Identification and cloning of waaF (rfaF) from Bordetella pertussis and use to generate mutants of Bordetella spp. with deep rough lipopolysaccharide

Construction of the waaF Subunit and DNA Vaccine Against Escherichia coli in Cow Mastitis and Preliminary Study on Their Immunogenicity

Escherichia coli (E. coli) is one of the major pathogenic bacteria in bovine mastitis, which usually triggers systemic symptoms by releasing lipopolysaccharide (LPS). waaF is the core in LPS pathogenicity. In this study, a new waaF vaccine candidate was identified, constructed with the pcDNA3.1 (+)HisB-waaF plasmid to create to a DNA vaccine (pcwaaF), and transfected into MCF-7 cells to produce recombinant waaF subunit vaccine (rwaaF). After that, the safety of the two vaccine candidates was evaluated in mouse model. Immunogenicity and mortality of challenged mice were compared in 20 and 40 μg per dose, respectively. The results showed that rwaaF and pcwaaF were successfully constructed and the complete blood count and serum biochemical indicated that both of the vaccine candidates were safe (p > 0.05). In addition, histopathological staining showed no obvious pathological changes. The immune response induced by rwaaF was significantly higher than that of pcwaaF (p < 0.01), indicated by levels of serum concentration of IgG IL-2, IL-4, and IFN-γ, and feces concentration of sIgA. Survival rates of mice in rwaaF groups (both 80%) were also higher than in the pcwaaF groups (40 and 50%, respectively). Comparing the safety, immunogenicity, and E. coli challenge of two vaccine candidates, rwaaF had the better effect and 20 μg rwaaF was more economical. In conclusion, this study demonstrates the utility of a new E. coli vaccine and provides a rationale for further investigation of bovine mastitis therapy and management.

Engineering Escherichia coli to produce Bordetella pertussis oligosaccharide with multiple trisaccharide units

The immunogenicity of the pertussis vaccine can be significantly improved by adding Bordetella pertussis oligosaccharide with multiple trisaccharide units. The more trisaccharide units there are, the better the efficiency of the immune response induction. However, natural B. pertussis oligosaccharides usually contain only a single terminal trisaccharide unit. In addition, B. pertussis is pathogenic, and there are potential safety hazards when preparing oligosaccharides from B. pertussis. In this study, Escherichia coli MG1655 was engineered to produce B. pertussis oligosaccharides containing multiple trisaccharide units. Fifty-nine genes relevant to the biosynthesis of the O-antigen and core oligosaccharide of lipopolysaccharide, enterobacterial common antigen, and colanic acid were deleted in MG1655, resulting in strain MDCO020. Then, 25 genes relevant to the biosynthesis of the oligosaccharide antigen in B. pertussis and 3 genes relevant to the repeating trisaccharide unit in Pseudomonas aeruginosa PAO1 were overexpressed in MDCO020, resulting in the recombinant E. coli MDCO020/pWpBpD5. The production of B. pertussis oligosaccharide with multiple trisaccharide units by MDCO020/pWpBpD5 was confirmed by SDS-PAGE and ¹H NMR analyses, and its immune response-stimulating activity was confirmed by using rabbit anti-pertussis serum.

Phenotype and genomic background of Arcobacter butzleri strains and taxogenomic assessment of the species

In this study the phenotypic and genomic characterization of two Arcobacter butzleri (Ab) strains (Ab 34_O and Ab 39_O) isolated from pre-cut ready-to-eat vegetables were performed. Results provided useful data about their taxonomy and their overall virulence potential with particular reference to the antibiotic and heavy metal susceptibility. These features were moreover compared with those of two Ab strains isolated from shellfish and a genotaxonomic assessment of the Ab species was performed. The two Ab isolated from vegetables were confirmed to belong to the Aliarcobacter butzleri species by 16S rRNA gene sequence analysis, MLST and genomic analyses. The genome-based taxonomic assessment of the Ab species brought to the light the possibility to define different subspecies reflecting the source of isolation, even though further genomes from different sources should be available to support this hypothesis. The strains isolated from vegetables in the same geographic area shared the same distribution of COGs with a prevalence of the cluster "inorganic ion transport and metabolism", consistent with the lithotrophic nature of Arcobacter spp. None of the Ab strains (from shellfish and from vegetables) metabolized carbohydrates but utilized organic acids and amino acids as carbon sources. The metabolic fingerprinting of Ab resulted less discriminatory than the genome-based approach. The Ab strains isolated from vegetables and those isolated from shellfish endowed multiple resistance to several antibiotics and heavy metals.

