Sequence and structural analysis of OmpW protein of Pasteurella multocida strains reveal evolutionary conservation among members of Pasteurellaceae along with its homologues

Conservation of ptfA gene encoded Type IV fimbrial protein among circulating Pasteurella multocida serogroup A strains causing pneumonia in sheep

Respiratory infections are most common in small ruminants. Differentiation of homogenous bacterial strains originated from similar clinical forms (acute or chronic) of infections in a particular or diverse host origin and regions posses a greater challenge for rapid epidemiological studies. Pasteurella multocida, being a multi-host pathogen with wide range of infections among small ruminants especially sheep, is of greater economical concern among small and marginal farmers. In our study, we report ptfA gene sequence based analysis of circulating P. multocida strains recovered from clinically ailing sheep either with pneumonia or septicaemia belonging to different geographical regions of Karnataka. All the 29 P. multocida strains were characterized by conventional methods as well as molecular methods which indicated homogeneity as they belonged to serogroup A and possessed highly conserved ptfA gene by phylogenetic analysis. The study highlighted the conservation of ptfA gene/fimbrial protein among P. multocida strains from identical/diverse clinical conditions and could be employed in rapid epidemiological studies in routine surveillance of circulating pathogenic bacterial strains as well as pasteurellosis outbreak investigations among animals and birds.

Comparative genetic diversity analysis based on virulence and repetitive genes profiling of circulating Pasteurella multocida isolates from animal hosts

Virulence associated and/or housekeeping/repetitive genes either in single or multiple copies are being extensively targeted for bacterial pathogen detection and differentiation in epidemiological studies. In the present study, isolation of Pasteurella multocida from different animals and their genetic profiling based on the capsular types, virulence and repetitive elements (ERIC/REP) were carried out. A total 345 clinical samples from apparently healthy and diseased (pneumonic, septicaemia) animals (sheep, goat, pig, cattle, buffalo and rabbits) from different geographical regions of Karnataka, Uttar Pradesh, Mizoram and Assam states of India were screened. A total of 32% of the samples were found positive, of which 41 P. multocida isolates recovered. Virulence profiling of isolates indicated that omp87, ompA, ptfA, sodA, sodC, nanB, fur and exbB were present in 100% of isolates. Whereas, prevalence of other genes were; nanH (90%), ompH (71%), pfhA (63%), plpB (80%), hsf-1 (12%), hsf-2 (37%), pmHAS (78%), toxA (73%), hgbA (37%), hgbB (81%), tbpA (78%) and fimA (98%), among isolates. There was no influence of host or place on prevalence of virulence genes when assessed by fitting a Hierarchial Bayesian ordinal regression model. There was correlation (positive and negative) between broad groups of virulence genes. Both repetitive gene profiles (ERIC and REP) generated multiple amplicons (~200 to ~4000 bp). Cluster analysis with ERIC profiles revealed 5 clusters and 3 non- typable isolates with higher discriminatory power (D = 0.7991) than the REP-PCR profiles (D = 00.734) which revealed 4 clusters and 6 non- typable isolates. The results showed that a considerable level of genetic diversity exists among circulating P. multocida isolates despite belonging to the same geographical origin. The genetic diversity or clustering based on either virulence or repetitive elements among isolates could be largely driven by multiple factors acting together which lead to manifestations of particular disease symptoms.

Variability in in vitro biofilm production and antimicrobial sensitivity pattern among Pasteurella multocida strains

Biofilm production, hitherto an uncharacterized feature among circulating Pasteurella multocida strains, was studied along with the antibiotic susceptibility pattern. On the basis of biofilm formation ability, all the strains were categorized into four groups under six different culture conditions: strong biofilm-forming (22%), moderate (19%), weak (51%), and non-adherent (7%). Strains from serogroups A and B formed significant biofilms in at least one culture condition whereas strains from serogroup D were unable to form biofilms. All strains were found to be susceptible to tetracycline. In addition, the correlation between diverse factors (host, capsule type, clinical condition and the tadD gene) as well as antimicrobial susceptibility in biofilm production were analyzed by Joint distribution models, and showed that enrofloxacin and azithromycin resistant strains were positively correlated with strong biofilm production.

Immunogenicity of recombinant outer membrane protein (OmpW) of Pasteurella multocida serogroup B:2 in mouse model

Haemorrhagic septicaemia (HS) caused by Pasteurella multocida serogroup B:2, in cattle and buffalo especially in tropical regions of Asian and African countries, is known to possess several outer membrane proteins (OMPs) as virulent factors which are being targeted to evaluate their immunogenicity and protective efficacy as candidate antigens for vaccine. In the present study, ompW gene encoding for OmpW protein of P. multocida serogroup B:2 strain P52, an Indian HS vaccine strain, has been cloned and over-expressed in recombinant Escherichia coli. The recombinant OmpW fusion protein (~37 kDa) including histidine tag was purified by affinity chromatography under denaturing condition and confirmed by Western blotting. Further, mice immunized with rOmpW (50μg/ dose) along with FCA/FIA resulted in antigen specific IgG antibodies as well as subtypes (IgG1 and IgG2a). The study indicated the potential possibilities to use the rOmpW antigen in developing subunit vaccine for HS as well as other diseases caused by members of Pasteurellaceae.