Identification and purification of transferrin- and lactoferrin-binding proteins of Bordetella pertussis and Bordetella bronchiseptica

Nanomotion Detection Method for Testing Antibiotic Resistance and Susceptibility of Slow-Growing Bacteria

Infectious diseases are caused by pathogenic microorganisms and are often severe. Time to fully characterize an infectious agent after sampling and to find the right antibiotic and dose are important factors in the overall success of a patient's treatment. Previous results suggest that a nanomotion detection method could be a convenient tool for reducing antibiotic sensitivity characterization time to several hours. Here, the application of the method for slow-growing bacteria is demonstrated, taking Bordetella pertussis strains as a model. A low-cost nanomotion device is able to characterize B. pertussis sensitivity against specific antibiotics within several hours, instead of days, as it is still the case with conventional growth-based techniques. It can discriminate between resistant and susceptible B. pertussis strains, based on the changes of the sensor's signal before and after the antibiotic addition. Furthermore, minimum inhibitory and bactericidal concentrations of clinically applied antibiotics are compared using both techniques and the suggested similarity is discussed.

Attenuated Bordetella pertussis vaccine protects against respiratory syncytial virus disease via an IL-17-dependent mechanism

RATIONALE

We attenuated virulent Bordetella pertussis by genetically eliminating or detoxifying three major toxins. This strain, named BPZE1, is being developed as a possible live nasal vaccine for the prevention of whooping cough. It is immunogenic and safe when given intranasally in adult volunteers.

OBJECTIVES

Before testing in human infants, we wished to examine the potential effect of BPZE1 on a common pediatric infection (respiratory syncytial virus [RSV]) in a preclinical model.

METHODS

BPZE1 was administered before or after RSV administration in adult or neonatal mice. Pathogen replication, inflammation, immune cell recruitment, and cytokine responses were measured.

MEASUREMENTS AND MAIN RESULTS

BPZE1 alone did not cause overt disease, but induced efflux of neutrophils into the airway lumen and production of IL-10 and IL-17 by mucosal CD4(+) T cells. Given intranasally before RSV infection, BPZE1 markedly attenuated RSV, preventing weight loss, reducing viral load, and attenuating lung cell recruitment. Given neonatally, BPZE1 also protected against RSV-induced weight loss even through to adulthood. Furthermore, it markedly increased IL-17 production by CD4(+) T cells and natural killer cells and recruited regulatory cells and neutrophils after virus challenge. Administration of anti-IL-17 antibodies ablated the protective effect of BPZE1 on RSV disease.

CONCLUSIONS

Rather than enhancing RSV disease, BPZE1 protected against viral infection, modified viral responses, and enhanced natural mucosal resistance. Prevention of RSV infection by BPZE1 seems in part to be caused by induction of IL-17. Clinical trial registered with www.clinicaltrials.gov (NCT 01188512).

Protective role of adenylate cyclase in the context of a live pertussis vaccine candidate

Despite high vaccination coverage, pertussis remains an important respiratory infectious disease and the least-controlled vaccine-preventable infectious disease in children. Natural infection with Bordetella pertussis is known to induce strong and long-lasting immunity that wanes later than vaccine-mediated immunity. Therefore, a live attenuated B. pertussis vaccine, named BPZE1, has been developed and has recently completed a phase I clinical trial in adult human volunteers. In this study, we investigated the contribution of adenylate cyclase (CyaA) in BPZE1-mediated protection against pertussis. A CyaA-deficient BPZE1 mutant was thus constructed. Absence of CyaA did not compromise the adherence properties of the bacteria onto mammalian cells. However, the CyaA-deficient mutant displayed a slight impairment in the ability to survive within macrophages compared to the parental BPZE1 strain. In vivo, whereas the protective efficacy of the CyaA-deficient mutant was comparable to the parental strain at a vaccine dose of 5 × 10(5) colony forming units (CFU), it was significantly impaired at a vaccine dose of 5 × 10(3) CFU. This impairment correlated with impaired lung colonization ability, and impaired IFN-γ production in the animal immunized with the CyaA-deficient BPZE1 mutant while the pertussis-specific antibody profile and Th17 response were comparable to those observed in BPZE1-immunized mice. Our findings thus support a role of CyaA in BPZE1-mediated protection through induction of cellular mediated immunity.

Interaction of Bordetella bronchiseptica and Its Lipopolysaccharide with In Vitro Culture of Respiratory Nasal Epithelium

The nasal septa of fetal rabbits at 26 days of gestation were harvested by cesarean section of the does while under anesthesia and then exposed to Bordetella bronchiseptica or its lipopolysaccharide (LPS) for periods of 2 and 4 hours. A total of 240 explants were used. The tissues were examined using the Hematoxylin & Eosin technique. Then, semithin sections (0.5 μm) were stained with toluidine blue and examined with indirect immunoperoxidase (IPI) and lectin histochemistry. The most frequent and statistically significant findings were as follows: (1) cell death and increased goblet cell activity when exposed to bacteria and (2) cell death, cytoplasmic vacuolation and infiltration of polymorphonuclear leukocytes when exposed to LPS. The lesions induced by the bacterium were more severe than with LPS alone, except for the cytoplasmic vacuolation in epithelial cells. IPI stained the ciliated border of the epithelium with the bacterium more intensely, while LPS lectin histochemistry preferentially labeled the cytoplasm of goblet cell. These data indicate that B. bronchiseptica and its LPS may have an affinity for specific glycoproteins that would act as adhesion receptors in both locations.

Involvement of multiple distinct Bordetella receptor proteins in the utilization of iron liberated from transferrin by host catecholamine stress hormones

Bordetella bronchiseptica is a pathogen that can acquire iron using its native alcaligin siderophore system, but can also use the catechol xenosiderophore enterobactin via the BfeA outer membrane receptor. Transcription of bfeA is positively controlled by a regulator that requires induction by enterobactin. Catecholamine hormones also induce bfeA transcription and B. bronchiseptica can use the catecholamine noradrenaline for growth on transferrin. In this study, B. bronchiseptica was shown to use catecholamines to obtain iron from both transferrin and lactoferrin in the absence of siderophore. In the presence of siderophore, noradrenaline augmented transferrin utilization by B. bronchiseptica, as well as siderophore function in vitro. Genetic analysis identified BfrA, BfrD and BfrE as TonB-dependent outer membrane catecholamine receptors. The BfeA enterobactin receptor was found to not be involved directly in catecholamine utilization; however, the BfrA, BfrD and BfrE catecholamine receptors could serve as receptors for enterobactin and its degradation product 2,3-dihydroxybenzoic acid. Thus, there is a functional link between enterobactin-dependent and catecholamine-dependent transferrin utilization. This investigation characterizes a new B. bronchiseptica mechanism for iron uptake from transferrin that uses host stress hormones that not only deliver iron directly to catecholamine receptors, but also potentiate siderophore activity by acting as iron shuttles.

