Nonradioactive colony lift-hybridization assay for detection of Bordetella bronchiseptica infection in swine

Occurrence of Bordetella infection in pigs in northern India

Bordetella bronchiseptica infection causing atrophic rhinitis in pigs is reported from almost all countries. In the present study, occurrence of Bordetella infection in apparently healthy pigs was determined in 392 pigs sampled to collect 358 serum samples and 316 nasal swabs from Northern India by conventional bacterioscopy, detection of antigen with multiplex polymerase chain reaction (mPCR), and detection of antibodies with microagglutination test (MAT) and enzyme linked immune-sorbent assay (ELISA). Bordetella bronchiseptica could be isolated from six (1.92%) nasal swabs. Although isolates varied significantly in their antimicrobial sensitivity, they had similar plasmid profile. The genus specific and species specific amplicons were detected from 8.2% and 4.4% nasal swabs using mPCR with alc gene (genus specific) and fla gene and fim2 gene (species specific) primers, respectively. Observations revealed that there may be other bordetellae infecting pigs because about 50% of the samples positive using mPCR for genus specific amplicons failed to confirm presence of B. bronchiseptica. Of the pig sera tested with MAT and ELISA for Bordetella antibodies, 67.6% and 86.3% samples, respectively, were positive. For antigen detection mPCR was more sensitive than conventional bacterioscopy while for detection of antibodies neither of the two tests (MAT and ELISA) had specificity in relation to antigen detection. Study indicated high prevalence of infection in swine herds in Northern India.

Performance of transport and selective media for swine Bordetella bronchiseptica recovery and it comparison to polymerase chain reaction detection

Three comparative assays were performed seeking to improve the sensitivity of the diagnosis of Bordetella bronchiseptica infection analyzing swine nasal swabs. An initial assay compared the recovery of B. bronchiseptica from swabs simultaneously inoculated with B. bronchiseptica and some interfering bacteria, immersed into three transport formulations (Amies with charcoal, trypticase soy broth and phosphate buffer according to Soerensen supplemented with 5% of bovine fetal serum) and submitted to different temperatures (10°C and 27°C) and periods of incubation (24, 72 and 120 hours). A subsequent assay compared three selective media (MacConkey agar, modified selective medium G20G and a ceftiofur medium) for their recovery capabilities from clinical specimens. One last assay compared the polymerase chain reaction to the three selective media. In the first assay, the recovery of B. bronchiseptica from transport systems was better at 27°C and the three formulations had good performances at this temperature, but the collection of qualitative and quantitative analysis indicated the advantage of Amies medium for nasal swabs transportation. The second assay indicated that MacConkey agar and modified G20G had similar results and were superior to the ceftiofur medium. In the final assay, polymerase chain reaction presented superior capability of B. bronchiseptica detection to culture procedures.

Analytical verification of a multiplex PCR for identification of Bordetella bronchiseptica and Pasteurella multocida from swine

Bordetella bronchiseptica and Pasteurella multocida are etiologic agents of progressive atrophic rhinitis (PAR) and bronchopneumonia in swine. Only dermonecrotic toxin-producing strains of P. multocida play a role in atrophic rhinitis while both toxigenic and nontoxigenic strains have been associated with pneumonia. Monitoring and investigation of outbreaks involving these bacteria require sensitive and accurate identification and reliable determination of the toxigenic status of P. multocida isolates. In the present study, we report the development, optimization, and performance characteristics of a multiplex PCR assay for simultaneous amplification of up to three different targets, one common to all P. multocida strains, one found only in toxigenic P. multocida strains, and one common to B. bronchiseptica strains. Based on analysis of 94 P. multocida isolates (31 toxigenic) and 126 B. bronchiseptica isolates assay sensitivity is 100% for all amplicons. Evaluation of 22 isolates of other bacterial genera and species commonly found in the swine respiratory tract demonstrated a specificity of 100% for all gene targets. The limit of detection for simultaneous amplification of all targets is 1-10pg of DNA per target, corresponding to a few hundred genomes or less. Amplicon mobility in agarose gels and sequence analysis indicate the amplicons are highly stable. The data presented establish this multiplex PCR as a reliable method for identification of B. bronchiseptica and both toxigenic and nontoxigenic P. multocida that may greatly simplify investigations of swine PAR and bronchopneumonia.

