Characterization of Haemophilus spp. isolated from healthy swine and evaluation of cross-reactivity of complement-fixing antibodies to Haemophilus pleuropneumoniae and Haemophilus taxon "minor group"

Comparative Genomics of the First and Complete Genome of "Actinobacillus porcitonsillarum" Supports the Novel Species Hypothesis

“Actinobacillus porcitonsillarum” is considered a nonpathogenic member of the Pasteurellaceae family, which phenotypically resembles the pathogen Actinobacillus pleuropneumoniae. Previous studies suggested that “A. porcitonsillarum” may represent a new species closely related to Actinobacillus minor, yet no full genome has been sequenced so far. We implemented the Oxford Nanopore and Illumina sequencing technologies to obtain the highly accurate and complete genome sequence of the “A. porcitonsillarum” strain 9953L55. After validating our de novo assembly strategy by comparing the A. pleuropneumoniae S4074^T genome sequence obtained by Oxford Nanopore Technology combined with Illumina reads with a PacBio-sequenced S4074^T genome from the NCBI database, we performed comparative analyses of the 9953L55 genome with the A. minor type strain NM305^T, A. minor strain 202, and A. pleuropneumoniae S4074^T. The 2,263,191 bp circular genome of 9953L55 consisted of 2168 and 2033 predicted genes and proteins, respectively. The lipopolysaccharide cluster resembled the genetic organization of A. pleuropneumoniae serotypes 1, 9, and 11, possibly explaining the positive reactions observed previously in serotyping tests. In contrast to NM305^T, we confirmed the presence of a complete apxIICABD operon in 9953L55 and 202 accounting for their hemolytic phenotype and Christie-Atkins-Munch-Petersen (CAMP) reaction positivity. Orthologous gene cluster analysis provided insight into the differential ability of strains of the A. minor/“porcitonsillarum” complex and A. pleuropneumoniae to ferment lactose, raffinose, trehalose, and mannitol. The four strains showed distinct and shared transposable elements, CRISPR/Cas systems, and integrated prophages. Genome comparisons based on average nucleotide identity and in silico DNA-DNA hybridization confirmed the close relationship among strains belonging to the A. minor/“porcitonsillarum” complex compared to other Actinobacillus spp., but also suggested that 9953L55 and 202 belong to the same novel species closely related to A. minor, namely, “A. porcitonsillarum.” Recognition of the taxon as a separate species would improve diagnostics and control strategies of pig pleuropneumonia.

Effect of enrofloxacin in the carrier stage of Haemophilus parasuis in naturally colonized pigs

The purpose of this study was to determine the effect of enrofloxacin in the carrier stage of Haemophilus parasuis in naturally colonized weaned pigs. Twenty-three pigs colonized by H. parasuis received either 7.5 mg/kg body weight (BW) of enrofloxacin or a saline solution intramuscularly at weaning. Nasal and tonsillar swab samples were collected daily throughout the study and at necropsy and tested by quantitative polymerase chain reaction (qPCR). The H. parasuis isolates obtained from samples collected at necropsy were subjected to genotyping by enterobacterial repetitive intergenic consensus polymerase chain reaction (ERIC-PCR) and a multiplex PCR for the detection of the virulence-associated trimeric autotransporter (vtaA) genes. Haemophilus parasuis was detected in the nasal cavity and tonsils of pigs in the control group throughout the study. Antibiotic-treated pigs tested negative for H. parasuis at 1 d post-treatment and the proportion of nasal samples that tested positive was higher for control pigs than for treated pigs at 1, 2, 3, 4, 5, 6, and 7 d post-treatment and at 2, 4, and 5 d post-treatment for tonsil samples (P < 0.003). Genotyping by ERIC-PCR demonstrated that pigs were colonized with a common H. parasuis strain at the end of the study. Isolates were negative for the vtaA gene, which indicates the absence of vtaA virulence factor. In conclusion, enrofloxacin significantly reduced the H. parasuis load in naturally colonized pigs, but was unable to completely eliminate the organism.

Non-pathogenic Actinobacillus isolates antigenically and biochemically similar to Actinobacillus pleuropneumoniae: a novel species?

