Isolation, antibiogram and whole genome sequence analysis of Pasteurella multocida type A from layer birds

Fowl cholera (FC), caused by Pasteurella multocida type A, represents a major threat to poultry production worldwide. Detailed characterization of the genotypic, phenotypic, and antimicrobial resistance profiles is essential for advancing epidemiological surveillance and guiding effective intervention strategies. A total of 80 suspected FC field samples were collected from which P. multocida was isolated and identified through conventional culture techniques, Gram staining, and PCR. Antimicrobial susceptibility testing was performed using the disc diffusion method with 16 antimicrobial drugs. Whole-genome sequencing of a representative isolate was conducted using the Illumina MiSeq platform, and genomic analysis was carried out with multiple bioinformatics tools. P. multocida type A was confirmed in 12 isolates (15%). RAST annotation revealed a genome size of 2,346,689 bp with 2,205 predicted coding sequences, 59 RNA genes, and a GC content of 40.2%. Phenotypic analyses showed resistance to cefixime, ceftriaxone, ertapenem, and meropenem, while the highest sensitivity was observed for ciprofloxacin, doxycycline, tetracycline, and levofloxacin. PathogenFinder predicted the isolate as a potential human pathogen with a probability score of 0.891. Virulence-associated genes identified included wecA, galU, manB, rfaD, rfaE, rfaF, lpxB, lpxC, and msbA, supporting the pathogenic potential of the isolates and suggesting a possible role in host immune evasion. Phylogenetic analysis using MEGA X with the maximum likelihood method revealed that the isolate was clustered within the monophyletic clade and that it showed closest genetic relatedness to strains from Australia, China, and Malaysia. These findings highlight the genomic basis of virulence and antimicrobial resistance in P. multocida type A from Bangladeshi layer for the first time. The isolate characterized in this study provides valuable genomic insights and the selection of targeted antimicrobials to improve fowl cholera control strategies.