A Newly Discovered Drug Resistance Gene rfaF In Helicobacter pylori

BACKGROUND

The purpose of this study was to understand the function of rfaF gene in Helicobacter pylori antibiotic resistance.

METHODS

The gene homologous recombination method was used for knockout and complementation of H. pylori rfaF gene. Various constructed strains were analysed for drug sensitivity to amoxicillin (AMO), tetracycline (TET), clarithromycin (CLA), metronidazole (MET), levofloxacin (LEV), and chloramphenicol (CHL) by agar plate dilution method. Drug sensitivity was further confirmed using a growth inhibition curve. Ethidium bromide (EB) accumulation experiments were performed to assess cell membrane permeability. PCR and sequence analysis were used to detect the rfaF gene.

RESULTS

The minimum inhibitory concentrations (MIC) of TET, CHL, AMO, and CLA in 11,637 rfaF knockout strain (ΔrfaF strain) were 4, 4, 2, and 2 times higher than those in 11,637 wild type (WT) strain, respectively. A multidrug-resistant (MDR) ΔrfaF strain also displayed the same trend; however, the degrees of increase were relatively small. Growth inhibition experiments indicated that the growth of the 11,637 ΔrfaF strain was higher with antibiotics at the MIC of the 11,637 WT strain than that of 11,637 rfaF-complemented strain (ΔrfaF/rfaF strain), whereas the 11,637 WT strain did not exhibit any growth. The 11,637 ΔrfaF strain was significantly reduced compared with the cumulative EB fluorescence intensity of the 11,637 WT and of 11,637ΔrfaF/rfaF strain, and the same trend appeared in the MDR strain. Among the 10 clinical strains, 9 clinical strains were found to have mutations in the conserved sequence of rfaF amino acids.

CONCLUSION

We found a new drug resistance gene, rfaF, in H. pylori, which changes the permeability of cell membrane to confer cross-resistance to AMO, TET, CLA, and CHL and is involved in clinical strain drug resistance. It can be used as a drug target.

Modifications of Bordetella bronchiseptica core lipopolysaccharide influence immune response without affecting protective activity

Bordetella bronchiseptica produces respiratory disease primarily in mammals including humans. Although a considerably amount of research has been generated regarding lipopolysaccharide (LPS) role during infection and stimulating innate and adaptive immune response, mechanisms involved in LPS synthesis are still unknown. In this context we searched in B. bronchiseptica genome for putative glycosyltransferases. We found possible genes codifying for enzymes involved in sugar substitution of the LPS structure. We decided to analyse BB3394 to BB3400 genes, closed to a previously described LPS biosynthetic locus in B. pertussis. Particularly, conservation of BB3394 in sequenced B. bronchiseptica genomes suggests the importance of this gene for bacteria normal physiology. Deletion of BB3394 abolished resistance to naive serum as described for other LPS mutants. When purified LPS was analyzed, differences in the LPS core structure were found. Particularly, a GalNA branched sugar substitution in the core was absent in the LPS obtained from BB3394 deletion mutant. Absence of GalNA in core LPS alters immune response in vivo but is able to induce protective response against B. bronchiseptica infection.

Invited review: Lipopolysaccharide biosynthesis: which steps do bacteria need to survive?

A detailed knowledge of LPS biosynthesis is of the utmost importance in understanding the function of the outer membrane of Gram-negative bacteria. The regulation of LPS biosynthesis affects many more compartments of the bacterial cell than the outer membrane and thus contributes to the understanding of the physiology of Gram-negative bacteria in general, on the basis of which only mechanisms of virulence and antibiotic resistance can be studied to find new targets for antibacterial treatment. The study of LPS biosynthesis is also an excellent example to demonstrate the limitations of `genomics' and `proteomics', since secondary gene products can be studied only by the combined tools of molecular genetics, enzymology and analytical structural biochemistry. Thus, the door to the field of `glycomics' is opened.