Two unusual Actinobacillus isolates were recovered from pigs with no clinical signs, no lesions and no history of swine pleuropneumonia. Two representative strains (9953L55 and 0347) analyzed in this study were initially biochemically and antigenically identified as A. pleuropneumoniae serotypes 1 and 9, respectively, by traditional identification methods. Both strains presented, however, negative results with three A. pleuropneumoniae-specific PCR tests and revealed in particular the absence of the apxIV toxin genes. However, both strains produced and secreted ApxII toxin although they only harbored the toxin genes apxIICA, which is an uncommon feature for any of the known A. pleuropneumoniae serotypes. Upon experimental inoculation of pigs, these strains proved to be totally non-pathogenic. Animals infected with one of the strains produced antibodies that cross-react with A. pleuropneumoniae serotypes 1-9-11-specific LC-LPS ELISA. Phylogenetic analysis based on 16S rRNA gene sequence analysis revealed that these strains form a separate phylogenetic group that is distinct from other Actinobacillus species and is particularly different from A. pleuropneumoniae.

Phenotypic and genetic characterization of NAD-dependent Pasteurellaceae from the respiratory tract of pigs and their possible pathogenetic importance

Nicotinamide adenine dinucleotide (NAD)-dependent Pasteurellaceae other than Actinobacillus pleuropneumoniae and Haemophilus parasuis are frequently isolated from the respiratory tract of pigs. The taxonomic classification and relevance for pathogenicity of these bacteria deserves further attention. In the present study, 107 of these NAD-dependent isolates from the porcine respiratory tract, primarily from lungs with pathological changes, were investigated. On the basis of phenotypic criteria, such as haemolysis, urease, catalase, and indole formation as well as other fermentative activities, 50 of the isolates were assigned to Actinobacillus minor, 36 isolates to Actinobacillus porcinus and 21 isolates to Actinobacillus indolicus. However, many isolates among the three species showed fermentative activities differing from those of the respective type strain of the species. Serotyping on the basis of heat-stable polysaccharide antigens and 16 rDNA sequencing also revealed substantial heterogeneity within each of the three species although they clustered together in three distinct groups in the phylogenetic analysis. These three groups of NAD-dependent bacteria are different from, or in a borderline position, to the existing species or genera within the family Pasteurellaceae. A considerable number of isolates of these three groups were isolated in pure cultures from pneumonic lungs. Consequently, it will be necessary to critically review the opinion, that these NAD-dependent Pasteurellaceae are only "agents colonizing the mucosa". Further, taxonomic examinations of the strains within these three groups are indispensable to testing isolates for their virulence in gnotobiotic pigs.

Development of an oligonucleotide-specific capture plate hybridization assay for detection of Haemophilus parasuis

An oligonucleotide-specific capture plate hybridization assay has been developed to rapidly, specifically, and sensitively detect Haemophilus parasuis from nasal swabs. Several in vitro studies have been performed to determine the sensitivity and specificity of the test, and in vivo studies have validated this technique in pigs. Results suggest that the assay detects <100 colony-forming units/ml in a pure culture and gives a positive result when H. parasuis is present in a ratio of 1:10(3)-10(4) in a mixed culture, and the probe does not hybridize with other related species found in the upper respiratory tract. This assay is more sensitive than culture for detection of the microorganism from nasal swabs and lesions.

Characterization of V factor-dependent organisms of the family Pasteurellaceae isolated from porcine pneumonic lungs in Spain

116 V factor (NAD)-dependent strains belonging to the family Pasterurellaceae isolated from porcine pneumonic lungs were collected in Spain over a period of 1 yr and studied using 52 biochemical characters. In addition to Actinobacillus pleuropneumoniae (72 strains), Haemophilus taxon minor group (37 strains) and Taxon D (four strains), other taxon (three strains) were observed. This taxon, provisionally designated as Haemophilus sp. sorbitol+, is closed to A. pleuropneumoniae but differed by some biochemical characteristics. Among A. pleuropneumoniae strains, nine different serotypes were detected, the most frequent being serotypes 4 and 2.

