A siderophore production mutant of Bordetella bronchiseptica cannot use lactoferrin as an iron source

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.

Bordetella bronchiseptica infection in the cat

Feline Bordetella bronchiseptica infection had received little consideration until recent years when it has been increasingly documented in association with respiratory disease. This article reviews current knowledge on the organism; its epidemiology, pathogenesis, and clinical, diagnostic and therapeutic features.

Early colonization of the rat upper respiratory tract by temperature modulated Bordetella bronchiseptica

The ability of nonmodulated Bvg+ phase cultures, temperature modulated Bvg- phase cultures, and a Bvg- phase-locked mutant of Bordetella bronchiseptica to colonize the rat upper respiratory tract was investigated. Initially, greater numbers of the temperature modulated Bvg- phase bacteria adhered to the nasal cavity of the rats. The temperature modulated Bvg- phase bacteria appeared to be quickly cleared to levels lower than the Bvg+ phase bacteria by 4 h after inoculation and stayed lower until 48 h after inoculation when colonization levels were equal to the Bvg+ phase bacteria. The level of colonization with the Bvg- phase-locked mutant of B. bronchiseptica was lower than both the nonmodulated Bvg+ phase and temperature modulated Bvg- phase cultures and declined over time during the experiment. These findings suggest that there may be increased adherence from an environmental phase to ensure bacteria survive initial clearance mechanisms until the switch to the Bvg+ phase occurs.

Two iron-regulated putative ferric siderophore receptor genes in Bordetella bronchiseptica and Bordetella pertussis

Two iron-regulated genes with deduced homology to TonB-dependent ferric siderophore receptors were cloned from Bordetella bronchiseptica by screening a library of TnphoA insertion mutants. bfrB and bfrC were iron-repressed in B. bronchiseptica by a Fur-dependent mechanism, and were expressed from promoters overlapped by potential Fur-binding sites. Both genes were highly conserved among Bordetella species and were also iron-regulated in Bordetella pertussis. bfrB and bfrC mutants of both species and a bfrB-bfrC double mutant of B. bronchiseptica had no discernible defects in utilization of known iron sources for Bordetella.

A highly adherent phenotype associated with virulent Bvg+-phase swine isolates of Bordetella bronchiseptica grown under modulating conditions

The ability of Bvg(-)-phase and Bvg(+)-phase Bordetella bronchiseptica swine isolates, grown under modulating or nonmodulating conditions, to adhere to swine ciliated nasal epithelial cells was determined. When virulent strains were cultivated at 37 degrees C in the Bvg+ phase, numerous adherent bacteria (approximately eight per cell, depending on the strain used) were observed. However, when such strains were grown under modulating conditions (23 degrees C), a significant increase in the level of attachment was seen, suggesting that B. bronchiseptica produces a Bvg-repressed adhesin under these conditions. bvg mutant strains, including an isogenic bvgS mutant, adhered minimally. Western blots indicated that two putative B. bronchiseptica adhesins, filamentous hemagglutinin and pertactin, were not detectable in cultures displaying the highly adherent phenotype. Several proteins apparent in Western blots obtained by using bacterial extracts enriched in outer membrane proteins derived from B. bronchiseptica grown at 23 degrees C were not present in similar extracts prepared from an isogenic bvgS mutant grown at 23 degrees C or from the parent strain grown at 37 degrees C. Adherence of bacteria cultivated at 23 degrees C was almost completely abolished by pretreatment of organisms at 60 degrees C; adherence was reduced by 57% when bacteria were pretreated with pronase E. Temperature shift experiments revealed that the heightened level of adhesion that occurs following growth at 23 degrees C was maintained for up to 18 h when bacteria were subsequently incubated at 37 degrees C. We propose that a Bvg-repressed adhesin, expressed only by modulated bvg+ strains of B. bronchiseptica, may play a key role in the initial colonization of naturally infected swine.

Species selectivity of new siderophore-drug conjugates that use specific iron uptake for entry into bacteria