Vaccine-Mediated Activation of Human TLR4 Is Affected by Modulation of Culture Conditions during Whole-Cell Pertussis Vaccine Preparation

The potency of whole-cell pertussis (wP) vaccines is still determined by an intracerebral mouse protection test. To allow development of suitable in vitro alternatives to this test, insight into relevant parameters to monitor the consistency of vaccine quality is essential. To this end, a panel of experimental wP vaccines of varying quality was prepared by sulfate-mediated suppression of the BvgASR master virulence regulatory system of Bordetella pertussis during cultivation. This system regulates the transcription of a range of virulence proteins, many of which are considered important for the induction of effective host immunity. The protein compositions and in vivo potencies of the vaccines were BvgASR dependent, with the vaccine containing the highest amount of virulence proteins having the highest in vivo potency. Here, the capacities of these vaccines to stimulate human Toll-like receptors (hTLR) 2 and 4 and the role these receptors play in wP vaccine-mediated activation of antigen-presenting cells in vitro were studied. Prolonged BvgASR suppression was associated with a decreased capacity of vaccines to activate hTLR4. In contrast, no significant differences in hTLR2 activation were observed. Similarly, vaccine-induced activation of MonoMac-6 and monocyte-derived dendritic cells was strongest with the highest potency vaccine. Blocking of TLR2 and TLR4 showed that differences in antigen-presenting cell activation could be largely attributed to vaccine-dependent variation in hTLR4 signalling. Interestingly, this BvgASR-dependent decrease in hTLR4 activation coincided with a reduction in GlcN-modified lipopolysaccharides in these vaccines. Accordingly, expression of the lgmA-C genes, required for this glucosamine modification, was significantly reduced in bacteria exposed to sulfate. Together, these findings demonstrate that the BvgASR status of bacteria during wP vaccine preparation is critical for their hTLR4 activation capacity and suggest that including such parameters to assess consistency of newly produced vaccines could bring in vitro testing of vaccine quality a step closer.

Identification of a novel lipopolysaccharide core biosynthesis gene cluster in Bordetella pertussis, and influence of core structure and lipid A glucosamine substitution on endotoxic activity

Lipopolysaccharide (LPS), also known as endotoxin, is one of the main constituents of the gram-negative bacterial outer membrane. Whereas the lipid A portion of LPS is generally considered the main determinant for endotoxic activity, the oligosaccharide moiety plays an important role in immune evasion and the interaction with professional antigen-presenting cells. Here we describe a novel four-gene cluster involved in the biosynthesis of the Bordetella pertussis core oligosaccharide. By insertionally inactivating these genes and studying the resulting LPS structures, we show that at least two of the genes encode active glycosyltransferases, while a third gene encodes a deacetylase also required for biosynthesis of full-length oligosaccharide. In addition, we demonstrate that mutations in the locus differentially affect LPS and whole-cell endotoxic activities. Furthermore, while analyzing the mutant LPS structures, we confirmed a novel modification of the lipid A phosphate with glucosamine and found that inactivation of the responsible glycosyltransferase reduces the endotoxic activity of the LPS.

Different mechanisms of vaccine-induced and infection-induced immunity to Bordetella bronchiseptica

A recent resurgence in the number of cases of whooping cough, and other respiratory diseases caused by members of the bordetellae, in vaccinated populations has demonstrated the need for a thorough understanding of vaccine-induced immunity to facilitate more intelligent vaccine design. In this work, we use a murine model of respiratory infection using the highly successful animal pathogen, Bordetella bronchiseptica. Since previously infected animals have been shown to resist re-infection by B. bronchiseptica, we sought to examine the differences between vaccine-induced immunity and infection-induced immunity. Both prior infection and vaccination conferred nearly complete protection in the lungs, however, only prior infection resulted in significant protection in the upper respiratory tract. While immunity induced by prior infection offered significant protection even in the absence of complement or FcgammaRs, vaccination-induced protection required both complement and FcgammaRs. Although vaccination induced higher titers of B. bronchiseptica-specific antibodies, this serum was less effective than infection-induced serum in clearing bacteria from the lower respiratory tract. Together these findings highlight substantial differences between the mechanisms involved in vaccine- and infection-induced protective immunity.

Bordetella pertussis, the causative agent of whooping cough, evolved from a distinct, human-associated lineage of B. bronchiseptica

Bordetella pertussis, B. bronchiseptica, B. parapertussis(hu), and B. parapertussis(ov) are closely related respiratory pathogens that infect mammalian species. B. pertussis and B. parapertussis(hu) are exclusively human pathogens and cause whooping cough, or pertussis, a disease that has resurged despite vaccination. Although it most often infects animals, infrequently B. bronchiseptica is isolated from humans, and these infections are thought to be zoonotic. B. pertussis and B. parapertussis(hu) are assumed to have evolved from a B. bronchiseptica-like ancestor independently. To determine the phylogenetic relationships among these species, housekeeping and virulence genes were sequenced, comparative genomic hybridizations were performed using DNA microarrays, and the distribution of insertion sequence elements was determined, using a collection of 132 strains. This multifaceted approach distinguished four complexes, representing B. pertussis, B. parapertussis(hu), and two distinct B. bronchiseptica subpopulations, designated complexes I and IV. Of the two B. bronchiseptica complexes, complex IV was more closely related to B. pertussis. Of interest, while only 32% of the complex I strains were isolated from humans, 80% of the complex IV strains were human isolates. Comparative genomic hybridization analysis identified the absence of the pertussis toxin locus and dermonecrotic toxin gene, as well as a polymorphic lipopolysaccharide biosynthesis locus, as associated with adaptation of complex IV strains to the human host. Lipopolysaccharide structural diversity among these strains was confirmed by gel electrophoresis. Thus, complex IV strains may comprise a human-associated lineage of B. bronchiseptica from which B. pertussis evolved. These findings will facilitate the study of pathogen host-adaptation. Our results shed light on the origins of the disease pertussis and suggest that the association of B. pertussis with humans may be more ancient than previously assumed.