FHA-mediated cell-substrate and cell-cell adhesions are critical for Bordetella pertussis biofilm formation on abiotic surfaces and in the mouse nose and the trachea

Bordetella spp. form biofilms in the mouse nasopharynx, thereby providing a potential mechanism for establishing chronic infections in humans and animals. Filamentous hemagglutinin (FHA) is a major virulence factor of B. pertussis, the causative agent of the highly transmissible and infectious disease, pertussis. In this study, we dissected the role of FHA in the distinct biofilm developmental stages of B. pertussis on abiotic substrates and in the respiratory tract by employing a murine model of respiratory biofilms. Our results show that the lack of FHA reduced attachment and decreased accumulation of biofilm biomass on artificial surfaces. FHA contributes to biofilm development by promoting the formation of microcolonies. Absence of FHA from B. pertussis or antibody-mediated blockade of surface-associated FHA impaired the attachment of bacteria to the biofilm community. Exogenous addition of FHA resulted in a dose-dependent inhibitory effect on bacterial association with the biofilms. Furthermore, we show that FHA is important for the structural integrity of biofilms formed on the mouse nose and trachea. Together, these results strongly support the hypothesis that FHA promotes the formation and maintenance of biofilms by mediating cell-substrate and inter-bacterial adhesions. These discoveries highlight FHA as a key factor in establishing structured biofilm communities in the respiratory tract.

Lcl of Legionella pneumophila is an immunogenic GAG binding adhesin that promotes interactions with lung epithelial cells and plays a crucial role in biofilm formation

Legionellosis is mostly caused by Legionella pneumophila and is defined by a severe respiratory illness with a case fatality rate ranging from 5 to 80%. In vitro and in vivo, interactions of L. pneumophila with lung epithelial cells are mediated by the sulfated glycosaminoglycans (GAGs) of the host extracellular matrix. In this study, we have identified several Legionella heparin binding proteins. We have shown that one of these proteins, designated Lcl, is a polymorphic adhesin of L. pneumophila that is produced during legionellosis. Homologues of Lcl are ubiquitous in L. pneumophila serogroups but are undetected in other Legionella species. Recombinant Lcl binds to GAGs, and a Δlpg2644 mutant demonstrated reduced binding to GAGs and human lung epithelial cells. Importantly, we showed that the Δlpg2644 strain is dramatically impaired in biofilm formation. These data delineate the role of Lcl in the GAG binding properties of L. pneumophila and provide molecular evidence regarding its role in L. pneumophila adherence and biofilm formation.

Attenuated Bordetella pertussis protects against highly pathogenic influenza A viruses by dampening the cytokine storm

The threat of a pandemic spread of highly virulent influenza A viruses currently represents a top global public health problem. Mass vaccination remains the most effective way to combat influenza virus. However, current vaccination strategies face the challenge to meet the demands in a pandemic situation. In a mouse model of severe influenza virus-induced pneumonitis, we observed that prior nasal administration of an attenuated strain of Bordetella pertussis (BPZE1) provided effective and sustained protection against lethal challenge with two different influenza A virus subtypes. In contrast to most cross-protective effects reported so far, the protective window offered upon nasal treatment with BPZE1 lasted up to at least 12 weeks, suggesting a unique mechanism(s) involved in the protection. No significant differences in viral loads were observed between BPZE1-treated and control mice, indicating that the cross-protective mechanism(s) does not directly target the viral particles and/or infected cells. This was further confirmed by the absence of cross-reactive antibodies and T cells in serum transfer and in vitro restimulation experiments, respectively. Instead, compared to infected control mice, BPZE1-treated animals displayed markedly reduced lung inflammation and tissue damage, decreased neutrophil infiltration, and strong suppression of the production of major proinflammatory mediators in their bronchoalveolar fluids (BALFs). Our findings thus indicate that protection against influenza virus-induced severe pneumonitis can be achieved through attenuation of exaggerated cytokine-mediated inflammation. Furthermore, nasal treatment with live attenuated B. pertussis offers a potential alternative to conventional approaches in the fight against one of the most frightening current global public health threats.

Norepinephrine mediates acquisition of transferrin-iron in Bordetella bronchiseptica

Previous research demonstrated that the sympathoadrenal catecholamine norepinephrine could promote the growth of Bordetella bronchiseptica in iron-restricted medium containing serum. In this study, norepinephrine was demonstrated to stimulate growth of this organism in the presence of partially iron-saturated transferrin but not lactoferrin. Although norepinephrine is known to induce transcription of the Bordetella bfeA enterobactin catechol xenosiderophore receptor gene, neither a bfeA mutant nor a bfeR regulator mutant was defective in growth responsiveness to norepinephrine. However, growth of a tonB mutant strain was not enhanced by norepinephrine, indicating that the response to this catecholamine was the result of high-affinity outer membrane transport. The B. bronchiseptica genome encodes a total of 19 known and predicted iron transport receptor genes, none of which, when mutated individually, were found to confer a defect in norepinephrine-mediated growth stimulation in the presence of transferrin. Labeling experiments demonstrated a TonB-dependent increase in cell-associated iron levels when bacteria grown in the presence of (55)Fe-transferrin were exposed to norepinephrine. In addition, TonB was required for maximum levels of cell-associated norepinephrine. Together, these results demonstrate that norepinephrine facilitates B. bronchiseptica iron acquisition from the iron carrier protein transferrin and this process may represent a mechanism by which some bacterial pathogens obtain this essential nutrient in the host environment.

