Carboxyl terminus heterogeneity of type IV fimbrial subunit protein of Pasteurella multocida isolates

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.

Phylogenetic analysis of Indian isolates of Pasteurella multocida based on partial 16S rRNA gene sequences: Association of caprine isolate with lineage B

Pasteurella multocida is responsible for diseases, which are endemic and economically important in India, still comparative investigations on phylogenetic relations of Indian P. multocida isolates are scarce. Therefore, present study was undertaken to understand the phylogenetic relationship of several isolates belonging to different host, place of isolation and capsular types based on partial 16S rRNA gene sequencing. In the current study, a 838 bp fragment of 16S rRNA gene of 35 field isolates of P. multocida belonging to different capsular types, recovered from cattle, buffalo, sheep, goat, pigs and birds, collected from different states of India sequenced and analyzed. There were 12 unique 16S rRNA types among 35 isolates, which clustered into 2 distinct phylogenetic lineages, viz. A and B. There were strong correlations between the phylogenetic relations and capsular types, with maximum heterogeneity seen among isolates of capsular type A. However, there was no clustering based on the host or place of isolation indicating the potential hazard of interspecies sharing and the possibility of translocation of infected animals across international borders. Moreover, one of the caprine isolates belonged to lineage B. To the best of our knowledge, this is the first report of a caprine isolate in lineage B, since lineage B is reported to be exclusively associated with birds and cats. It may be alarming that the strains of lineage B are becoming adapted to different host species.

Immunogenicity of recombinant Omp16 protein of Pasteurella multocida B:2 in mouse model

Bacterial peptidoglycan-associated lipoproteins (PAL) are potential targets for the development of diagnostics/subunit vaccines for infectious diseases. Most commonly prevalent Omp16 lipoprotein is absolutely conserved among Pasteurella multocida strains, which are involved in multiple infectious diseases of livestock worldwide. In the present study, we cloned omp16 gene encoding for mature Omp16 of P. multocida B:2 strain P52 and overexpressed as a fusion protein in Escherichia coli. Mice immunized with purified recombinant non-lipidated Omp16 fusion protein (~32 kDa) resulted in elicitation of significant antigen specific serum antibody titres (total IgG and subtypes). A more pronounced increase in Th2 response (IgG1) was noticed. The study indicated the potential possibilities to use lipidated recombinant Omp16 protein in developing a composite subunit vaccine along with suitable adjuvant for haemorrhagic septicaemia/ pasteurellosis in livestock.

Outer membrane proteome analysis of Indian strain of Pasteurella multocida serotype B:2 by MALDI-TOF/MS analysis

Identification of outer membrane proteins (OMPs) is important to understand the bacteria structure and function, host-pathogen interaction, development of novel vaccine candidates, and diagnostic antigens. But till now the key antigens of P. multocida B:2 isolate causing haemorrhagic septicaemia (HS) in animals are not clearly defined. In this study, P52 strain of P. multocida serotype B:2 was grown in vitro under iron-rich and iron-limited condition. The OMPs were extracted by sarkosyl method followed by SDS-PAGE and the proteins were identified by MALDI-TOF/MS analysis. In total, 22 proteins were identified, of which 7 were observed exclusively under iron-limited condition. Most of the high molecular weight proteins (TbpA, HgbA, HgbB, HasR, IroA, and HemR) identified in this study were involved in iron acquisition. Some hypothetical proteins (HP-KCU-10206, HP and AAUPMB 08244, HP AAUPMB 21592, HP AAUPMB 19766, AAUPMB 11295) were observed for the first time in this study which could be unique to serotype B:2. Further functional in vivo study of the proteins identified are required to explore the utility of these proteins in developing diagnostics and vaccine against HS.

Recombinant transferrin binding protein A (rTbpA) fragments of Pasteurella multocida serogroup B:2 provide variable protection following homologous challenge in mouse model

Transferrin binding protein A (TbpA), an iron acquisition surface protein that also acts as virulence factor, is widely distributed among strains of Pasteurella multocida. In the present study, a total of seven clones of TbpA fragments (39D to F777; 39D to Q697; 188V to F777; 188V to Q697; 39D to P377; 188V to P377 and 39D to F187) belonging to P. multocida B:2 were constructed, over-expressed and purified as recombinant fusion proteins from Escherichia coli using affinity chromatography. Immunization of mice with rTbpA fragments resulted in a significant (p < 0.05) rise in antigen specific serum total IgG and subtypes (IgG1 and IgG2a) tires. All immunized mice challenged with 8 LD50 of P. multocida B:2 resulted in a variable protective efficacy up to 50%. The study indicated the potential possibilities to incorporate full length TbpA in subunit vaccine formulation composed of synergistic subunit antigens against haemorrhagic septicaemia (HS) in cattle and buffalo.