OpsX from Haemophilus influenzae represents a novel type of heptosyltransferase I in lipopolysaccharide biosynthesis

The inner core region of the lipopolysaccharide (LPS) of Haemophilus influenzae is characterized by the presence of a phosphorylated 3-deoxy-alpha-D-manno-octulosonic acid (Kdo). In this study, we show that the heptosyltransferase I adding the first L-glycero-D-manno-heptose residue to this acceptor is encoded by the gene opsX, which differs in substrate specificity from the other heptosyltransferase I, known as WaaC.

Interactions of pulmonary collectins with Bordetella bronchiseptica and Bordetella pertussis lipopolysaccharide elucidate the structural basis of their antimicrobial activities

Surfactant proteins A (SP-A) and D (SP-D) play an important role in the innate immune defenses of the respiratory tract. SP-A binds to the lipid A region of lipopolysaccharide (LPS), and SP-D binds to the core oligosaccharide region. Both proteins induce aggregation, act as opsonins for neutrophils and macrophages, and have direct antimicrobial activity. Bordetella pertussis LPS has a branched core structure and a nonrepeating terminal trisaccharide. Bordetella bronchiseptica LPS has the same structure, but lipid A is palmitoylated and there is a repeating O-antigen polysaccharide. The ability of SP-A and SP-D to agglutinate and permeabilize wild-type and LPS mutants of B. pertussis and B. bronchiseptica was examined. Previously, wild-type B. pertussis was shown to resist the effects of SP-A; however, LPS mutants lacking the terminal trisaccharide were susceptible to SP-A. In this study, SP-A was found to aggregate and permeabilize a B. bronchiseptica mutant lacking the terminal trisaccharide, while wild-type B. bronchiseptica and mutants lacking only the palmitoyl transferase or O antigen were resistant to SP-A. Wild-type B. pertussis and B. bronchiseptica were both resistant to SP-D; however, LPS mutants of either strain lacking the terminal trisaccharide were aggregated and permeabilized by SP-D. We conclude that the terminal trisaccharide protects Bordetella species from the bactericidal functions of SP-A and SP-D. The O antigen and palmitoylated lipid A of B. bronchiseptica play no role in this resistance.

Bordetella pertussis lipopolysaccharide resists the bactericidal effects of pulmonary surfactant protein A

Surfactant protein A (SP-A) plays an important role in the innate immune defense of the respiratory tract. SP-A binds to lipid A of bacterial LPS, induces aggregation, destabilizes bacterial membranes, and promotes phagocytosis by neutrophils and macrophages. In this study, SP-A interaction with wild-type and mutant LPS of Bordetella pertussis, the causative agent of whooping cough, was examined. B. pertussis LPS has a branched core structure with a nonrepeating trisaccharide, rather than a long-chain repeating O-Ag. SP-A did not bind, aggregate, nor permeabilize wild-type B. pertussis. LPS mutants lacking even one of the sugars in the terminal trisaccharide were bound and aggregated by SP-A. SP-A enhanced phagocytosis by human monocytes of LPS mutants that were able to bind SP-A, but not wild-type bacteria. SP-A enhanced phagocytosis by human neutrophils of LPS-mutant strains, but only in the absence of functional adenylate cyclase toxin, a B. pertussis toxin that has been shown to depress neutrophil activity. We conclude that the LPS of wild-type B. pertussis shields the bacteria from SP-A-mediated clearance, possibly by sterically limiting access to the lipid A region.