Utilization of lactoferrin-bound and transferrin-bound iron by Campylobacter jejuni

Campylobacter jejuni NCTC 11168 was capable of growth to levels comparable with FeSO4 in defined iron-limited medium (minimal essential medium alpha [MEMalpha]) containing ferrilactoferrin, ferritransferrin, or ferri-ovotransferrin. Iron was internalized in a contact-dependent manner, with 94% of cell-associated radioactivity from either 55Fe-loaded transferrin or lactoferrin associated with the soluble cell fraction. Partitioning the iron source away from bacteria significantly decreased cellular growth. Excess cold transferrin or lactoferrin in cultures containing 55Fe-loaded transferrin or lactoferrin resulted in reduced levels of 55Fe uptake. Growth of C. jejuni in the presence of ferri- and an excess of apoprotein reduced overall levels of growth. Following incubation of cells in the presence of ferrilactoferrin, lactoferrin became associated with the cell surface; binding levels were higher after growth under iron limitation. A strain carrying a mutation in the cj0178 gene from the iron uptake system Cj0173c-Cj0178 demonstrated significantly reduced growth promotion in the presence of ferrilactoferrin in MEMalpha compared to wild type but was not affected in the presence of heme. Moreover, this mutant acquired less 55Fe than wild type when incubated with 55Fe-loaded protein and bound less lactoferrin. Complementation restored the wild-type phenotype when cells were grown with ferrilactoferrin. A mutant in the ABC transporter system permease gene (cj0174c) showed a small but significant growth reduction. The cj0176c-cj0177 intergenic region contains two separate Fur-regulated iron-repressible promoters. This is the first demonstration that C. jejuni is capable of acquiring iron from members of the transferrin protein family, and our data indicate a role for Cj0178 in this process.

Highly attenuated Bordetella pertussis strain BPZE1 as a potential live vehicle for delivery of heterologous vaccine candidates

Bordetella pertussis, the causative agent of whooping cough, is a promising and attractive candidate for vaccine delivery via the nasal route, provided that suitable attenuation of this pathogen has been obtained. Recently, the highly attenuated B. pertussis BPZE1 strain has been described as a potential live pertussis vaccine for humans. We investigated here the use of BPZE1 as a live vehicle for heterologous vaccine candidates. Previous studies have reported the filamentous hemagglutinin (FHA), a major B. pertussis adhesin, as a carrier to express foreign antigens in B. pertussis. In this study, we also examined the BrkA autotransporter as a surface display system. Three copies of the neutralizing peptide SP70 from enterovirus 71 (EV71) were fused to FHA or in the passenger domain of BrkA, and each chimera was expressed in BPZE1. The FHA-(SP70)3 and BrkA-(SP70)3 chimeras were successfully secreted and exposed at the bacterial surface, respectively. Nasal administration of the live recombinant strains triggered a strong and sustained systemic anti-SP70 antibody response in mice, although the titers and neutralizing activities against EV71 were significantly higher in the sera of mice immunized with the BrkA-(SP70)3-producing strain. These data indicate that the highly attenuated BPZE1 strain is a potential candidate for vaccine delivery via the nasal route with the BrkA autotransporter as an alternative to FHA for the presentation of the heterologous vaccine antigens.

Profiling theBordetellapertussisProteome during Iron Starvation

Regulation of gene expression in response to local iron concentration is commonly observed in bacterial pathogens that face this nutrient limitation during host infection. In this study, a proteomic approach was used to analyze the differential protein expression of Bordetella pertussis under iron limitation. Whole cell lysates (WCL) and outer membrane fractions of bacteria grown either under iron-starvation or iron-excess conditions were analyzed by two-dimensional (2-D) gel electrophoresis. Statistical analysis revealed 36 proteins displaying differential expression, 9 with higher expression under iron-excess and 27 with increased expression under iron-starvation. These proteins were subjected to tryptic digestion and MALDI-TOF MS. Apart from those previously reported, we identified new low-iron-induced proteins that might help to explain the increased virulence of this phenotype. Additionally, we found evidence that at least one of the identified proteins, solely expressed under iron starvation, is highly immunogenic in infected individuals.

Bordetella iron transport and virulence

Bordetella pertussis, Bordetella parapertussis, and Bordetella bronchiseptica are pathogens with a complex iron starvation stress response important for adaptation to nutrient limitation and flux in the mammalian host environment. The iron starvation stress response is globally regulated by the Fur repressor using ferrous iron as the co-repressor. Expression of iron transport system genes of Bordetella is coordinated by priority regulation mechanisms that involve iron source sensing. Iron source sensing is mediated by distinct transcriptional activators that are responsive to the cognate iron source acting as the inducer.

Production of nontypeable Haemophilus influenzae HtrA by recombinant Bordetella pertussis with the use of filamentous hemagglutinin as a carrier

Bordetella pertussis, the etiologic agent of whooping cough, is a highly infectious human pathogen capable of inducing mucosal and systemic immune responses upon a single intranasal administration. In an attenuated, pertussis toxin (PTX)-deficient recombinant form, it may therefore constitute an efficient bacterial vector that is particularly well adapted for the delivery of heterologous antigens to the respiratory mucosa. Filamentous hemagglutinin (FHA) has been used as a carrier to present foreign antigens at the bacterial surface, thereby inducing local, systemic, and protective immune responses to these antigens in mice. Both full-length and truncated (Fha44) forms of FHA have been used for antigen presentation. To investigate the effect of the carrier (FHA or Fha44) on antibody responses to passenger antigens, we genetically fused the HtrA protein of nontypeable Haemophilus influenzae to either FHA form. The fha-htrA and Fha44 gene-htrA hybrids were expressed as single copies inserted into the chromosome of PTX-deficient B. pertussis. Both chimeras were secreted into the culture supernatants of the recombinant strains and were recognized by anti-FHA and anti-HtrA antibodies. Intranasal infection with the strain producing the FHA-HtrA hybrid led to significantly higher anti-HtrA and anti-FHA antibody titers than those obtained in mice infected with the Fha44-HtrA-producing strain. Interestingly, the B. pertussis strain producing the Fha44-HtrA chimera colonized the mouse lungs more efficiently than the parental, Fha44-producing strain and gave rise to higher anti-FHA antibody titers than those induced by the parental strain.

