Genetic diversity of Pasteurella multocida fowl cholera isolates as demonstrated by ribotyping and 16S rRNA and partial atpD sequence comparisons

The genetic diversity of Pasteurelia multocida, the aetiological agent of f owl cholera, was investigated. The strain collection comprised 69 clinical isolates representing a wide spectrum of hosts and geographic origin. The t hree type strains for the subspecies of P. multocida were also included. Av ian isolates of P. multocida subsp. multocida and P. multocida subsp. septi ca did not represent separate lines by Hpall ribotyping and the two type st rains of mammalian origin (porcine and cat bite) seemed to be representativ e of avian strains of A multocida subspp. multocida and septica. By ribotyp ing, all P. multocida subsp. gallicida strains, except one chicken isolate and the type strain, clustered together. This indicated that the bovine typ e strain was not representative of this subspecies and that most strains of P. multocida subsp. gallicida are genetically related and may be distantly related to other A multocida isolates, including those of avian origin. By 16S rRNA and atpD sequence comparisons of selected strains, including both A multocida isolated from birds and mammals and selected distantly related Pasteurelia species associated with birds and mammals, it was found that P . multocida is monophyletic. Extended DNA-DNA hybridizations are highly ind icated since strains may exist which would connect the existing subspecies at species level. The considerable genetic diversity of P. multocida fowl c holera isolates is probably related to the clonal nature of this organism, resulting in many divergent lines.