Identification, cloning and characterization of rfaE of Actinobacillus pleuropneumoniae serotype 1, a gene involved in lipopolysaccharide inner-core biosynthesis

Actinobacillus pleuropneumoniae is the causative agent of porcine pleuropneumonia and its lipopolysaccharides (LPS) have been identified as important adhesins involved in adherence to host cells. To better understand the role of LPS core in the virulence of this organism, the aim of the present study was to identify and clone genes involved in LPS core biosynthesis by complementation with Salmonella enterica serovar Typhimurium mutants (rfaC, rfaD, rfaE and rfaF). Complementation with an A. pleuropneumoniae 4074 genomic library was successful with Salmonella mutant SL1102. This Salmonella deep-rough LPS mutant is defective for the rfaE gene, which is an ADP-heptose synthase. Novobiocin was used to select transformants that had the smooth-LPS type, since Salmonella strains with wild-type smooth-LPS are less permeable, therefore more resistant to hydrophobic antibiotics like novobiocin. We obtained a clone that was able to restore the wild-type smooth-LPS Salmonella phenotype after complementation. The wild-type phenotype was confirmed using phage (Felix-O, P22c.2 and Ffm) susceptibility and SDS-PAGE (sodium dodecyl sulfate-polyacrylamide gel electrophoresis). One of the open reading frames contained in the 3.3-kb insert in the plasmid encoded a 475-amino-acid protein with 71% identity and 85% similarity to the RfaE protein of S. enterica. We then attempted to generate an A. pleuropneumoniae rfaE mutant by gene replacement. The rfaE gene seems essential in A. pleuropneumoniae viability as we were unable to isolate a heptose-less knockout mutant.

Comparison of bipA alleles within and across Bordetella species

The Bordetella BvgAS signal transduction system controls the expression of at least three phenotypic phases, the Bvg(+) or virulent phase, the Bvg(-) or avirulent phase, and the Bvg(i) or Bvg intermediate phase, which has been hypothesized to be important for transmission. bipA, the first identified Bvg(i)-phase gene, encodes a protein with similarity to the well-characterized bacterial adhesins intimin and invasin. Proteins encoded by the bipA genes present in Bordetella pertussis Tohama I and Bordetella bronchiseptica RB50 differ in the number of 90-amino-acid repeats which they possess and in the sequence of the C-terminal domain. To investigate the possibility that bipA alleles segregate according to host specificity and to gain insight into the role of BipA and the Bvg(i) phase in the Bordetella infectious cycle, we compared bipA alleles across members of the B. bronchiseptica cluster, which includes both human-infective (B. pertussis and B. parapertussis(hu)) and non-human-infective (B. bronchiseptica and B. parapertussis(ov)) strains. bipA genes were present in most, but not all, strains. All bipA genes present in B. bronchiseptica strains were identical to bipA of RB50 (at least with regard to the DNA sequence of the 3' C-terminal-domain-encoding region, the number of 90-amino-acid repeats encoded, and expression patterns). Although all bipA genes present in the other Bordetella strains were identical in the 3' C-terminal-domain-encoding region to bipA of B. pertussis Tohama I, they varied in the number of 90-amino-acid repeats that they encoded and in expression level. Notably, the genes present in B. parapertussis(hu) strains were pseudogenes, and the genes present in B. parapertussis(ov) strains were expressed at significantly reduced levels compared with the levels in B. pertussis and B. bronchiseptica strains. Our results indicate that there is a correlation between specific bipA alleles and specific hosts. They also support the hypothesis that both horizontal gene transfer and fine-tuning of gene expression patterns contribute to the evolution of host adaptation in lineages of the B. bronchiseptica cluster.

Role of antibodies in immunity to Bordetella infections

The persistence of Bordetella pertussis and B. parapertussis within vaccinated populations and the reemergence of associated disease highlight the need to better understand protective immunity. The present study examined host immunity to bordetellae and addressed potential concerns about the mouse model by using a comparative approach including the closely related mouse pathogen B. bronchiseptica. As previously observed with B. pertussis, all three organisms persisted throughout the respiratory tracts of B-cell-deficient mice, indicating that B cells are required for bacterial clearance. However, adoptively transferred antibodies rapidly cleared B. bronchiseptica but not human pathogens. These results obtained with the mouse model are consistent with human clinical observations, including the lack of correlation between antibody titers and protection, as well as the limited efficacy of intravenous immunoglobulin treatments against human disease. Together, this evidence suggests that the mouse model accurately reflects substantial differences between immunities to these organisms. Although both B. pertussis and B. parapertussis are more closely related to B. bronchiseptica than they are to each other, they share the ability to resist rapid clearance from the lower respiratory tract by adoptively transferred antibodies, an adaptation that correlates with their emergence as human pathogens that circulate within vaccinated populations.

