Fowl cholera (FC) is a highly contagious and economically important disease of poultry worldwide. This study was performed on 218 Pasteurella multocida isolates collected from separated breeding farms or backyards with acute and chronic FC cases in multiple localities across Hungary during the period 2005–2010. All isolates were characterized by a broad range of biochemical, serological, and molecular methods, as well as their antibiotic susceptibility to aminoglycosides (A), macrolides (M), penicillins (P), quinolones (Q), cephalosporins, sulphonamides (S), and tetracyclines (T) was determined. Fifty-two percent of all isolates belonged to a well-defined type that was highly virulent, caused acute FC, and had the same character: fermented L-arabinose, possessed capsule type A, identified as Heddleston serotype 1, and possessed allele type A of the ptfA fimbrial gene. This type was widely distributed among poultry in Hungary, especially in waterfowl flocks.
Isolates collected from the chronic FC cases were more diverse: none of them fermented L-arabinose; they possessed capsule type A (76%), F (9%), or was non-typeable (15%) with different Heddleston serotypes, mainly 1, 3, 4, and 5, or 7 and 16; in addition, possessed allele type B of ptfA fimbrial gene. Only 26 isolates presented characters similar to any of the chronic FC cases but caused severe disease.
The antibiotic susceptibility assay presented that 80% of all isolates were resistant to 1–5 of the studied antimicrobial agents. During the survey, after two years, there was a dramatic decline both in the number of the multi-drug resistance phenotypes and the prevalence of the highly virulent type of the isolates. In the next four years, multiresistant isolates were almost completely removed, whereas the number of isolates resistant to 1 or 2 drugs was constant.
Reduced frequency of antibiotic multiresistant, mostly L-arabinose-fermenting isolates, has been observed since 2007. This reduction may be a consequence of the elimination of multiple waterfowl flocks in Hungary during avian influenza outbreaks, which possibly created a break in the “transmission chain” of pathogenic P. multocida isolates.