Functional characterization of HgbB, a new hemoglobin binding protein of Pasteurella multocida

Molecular characterization of Pasteurella multocida from cats and antibiotic sensitivity of the isolates

BACKGROUND

Companion animals, including dogs and cats, are frequently identified as sources of Pasteurella multocida, a bacterium that can be transmitted to humans and cause infections.

OBJECTIVES

This survey defines the prevalence, antibiotic sensitivity, capsular types, lipopolysaccharide (LPS) types and virulence factors of P. multocida isolated from cats.

METHODS

A total of 100 specimens from various cat breeds were collected. P. multocida was characterized using both biochemical tests and PCR. Genotypes of isolates were determined using capsular and LPS typing methods. Additionally, virulotyping was performed by detecting the presence of 12 virulence-associated genes. Disk diffusion was used to determine the antibiotic sensitivity of the isolates.

RESULTS

The prevalence of P. multocida in cats was 29%. Among the isolates, the majority were capsular type A (96.5%) and type D (3.4%), with a predominant presence of type A. Twenty-six of the isolates (89.66%) belonged to LPS genotype L6, whereas three isolates (10.3%) belonged to genotype L3. Among the 12 virulence genes examined, sodC, oma87, ptfA, nanB and ompH showed remarkable prevalence (100%). The toxA gene was detected in four isolates (13.8%). Variations were observed in other virulence genes. The nanH gene was present in 93.1% of the isolates, whereas the pfhA gene was detected in 58.6% of the isolates. The exbD-tonB, hgbB, sodA and hgbA genes showed prevalence rates of 96.5%, 96.5%, 96.5% and 82.8%, respectively. Additionally, particular capsule and LPS types were associated with specific virulence genes. Specifically, the toxA and pfhA genes were found to be more prevalent in isolates with capsular type A and LPS genotype L6. Most isolates were resistant to ampicillin, clindamycin, lincomycin, streptomycin and penicillin.

CONCLUSIONS

According to this epidemiological and molecular data, P. multocida from cats possess several virulence-associated genes and are resistant to antimicrobial medicines commonly used in humans and animals. Thus, it is crucial to consider the public health concerns of P. multocida in humans.

Toxigenic and non-toxigenic Pasteurella multocida genotypes, based on capsular, LPS, and virulence profile typing, associated with pneumonic pasteurellosis in Iran

Pasteurella multocida is an important cause of pneumonic pasteurellosis in small ruminants. Its prevalence was investigated in 349 pneumonic lungs from sheep (n = 197) and goats (n = 152), and genotypes of isolates were determined by capsular and lipopolysaccharide (LPS) typing as well as by virulotyping based on the detection of 12 virulence-associated genes. P. multocida was isolated from 29.4 % of sheep lungs and 13.8 % of goat lungs. A (78.5 %) and D (21.5 %) capsular types, as well as L3 (41.8 %) and L6 (57.0 %) LPS genotypes, were detected, with the A:L6 genotype being the most prevalent in both sheep (59.6 %) and goat (52.4 %) isolates. A total of 19 virulence profiles (VP) were detected, seven non-toxigenic and 12 toxigenic, which correlated with the capsular-LPS genotype. All isolates of each VP belonged to the same LPS and capsular genotype, except for one isolate of VP1. The diversity in VP was higher among toxigenic (0.29) than non-toxigenic (0.18) isolates. Moreover, the toxigenic VPs showed more diversity in their capsular-LPS genotypes, with the two main toxigenic VPs belonging to genotypes D:L3 (VP2) and A:L3 (VP3). Therefore, the abundance of toxigenic isolates among sheep and goat isolates does not seem to correspond to the expansion of a more virulent lineage associated with pneumonic pasteurellosis in small ruminants. The most prevalent genotypes among sheep isolates were the non-toxigenic VP1:A:L6 (41.4 %) and the toxigenic VP3:A:L3 (17.2 %) genotypes, whereas the most prevalent among goat isolates were the toxigenic VP2:D:L3 (33.3 %) and the non-toxigenic VP1:A:L6 (14.3 %) and VP4:A:L6 (14.3 %) genotypes. These prevalent toxigenic and non-toxigenic genotypes seem to be epidemiologically relevant in pneumonic pasteurellosis of small ruminants.