Characterization of the Campylobacter jejuni heptosyltransferase II gene, waaF, provides genetic evidence that extracellular polysaccharide is lipid A core independent

Campylobacter jejuni produces both lipooligosaccharide (LOS) and a higher-molecular-weight polysaccharide that is believed to form a capsule. The role of these surface polysaccharides in C. jejuni-mediated enteric disease is unclear; however, epitopes associated with the LOS are linked to the development of neurological complications. In Escherichia coli and Salmonella enterica serovar Typhimurium the waaF gene encodes a heptosyltransferase, which catalyzes the transfer of the second L-glycero-D-manno-heptose residue to the core oligosaccharide moiety of lipopolysaccharide (LPS), and mutation of waaF results in a truncated core oligosaccharide. In this report we confirm experimentally that C. jejuni gene Cj1148 encodes the heptosyltransferase II enzyme, WaaF. The Campylobacter waaF gene complements an S. enterica serovar Typhimurium waaF mutation and restores the ability to produce full-sized lipopolysaccharide. To examine the role of WaaF in C. jejuni, waaF mutants were constructed in strains NCTC 11168 and NCTC 11828. Loss of heptosyltransferase activity resulted in the production of a truncated core oligosaccharide, failure to bind specific ligands, and loss of serum reactive GM(1), asialo-GM(1), and GM(2) ganglioside epitopes. The mutation of waaF did not affect the higher-molecular-weight polysaccharide supporting the production of a LOS-independent capsular polysaccharide by C. jejuni. The exact structural basis for the truncation of the core oligosaccharide was verified by comparative chemical analysis. The NCTC 11168 core oligosaccharide differs from that known for HS:2 strain CCUG 10936 in possessing an extra terminal disaccharide of galactose-beta(1,3) N-acetylgalactosamine. In comparison, the waaF mutant possessed a truncated molecule consistent with that observed with waaF mutants in other bacterial species.

Bacterial pathogen genomics and vaccines

Infectious diseases remain a major cause of deaths and disabilities in the world, the majority of which are caused by bacteria. Although immunisation is the most cost effective and efficient means to control microbial diseases, vaccines are not yet available to prevent many major bacterial infections. Examples include dysentery (shigellosis), gonorrhoea, trachoma, gastric ulcers and cancer (Helicobacter pylori). Improved vaccines are needed to combat some diseases for which current vaccines are inadequate. Tuberculosis, for example, remains rampant throughout most countries in the world and represents a global emergency heightened by the pandemic of HIV. The availability of complete genome sequences has dramatically changed the opportunities for developing novel and improved vaccines and facilitated the efficiency and rapidity of their development. Complete genomic databases provide an inclusive catalogue of all potential candidate vaccines for any bacterial pathogen. In conjunction with adjunct technologies, including bioinformatics, random mutagenesis, microarrays, and proteomics, a systematic and comprehensive approach to identifying vaccine discovery can be undertaken. Genomics must be used in conjunction with population biology to ensure that the vaccine can target all pathogenic strains of a species. A proof in principle of the utility of genomics is provided by the recent exploitation of the complete genome sequence of Neisseria meningitidis group B.

Lipopolysaccharide endotoxins

Bacterial lipopolysaccharides (LPS) typically consist of a hydrophobic domain known as lipid A (or endotoxin), a nonrepeating "core" oligosaccharide, and a distal polysaccharide (or O-antigen). Recent genomic data have facilitated study of LPS assembly in diverse Gram-negative bacteria, many of which are human or plant pathogens, and have established the importance of lateral gene transfer in generating structural diversity of O-antigens. Many enzymes of lipid A biosynthesis like LpxC have been validated as targets for development of new antibiotics. Key genes for lipid A biosynthesis have unexpectedly also been found in higher plants, indicating that eukaryotic lipid A-like molecules may exist. Most significant has been the identification of the plasma membrane protein TLR4 as the lipid A signaling receptor of animal cells. TLR4 belongs to a family of innate immunity receptors that possess a large extracellular domain of leucine-rich repeats, a single trans-membrane segment, and a smaller cytoplasmic signaling region that engages the adaptor protein MyD88. The expanding knowledge of TLR4 specificity and its downstream signaling pathways should provide new opportunities for blocking inflammation associated with infection.

