In vitro antibiotic susceptibility of field isolates of Mycoplasma hyopneumoniae and Mycoplasma hyorhinis from South Korea

Swine mycoplasma Mycoplasma hyopneumoniae (Mhp) and Mycoplasma hyorhinis (Mhr) are respiratory pathogens in pigs. They are associated with enzootic pneumonia (EP) and porcine respiratory disease complex (PRDC) causing huge loses to the porcine industry. Currently commercial vaccines are available only against Mhp; however, their protection ability is not complete. Therefore, use of antimicrobials often becomes necessary to limit the disease in the event of outbreak or as an additional measure to prevent mycoplasma disease. However, there is no recent information on antibiotic susceptibility of these mycoplasmas from South Korea. In the present study, minimum inhibitory concentration (MICs) of South Korean Mhp and Mhr isolates to tylvalosin and other commonly used antibiotics (tiamulin, lincomycin, tilmicosin and chlortetracycline) was determined.

Mhp and Mhr field isolates (twelve each), obtained from enzootic pneumonia (EP)-like lung lesions during 2009-2011 from South Korea. Each of these isolates was passaged 6 times before using in the antimicrobial assay. Both Mycoplasma species were propagated in Friis broth and used at final concentration of approximately 1 × 10⁵ cells/mL. MICs were determined using the broth microdilution method. Readings were taken after incubation of 7 days at 37°C, and the lowest concentration of antimicrobial inhibiting any detectable color change of the medium was defined as MIC of the drug.

Tylvalosin showed highest activity against both Mhp and Mhr field isolates with MIC₉₀ value of 0.06 µg/mL and 0.12 µg/mL, respectively. Tiamulin, lincomycin and tilmicosin also showed low MICs with MIC₉₀s of 0.12 µg/mL, 0.5 µg/mL and 4 µg/mL for Mhp isolates and MIC₉₀s of 0.25 µg/mL, 1 µg/mL and 4 µg/mL for Mhr isolates. The MIC₉₀ value of chlortetracycline was 64 µg/mL for both Mhp and Mhr field isolates.

The results indicate the antibiotic tylvalosin has highest efficiency against Mhp and Mhr field isolates. To conclude, in vitro susceptibility must be taken into consideration while treating these swine mycoplasma in South Korea and will help for a choice among several antibiotics.

Disclosure of Interest: None Declared.