Differences in Virulence Between Bovine-Derived Clinical Isolates of Pasteurella multocida Serotype A from the UK and the USA in a Model of Bovine Pneumonic Pasteurellosis

The time of onset and subsequent degree and progression of clinical signs, bacterial colonization and tissue pathology during experimental disease induced by intratracheal inoculation of either a UK or USA isolate of Pasteurella multocida serotype A recovered from clinical cases of bovine pneumonia were determined. Calves aged 8 weeks were challenged with 300 ml phosphate buffered saline (PBS) alone (group 1, n = 3, negative control) or containing 7.1 × 10(8) colony forming units (cfu) of UK isolate (group 2, n = 8) or 5.8 × 10(8) cfu of USA isolate (group 3, n = 8). Bronchoalveolar lavage (BAL) at 0, 1 and 4 days post challenge (dpc) and at the time of necropsy examination (7-8 dpc) showed no significant differences between groups 2 and 3 in bacterial numbers recovered. No P. multocida were recovered from group 1 animals. No clinical disease was present in group 1 calves and in group 3 was limited to scour in 1 calf at 1 dpc. All calves in group 2 had reduced food intake at 4-5 dpc, five had periods of dullness, three a mild nasal discharge at 1 dpc, four had mild to substantial respiratory stridor and one was killed at 6 dpc for humane reasons. Rectal temperatures remained about 39°C in group 1 calves, but increased in P. multocida-challenged calves to 40-41°C within 8-12 h of challenge. Significantly (P = 0.01) greater percentages of lung surface area were consolidated in group 2 (mean ± SD, 21 ± 10.1) compared with group 3 (7 ± 8.6) calves. Significantly more extensive and severe histological lesions were present in the lung lobes (P = 0.006) and lymph nodes (P = 0.02) of group 2 compared with group 3 calves. Pleurisy was present in group 2 calves only and no pathology was present in group 1. Pulsed-field gel electrophoresis (PFGE) produced 11 (group 2, UK isolate) or 10 (group 3, USA isolate) bands with differences in banding patterns. Results overall showed that two isolates, distinct geographically and genetically (by PFGE), caused pneumonic pasteurellosis in a single host with significantly different severity of pathology. This information is relevant to the development of novel vaccine control and interpretation of diagnostic results.

An ST11 clone of Pasteurella multocida, widely spread among farmed rabbits in the Iberian Peninsula, demonstrates respiratory niche association

Pasteurella multocida is a veterinary pathogen causing diseases with considerable economic repercussions in a wide range of animal hosts. In rabbits, P. multocida infections cause a variety of clinical manifestations including rhinitis, pneumonia, septicemia, abscesses, mastitis, and pyometra. In this study, 100 P. multocida isolates from different commercial rabbit farms located throughout the Iberian Peninsula were molecularly characterized by capsular typing, detection of four virulence-associated genes (tbpA, toxA, hgbB, and pfhA), and multilocus sequence typing (MLST). Rabbit P. multocida isolates belonged to three different capsular types: A (47.0%), D (28.0%), and F (25.0%). One group of P. multocida isolates of capsular type D and positive for the hgbB gene was significantly associated with the clinical presentation of respiratory disease (OR 5.91; 95%CI, 1.63-21.38). These isolates belonged to same sequence type, ST11, in the P. multocida Multi-host MLST database. The ST11 clone also includes isolates from porcine and avian pneumonia. This clonal group of epidemiologically unrelated P. multocida isolates could be a virulent clone with some degree of specificity for respiratory disease. These findings could be relevant in the development of vaccines for pasteurellosis prevention, especially respiratory disease.

Virulence genotyping of Pasteurella multocida isolated from multiple hosts from India

In this study, 108 P. multocida isolates recovered from various host animals such as cattle, buffalo, swine, poultry (chicken, duck, and emu) and rabbits were screened for carriage of 8 virulence associated genes. The results revealed some unique information on the prevalence of virulence associated genes among Indian isolates. With the exception of toxA gene, all other virulence associated genes were found to be regularly distributed among host species. Association study between capsule type and virulence genes suggested that pfhA, nanB, and nanH genes were regularly distributed among all serotypes with the exception of CapD, whereas toxA gene was found to be positively associated with CapD and CapA. The frequency of hgbA and nanH genes among swine isolates of Indian origin was found to be less in comparison to its equivalents around the globe. Interestingly, very high prevalence of tbpA gene was observed among poultry, swine, and rabbit isolates. Likewise, very high prevalence of pfhA gene (95.3%) was observed among Indian isolates, irrespective of host species origin.