Multiple roles for Bordetella lipopolysaccharide molecules during respiratory tract infection

Bordetella pertussis, Bordetella parapertussis, and Bordetella bronchiseptica are closely related subspecies that cause respiratory tract infections in humans and other mammals and express many similar virulence factors. Their lipopolysaccharide (LPS) molecules differ, containing either a complex trisaccharide (B. pertussis), a trisaccharide plus an O-antigen-like repeat (B. bronchiseptica), or an altered trisaccharide plus an O-antigen-like repeat (B. parapertussis). Deletion of the wlb locus results in the loss of membrane-distal polysaccharide domains in the three subspecies of bordetellae, leaving LPS molecules consisting of lipid A and core oligosaccharide. We have used wlb deletion (Deltawlb) mutants to investigate the roles of distal LPS structures in respiratory tract infection by bordetellae. Each mutant was defective compared to its parent strain in colonization of the respiratory tracts of BALB/c mice, but the location in the respiratory tract and the time point at which defects were observed differed significantly. Although the Deltawlb mutants were much more sensitive to complement-mediated killing in vitro, they displayed similar defects in respiratory tract colonization in C5(-/-) mice compared with wild-type (wt) mice, indicating that increased sensitivity to complement-mediated lysis is not sufficient to explain the in vivo defects. B. pertussis and B. parapertussis Deltawlb mutants were also defective compared to wt strains in colonization of SCID-beige mice, indicating that the defects were not limited to interactions with adaptive immunity. Interestingly, the B. bronchiseptica Deltawlb strain was defective, compared to the wt strain, in colonization of the respiratory tracts of BALB/c mice beginning 1 week postinoculation but did not differ from the wt strain in its ability to colonize the respiratory tracts of B-cell- and T-cell-deficient mice, suggesting that wlb-dependent LPS modifications in B. bronchiseptica modulate interactions with adaptive immunity. These data show that biosynthesis of a full-length LPS molecule by these three bordetellae is essential for the expression of full virulence for mice. In addition, the data indicate that the different distal structures modifying the LPS molecules on these three closely related subspecies serve different purposes in respiratory tract infection, highlighting the diversity of functions attributable to LPS of gram-negative bacteria.

Role of phosphoglucomutase of Bordetella bronchiseptica in lipopolysaccharide biosynthesis and virulence

The phosphoglucomutase (PGM)-encoding gene of Bordetella bronchiseptica is required for lipopolysaccharide (LPS) biosynthesis. An insertion mutant of the wild-type B. bronchiseptica strain BB7865 which disrupted LPS biosynthesis was created and characterized (BB7865pgm). Genetic analysis of the mutated gene showed it shares high identity with PGM genes of various bacterial species and forms part of an operon which also encompasses the gene encoding phosphoglucose isomerase. Functional assays for PGM revealed that enzyme activity is expressed in both bvg-positive and bvg-negative strains of B. bronchiseptica and is substantially reduced in BB7865pgm. Complementation of the mutated PGM gene with that from BB7865 restored the wild-type condition for all phenotypes tested. The ability of the mutant BB7865pgm to survive within J774. A1 cells was significantly reduced at 2 h (40% reduction) and 24 h (56% reduction) postinfection. BB7865pgm was also significantly attenuated in its ability to survive in vivo following intranasal infection of mice, being effectively cleared from the lungs within 4 days, whereas the wild-type strain persisted at least 35 days. The activities of superoxide dismutase, urease, and acid phosphatase were unaffected in the PGM-deficient strain. In contrast, the inability to produce wild-type LPS resulted in a reduced bacterial resistance to oxidative stress and a higher susceptibility to the antimicrobial peptide cecropin P.

Brucella melitensis 16M: characterisation of the galE gene and mouse immunisation studies with a galE deficient mutant

The galE gene of Streptomyces lividans was used to probe a cosmid library harbouring Brucella melitensis 16M DNA and the nucleotide sequence of a 2.5 kb ClaI fragment which hybridised was determined. An open reading frame encoding a predicted polypeptide with significant homology to UDP-galactose-4-epimerases of Brucella arbortus strain 2308 and other bacterial species was identified. DNA sequences flanking the B. melitensis galE gene shared no identity with other gal genes and, as for B. abortus, were located adjacent to a mazG homologue. A plasmid which encoded the B. melitensis galE open reading frame complemented a galE mutation in Salmonella typhimurium LB5010, as shown by the restoration of smooth lipopolysaccharide (LPS) biosynthesis, sensitivity to phage P22 infection and restoration of UDP-galactose-4-epimerase activity. The galE gene on the B. melitensis 16M chromosome was disrupted by insertional inactivation and these mutants lacked UDP-galactose-4-epimerase activity but no discernible differences in LPS structure between parent and the mutants were observed. One B. melitensis 16M galE mutant, Bm92, was assessed for virulence in CD-1 and BALB/c mice and displayed similar kinetics of invasion and persistence in tissues compared with the parent bacterial strain. CD-1 mice immunised with B. melitensis 16M galE were protected against B. melitensis 16M challenge.

