A 5-year retrospective report of Gallibacterium anatis and Pasteurella multocida isolates from chickens in Mississippi.

A 5-yr retrospective study (November 2006-December 2011) was conducted to determine the isolation frequency of Pasteurella multocida and Gallibacterium anatis and their antibiograms from chickens submitted to the Mississippi Poultry Research and Diagnostic Laboratory. The number of isolations of G. anatis increased over the last 5 yr in broiler and broiler breeder type chickens. For P. multocida, the number of isolations increased from 2006 to 2010, but decreased through 2011 with all isolations being from boiler breeder type chickens. Gallibacterium anatis demonstrated almost complete resistance to novobiocin, tylosin, lincosamide, and tetracycline antimicrobials with moderate to high sensitivity to sulfonamides, fluoroquinolones, and florfenicol. There was intermediate sensitivity for spectinomycin and erythromycin and variable resistance to β-lactam and aminoglycoside antimicrobials. In sharp contrast, P. multocida showed moderate to high sensitivity to β-lactam, novobiocin, and tetracycline antimicrobials, but had antibiograms similar to G. anatis for the other antimicrobials. Sensitivities were determined using minimum inhibitory concentration. This study examines the trends over a 5-yr period of the number of isolates of P. multocida and G. anatis and their sensitivities. These 2 pathogens produce very similar clinical signs and lesions (fowl cholera-like) in breeders despite having extremely antagonistic sensitivity patterns. This study shows the necessity for producers to attempt culture and sensitivity in suspect fowl cholera-like flocks before initiating antimicrobial treatment commonly used with P. multocida for fear that the culprit may actually be the more antimicrobial-resistant G. anatis.