Comparative genome analysis of an avirulent and two virulent strains of avian Pasteurella multocida reveals candidate genes involved in fitness and pathogenicity

BACKGROUND

Pasteurella multocida is the etiologic agent of fowl cholera, a highly contagious and severe disease of poultry causing significant mortality and morbidity throughout the world. All types of poultry are susceptible to fowl cholera. Turkeys are most susceptible to the peracute/acute forms of the disease while chickens are most susceptible to the acute and chronic forms of the disease. The whole genome of the Pm70 strain of P. multocida was sequenced and annotated in 2001. The Pm70 strain is not virulent to chickens and turkeys. In contrast, strains X73 and P1059 are highly virulent to turkeys, chickens, and other poultry species. In this study, we sequenced the genomes of P. multocida strains X73 and P1059 and undertook a detailed comparative genome analysis with the avirulent Pm70 strain. The goal of this study was to identify candidate genes in the virulent strains that may be involved in pathogenicity of fowl cholera disease.

RESULTS

Comparison of virulent versus avirulent avian P. multocida genomes revealed 336 unique genes among the P1059 and/or X73 genomes compared to strain Pm70. Genes of interest within this subset included those encoding an L-fucose transport and utilization system, several novel sugar transport systems, and several novel hemagglutinins including one designated PfhB4. Additionally, substantial amino acid variation was observed in many core outer membrane proteins and single nucleotide polymorphism analysis confirmed a higher dN/dS ratio within proteins localized to the outer membrane.

CONCLUSIONS

Comparative analyses of highly virulent versus avirulent avian P. multocida identified a number of genomic differences that may shed light on the ability of highly virulent strains to cause disease in the avian host, including those that could be associated with enhanced virulence or fitness.

Detection of virulence-associated genes of Pasteurella multocida isolated from cases of fowl cholera by multiplex-PCR

The current systems of breeding poultry, based on high population density, increase the risk of spreading pathogens, especially those causing respiratory diseases and those that have more than one host. Fowl Cholera (FC) is one such pathogen, and even though it represents one of several avian diseases that should be considered in the differential diagnosis of notifiable diseases that present with sudden death, the pathogenesis and virulence factors involved in FC are still poorly understood. The objective of this study was to investigate twelve genes related to virulence in 25 samples of Pasteurella multocida isolated from FC cases in the southern region of Brazil through the development of multiplex PCR protocols. The protocols developed were capable of detecting all of the proposed genes. The ompH, oma87, sodC, hgbA, hgbB, exBD-tonB and nanB genes were present in 100% of the samples (25/25), the sodA and nanH genes were present in 96% (24/25), ptfA was present in 92% (23/25), and pfhA was present in 60% (15/25). Gene toxA was not identified in any of the samples studied (0/25). Five different genetic profiles were obtained, of which P1 (negative to toxA) was the most common. We concluded that the multiplex-PCR protocols could be useful tools for rapid and simultaneous detection of virulence genes. Despite the high frequency of the analyzed genes and the fact that all samples belonged to the same subspecies of P. multocida, five genetic profiles were observed, which should be confirmed in a study with a larger number of samples.

Profiling of virulence associated genes of Pasteurella multocida isolated from cattle

