Tetracycline Susceptibility in Chlamydia suis Pig Isolates

Abstract

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.

Selective Pressure Promotes Tetracycline Resistance of Chlamydia Suis in Fattening Pigs

“…We found that 1) the estimated number of gene copies in a clinical sample by real-time PCR is a good predictor to assess successful isolation, and 2) isolation from conjunctival swabs is far less successful compared to fecal samples suggesting that fecal contamination rather than actual conjunctival infection occurred. A selection of isolates (n = 59) were further tested for tet (C) by PCR as well as their antibiotic susceptibility in vitro , confirming previous findings that positive tet (C) results do not necessarily mean that the isolate is also phenotypically resistant [11]. Furthermore, we show that the number of tetracycline resistant C .…”

“…For analysis, the number of inclusions at 200-fold magnification throughout the entire coverslip was counted and used to determine the number of inclusion-forming units per milliliter (IFU/ml). Each antibiotic susceptibility determination was performed with approximately 5 x 10 3 IFU/ml per investigated isolate as previously described [11]. …”

“…Following incubation at 37°C for 48 h, one infected monolayer per tetracycline concentration was fixed with methanol, and immunolabeled, as described above (Material and Methods section). The minimum inhibitory concentration (MIC) of tetracycline was defined as “the lowest concentration preventing the detection of more than 90% of the chlamydial inclusions compared with the drug-free control” [11, 16]. In parallel, media of the remaining Trac bottles was replaced with tetracycline-free chlamydiae cultivation medium after washing the coverslips with PBS.…”

“…The tetracycline resistance found in C . suis is defined by the presence of an efflux pump encoding gene called tetracycline resistance gene class C [ tet (C)] within a genomic island [7], though its presence does not necessarily translate into antibiotic resistance in vitro [11]. C .…”

Water-filtered infrared A reduces chlamydial infectivity in vitro without causing ex vivo eye damage in pig and mouse models

“…Of particular interest is the emergence of tetracycline resistance in C. suis, a growing problem in the pig rearing industry and probably the result of excessive tetracycline use for therapeutic purposes and as growth promoters in livestock since the 1950s (7)(8)(9)(10)(11). C. suis is primarily known to inapparently infect the porcine gastrointestinal tract with a prevalence of up to 90 % in fattening pigs (12).…”