ANTIMICROBIAL SUSCEPTIBILITY OF ILEAL SYMBIONT INTRACELLULARIS ISOLATED FROM PIGS WITH PROLIFERATIVE ENTEROPATHY

Proliferative enteropathy is caused by the microaerophilic obligate in tracellular bacterium ileal symbiont (IS) intracellularis. Treatment o f this disease is problematic because of the lack of in vivo or in vit ro data on the activities of antimicrobial agents, A new procedure for determining the susceptibility of IS intracellularis was developed by using a tissue culture system which promotes the in vitro multiplicat ion of this organism. Nineteen antimicrobial agents were evaluated in triplicate cultures for their intracellular and extracellular activiti es against up to three IS intracellularis strains isolated from pigs w ith proliferative enteropathy, The MIC was defined as the lowest conce ntration which prevented multiplication of 99% of the IS intracellular is isolates. Penicillin, erythromycin, difloxacin, virginiamycin, and chlortetracycline were the most active compounds tested, all,vith MICs of less than or equal to 1 mu g/ml. Tiamulin and tilmicosin were the next most active compounds, with MICs of less than or equal to 4 mu g/ ml. The MICs of aminoglycosides were generally >32 mu g/ml. Both linco mycin and tylosin were relatively inactive against the IS intracellula ris strains tested, with MICs of 32 and 64 mu g/ml, respectively. Thes e results indicate that some compounds capable of intracytoplasmic acc umulation and blocking bacterial protein synthesis were active against IS intracellularis strains isolated from pigs with proliferative ente ropathy, The in vitro cultivation system shows promise as a method far studying the interaction between IS intracellularis and antimicrobial agents and for Screening new antibiotics for use in therapy.