Characterization of a WaaF (RfaF) homolog expressed by Haemophilus ducreyi

Haemophilus ducreyi lipooligosaccharide (LOS) is capable of inducing an inflammatory response in skin (A. A. Campagnari, L. M. Wild, G. Griffiths, R. J. Karalus, M. A. Wirth, and S. M. Spinola, Infect. Immun. 59:2601-2608, 1991) and likely contributes to the virulence of this sexually transmitted pathogen (B. A. Bauer, M. K. Stevens, and E. J. Hansen, Infect. Immun. 68:4290-4298, 1998). An open reading frame in H. ducreyi 35000 was found to encode a predicted protein that was 59% identical to the protein product of the rfaF (waaF) gene of Salmonella typhimurium. The H. ducreyi waaF gene was able to complement an S. typhimurium rfaF (waaF) mutant, a result which confirmed the identity of this gene. In contrast to the rfaF (waaF) gene of enteric bacteria, the H. ducreyi waaF gene was not located adjacent to other genes involved in lipopolysaccharide expression. Inactivation of the H. ducreyi waaF gene by insertion mutagenesis resulted in expression of a LOS that migrated much faster than wild-type LOS in sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The LOS of this mutant also did not bind a monoclonal antibody directed against a cell surface-exposed epitope of wild-type H. ducreyi LOS. Testing of the wild-type H. ducreyi strain and its isogenic waaF mutant in the temperature-dependent rabbit model for dermal lesion production by H. ducreyi revealed that this waaF mutant was less virulent than the wild-type parent strain. Complementation of the H. ducreyi waaF mutant with the wild-type H. ducreyi waaF gene resulted in expression of both wild-type LOS and wild-type virulence by this mutant.

Implications of sequencing bacterial genomes for pathogenesis and vaccine development

Improvements in homology search methodology and functional predictions are being complemented by the increase in the volume of sequence data with which comparative analyses can be performed. The experimental methods needed for investigation of gene function and expression in a variety of model systems of infection continue to develop. The identification of surface-exposed microbial structures and their conservation in natural populations of pathogenic species offers prospects for developing novel vaccines. A major challenge is the development of efficient screening methods to select the most promising candidates, such as immunisation with DNA.

Molecular and functional analysis of the lipopolysaccharide biosynthesis locus wlb from Bordetella pertussis, Bordetella parapertussis and Bordetella bronchiseptica

The Bordetella pertussis wlb locus (wlbpe, formerly bpl) is required for the biosynthesis of a trisaccharide that, when attached to the B. pertussis lipopolysaccharide (LPS) core (band B), generates band A LPS. The equivalent loci in Bordetella bronchiseptica (wlbbr) and Bordetella parapertussis (wlbpa) were identified and cloned. The wlbbr and wlbpa loci differ from wlbpe in that they lack the insertion sequence that defines the right-hand terminus of wlbpe. Deletion of 12 kb of DNA containing the whole wlb locus (delta wlb) by allelic exchange in each of the three bordetellae had no effect on band B biosynthesis, whereas band A biosynthesis was prevented in B. pertussis and B. bronchiseptica. In B. bronchiseptica and B. parapertussis, delta wlb mutants also lacked O-antigen. Reintroduction of the wlbpe or wlbbr loci on a shuttle vector into the three delta wlb mutants restored the wild-type LPS phenotype in the B. pertussis and B. bronchiseptica mutants. In the case of B. parapertussis, which normally does not synthesize an apparent band A structure, introduction of the wlbpe or wlbbr loci now enabled the generation of band A. This suggests that the attachment point for band A trisaccharide on the LPS core is present in B. parapertussis, and further suggests that the wild-type wlbpa locus is not fully functional. Introduction of the wlbpa locus into the delta wlbpe, delta wlbbr and delta wlbpa mutants had interesting consequences. The B. bronchiseptica and B. parapertussis recipients were now able to biosynthesize O-antigen, but no band A was generated. In the B. pertussis recipient, a truncated band A was expressed consistent with a mutation in the wlbH gene, but on Western blotting the expression of a small amount of full-length band A was also seen. Evidence that the wlbHpa protein is not fully functional was provided by the failure of the wlbpa locus to fully complement a B. pertussis wlbH (delta wlbHpe) mutant. This was supported by DNA sequence data showing that a single amino acid, conserved between homologous proteins from a range of bacteria, is altered in the B. parapertussis WlbH protein.