Pasteurella multocida is a causative agent of many major diseases of which haemorrhagic septiciemia (HS) in cattle & a buffalo is responsible for significant losses to livestock sector in India and south Asia. The disease outcome is affected by various host- and pathogen-specific determinants. Several bacterial species-specific putative virulence factors including the capsular and virulence associated genes have been proposed to play a key role in this interaction. A total of 23 isolates of P. multocida were obtained from 335 cases of various clinically healthy and diseased cattle. These isolates were examined for capsule synthesis genes (capA, B, D, E and F) and eleven virulence associated genes (tbpA, pfhA, toxA, hgbB, hgbA, nanH, nanB, sodA, sodC, oma87 and ptfA) by PCR. A total of 19 P. multocida isolates belonging to capsular type B and 4 of capsular type A were isolated. All isolates of capsular type B harboured the virulence associated genes: tbpA, pfhA, hgbA, sodC and nanH, coding for transferrin binding protein, filamentous hemagglutinin, haemoglobin binding protein, superoxide dismutase and neuraminidases, respectively; while isolates belonging to capsular type A also carried tbpA, pfhA, hgbA and nanH genes. Only 50 % of capsular type A isolates contained sodC gene while 100 % of capsular type B isolates had sodC gene. The gene nanB and toxA were absent in all the 23 isolates. In capsular type A isolates, either sodA or sodC gene was present & these genes did not occur concurrently. The presence of virulence associated gene ptfA revealed a positive association with the disease outcome in cattle and could therefore be an important epidemiological marker gene for characterizing P. multocida isolates.

Pasteurella multocida: diseases and pathogenesis

Pasteurella multocida is an enigmatic pathogen. It is remarkable both for the number and range of specific disease syndromes with which it is associated, and the wide range of host species affected. The pathogenic mechanisms involved in causing the different syndromes are, for the most part, poorly understood or completely unknown. The biochemical and serological properties of some organisms responsible for quite different syndromes appear to be similar. Thus, the molecular basis for host predilection remains unknown. The recent development of genetic manipulation systems together with the availability of multiple genome sequences should help to explain the association of particular pathological conditions with particular hosts as well as helping to elucidate pathogenic mechanisms.

Identification of iron-acquisition proteins of Avibacterium paragallinarum

When Avibacterium paragallinarum reference strain 0083 (serovar A) was grown in an iron-restricted culture medium, the expression of the 60, 68 and 93 kDa outer membrane proteins increased as compared with normal media. Sera of chickens experimentally infected with Av. paragallinarum recognized these iron-restriction induced proteins, suggesting their expression in vivo. The three outer membrane proteins were identified as transferrin receptor and iron transport proteins by mass spectroscopy and a search in sequence databases. As these proteins have been reported to be regulated by the Fur protein in many bacteria, we investigated, through molecular methods, the presence of the fur gene in Av. paragallinarum. A candidate fur gene of Av. paragallinarum was amplified by polymerase chain reaction using complementary primers to conserved regions of fur gene sequences from members of the Pasteurellaceae family. The nucleotide sequence of the cloned gene, from ATG to TAA stop codon, was 453 base pairs in length and the deduced amino acid sequence showed 94% identity with Fur sequences of Actinobacillus pleuropneumoniae and Haemophilus ducreyi. The Av. paragallinarum deduced Fur protein (17.8 kDa) amino acid sequence contains the N-terminal helix-turn-helix DNA-binding domain and the two iron-binding sites in the C-terminal end, typical of other described Fur proteins. The study of iron-restriction-induced proteins and the mechanism regulating their expression could lead to an understanding of the responses of Av. paragallinarum to survive in an iron-restricted environment on host mucosal surfaces.

Pasteurella multocidaand bovine respiratory disease

Pasteurella multocidais a pathogenic Gram-negative bacterium that has been classified into three subspecies, five capsular serogroups and 16 serotypes.P. multocidaserogroup A isolates are bovine nasopharyngeal commensals, bovine pathogens and common isolates from bovine respiratory disease (BRD), both enzootic calf pneumonia of young dairy calves and shipping fever of weaned, stressed beef cattle.P. multocidaA:3 is the most common serotype isolated from BRD, and these isolates have limited heterogeneity based on outer membrane protein (OMP) profiles and ribotyping. Development ofP. multocida-induced pneumonia is associated with environmental and stress factors such as shipping, co-mingling, and overcrowding as well as concurrent or predisposing viral or bacterial infections. Lung lesions consist of an acute to subacute bronchopneumonia that may or may not have an associated pleuritis. Numerous virulence or potential virulence factors have been described for bovine respiratory isolates including adherence and colonization factors, iron-regulated and acquisition proteins, extracellular enzymes such as neuraminidase, lipopolysaccharide, polysaccharide capsule and a variety of OMPs. Immunity of cattle against respiratory pasteurellosis is poorly understood; however, high serum antibodies to OMPs appear to be important for enhancing resistance to the bacterium. Currently availableP. multocidavaccines for use in cattle are predominately traditional bacterins and a live streptomycin-dependent mutant. The field efficacy of these vaccines is not well documented in the literature.