Differential modulation of Bordetella pertussis virulence genes as evidenced by DNA microarray analysis

The production of most factors involved in Bordetella pertussis virulence is controlled by a two-component regulatory system termed BvgA/S. In the Bvg+ phase virulence-activated genes (vags) are expressed, and virulence-repressed genes (vrgs) are down-regulated. The expression of these genes can also be modulated by MgSO(4) or nicotinic acid. In this study we used microarrays to analyse the influence of BvgA/S or modulation on the expression of nearly 200 selected genes. With the exception of one vrg, all previously known vags and vrgs were correctly assigned as such, and the microarray analyses identified several new vags and vrgs, including genes coding for putative autotransporters, two-component systems, extracellular sigma factors, the adenylate cyclase accessory genes cyaBDE, and two genes coding for components of a type III secretion system. For most of the new vrgs and vags the results of the microarray analyses were confirmed by RT-PCR analysis and/or lacZfusions. The degree of regulation and modulation varied between genes, and showed a continuum from strongly BvgA/S-activated genes to strongly BvgA/S-repressed genes. The microarray analyses also led to the identification of a subset of vags and vrgs that are differentially regulated and modulated by MgSO(4) or nicotinic acid, indicating that these genes may be targets for multiple regulatory circuits. For example, the expression of bilA, a gene predicted to encode an intimin-like protein, was found to be activated by BvgA/S and up-modulated by nicotinic acid. Furthermore, surprisingly, in the strain analysed here, which produces only type 2 fimbriae, the fim3 gene was identified as a vrg, while fim2 was confirmed to be a vag.

Eighty-kilodalton N-terminal moiety of Bordetella pertussis filamentous hemagglutinin: adherence, immunogenicity, and protective role

Bordetella pertussis, the etiological agent of whooping cough, produces a number of factors, such as toxins and adhesins, that are required for full expression of virulence. Filamentous hemagglutinin (FHA) is the major adhesin of B. pertussis. It is a protein of approximately 220 kDa, found both associated at the bacterial cell surface and secreted into the extracellular milieu. Despite its importance in B. pertussis pathogenesis and its inclusion in most acellular pertussis vaccines, little is known about the functional importance of individual domains in infection and in the induction of protective immunity. In this study, we analyzed the role of the approximately 80-kDa N-terminal domain of FHA, designated Fha44, in B. pertussis adherence, colonization, and immunogenicity. Although Fha44 contains the complete heparan sulfate-binding domain, it is not sufficient for adherence to epithelial cells or macrophages. It also cannot replace FHA during colonization of the mouse respiratory tract. Infection with a B. pertussis strain producing Fha44 instead of FHA does not induce anti-FHA antibodies, whereas such antibodies can readily be induced by intranasal administration of purified Fha44. In addition, mice immunized with purified Fha44 were protected against challenge with wild-type B. pertussis, indicating that Fha44 contains protective epitopes. Compared to FHA, Fha44 is much smaller and much more soluble and is therefore easier to purify and to store. These advantages may perhaps warrant considering Fha44 for inclusion in acellular pertussis vaccines.

Linear B-cell epitopes in Lambert-Eaton myasthenic syndrome defined by cell-free synthetic peptide binding

Lambert-Eaton Myasthenic Syndrome (LEMS) is a rare autoimmune disorder characterized by autoantibodies that bind to P/Q voltage-gated calcium channels at the neuromuscular junction. Using cell-free direct peptide binding in 12 LEMS patients, we find linear B-cell epitopes that reside on the extracellular peptide linkers between the S5-S6 transmembrane peptides of Domains II and IV. A major epitope is located within the S5-S6 linker peptide of Domain IV defined by the acidic amino acid sequence EDEDSDEDE.

Interaction of human Tamm-Horsfall glycoprotein with Bordetella pertussis toxin

Tamm-Horsfall glycoprotein (THP), which is synthesized by renal tubular cells, is the most abundant protein in normal human urine. Although its physiological function remains unclear, it has been proposed that THP may act as a defence factor against urinary tract infections by inhibiting the binding of S- and P-fimbriated Escherichia coli to renal epithelial cells. Because THP-related proteins are also found in the superficial layers of the oral mucosa, the authors investigated the ability of THP to interfere with the cytoadherence of pathogenic bacteria that colonize mucosal surfaces other than those of the urogenital tract. In this report, it is shown that THP binds to virulent Bordetella pertussis and reduces its adherence to both renal and pulmonary epithelial cells. This cytoadherence inhibitory effect was not observed with a B. pertussis mutant lacking the pertussis toxin (PTX) operon, and was dependent on the direct interaction of THP with the S2 subunit within the PTX B oligomer. The authors also show that the glycosylation moiety of THP is crucial for its binding to PTX. The THP-PTX interaction was exploited to develop an affinity chromatography method that allows a one-step purification of active PTX. These observations suggest that besides its anti-adherence activity, THP may also trap toxins produced by pathogenic bacteria that colonize mucosal surfaces.

Bordetella interspecies allelic variation in AlcR inducer requirements: identification of a critical determinant of AlcR inducer responsiveness and construction of an alcR(Con) mutant allele

Previous studies established the critical roles of AlcR and alcaligin inducer in positive regulation of alcaligin siderophore biosynthesis and transport genes in Bordetella pertussis and Bordetella bronchiseptica. Transcriptional analyses using plasmid-borne alcR genes of B. pertussis UT25 and B. bronchiseptica B013N to complement the alcR defect of B. bronchiseptica strain BRM13 (Delta alcR1 alcA::mini-Tn5 lacZ1) revealed interspecies differences in AlcR inducer requirements for activation of alcABCDER operon transcription. Whereas the B. pertussis UT25 AlcR protein retained strong inducer dependence when produced from multicopy plasmids, B. bronchiseptica B013N alcR partially suppressed the alcaligin requirement for transcriptional activation. Functional analysis of AlcR chimeras produced by interspecies domain swapping and interspecies reciprocal site-specific mutagenesis determined that the phenotypic difference in AlcR inducer dependence was due to a single amino acid difference within the proposed inducer-binding and multimerization domain of AlcR. Structural predictions guided the design of a mutant AlcR protein with a single amino acid substitution at this critical position, AlcR(S103T), that was fully constitutive not only when produced from multicopy plasmids but also at a single-copy gene dosage. These results indicate that AlcR residue 103 affects a critical determinant of alcaligin inducer dependence of AlcR-mediated transcriptional activation. The alcR(S103T) mutant allele is the first alcR(Con) mutant allele identified.

Identification of lactoferrin-binding proteins in Streptococcus dysgalactiae subsp. dysgalactiae and Streptococcus agalactiae isolated from cows with mastitis

Three strains of Streptococcus dysgalactiae subsp. dysgalactiae (S. dysgalactiae) and five strains of Streptococcus agalactiae were used to identify lactoferrin-binding proteins (LBPs). LBPs from extracted surface proteins were detected by polyacrylamide gel electrophoresis and Western blotting. All strains of S. dysgalactiae evaluated had 52- and 74-kDa protein bands. All strains of S. agalactiae evaluated had 52-, 70- and 110-kDa protein bands. In addition, a 45-kDa band was detected in two of five S. agalactiae strains evaluated. This study demonstrated that S. dysgalactiae and S. agalactiae of bovine origin contain two and three major LBPs, respectively.