An abattoir survey of pneumonia and pleuritis in slaughter weight swine from 9 selected herds. III. Serological findings and their relationship to pathomorphological and microbiological findings

Blood samples from 777 pigs, originating from 9 different herds, were collected at slaughter and examined for antibodies to Mycoplasma hyopneumoniae and Actinobacillus (Haemophilus) pleuropneumoniae by the indirect hemagglutination assay (IHA) and the complement fixation (CF) test, respectively. Results were compared to pathological and microbiological findings. Antibodies to M. hyopneumoniae in positive titers of 1/80 or higher were found in 62% of the samples. The relationship between positive IHA titers to M. hyopneumoniae and gross findings indicative of enzootic pneumonia of pigs (EPP), histological findings indicative of EPP, the isolation of M. hyopneumoniae and the demonstration of M. hyopneumoniae by indirect immunofluorescent testing ranged from 64% to 68%. No correlation was noted between positive IHA titers and the isolation of Mycoplasma flocculare. Positive antibody titers to A. pleuropneumoniae of 1/10 or higher were detected in 5% to 85% of the samples from individual herds. Positive titers to A. pleuropneumoniae serotype 2 were found in 71% to 79% of the sampled animals from herds with high frequencies of pneumonic lesions indicative of pleuropneumonia. In herds with low frequencies of pleuropneumonia, positive titers were recorded in from 0 to 4% of the tested pigs. However, no statistical association was found between pleuropneumonia and positive titers to A. pleuropneumoniae serotype 2 in individual animals. Twenty-one per cent of samples with positive CF titers to A. pleuropneumoniae showed antibodies to more than one serotype.

An abattoir survey of pneumonia and pleuritis in slaughter weight swine from 9 selected herds. III. Serological findings and their relationship to pathomorphological and microbiological findings

Blood samples from 777 pigs, originating from 9 different herds, were collected at slaughter and examined for antibodies to Mycoplasma hyopneumoniae and Actinobacillus (Haemophilus) pleuropneumoniae by the indirect hemagglutination assay (IHA) and the complement fixation (CF) test, respectively. Results were compared to pathological and microbiological findings. Antibodies to M. hyopneumoniae in positive titers of 1/80 or higher were found in 62% of the samples. The relationship between positive IHA titers to M. hyopneumoniae and gross findings indicative of enzootic pneumonia of pigs (EPP), histological findings indicative of EPP, the isolation of M. hyopneumoniae and the demonstration of M. hyopneumoniae by indirect immunofluorescent testing ranged from 64% to 68%. No correlation was noted between positive IHA titers and the isolation of Mycoplasma flocculare. Positive antibody titers to A. pleuropneumoniae of 1/10 or higher were detected in 5% to 85% of the samples from individual herds. Positive titers to A. pleuropneumoniae serotype 2 were found in 71% to 79% of the sampled animals from herds with high frequencies of pneumonic lesions indicative of pleuropneumonia. In herds with low frequencies of pleuropneumonia, positive titers were recorded in from 0 to 4% of the tested pigs. However, no statistical association was found between pleuropneumonia and positive titers to A. pleuropneumoniae serotype 2 in individual animals. Twenty-one per cent of samples with positive CF titers to A. pleuropneumoniae showed antibodies to more than one serotype.

V factor-dependent members of the family Pasteurellaceae in the porcine upper respiratory tract

A study was performed to obtain a better understanding of the diversity and ecology of members of the family Pasteurellaceae in the porcine respiratory tract. A collection of 132 V factor-dependent strains of Pasteurellaceae selected from porcine field isolates mainly from the respiratory tract were subjected to detailed characterization. In addition to the three hitherto recognized species Actinobacillus pleuropneumoniae, Haemophilus parasuis, and Haemophilus taxon "minor group," three distinct taxa were observed. Some of these taxa, which are provisionally designated taxa D, E, and F, would by traditional criteria be mistaken for H. parasuis but differed by several biochemical characteristics. To study the ecology of the V factor-dependent species, swabs from the nasal and oral cavities of 29 pigs were cultivated on selective and nonselective media. By studying approximately 30 isolates from each sample, the distribution and relative proportion of the individual taxa were determined. A. pleuropneumoniae was detected in samples from the tonsil areas of only two acutely ill animals. H. parasuis was isolated from the nasal cavities of four out of nine healthy pigs but from the oral cavities of only two animals. In contrast, taxon "minor group" and taxa D, E, and F were present in the oral cavities of the majority of pigs but were not detected in samples from their nasal cavities. The results indicate that all the observed V factor-dependent species of Pasteurellaceae except A. pleuropneumoniae, are members of the resident microflora of various mucosal surfaces of the porcine upper respiratory tract.