Complex role of hemoglobin and hemoglobin-haptoglobin binding proteins in Haemophilus influenzae virulence in the infant rat model of invasive infection

Haemophilus influenzae requires an exogenous heme source for aerobic growth in vitro. Hemoglobin or hemoglobin-haptoglobin satisfies this requirement. Heme acquisition from hemoglobin-haptoglobin is mediated by proteins encoded by hgp genes. Both Hgps and additional proteins, including those encoded by the hxu operon, provide independent pathways for hemoglobin utilization. Recently we showed that deletion of the set of three hgp genes from a nontypeable strain (86-028NP) of H. influenzae attenuated virulence in the chinchilla otitis media model of noninvasive disease. The present study was undertaken to investigate the role of the hgp genes in virulence of the wild-type serotype b clinical isolate HI689 in the infant rat model of hematogenous meningitis, an established model of invasive disease requiring aerobic growth. Bacteremia of high titer and long duration (>14 days) and histopathologically confirmed meningitis occurred in >95% of infant rats challenged at 5 days of age with strain HI689. While mutations disrupting either the Hgp- or Hxu-mediated pathway of heme acquisition had no effect on virulence in infant rats, an isogenic mutant deficient for both pathways was unable to sustain bacteremia or produce meningitis. In contrast, mutations disrupting either pathway decreased the limited ability of H. influenzae to initiate and sustain bacteremia in weanling rats. Biochemical and growth studies also indicated that infant rat plasma contains multiple heme sources that change with age. Taken together, these data indicate that both the hgp genes and the hxuC gene are virulence determinants in the rat model of human invasive disease.

Theileria orientalis: cloning a cDNA encoding a protein similar to thiol protease with haemoglobin-binding activity

A gene encoding a protein (Tocp1) from Theileria orientalis was isolated from a cDNA library and the deduced amino acid sequence of Tocp1 has 476 amino acids. The primary structure of Tocp1 is similar to eukaryotic thiol proteases (EC 3.4.22.-), but no enzymatic activity was observed with the substitution of essential cysteine at the cysteine active site for glycine. Southern blot analysis showed that multiple genes similar to Tocp1 were present in the parasite genome. Sequence analysis of the genome of the parasite showed that there are at least five different genes similar to Tocp1. Tocp1 transcripts were detected in the T. orientalis piroplasma by Northern blot analysis. Western blot analysis showed that Tocp1 was expressed in the piroplasm of T. orientalis. To address the role of Tocp1 in the life cycle of T. orientalis, Tocp1 was expressed using pET32 expression system. Binding affinity to haemoglobin was demonstrated by enzyme-linked immunosorbent assay.

Iron acquisition by Actinobacillus suis: Identification and characterization of a single-component haemoglobin receptor and encoding gene

Actinobacillus suis is an important swine pathogen. As with other pathogens, the ability of A. suis to acquire iron within the host is crucial for virulence. Here, we investigated the ability of seven strains of A. suis to acquire iron from haemoglobins. In growth assays, all strains could use porcine, bovine and human haemoglobins as iron sources for growth. Using solid phase binding assays, membranes derived from all strains, grown under iron-restricted conditions, were shown to bind all three haemoglobins. Competition binding assays indicated that these haemoglobins were bound by the same receptor and an affinity procedure allowed the isolation and identification of an iron-repressible, haemoglobin-binding polypeptide (approximately 105 kDa) from all strains. Nucleotide sequence analyses revealed that A. suis possesses a gene (hgbA) that encodes a homologue of the Actinobacillus pleuropneumoniae haemoglobin-binding protein, HgbA. hgbA, encoding a mature protein of 105 kDa, was shown to be preceded by a hugZ homologue; putative promoter sequences and a putative Fur box were located upstream of hugZ and RT-PCR revealed that hugZ and hgbA are co-transcribed and iron-repressible. It is concluded that the acquisition of haemoglobin-bound iron by A. suis involves a single-component receptor that is up-regulated in response to iron restriction.