Role of ADP-ribosyltransferase activity of pertussis toxin in toxin-adhesin redundancy with filamentous hemagglutinin during Bordetella pertussis infection

Pertussis toxin (PT) and filamentous hemagglutinin (FHA) are two major virulence factors of Bordetella pertussis. FHA is the main adhesin, whereas PT is a toxin with an A-B structure, in which the A protomer expresses ADP-ribosyltransferase activity and the B moiety is responsible for binding to the target cells. Here, we show redundancy of FHA and PT during infection. Whereas PT-deficient and FHA-deficient mutants colonized the mouse respiratory tract nearly as efficiently as did the isogenic parent strain, a mutant deficient for both factors colonized substantially less well. This was not due to redundant functions of PT and FHA as adhesins, since in vitro studies of epithelial cells and macrophages indicated that FHA, but not PT, acts as an adhesin. An FHA-deficient B. pertussis strain producing enzymatically inactive PT colonized as poorly as did the FHA-deficient, PT-deficient strain, indicating that the ADP-ribosyltransferase activity of PT is required for redundancy with FHA. Only strains producing active PT induced a local transient release of tumor necrosis factor alpha (TNF-alpha), suggesting that the pharmacological effects of PT are the basis of the redundancy with FHA, through the release of TNF-alpha. This may lead to damage of the pulmonary epithelium, allowing the bacteria to colonize even in the absence of FHA.

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.

Mycobacterium smegmatis laminin-binding glycoprotein shares epitopes with Mycobacterium tuberculosis heparin-binding haemagglutinin

Mycobacterium tuberculosis, the causative agent of tuberculosis, produces a heparin-binding haemagglutinin adhesin (HBHA), which is involved in its epithelial adherence. To ascertain whether HBHA is also present in fast-growing mycobacteria, Mycobacterium smegmatis was studied using anti-HBHA monoclonal antibodies (mAbs). A cross-reactive protein was detected by immunoblotting of M. smegmatis whole-cell lysates. However, the M. tuberculosis HBHA-encoding gene failed to hybridize with M. smegmatis chromosomal DNA in Southern blot analyses. The M. smegmatis protein recognized by the anti-HBHA mAbs was purified by heparin-Sepharose chromatography, and its amino-terminal sequence was found to be identical to that of the previously described histone-like protein, indicating that M. smegmatis does not produce HBHA. Biochemical analysis of the M. smegmatis histone-like protein shows that it is glycosylated like HBHA. Immunoelectron microscopy demonstrated that the M. smegmatis protein is present on the mycobacterial surface, a cellular localization inconsistent with a histone-like function, but compatible with an adhesin activity. In vitro protein interaction assays showed that this glycoprotein binds to laminin, a major component of basement membranes. Therefore, the protein was called M. smegmatis laminin-binding protein (MS-LBP). MS-LBP does not appear to be involved in adherence in the absence of laminin but is responsible for the laminin-mediated mycobacterial adherence to human pneumocytes and macrophages. Homologous laminin-binding adhesins are also produced by virulent mycobacteria such as M. tuberculosis and Mycobacterium leprae, suggesting that this adherence mechanism may contribute to the pathogenesis of mycobacterial diseases.

Transcriptional activation of Bordetella alcaligin siderophore genes requires the AlcR regulator with alcaligin as inducer

Genetic and biochemical studies have established that Fur and iron mediate repression of Bordetella alcaligin siderophore system (alc) genes under iron-replete nutritional growth conditions. In this study, transcriptional analyses using Bordetella chromosomal alc-lacZ operon fusions determined that maximal alc gene transcriptional activity under iron starvation stress conditions is dependent on the presence of alcaligin siderophore. Mutational analysis and genetic complementation confirmed that alcaligin-responsive transcriptional activation of Bordetella alcaligin system genes is dependent on AlcR, a Fur-regulated AraC-like positive transcriptional regulator encoded within the alcaligin gene cluster. AlcR-mediated transcriptional activation is remarkably sensitive to inducer, occurring at extremely low alcaligin concentrations. This positive autogenous control circuit involving alcaligin siderophore as the inducer for AlcR-mediated transcriptional activation of alcaligin siderophore biosynthesis and transport genes coordinates environmental and intracellular signals for maximal expression of these genes under conditions in which the presence of alcaligin in the environment is perceived.

Bordetella pertussis TonB, a Bvg-independent virulence determinant

In gram-negative bacteria, high-affinity iron uptake requires the TonB/ExbB/ExbD envelope complex to release iron chelates from their specific outer membrane receptors into the periplasm. Based on sequence similarities, the Bordetella pertussis tonB exbB exbD locus was identified on a cloned DNA fragment. The tight organization of the three genes suggests that they are cotranscribed. A putative Fur-binding sequence located upstream from tonB was detected in a Fur titration assay, indicating that the tonB exbB exbD operon may be Fur-repressed in high-iron growth conditions. Putative structural genes of the beta-subunit of the histone-like protein HU and of a new two-component regulatory system were identified upstream from tonB and downstream from exbD, respectively. A B. pertussis DeltatonB exbB::Km(r) mutant was constructed by allelic exchange and characterized. The mutant was impaired for growth in low-iron medium in vitro and could not use ferrichrome, desferal, or hemin as iron sources. Levels of production of the major bacterial toxins and adhesins were similar in the TonB(+)/TonB(-) pair. The DeltatonB exbB mutant was still responsive to chemical modulators of virulence; thus, the BvgA/BvgS two-component system is not TonB dependent. Nevertheless, in vivo in the mouse respiratory infection model, the colonization ability of the mutant was reduced compared to the parental strain.