Role of the dermonecrotic toxin of Bordetella bronchiseptica in the pathogenesis of respiratory disease in swine

Bordetella bronchiseptica is one of the etiologic agents causing atrophic rhinitis and pneumonia in swine. It produces several purported virulence factors, including the dermonecrotic toxin (DNT), which has been implicated in the turbinate atrophy seen in cases of atrophic rhinitis. The purpose of these experiments was to clarify the role of this toxin in respiratory disease by comparing the pathogenicity in swine of two isogenic dnt mutants to their virulent DNT(+) parent strains. Two separate experiments were performed, one with each of the mutant-parent pairs. One-week-old cesarean-derived, colostrum-deprived pigs were inoculated intranasally with the parent strain, the dnt mutant strain, or phosphate-buffered saline. Weekly nasal washes were performed to monitor colonization of the nasal cavity, and the pigs were euthanized 4 weeks after inoculation to determine colonization of tissues and to examine the respiratory tract for pathology. There was evidence that colonization of the upper respiratory tract, but not the lower respiratory tract, was slightly greater for the parent strains than for the dnt mutants. Moderate turbinate atrophy and bronchopneumonia were found in most pigs given the parent strains, while there was no turbinate atrophy or pneumonia in pigs challenged with the dnt mutant strains. Therefore, production of DNT by B. bronchiseptica is necessary to produce the lesions of turbinate atrophy and bronchopneumonia in pigs infected with this organism.

Reduced virulence of a Bordetella bronchiseptica siderophore mutant in neonatal swine

One means by which Bordetella bronchiseptica scavenges iron is through production of the siderophore alcaligin. A nonrevertible alcaligin mutant derived from the virulent strain 4609, designated DBB25, was constructed by insertion of a kanamycin resistance gene into alcA, one of the genes essential for alcaligin biosynthesis. The virulence of the alcA mutant in colostrum-deprived, caesarean-delivered piglets was compared with that of the parent strain in two experiments. At 1 week of age, piglets were inoculated with phosphate-buffered saline, 4609, or DBB25. Two piglets in each group were euthanatized on day 10 postinfection. The remainder were euthanatized at 21 days postinfection. Clinical signs, including fever, coughing, and sneezing, were present in both groups. Nasal washes performed 7, 14, and 21 days postinoculation demonstrated that strain DBB25 colonized the nasal cavity but did so at levels that were significantly less than those achieved by strain 4609. Analysis of colonization based on the number of CFU per gram of tissue recovered from the turbinate, trachea, and lung also demonstrated significant differences between DBB25 and 4609, at both day 10 and day 21 postinfection. Mild to moderate turbinate atrophy was apparent in pigs inoculated with strain 4609, while turbinates of those infected with strain DBB25 developed no or mild atrophy. We conclude from these results that siderophore production by B. bronchiseptica is not essential for colonization of swine but is required for maximal virulence. B. bronchiseptica mutants with nonrevertible defects in genes required for alcaligin synthesis may be candidates for evaluation as attenuated, live vaccine strains in conventionally reared pigs.

Restriction endonuclease analysis discriminates Bordetella bronchiseptica isolates

One hundred ninety-five Bordetella bronchiseptica isolates from 12 different host species worldwide were characterized by restriction enzyme analysis (REA). These isolates had previously been categorized into 19 PvuII ribotypes. Twenty restriction endonucleases were evaluated for use in REA. Digestion of chromosomal DNA with HinfI, followed by submarine electrophoresis in agarose gels and staining with ethidium bromide, produced DNA fragments in the 4.0- to 10-kb range, which readily discriminated B. bronchiseptica isolates, resulting in 48 fingerprint patterns. Moreover, AluI digestion of chromosomal DNA produced 39 distinct fingerprint profiles with DNA fragments ranging from 6.0 to 20.0 kb. While REA frequently provided more discriminatory power than ribotyping, there were examples where the use of ribotyping was more discriminatory than REA. Passage of selected isolates up to passage 25 did not change the REA profile. Moreover, the Bvg phase did not alter the fingerprint profile of chromosomal DNA from B. bronchiseptica strains digested with HinfI or AluI. Based on the results presented herein, the combination of REA and ribotyping should provide valuable information in understanding the molecular epidemiology of B. bronchiseptica infections.