Immunogenicity of iron-regulated outer membrane proteins of Pasteurella multocida A:3 in cattle: molecular characterization of the immunodominant heme acquisition system receptor (HasR) protein

The iron-regulated outer membrane proteins (IROMPs) of Pasteurella multocida A:3 strain 232 (Pm232), a bovine isolate, were investigated as potential immunogens in cattle. We addressed the ability of P. multocida IROMP-enriched fractions to induce antibody responses in cattle by different vaccination strategies and the protective efficacy of these antibodies using a P. multocida-induced pneumonia challenge model. Vaccination of cattle with outer membrane-enriched fractions derived from Pm232 grown on either iron-depleted (IROMPs) or iron-sufficient (OMPs) conditions induced significant antibody responses; however, the correlation with lung lesion scores was not significant (P = 0.01 and P < 0.07, respectively). SDS-PAGE, Western blots and densitometric analyses of Pm232 grown under iron-deficient conditions revealed five major IROMPs including an immunodominant 96 kDa protein band. Mass spectrometry analysis of the 96kDa protein band suggested homology with the heme acquisition system receptor (HasR) of avian P. multocida (strain Pm70) and was confirmed by DNA sequence analysis of the cloned Pm232 hasR gene. Further analyses indicated that Pm232 HasR is a surface-exposed OMP and conserved among most P. multocida isolates investigated. In addition, cattle vaccinated with live Pm232 or IROMPs had significantly higher antibody responses to the 96 kDa protein band and the correlation with lung lesion scores approached significance (P = 0.056). These results indicate that antibody responses in cattle are induced by P. multocida IROMPs, and that the 96 kDa HasR protein is an immunodominant IROMP.

Identification of a hemin utilization protein of Moraxella catarrhalis (HumA)

Moraxella catarrhalis is a major cause of acute otitis media in young children and has also been implicated as an important cause of exacerbations in adults with underlying pulmonary disease. Due to the considerable level of antibiotic resistance and the high degree of carriage rates in young children, it is likely that the incidence of M. catarrhalis infections will continue to rise. M. catarrhalis is a strict human respiratory pathogen, and this bacterium uses both transferrin and lactoferrin receptors to fulfill the essential iron requirement for survival in vivo. However, these are the only described iron acquisition systems for this organism. In this report we have demonstrated that M. catarrhalis can also utilize hemin as a sole source of iron for growth. In addition, we have identified and characterized an outer membrane protein with homology (26 to 28% similarity) to other known hemin binding and uptake proteins in related gram-negative organisms (i.e., Bordetella and Yersinia spp.). This newly described M. catarrhalis protein, termed HumA, is capable of directly binding to hemin coupled to a solid-phase matrix. M. catarrhalis HumA expressed on the surface of an Escherichia coli hemA-deficient strain (K-12 EB53) is fully capable of complementing the defect and thus restoring the ability of this strain to grow in the presence of hemin. When M. catarrhalis is grown in the presence of hemin, HumA expression is clearly increased as shown by Western blotting with polyclonal antiserum developed against a HumA peptide. In addition, growth analyses revealed that a HumA-deficient mutant of M. catarrhalis (7169::humA) is restricted for growth in the presence of hemin as the sole iron source compared to the wild-type strain. We conclude that HumA is an essential component of a hemin uptake and utilization system previously undescribed for M. catarrhalis, thus providing another mechanism of iron acquisition that may facilitate persistent colonization of the mucosal surface.

Pasteurella multocida contains multiple immunogenic haemin- and haemoglobin-binding proteins

Iron-dependent outer membrane proteins (IROMPs) play an important role in bacterial pathogenesis and present several attributes of potential vaccine candidates. TBLASTN analysis of the Pasteurella multocida Pm70 genome using the same molecules of other bacterial pathogens as a query identified eight putative haemin and haemoglobin receptors for this organism. Quantitative binding assays have demonstrated that the proteins PM0040, PM0236, PM0741, PM1081, PM1428, PM0592 and HgbA bind both haemin and haemoglobin, whereas PM0576 and PM1282 ORFs only bind either haemoglobin or haemin, respectively. Furthermore, Western blot analysis showed that P. multocida-infected mice generate specific antibodies against PM0040, PM0236, PM0741, PM1081, PM1428, PM0592 and HgbA proteins. Nevertheless, inoculation of mice with any single one of these receptors alone did not protect against P. multocida infection.