Background
Colonization by livestock-associated MRSA (LA-MRSA) has increasingly been reported in the swine population worldwide. The aim of this study was to assess the prevalence of MRSA nasal carriage in healthy pigs, including the black (
Calabrese
) breed, from farms in the Calabria Region (Southern Italy). Between January and March 2018, a total of 475 healthy pigs reared in 32 farms were sampled by nasal swabbing. MRSA isolates were characterized by
spa
, MLST and SCC
mec
typing, and susceptibility testing to 17 antimicrobials.
Results
22 of 32 (66.8%) pig farms resulted positive for MRSA. The prevalence of MRSA was 46.1% (219 MRSA culture-positive out of 475 samples). MRSA colonization was significantly higher in intensive farms and in pigs with a recent or ongoing antimicrobial treatment. All 219 MRSA isolates were assigned to ST398. The most common
spa
types were t011 (37.0%), t034 (22.4%) and t899 (15.1%). A novel
spa
type (t18290) was detected in one isolate. An insertion of IS
256
in the ST398-specific A07 fragment of the SAPIG2195 gene was detected in 10 out of 81 t011 isolates. Nearly all isolates carried the SCC
mec
type V element, except 11 isolates that carried the SCC
mec
type IVc. None of the isolates was positive for the Panton-Valentine leukocidin. All isolates were resistant to tetracycline. High resistance rates were also found for clindamycin (93.1%), trimethoprim/sulfamethoxazole (68.4%), fluoroquinolones (47.9–65.3%) and erythromycin (46.1%). None of the isolates was resistant to vancomycin and fusidic acid. Overall, a multidrug resistant phenotype was observed in 88.6% of isolates.
Conclusions
We report a high prevalence of MRSA among healthy swine in Southern Italy farms, with higher isolation frequency associated with intensive farming. The epidemiological types identified in our study reflect those reported in other European countries. Our findings underscore the importance of monitoring the evolution of LA-MRSA in pig farms in order to implement control measures and reduce the risk of spread in the animal population.
Electronic supplementary material
The online version of this article (10.1186/s12866-019-1422-x) contains supplementary material, which is available to authorized users.