Iron starvation of Bordetella avium stimulates expression of five outer membrane proteins and regulates a gene involved in acquiring iron from serum

Iron starvation of Bordetella avium induced expression of five outer membrane proteins with apparent molecular masses of 95, 92, 91.5, 84, and 51 kDa. Iron-responsive outer membrane proteins (FeRPs) of similar sizes were detected in six of six strains of B. avium, suggesting that the five FeRPs are common constituents of the outer membrane of most, if not all, strains of B. avium. Iron-regulated genes of B. avium were targeted for mutagenesis with the transposon TnphoA. Two mutants with iron-responsive alkaline phosphatase activities were isolated from the transposon library. The transposon insertion did not alter the iron-regulated expression of the five FeRPs in mutant Pho-6. The mutant Pho-20 exhibited a loss in expression of the 95-kDa FeRP and the 84-kDa FeRP. Both Pho-6 and Pho-20 were able to use free iron as a nutrient source. However, Pho-20 was severely compromised in its ability to use iron present in turkey serum. The data indicated that the mutation in Pho-20 affected expression of one or more components of an uptake machinery that is involved in acquisition of iron from organic ferricomplexes.

Cloning and expression of the Moraxella catarrhalis lactoferrin receptor genes

The lactoferrin receptor genes from two strains of Moraxella catarrhalis have been cloned and sequenced. The lfr genes are arranged as lbpB followed by lbpA, a gene arrangement found in lactoferrin and transferrin receptor operons from several bacterial species. In addition, a third open reading frame, orf3, is located one nucleotide downstream of lbpA. The deduced lactoferrin binding protein A (LbpA) sequences from the two strains were found to be 99% identical, the LbpB sequences were 92% identical, and the ORF3 proteins were 98% identical. The lbpB gene was PCR amplified and sequenced from a third strain of M. catarrhalis, and the encoded protein was found to be 77% identical and 84% similar to the other LbpB proteins. Recombinant LbpA and LbpB proteins were expressed from Escherichia coli, and antisera raised to the purified proteins were used to assess antigenic conservation in a panel of M. catarrhalis strains. The recombinant proteins were tested for the ability to bind human lactoferrin following gel electrophoresis and electroblotting, and rLbpB, but not rLbpA, was found to bind lactoferrin. Bactericidal antibody activity was measured, and while the anti-rLbpA antiserum was not bactericidal, the anti-rLbpB antisera were found to be weakly bactericidal. Thus, LbpB may have potential as a vaccine candidate.

Iron repressibility of siderophore and transferrin-binding protein in Staphylococcus aureus

In order to investigate whether the iron acquisition mechanisms of Staphylococcus aureus are induced by iron restriction in vitro, we examined S. aureus ATCC 6538 for production of siderophore and expression of transferrin-binding protein (SA-tbp) in normal or deferrated brain heart infusion broth (BHI). Siderophore production was earlier and greater in the deferrated BHI. The SA-tbp, detected by ligand blot assay, was expressed only in the deferrated BHI. When human transferrin was added to the deferrated BHI, siderophore production was later and lower than when transferrin was not present. In conclusion, both iron acquisition mechanisms of S. aureus were found to be iron-repressible and via both of them, human transferrin-bound iron was utilized for growth under iron-restricted condition.

Identification of AlcR, an AraC-type regulator of alcaligin siderophore synthesis in Bordetella bronchiseptica and Bordetella pertussis

A Fur titration assay was used to isolate DNA fragments bearing putative Fur binding sites (FBS) from a partial Bordetella bronchiseptica genomic DNA library. A recombinant plasmid bearing a 3.5-kb DNA insert was further studied. Successive deletions in the cloned fragment enabled us to map a putative FBS at about 2 kb from one end. Sequence analysis revealed the presence of an FBS upstream from a new gene encoding an AraC-type transcriptional regulator. The deduced protein displays similarity to PchR, an activator of pyochelin siderophore and ferripyochelin receptor synthesis in Pseudomonas aeruginosa. Homologous genes in Bordetella pertussis and Bordetella parapertussis were PCR amplified, and sequence comparisons indicated a very high conservation in the three species. The B. pertussis and B. bronchiseptica chromosomal genes were inactivated by allelic exchange. Under low-iron growth conditions, the mutants did not secrete the alcaligin siderophore and lacked AlcC, an alcaligin biosynthetic enzyme. Alcaligin production was restored after transformation with a plasmid bearing the wild-type gene. On the basis of its role in regulation of alcaligin biosynthesis, the new gene was designated alcR. Additional sequence determination showed that alcR is located about 2 kb downstream from the alcABC operon and is transcribed in the same orientation. Two tightly linked open reading frames, alcD and alcE, were identified between alcC and alcR. AlcE is a putative iron-sulfur protein; AlcD shows no homology with the proteins in the database. The production of major virulence factors and colonization in the mouse respiratory infection model are AlcR independent.

Identification, characterization, and immunogenicity of the lactoferrin-binding protein from Helicobacter pylori

Iron acquisition plays an important role in bacterial virulence. Different studies have been initiated to define the mechanism by which Helicobacter pylori acquires iron. We had previously demonstrated that human lactoferrin (HLf) supported full growth of the bacteria in media lacking other iron sources. The ability of H. pylori to use HLf as an iron source had been found to be dependent on cell-to-protein contact. Since lactoferrin has been found in significant amounts in human stomach resection specimens from patients with superficial or atrophic gastritis, the iron uptake of H. pylori via a specific HLf receptor may play a major role in the virulence of H. pylori infection. In this study, by using affinity chromatography with biotinylated HLf and streptavidin-agarose, we identified a 70-kDa lactoferrin-binding protein (Lbp) from outer membrane proteins of H. pylori. This Lbp was only present when H. pylori was grown in an iron-starved medium, suggesting that it serves in iron uptake. Direct binding assays with increasing concentrations of biotinylated HLf demonstrated that the lactoferrin interaction with the outer membrane of H. pylori grown in iron-restricted medium was saturable. Competitive binding experiments with bovine and human lactoferrin and with transferrin of horse, bovine, and human origin indicated that this Lbp appeared highly specific for HLf. A number of other studies have focused on the importance of transferrin and lactoferrin receptors in pathogenic bacteria and their specificity with the host species. This observation might explain the very strict human specificity of H. pylori.

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.

Effect of concentration of compounds containing iron on the growth of Porphyromonas gingivalis

We examined the effect of the concentration of various types of iron molecules on the regulation of growth of Porphyromonas gingivalis. Bacterial growth was monitored spectrophotometrically. The hemin-depleted cells of P. gingivalis 381 were incubated in the basal medium plus test substrates such as hemoglobin, hemin, transferrin and various inorganic iron compounds. The relationship between the specific growth rate of organisms and the concentration of iron-containing compounds was determined. The value of Ks, a parameter analogous to the Michaelis-Menten constant, was estimated. P. gingivalis 381 showed a Ks value of 3.85, 4.91 and 0.0017 microM for hemin, transferrin and hemoglobin, respectively. However, the inorganic iron compounds tested did not support growth of P. gingivalis. These findings suggest that P. gingivalis utilizes hemoglobin as an iron source much more effectively than other iron-containing compounds under an iron-limited environment.

