Characterisation of a multiresistant Pasteurella multocida strain isolated from cattle.

The emergence of simultaneous resistance to multiple classes of antibiotics presents an increasing threat. Plasmid-borne multiresistance and integrative conjugative elements have been reported in Pasteurella multocida. We report an alternative strategy for the development of multiresistance observed in a P. multocida strain (Pm238) isolated from calf pneumonia. We identified genes integrated into the chromosomal DNA without known integrative and conjugative elements. These genes conferred resistance to streptomycin (strA), tetracycline (tetB), chloramphenicol (catAIII), and sulphonamides (sulII). We also detected mutation in the quinolone-resistance-determining regions of parC. No plasmids could be isolated from strain Pm238. These results suggest that P. multocida can accumulate multiple resistance determinants on the chromosome as single genes.