Antimicrobial susceptibility and genetic characterization of Trueperella pyogenes isolates from pigs reared under intensive and extensive farming practices.

Trueperella pyogenes is an opportunistic pathogen associated with a variety of diseases and responsible for important economic losses for pig production. Minimal Inhibitory Concentration (MIC) and Pulsed Field Gel Electrophoresis (PFGE) typing analysis were used to determine the MIC distribution and to genetically characterize a total of 180 T. pyogenes isolates obtained from slaughtered pigs reared under intensive (TpIN, n = 89) and extensive (TpEX, n = 91) farming practices. Low MIC values for penicillin and amoxicillin (0.008 and 0.06 μg/ml, respectively), ceftiofur, gentamicin and enrofloxacin (1 μg/ml, respectively) were obtained, so they could be of choice for the empiric treatment of T. pyogenes infections. Except for the penicillin, amoxicillin and ceftiofur, a statistically significant difference was observed in the MIC distribution of all antimicrobials analysed between TpIN and TpEX isolates. Also, MIC values were higher in TpIN than in TpEX isolates for neomycin and streptomycin (32 μg/ml vs 8 μg/ml), sulfamethoxazole/trimethoprim (30.4/1.6 μg/ml vs 1.90/0.10 μg/ml) and tylosin (≥1024 μg/ml vs 1 μg/ml). A relatively lower genetic diversity was detected in TpIN in comparison with TpEX isolates (GD 0.42 and GD 0.47, respectively). All isolates were distributed in three clusters (A, B, C). TpIN isolates were statistically associated with cluster A (P = 0.0002; OR 3.21; CI 1.74-5.93), whereas the TpEX were distributed throughout the dendrogram, showing more genetic diversity. These data suggest that the antimicrobial susceptibility and genetic variability of the T. pyogenes isolates could be influenced by the management systems.