Prevalence, virulence attributes, and antibiogram of Bordetella avium isolated from turkeys in Egypt.

Turkey coryza is a major respiratory disease caused by Bordetella avium (B. avium). It occurs in all ages of turkeys and is characterized by high morbidity and low mortality rates. The present study aimed firstly at determination of the prevalence rates of B. avium in turkeys reared in Egypt at different ages using various diagnostic methods including clinical examination, histopathology, enzyme-linked immunosorbent assay (ELISA), bacterial culture, and polymerase chain reaction (PCR). Using PCR, virulence-associated genes were detected in the confirmed B. avium isolates. Furthermore, the antibiotic resistance profiles of the confirmed B. avium isolates were examined. The achieved results indicated isolation and identification of B. avium infection at different ages of turkeys reared in Egypt. The overall PCR-confirmed prevalence rate of B. avium was 22.95%. The identified B. avium strains harbored virulence-associated genes responsible for colonization in the respiratory tract of turkeys including Bordetella virulence gene (100%), fimbriae (71.14%), and filamentous hemagglutinin (85.68%). The isolated B. avium strains showed multidrug resistance profiles. B. avium isolates were resistant to penicillin (92.82%), ceftiofur (85.68%), nalidixic acid (78.54%), and lincomycin (71.40%). The identified B. avium strains showed clear sensitivities to both gentamicin and neomycin, suggesting these as possible antimicrobial candidates for the control of B. avium infection in turkeys.

Biofilm formation and cellulose expression by Bordetella avium 197N, the causative agent of bordetellosis in birds and an opportunistic respiratory pathogen in humans.

Although bacterial cellulose synthase (bcs) operons are widespread within the Proteobacteria phylum, subunits required for the partial-acetylation of the polymer appear to be restricted to a few γ-group soil, plant-associated and phytopathogenic pseudomonads, including Pseudomonas fluorescens SBW25 and several Pseudomonas syringae pathovars. However, a bcs operon with acetylation subunits has also been annotated in the unrelated ß-group respiratory pathogen, Bordetella avium 197N. Our comparison of subunit protein sequences and GC content analyses confirms the close similarity between the B. avium 197N and pseudomonad operons and suggests that, in both cases, the cellulose synthase and acetylation subunits were acquired as a single unit. Using static liquid microcosms, we can confirm that B. avium 197N expresses low levels of cellulose in air-liquid interface biofilms and that biofilm strength and attachment levels could be increased by elevating c-di-GMP levels like the pseudomonads, but cellulose was not required for biofilm formation itself. The finding that B. avium 197N is capable of producing cellulose from a highly-conserved, but relatively uncommon bcs operon raises the question of what functional role this modified polymer plays during the infection of the upper respiratory tract or survival between hosts, and what environmental signals control its production.

The autotransporter protein from Bordetella avium, Baa1, is involved in host cell attachment.

Bordetella avium is a Gram negative upper respiratory tract pathogen of birds. B. avium infection of commercially raised turkeys is an agriculturally significant problem. Here we describe the functional analysis of the first characterized B. avium autotransporter protein, Baa1. Autotransporters comprise a large family of proteins found in all groups of Gram negative bacteria. Although not unique to pathogenic bacteria, autotransporters have been shown to perform a variety of functions implicated in virulence. To test the hypothesis that Baa1 is a B. avium virulence factor, unmarked baa1 deletion mutants (Δbaa1) were created and tested phenotypically. It was found that baa1 mutants have wild-type levels of serum sensitivity and infectivity, yet significantly lower levels of turkey tracheal cell attachment in vitro. Likewise, semi-purified recombinant His-tagged Baa1, expressed in Escherichia coli, was shown to bind specifically to turkey tracheal cells via western blot analysis. Taken together, we conclude that Baa1 acts as a host cell attachment factor and thus plays a role B. avium virulence.

The Bordetella avium BAV1965-1962 fimbrial locus is regulated by temperature and produces fimbriae involved in adherence to turkey tracheal tissue.

Bordetella pertussis, Bordetella parapertussis, and Bordetella bronchiseptica cause respiratory tract disease in mammals, whereas Bordetella avium causes respiratory tract disease in avian hosts. While there are striking similarities between the diseases caused by the mammalian- and avian-adapted bordetellae, differences at the genetic level may account for their different host tropisms. Bacterial pathogens utilize the chaperone-usher pathway to assemble extracellular multisubunit structures (fimbriae) that play a role in virulence. Fimbriae of the mammalian bordetellae mediate attachment to the host respiratory epithelium. They are assembled by a single chaperone/usher system encoded by the fimbrial biogenesis operon fimA-D. B. avium contains a homologous fimbrial operon (BAV1965-1962), and we report here the functionality of this locus. Reverse transcription (RT)-PCR and quantitative PCR analyses demonstrated that transcription of the locus is regulated by temperature. By immuno-transmission electron microscopy (TEM), BAV1965-containing fimbriae were observed on bacteria grown at 37°C but not those grown at 22°C. A mutant in which BAV1965-1962 was deleted displayed significantly lower levels of adherence to turkey tracheal rings than the wild type. Thus, the BAV1965-1962 fimbrial locus is functional, its expression is regulated in response to temperature, and it produces fimbriae involved in adherence to host respiratory tract tissue.