In vitro susceptibility of porcine isolates of Clostridium perfringens to selected antimicrobials

Increasing antimicrobial resistance is one of the major problems concerning both veterinary medicine and human health. There are but few reports on antimicrobial susceptibility of C. perfringens from pigs. The aim of this study was to evaluate the susceptibility of porcine isolates of C. perfringens to antimicrobial agents commonly used in swine diseases therapy.

A total of 159 C. perfringens isolates were obtained from both diarrheic and healthy: piglets, weaned pigs and fatteners. The isolates were collected in the National Veterinary Research Institute (NVRI) over the period of 2008-2015.

The minimum inhibitory concentration (MIC) of amoxicillin/clavulanic acid, ampicillin, ceftiofur, colistin, enrofloxacin, florfenicol, gentamicin, neomycin, spectinomycin, oxytetracycline, tylosin, tiamulin and trimethoprim/sulphamethoxazole was determined by broth microdilution using Sensititre plates (TREK Diagnostics).

The test and the classification of the strains were carried out in accordance with the Clinical and Laboratory Standards Institute (CLSI) guidelines and European Committee on Antimicrobial Susceptibility Testing (EUCAST). For each antimicrobial, the range of results, MIC50 and MIC90 were calculated.

More than 80% of isolates had MIC value < 0.5 µg/mL of amoxicillin/clavulanic acid and ampicillin. Almost 90% of isolates had MIC value < 1 µg/mL of florfenicol. Over 90% of isolates had MIC value > 64 of neomycin and almost 75% had MIC value > 16 of gentamicin. MIC50 and MIC90 of trimethoprim/sulphamethoxazole were 32 and 64, respectively.

Important differences between MIC50 and MIC90 were noticed (≥ 5-fold dilutions) regarding ampicillin (MIC50/MIC90 – < 0.5/128 µg/mL), enrofloxacin (MIC50/MIC90 – 0.25/16 µg/mL), tylosin (MIC50/MIC90 – < 0.25/> 128 µg/mL) and tiamulin (MIC50/MIC90 – 2/> 128 µg/mL), revealing variability of the isolates as far as antimicrobial susceptibility is concerned.

The results of our study confirm a high sensitivity of C. perfringens isolated from pigs to beta-lactams. However, increasing resistance to this group of antimicrobials has also been observed in this study.

Both the MIC50 and MIC90 values for florfenicol were low. These results suggest that in vivo resistance exists in a slight proportion of the isolates.

Studies with other domestic species indicate a high degree of susceptibility of C. perfringens isolates to this antibiotic. Neomycin, gentamicin and trimethoprim/sulphamethoxazole had high MICs, suggesting poor efficacy of these antibiotics against C. perfringens isolates from pigs; this phenomenon was reported previously by other researchers.

Disclosure of Interest: None Declared.