Indirect enzyme-linked immunosorbent assay for detection of antibody to a 110,000-molecular-weight hemolysin of Actinobacillus pleuropneumoniae

An indirect enzyme-linked immunosorbent assay (ELISA) was developed to detect swine antibody to a 110,000-molecular-weight hemolysin (110K hemolysin) of Actinobacillus pleuropneumoniae. Affinity-purified rabbit polyclonal or mouse monoclonal immunoglobulin G to the hemolysin of A. pleuropneumoniae serotype 5 strain J45, followed by hemolysin-rich concentrated culture supernatant, was used to bind swine antibody to hemolysin to microdilution plates. Sixty-nine serum samples from swine that were clinically normal, presented with clinical evidence of pleuropneumonia, were experimentally immunized or challenged, or were free of pleuropneumonia were tested, and their ELISA titers were compared with complement fixation (CF) titers. On the basis of serum samples from swine that were clinically normal and negative by CF, an ELISA titer of 1:320 or greater was considered positive. In comparison with CF, the sensitivity of the ELISA was 98.1% and the specificity was 90%. The two samples negative by CF and positive by indirect ELISA were, however, also positive for antibody to serotype 5 capsule by ELISA. Immunization of normal pigs with whole cells or purified hemolysin boosted titers 4- to 128-fold within 4 weeks. Immunoblotting demonstrated that the affinity-purified immunoglobulin G to hemolysin used for capture in the assay recognized only a 110K protein of A. pleuropneumoniae serotypes 1 to 7, although the reactivity was quantitatively variable between serotypes. Therefore, the indirect ELISA is capable of identifying animals infected with or exposed to most, if not all, serotypes of A. pleuropneumoniae. If an indirect ELISA titer of 1:320 or greater is considered positive, the assay can be a valuable diagnostic tool in both clinical and research laboratories.

Detection of serotype-specific antibodies or capsular antigen of Actinobacillus pleuropneumoniae by a double-label radioimmunoassay

Diagnostic tests for Actinobacillus pleuropneumoniae have been problematic because current tests do not use a purified antigen and in most cases measure either antibody or antigen, but not both. We describe a Farr-type double-label radioimmunoassay that utilizes purified, serotype-specific, 3H-capsule to measure antibody to capsule directly or that can measure capsule in a sample indirectly by inhibition of antibody binding. The assay could detect about 1 ng of serotype-specific antibody in serum or at least 100 pg of capsule in a sample. Due to the sensitivity of the assay, false-positive results were common with neat sera (probably due to cross-reacting antibodies to unrelated antigens), but the specificity was improved when the sera were diluted 1:100. The radioimmunoassay should prove to be a useful reference method for research and diagnostic testing and for comparison of new assays for detection of capsule or antibodies to capsule.

Preliminary assessment of a Haemophilus parasuis bacterin for use in specific pathogen free swine

A whole cell formalin killed trivalent Haemophilus parasuis bacterin was tested for efficacy in four week old, weaned specific pathogen free pigs challenged under laboratory conditions. The vaccine contained three field strains of H. parasuis selected from confirmed cases of Glasser's disease. Two different formulations were evaluated in separate trials. In trial 1, ten pigs received 5 mL of bacterin subcutaneously in the neck, followed by a second 5 mL dose two weeks later. Another ten pigs served as nonvaccinated controls. One week after the second dose, all pigs were subjected to an aerosol challenge containing the strains of H. parasuis present in the vaccine. In trial 2, a broth rather than a saline based vaccine was prepared, and tested as in trial 1. In both trials, the vaccinated pigs remained healthy postchallenge, while eight of nine (Trial 1) and eight of ten (Trial 2) nonvaccinated pigs succumbed to Glasser's disease.