Ribotyping and restriction endonuclease analysis reveal a novel clone of Bordetella bronchiseptica in seals

The goal of the present study was to characterize, by ribotyping and restriction endonuclease analysis (REA), 35 phocine Bordetella bronchiseptica isolates and to ascertain their relationship to one another and to isolates acquired from other host species. Thirty-four isolates were obtained in Scotland during a 10-year period encompassing the 1988 epizootic; the remaining isolate was obtained independently in Denmark. All phocine isolates had an identical Pvu II ribotype unique from the 18 ribotypes previously detected in strains from heterologous hosts. Alternative restriction enzymes, useful for subgrouping strains within Pvu II ribotypes, also failed to discriminate among isolates from seals. The exclusive occurrence of a single ribotype of B. bronchiseptica in a particular host species has not been previously observed. Similarly, REA based on either HinfI or Dde I profiles did not reveal detectable polymorphisms, although unique patterns were readily distinguished among a limited number of isolates from other host species. This is the first report demonstrating the utility of REA using frequently cutting enzymes for discrimination of B. bronchiseptica strains. These data suggest that B. bronchiseptica-induced respiratory disease in seals along the Scottish shore may be due to the circulation of a single, unique clone.

Two-color hybridization assay for simultaneous detection of Bordetella bronchiseptica and toxigenic Pasteurella multocida from swine

Bordetella bronchiseptica and toxigenic Pasteurella multocida are the etiologic agents of swine atrophic rhinitis. Methods currently used for their identification are time-consuming and suffer from a lack of sensitivity. We describe a colony lift-hybridization assay for detection of B. bronchiseptica and toxigenic P. multocida that can be performed with a single colony lift derived from a primary isolation plate without the need for pure subcultures of suspect bacteria. Membranes are hybridized simultaneously to probes derived from the B. bronchiseptica alcA gene and the P. multocida toxA gene. A multicolor development procedure permits sequential detection of bound probes. The assay was tested with 84 primary isolation plates generated from nasal swabs from swine with clinical signs of atrophic rhinitis. Comparison of the results from the colony lift-hybridization assay with those from conventional testing, based on a combination of colony morphology, biochemical reactions, mouse lethality, and enzyme-linked immunosorbent assay, indicated that the colony lift assay has superior sensitivity and comparable specificity. This technique has wide application for diagnostic and experimental studies.

A porcine model for the evaluation of virulence of Bordetella bronchiseptica

Studies of virulence factors of Bordetella bronchiseptica require a suitable system. Such a system was devised in colostrum-deprived, caesarean-derived pigs, aged 7 d. In two different experiments, pigs (n = 11) were inoculated intranasally with 10(6) colony-forming units of the virulent strain 4609. In the same way, further pigs (n = 11) were inoculated with a strain (B133) of unknown virulence. No significant differences between 4609 and B133 colonization were seen. However, colonization of the turbinates was significantly higher than that of the trachea, lung and tonsil, and a significantly higher degree of colonization was present at 11 d post-inoculation (PI) than at 15 days. Moderate turbinate atrophy was present by 11 d PI, and peribronchiolar fibrosis was present at 15 days. Immunocytochemical methods showed that all pigs had bacterial antigen in the ciliated cells of the turbinates and trachea, and in the lung; some pigs also had antigen in the bronchi. Bacterial antigen was present in some bronchioles and within the cytoplasm of pulmonary macrophages and neutrophils. This model should prove useful for comparing strains of B. bronchiseptica and isogenic mutants deficient in putative virulence factors.