Mannheimia haemolytica is the causative agent of several economically significant diseases of cattle and sheep, however, its role in causing infection in poultry is limited as secondary pathogen, co-infecting with viral pathogens like infectious bronchitis virus (IBV), infectious laryngotracheitis virus (ILTV) etc. The present study reports first time in this country regarding the isolation of M. haemolytica from adult commercial poultry flocks, initially reported with severe respiratory distress. Necropsy findings were quite similar to those found in Fowl cholera infection. The samples were also processed for the detection of any avian respiratory viruses in addition to testing for bacterial presence. The lab investigations led to the detection of M. haemolytica from the clinical samples and subsequent use of norfloxacin, selected on the basis of sensitivity pattern of the organism, resulted in curing of the flock. To further confirm the pathogenic potential of this organism, 7-day old broilers were challenged with the new isolate. The bacterium M. haemolytica was subsequently recovered from the birds which died within 3 weeks post-infection, confirming the pathogenic potential of this organism in poultry. The drug susceptibility pattern of the recovered bacterium was similar to the original isolate. This study further identifies the role of different management factors leading to infection of birds with M. haemolytica and suggests appropriate control measures in poultry flocks.

Key words: Antibiotic sensitivity, Isolation & identification, Mannheimia (Pasteurella) haemolytica, Pakistan, Pathogenesis