Characterisation and antimicrobial sensitivity of haemophili isolated from pigs

A total of 70 haemophili from Australia pigs was compared with a range of reference strains of porcine haemophili. Forty-eight of the isolates were identified as Actinobacillus pleuropneumoniae biovar 1 and the remaining 22 isolates as Haemophilus parasuis. Forty one of the A. pleuropneumoniae isolates were used in a study to determine to the minimal inhibitory concentration (MIC) of 12 antimicrobial agents, or combinations of agents. Penicillin, neomycin, trimethoprim, trimethoprim-sulphamethoxazole and tetracycline all showed low MIC values, indicating their potential for the treatment of porcine pleuropneumonia, although 2 isolates showed resistance to tetracycline. A wide range of MIC values was encountered with the sulphonamides.

Serotype specificity and immunogenicity of the capsular polymer of Haemophilus pleuropneumoniae serotype 5

Serotyping of Haemophilus pleuropneumoniae and serologic assays for detection of serotype-specific antibody are problematic due to the potential cross-reactivity of the crude antigens used for raising immune serum or for serology. The capsular polymer (CP) of H. pleuropneumoniae serotype 5 was investigated for serotype-specific activity with antiserum to whole cells or with antiserum made monospecific to CP by adsorption with a capsule-deficient mutant. When antiserum to whole cells or monospecific antiserum to CP was tested against purified CP from serotypes 1 to 7 by immunodiffusion or enzyme-linked immunosorbent assay, only capsules of serotype 5 were reactive. In addition, only encapsulated serotype 5 cells reacted with serum monospecific to CP in an indirect immunofluorescent-antibody assay. Serotype-specific antibody was completely inhibited in each assay by preincubation of purified CP with the serum. Antiserum to whole cells of H. pleuropneumoniae serotype 5 contained antibodies to proteins and lipopolysaccharide; these antibodies cross-reacted with antigens of heterologous serotypes by dot-blot enzyme-linked immunosorbent assay and immunoblotting. The antigenic activity of CP was stable after heating for at least 30 min at 100 degrees C. High titers of antibody to CP were present in the sera of rabbits immunized intravenously with whole log-phase cells or in the convalescent sera of pigs experimentally infected with H. pleuropneumoniae serotype 5. However, the purified CP was poorly immunogenic in rabbits and swine. Our results indicate that the capsule is the serotype-specific antigen of H. pleuropneumoniae and that a monospecific antiserum to capsule or purified capsule should be used for serotyping or serologic assays, respectively.

Analysis of major antigens of Haemophilus (Actinobacillus) pleuropneumoniae and related organisms

Outer membrane protein (OMP)-enriched extracts and whole-cell protein preparations of Haemophilus (Actinobacillus) pleuropneumoniae and related organisms were examined by polyacrylamide gel electrophoresis and immunoblotting. Both the OMP-enriched and whole-cell protein profiles of Actinobacillus suis, A. pleuropneumoniae (NAD-independent biovar), A. lignieresii, and Pasteurella haemolytica were very similar to those of H. pleuropneumoniae serotypes 1 to 8. Antisera prepared against H. pleuropneumoniae typically recognized three major OMP antigens with approximate molecular weights of 17,000 (17K), 32K, and 42K in immunoblots of H. pleuropneumoniae serotypes 1 to 8, Actinobacillus spp., and P. haemolytica. Antisera prepared against Actinobacillus spp. and Haemophilus sp. "minor group" also recognized these 17K, 32K, and 42K antigens. Using absorbed sera, we demonstrated that the 17K antigen had an epitope (or epitopes) common to all the gram-negative organisms examined, including Escherichia coli. The 32K and 42K antigens had epitopes common to members of the family Pasteurellaceae but, in the case of the 32K antigen, also contained unique epitopes. These results provide a basis for understanding the lack of specificity of serodiagnostic tests for H. pleuropneumoniae infection and provide another line of evidence for the association of H. pleuropneumoniae with the genus Actinobacillus.