The present study was conducted to investigate the incidence of Pasteruella multocida infection in Youngnam swine herds during the period from March 1988 to Ferbruary 1989 and some properties of the isolated organisms. P multocida was isolated from 22 (43.1 %) of 51 growing pigs of 4 to 12 weeks of age and from 8 (80.0 %) of 10 herds. From nasal turbinates of 102 slaughtered pigs, 47 (46.1 %) pigs were culture positive and pigs from 8 (88.9 %) of 9 heards were found to be infected with P multocida. From lungs of 101 slaughtered pigs, 42 (41.6 %) pigs were culture positive and the pigs from 11 (91.7 %) of 12 herds were found to be infected with P multocida. The majority of biochemical and cultural propertis of the P multocida isolates were identical to those of the standard strains. The isolation frequencies of P multocida in relation to pig snout lesion grades of 0 to 5 were 28.6 %, 41.6 %, 48.0 %, 50.0 % 85.7 %, and 100 %, respectively

The capsular serogroupes and drug susceptibility of 111 isolates of Pasteurella multocida from pigs with atrophic rhinitis and pneumonic lesions were investigated. Of the 111 P multocida isolates, 42 were from lung lesions, 47 from nasal turbinate lesions and the remaining 22 from the nasal swabs. P multocida isolates were typed for capsular serogroupes A by hyaluronidase inhibition of capsule and D by acriflavine auto-agglutination. Most isolates (64.9 %) were type A, 23.4 % were type D and the remaining 11.7 % were untypable. Resistance to triple sulfa (97.3 %) was most frequent, followed by resistance to tiamulin (71.2 %), tylosin (56.8 %), streptomycin (36.9 %), and neomycin (36.0 %). The majority of the organisms were susceptible in order of prevalence to baytril (100 %), ampicillin (98.2 %), linsmycin (97.3 %), cephalothin (94.6 %), gentamycin (93.7 %), amikacin (92.3 %), tetracycline (91.9 %), trimethoprim/sulfamethoxazole (91.0 %), and kanamycin (90.1 %). No differneces in drug resistance in relation to capsular serogroupes of P multocida and the origin of lesions were noted. A high prevalence of multiple drug resistance was observed and the most common resistant patterns were Sss, Tm, Ty (12.6 %) and Sm, Sss, Tm, Ty (8.1 %) patterns