Bordetella pertussis fur gene restores iron repressibility of siderophore and protein expression to deregulated Bordetella bronchiseptica mutants

We report the isolation and preliminary phenotypic characterization of manganese-resistant Bordetella bronchiseptica mutants with respect to deregulation of siderophore and iron-regulated protein expression. The fur gene of Bordetella pertussis was cloned by genetic complementation of this deregulated phenotype and confirmed as fur by nucleotide sequence analysis.

Surface-associated filamentous hemagglutinin induces autoagglutination of Bordetella pertussis

Filamentous hemagglutinin (FHA) is a major adhesin produced by Bordetella pertussis, the etiologic agent of whooping cough. FHA has been shown to be surface associated but is also secreted by virulent bacteria. Microscopic observations of lungs of mice infected with B. pertussis showed that the bacteria grow as clusters within the alveolar lumen. When B. pertussis was cultivated in vitro with chemically defined medium, bacteria grew as aggregates, mimicking growth observed in vivo. This aggregation was abolished by the addition of cyclodextrin (CDX) to the growth medium and depended on the production of FHA, because a mutant lacking the FHA structural gene failed to form aggregates in a CDX-free medium. Western blot (immunoblot) analyses revealed that, in the absence of CDX, FHA was attached to the bacterial surface and was not efficiently released into the growth medium. Hydrophobic chromatography of FHA showed that CDX drastically reduced the hydrophobicity of FHA, suggesting a direct binding of CDX to FHA, which was further supported by the partial protection of FHA from trypsin digestion in the presence of CDX. In addition, free FHA can interact in a CDX-inhibitable manner with solid phase-immobilized FHA. It can therefore be postulated that the B. pertussis aggregates are most likely due to direct FHA-FHA interaction.

Staphylococci express a receptor for human transferrin: identification of a 42-kilodalton cell wall transferrin-binding protein

Staphylococcus aureus and the coagulase-negative staphylococci are commonly responsible for peritonitis in renal patients undergoing continuous ambulatory peritoneal dialysis. To simulate growth conditions in vivo, staphylococci isolated from peritoneal infections were cultured in used human peritoneal dialysate (HPD). Immunoblotting experiments using cell wall preparations from these staphylococci revealed the presence of the host iron-binding glycoprotein transferrin bound to S. aureus, S. epidermidis, S. capitis, S. haemolyticus, and S. hominis but not to S. warneri or S. saprophyticus. Similar results were obtained by incubating broth-grown staphylococci with human transferrin, although, in contrast to S. aureus, the coagulase-negative staphylococci bound more transferrin after growth in iron-restricted broth. To determine whether the staphylococci express a saturable specific receptor for human transferrin, the interaction of human 125I-transferrin with the staphylococci was examined. Both S. aureus and S. epidermidis bound the radiolabelled iron-saturated ligand in a time- and concentration-dependent manner. From competition binding assays, the affinity (Kd) and number of receptors were estimated for S. epidermidis (Kd, 0.27 microM; 4,200 receptors per cell) and S. aureus (Kd, 0.28 microM; 4,200 receptors per cell). S. epidermidis but not S. aureus receptor activity was partially iron regulated. Human apotransferrin and iron-saturated transferrin and rabbit and rat transferrins competed equally well for the staphylococcal receptor. Bovine and porcine transferrins and ovotransferrin as well as human and bovine lactoferrins were much less effective at competing with human transferrin. Treatment of whole staphylococci with protease abolished transferrin binding, indicating the involvement of cell surface protein. Western blots (immunoblots) of cell wall preparations probed with human transferrin revealed the presence of a 42-kDa transferrin-binding protein common to both S. aureus and S. epidermidis. On Western strip blots, the binding of human transferrin to this protein was blocked by labelled human transferrin but not by albumin, immunoglobulin G, or bovine transferrin or ovotransferrin. To assess the conservation of the 42-kDa transferrin-binding protein, cell wall proteins of S. epidermidis, S. haemolyticus, S. capitis, S. hominis, S. warneri, and S. saprophyticus were Western blotted and probed with human transferrin. Only S. warneri and S. saprophyticus lacked the 42-kDa wall protein, consistent with their inability to bind transferrin. These data show that the staphylococci express a specific receptor for human transferrin based at least in part on a common 42-kDa cell wall protein.

Acquisition of iron from transferrin and lactoferrin by the protozoan Leishmania chagasi

Leishmania chagasi, the cause of South American visceral leishmaniasis, requires iron for its growth. However, the extent to which different iron sources can be utilized by the parasite is not known. To address this question, we studied acquisition of iron from lactoferrin and transferrin by the extracellular promastigote form of L. chagasi during growth in vitro. A promastigote growth medium based on minimal essential medium supplemented with iron-depleted serum supported promastigote growth only after the addition of exogenous iron. The addition of 8 microM iron chelated to lactoferrin or hemin resulted in normal promastigote growth. Ferritransferrin also supported promastigote growth, but only after a considerable lag. Promastigotes grown in all three iron sources generated similar amounts of hydroxyl radical upon exposure to hydrogen peroxide, indicating that none of these protected parasites against generation of this toxic radical. Promastigotes were able to take up 59Fe chelated to either transferrin or lactoferrin, although uptake from 59Fe-lactoferrin occurred more rapidly. 59Fe uptake from either 59Fe-transferrin or 59Fe-lactoferrin was inhibited by a 10-fold excess of unlabeled ferrilactoferrin, ferritransferrin, apolactoferrin, apotransferrin, or iron nitrilotriacetate but not ferritin or bovine serum albumin. There was no evidence for a role for parasite-derived siderophores or proteolytic cleavage of ferritransferrin or ferrilactoferrin in the acquisition of iron by promastigotes. Thus, L. chagasi promastigotes can acquire iron from hemin, ferrilactoferrin, or ferritransferrin. This capacity to utilize several iron sources may contribute to the organism's ability to survive in the diverse environments it encounters in the insect and mammalian hosts.