Siderophores selectively bind ferric iron and are involved in receptor-specific iron transport into bacteria. Several types of siderophores were synthesized, and growth-promoting or inhibitory activities when they were conjugated to carbacephalosporin, erythromycylamine, or nalidixic acid were investigated. Overall, 11 types of siderophores and 21 drug conjugates were tested against seven different bacterial species: Escherichia coli, Bordetella bronchiseptica, Pasteurella multocida, Pasteurella haemolytica, Streptococcus suis, Staphylococcus aureus, and Staphylococcus epidermidis. In some species, the inhibitory activities of the drug conjugates were associated with the ability of the bacteria to use the siderophore portion of the molecules for growth promotion in disc diffusion tests (0.04 mumol of conjugate or siderophore per disc). E. coli used catechol-based siderophore portions as well as hydroxamate-based tri-delta-OH-N-OH-delta-N-acetyl-L-ornithine ferric iron ligands for growth under iron-restricted conditions achieved by supplemental ethylenediamine di (O-hydroxyphenylacetic acid) (100 micrograms/ml) and was sensitive to carbacephalosporin conjugated to these siderophore types (up to a 34-mm-diameter inhibition zone). B. bronchiseptica used desferrioxamine B and an isocyanurate-based or trihydroxamate in addition to catechol-based siderophore portions for promotion but was not inhibited by beta-lactam conjugates partly because of the presence of beta-lactamase. P. multocida and P. haemolytica did not use any of the synthetic siderophores for growth promotion, and the inhibitory activities of some conjugates seemed partly linked to their ability to withhold iron from these bacteria, since individual siderophore portions showed some antibacterial effects. Individual siderophores did not promote S. suis growth in restrictive conditions, but the type of ferric iron ligands attached to beta-lactams affected inhibitory activities. The antibacterial activities of the intracellular-acting agents erythromycylamine and nalidixic acid were reduced or lost, even against S. aureus and S. epidermidis, when the agents were conjugated to siderophores. Conjugate-resistant E. coli mutants showed the absence of some iron-regulated outer membrane proteins in gel electrophoresis profiles and in specific phage or colicin sensitivity tests, implying that the drugs used outer membrane receptors of ferric complexes to get into cells.

Identification of alcA, a Bordetella bronchiseptica gene necessary for alcaligin production

The alcA gene, essential for the production of the dihydroxamate siderophore, alcaligin, by Bordetella bronchiseptica, was cloned and sequenced. The alcA gene was identified on a 4.7-kb EcoRI genomic fragment adjacent to a Tn5lac transposon insertion that inactivated alcaligin production in strain MBORD846. Analysis of the alcA nucleotide sequence revealed a putative Fur-binding site, suggesting that expression of this gene is repressed by iron. The deduced amino-acid sequence of this open reading frame had significant homology with the Escherichia coli iucD gene product, an enzyme required for biosynthesis of the dihydroxamate siderophore aerobactin.

bvg Repression of alcaligin synthesis in Bordetella bronchiseptica is associated with phylogenetic lineage

Recent studies have shown that Bordetella bronchiseptica utilizes a siderophore-mediated transport system for acquisition of iron from the host iron-binding proteins lactoferrin and transferrin. We recently identified the B. bronchiseptica siderophore as alcaligin, which is also produced by B. pertussis. Alcaligin production by B. bronchiseptica is repressed by exogenous iron, a phenotype of other microbes that produce siderophores. In this study, we report that alcaligin production by B. bronchiseptica RB50 and GP1SN was repressed by the Bordetella global virulence regulator, bvg, in addition to being Fe repressed. Modulation of bvg locus expression with 50 mM MgSO4 or inactivation of bvg by deletion allowed strain RB50 to produce alcaligin. In modulated organisms, siderophore production remained Fe repressed. These observations contrasted with our previous data indicating that alcaligin production by B. bronchiseptica MBORD846 and B. pertussis was repressed by Fe but bvg independent. Despite bvg repression of alcaligin production, strain RB50 was still able to acquire Fe from purified alcaligin, suggesting that expression of the bacterial alcaligin receptor was not repressed by bvg. We tested 114 B. bronchiseptica strains and found that bvg repression of alcaligin production was strongly associated with Bordetella phylogenetic lineage and with host species from which the organisms were isolated.

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

Current methods for the isolation and identification of Bordetella bronchiseptica from clinical samples are time-consuming and are based, in part, on subjective observations. We describe the use of a Bordetella-specific DNA probe in a nonradioactive colony lift-hybridization assay for the identification of B. bronchiseptica. Eleven of 82 clinical specimens were found to contain B. bronchiseptica by this method, while only 5 of these were reported to contain the organism when the specimens were analyzed by traditional methods. The chromosomal fragment containing a sequence complementary to the probe appeared to be conserved in B. bronchiseptica isolates from swine from a variety of sources. The assay is more rapid than culture and biochemical testing since it can be performed directly on primary culture plates, even when they are heavily contaminated with other bacterial species. Only minimal training is required to accomplish the assay successfully, and the results are easy to interpret.

Identification of alcaligin as the siderophore produced by Bordetella pertussis and B. bronchiseptica

The siderophores produced by iron-starved Bordetella pertussis and B. bronchiseptica were purified and were found to be identical. Using mass spectrometry and proton nuclear magnetic resonance, we determined that the siderophore produced by these organisms was identical to alcaligin, a siderophore produced by Alcaligenes denitrificans.