned, in comparison to the five strains of C. trachomatis, C. psittaci, C. abortus, C. pecorum and C. felis which were sensitive to doxycycline with MIC and MBC ranging from 0.03 to 0.125 µg/ml, respectively, the MIC and MBC values of doxycycline ranged from 4 to 8 µg/ml, respectively, in most swine isolates tested. All the C. suis isolates carried an identical nucleotide sequence that showed 100 per cent homology with those of the structural gene tet (C).