Heparin-inhibitable lectin activity of the filamentous hemagglutinin adhesin of Bordetella pertussis

Bordetella pertussis, the etiologic agent of whooping cough, produces an outer membrane-associated filamentous hemagglutinin (FHA) which is the major adhesin of this organism. FHA exhibits a lectin-like activity for heparin and dextran sulfate. By using in vitro adherence assays to cultured epithelial cells, the attachment of B. pertussis was reduced in the presence of sulfated polysaccharides such as heparin and dextran sulfate but not in the presence of dextran, indicating the crucial role of polysaccharide sulfation. In addition, inhibition of cellular sulfation by chlorate treatment of the cells resulted in a reduction of B. pertussis adherence, suggesting that epithelial cell surface-exposed sulfated glycoconjugates may serve as receptors for the microorganism. B. pertussis mutant strains deficient in FHA production expressed residual adherence that was no longer inhibited by sulfated polysaccharides. In addition, purified FHA displayed heparin-inhibitable binding to epithelial cells. Mapping experiments of the heparin-binding site of FHA indicated that this site is different from the RGD site and the recently proposed carbohydrate-binding site involved in the interaction of FHA with lactosylceramide. This result demonstrates that FHA contains at least three different binding sites, a feature unusual for bacterial adhesions but similar to features of eukaryotic adhesins and extracellular matrix proteins.

Expression of the Haemophilus influenzae transferrin receptor is repressible by hemin but not elemental iron alone

The absolute requirement for elemental iron and the porphyrin nucleus for growth of Haemophilus influenzae led us to investigate the role of iron and hemin in regulation of expression of the H. influenzae transferrin receptor. H. influenzae type b strain H1689 was grown in brain heart infusion broth supplemented with beta-NAD and either 10 or 0.1 microgram of hemin ml-1. Transferrin-binding ability was determined with a dot blot assay using human transferrin-horseradish peroxidase conjugate. Cells grown in media with 0.1 microgram of hemin ml-1 bound transferrin, but organisms grown in media with 10 micrograms ml-1 did not. In hemin-restricted media, transferrin binding occurred despite addition of up to 10 mM ferric nitrate, ferric citrate, or ferric PPi, whereas addition of 10 micrograms of hemoglobin ml-1 repressed expression. The breadth of species distribution of this mode of regulation was determined with strains previously characterized by multilocus enzyme electrophoresis. When grown in hemin-restricted media, 24 of 28 type b strains and 52 of 57 serologically nontypeable strains exhibited transferrin binding, although none did so in hemin- and iron-sufficient media. Strain H1689 and serologically nontypeable strain HI1423 grown in heat-inactivated pooled normal human serum, human cerebrospinal fluid, or human breast milk exhibited transferrin binding. Growth in these fluids with 10 micrograms of added hemin ml-1 abolished transferrin binding, whereas addition of 10 mM ferric nitrate did not. These data suggest that the transferrin receptor of H. influenzae is regulated by levels of hemin but not elemental iron alone and that this property is widely distributed among several major cloned families in the species.

Neisseria meningitidis transferrin-binding protein 1 expressed in Escherichia coli is surface exposed and binds human transferrin

A gene library of Neisseria meningitidis B15 P1.16 DNA was established in lambda Zap II and clones containing DNA encoding transferrin binding protein 1 (TBP-1) identified following hybridisation with a 63-bp DNA probe based on the codon assignment for the first 21 N-terminal amino acids of TBP-1. Sequencing of the cloned DNA demonstrated that all of the intergenic DNA (i.e. upstream of tbp-1 running through to the 3' end of the transferrin-binding protein 2 gene) and approx. 15% of tbp-1 had been cloned. The complete gene was generated using a polymerase chain reaction, with the primer for the 3' end being based on tbp-A of N. gonorrhoeae, and the approx. 2.9-kb DNA product cloned into pGem-3Z. The expressed protein (approx. 100 kDa) reacted with antiserum to an N-terminal peptide of TBP-1. In addition, the native product was surface-expressed by Escherichia coli and bound human transferrin.

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

Bordetella bronchiseptica secreted a hydroxamate siderophore when grown in Fe-depleted medium. A Tn5lac insertion mutant of B. bronchiseptica, DBB22, did not produce this hydroxamate siderophore and was incapable of using lactoferrin as an Fe source. Our data suggest that B. bronchiseptica uses a siderophore for removal of Fe from lactoferrin and transferrin rather than relying upon a receptor for these host Fe-binding proteins.

Signal transduction and virulence regulation in human and animal pathogens

Pathogens have developed many strategies for survival in animals and humans which possess very effective defense mechanisms. Although there are many different ways, in which pathogenic bacteria solved the problem to overcome the host defense, some common features of virulence mechanisms can be detected even in phylogenetically very distant bacteria (Finlay and Falkow (1989) Microb. Rev. 6, 1375-1383). One important feature is that the regulation of expression of virulence factors and the exact timing of their expression is very important for many of the pathogenic bacteria, as most of them have to encounter different growth situations during an infection cycle, which require a fast adaptation to the new situation by the expression of different factors. This review gives an overview about the mechanisms used by pathogenic bacteria to accomplish the difficult task of regulation of their virulence potential in response to environmental changes. In addition, the relationship of these virulence regulatory systems with other signal transduction mechanisms not involved in pathogenicity is discussed.

Isolation and characterization of Bordetella bronchiseptica mutants deficient in siderophore activity

Iron acquisition by the gram-negative pathogens Bordetella bronchiseptica and Bordetella pertussis is thought to occur by hydroxamate siderophore-mediated transport as well as an apparently siderophore-independent process by which host transferrins bind to bacterial surface receptors. We constructed B. bronchiseptica mutants deficient in siderophore activity by insertional mutagenesis with miniTn5/lacZ1. The mutants could be placed into four distinct complementation groups, as determined from cross-feeding assays which demonstrated restored siderophore synthesis. Mutants deficient in siderophore activity were BRM1, BRM6, and BRM9, exhibiting approximately 36 to 41% of wild-type siderophore levels, and BRM3 and BRM8, which appeared to produce very little or no detectable siderophore. Mutant BRM4 was found to be a leucine auxotroph, while mutants BRM2 and BRM7 could synthesize siderophore only in low-iron medium which was supplemented with various amino acids. Evaluation of all transcriptional fusions revealed an apparent lack of iron-regulated lacZ expression. Genomic regions flanking the transposable element in the siderophore mutants were homologous with B. pertussis chromosomal DNA, while bioassays suggested siderophore cross-feeding between B. pertussis and B. bronchiseptica. These results indicate probable similarity between the siderophore biosynthetic and transport systems of the two species.