Antigenic and phenotypic characterization of Pasteurella multocida strains isolated from the lungs of pigs with pneumonia and/or pleuritic lesions.

The antigenic and phenotypic variation among 22 strains of Pasteurella multocida isolated from pig lungs with pneumonia and/or pleuritic lesions was studied. Phenotypic tests consisted of biochemical assays and antimicrobial sensitivity tests. All isolates fermented mannitol and sorbitol, but none fermented arabinose. Fourteen fermented xylose, 4 trehalose, 2 dulcitol and I maltose. Analyzing these characteristics, 5 different biochemical groups were revealed. There was a wide variation in the results of antimicrobial sensitivity testing to 9 products, with 50% of isolates showing sensitivity at least to 7. No antimicrobial agent was able to inhibit all strains. The highest efficiency (72% sensitivity) was observed with amoxycillin (30 mg). Spectinomycin (100 mg) presented the lowest efficiency, 45.5%. Antigenic characterization consisted in capsular serotyping and assessment of variability of an outer membrane protein gene (ompH), using polymerase chain reaction (PCR) and digestion with 5 endonuclease enzymes (restriction fragment length polymorphism, RFLP). Out of 22 strains, 21 were classified as capsular type A and one as type D. Characterization of ompH revealed 7 different patterns. They corresponded well to previously established biochemical groups.