Distinct antigenic and genetic properties of the immunoglobulin A1 protease produced by Haemophilus influenzae biogroup aegyptius associated with Brazilian purpuric fever in Brazil

Tracing phylogenomic events leading to diversity of Haemophilus influenzae and the emergence of Brazilian Purpuric Fever (BPF)-associated clones

Here we report the use of a multi-genome DNA microarray to elucidate the genomic events associated with the emergence of the clonal variants of Haemophilus influenzae biogroup aegyptius causing Brazilian Purpuric Fever (BPF), an important pediatric disease with a high mortality rate. We performed directed genome sequencing of strain HK1212 unique loci to construct a species DNA microarray. Comparative genome hybridization using this microarray enabled us to determine and compare gene complements, and infer reliable phylogenomic relationships among members of the species. The higher genomic variability observed in the genomes of BPF-related strains (clones) and their close relatives may be characterized by significant gene flux related to a subset of functional role categories. We found that the acquisition of a large number of virulence determinants featuring numerous cell membrane proteins coupled to the loss of genes involved in transport, central biosynthetic pathways and in particular, energy production pathways to be characteristics of the BPF genomic variants.

Emergence and disappearance of a virulent clone of Haemophilus influenzae biogroup aegyptius, cause of Brazilian purpuric fever

SUMMARY

In 1984, children presented to the emergency department of a hospital in the small town of Promissão, São Paulo State, Brazil, with an acute febrile illness that rapidly progressed to death. Local clinicians and public health officials recognized that these children had an unusual illness, which led to outbreak investigations conducted by Brazilian health officials in collaboration with the U.S. Centers for Disease Control and Prevention. The studies that followed are an excellent example of the coordinated and parallel studies that are used to investigate outbreaks of a new disease, which became known as Brazilian purpuric fever (BPF). In the first outbreak investigation, a case-control study confirmed an association between BPF and antecedent conjunctivitis but the etiology of the disease could not be determined. In a subsequent outbreak, children with BPF were found to have bacteremia caused by Haemophilus influenzae biogroup aegyptius (H. aegyptius), an organism previously known mainly to cause self-limited purulent conjunctivitis. Molecular characterization of blood and other isolates demonstrated the clonal nature of the H. aegyptius strains that caused BPF, which were genetically distant from the diverse strains that cause only conjunctivitis. This led to an intense effort to identify the factors causing the unusual invasiveness of the BPF clone, which has yet to definitively identify the virulence factor or factors involved. After a series of outbreaks and sporadic cases through 1993, no additional cases of BPF have been reported.

Characterization of igaB, a second immunoglobulin A1 protease gene in nontypeable Haemophilus influenzae

Nontypeable Haemophilus influenzae is an important respiratory pathogen, causing otitis media in children and lower respiratory tract infection in adults with chronic obstructive pulmonary disease (COPD). Immunoglobulin A1 (IgA1) protease is a well-described protein and potential virulence factor in this organism as well as other respiratory pathogens. IgA1 proteases cleave human IgA1, are involved in invasion, and display immunomodulatory effects. We have identified a second IgA1 protease gene, igaB, in H. influenzae that is present in addition to the previously described IgA1 protease gene, iga. Reverse transcriptase PCR and IgA1 protease assays indicated that the gene is transcribed, expressed, and enzymatically active in H. influenzae. The product of this gene is a type 2 IgA1 protease with homology to the iga gene of Neisseria species. Mutants that were deficient in iga, igaB, and both genes were constructed in H. influenzae strain 11P6H, a strain isolated from a patient with COPD who was experiencing an exacerbation. Analysis of these mutants indicated that igaB is the primary mediator of IgA1 protease activity in this strain. IgA1 protease activity assays on 20 clinical isolates indicated that the igaB gene is associated with increased levels of IgA1 protease activity. Approximately one-third of 297 strains of H. influenzae of diverse clinical and geographic origin contained igaB. Significant differences in the prevalence of igaB were observed among isolates from different sites of isolation (sputum > middle ear > nasopharynx). These data support the hypothesis that the newly discovered igaB gene is a potential virulence factor in nontypeable H. influenzae.

Characterization of the IgA1 protease from the Brazilian purpuric fever strain F3031 of Haemophilus influenzae biogroup aegyptius

Brazilian purpuric fever is a severe vascular disease caused by an invasive clone of Haemophilus influenzae biogroup aegyptius, which normally causes self-limiting eye infections. A previous genome subtraction procedure resulted in the isolation of a DNA fragment, which encodes a putative IgA1 protease, specific to the F3031 Brazilian purpuric fever type strain. Cloning and sequencing of the entire F3031 iga1 gene showed that the subtracted DNA fragment encompasses the iga1 region encoding the active site and the cleavage specificity determinant of the protein, which are different from the cognate regions of the proteases produced by other H. influenzae strains. Western and IgA cleavage assays together with clustering analysis showed that the F3031 IgA1 protease is most similar to the type 2 proteases produced by H. influenzae type c and e strains. Analysis of the promoter region of the F3031 iga1 gene revealed the presence of Fur binding sites. However, real-time PCR analysis and transcriptional fusion assays showed that the expression of iga1 is not regulated by iron or hemin under the conditions tested.

Evolution of the paralogous hap and iga genes in Haemophilus influenzae: evidence for a conserved hap pseudogene associated with microcolony formation in the recently diverged Haemophilus aegyptius and H. influenzae biogroup aegyptius

Certain non-capsulate strains belonging to the Haemophilus influenzae/Haemophilus aegyptius complex show unusually high pathogenicity, but the evolutionary origin of these virulent phenotypes, termed H. influenzae biogroup aegyptius, is as yet unknown. The aim of the present study was to elucidate the mechanisms of evolution of two paralogous genes, hap and iga, which encode the adhesion and penetration Hap protein and the IgA1 protease respectively. Partial sequencing of hap and iga genes in a comprehensive collection of strains belonging to the H. influenzae/H. aegyptius complex revealed considerable genetic polymorphism and pronounced mosaic-like patterns in both genes, but no evidence of intrastrain recombination between the two genes. A conserved hap pseudogene was present in all strains of H. aegyptius and H. influenzae biogroup aegyptius, each of which constituted distinct subpopulations as revealed by phylogenetic analysis. There was no evidence for a second, functional copy of the hap gene in these strains. The perturbed expression of the Hap serine protease appears to be associated with the formation of elongated bacterial cells growing in chains and a distinct colonization pattern on conjunctival cells, previously termed microcolony formation. The fact that individual hap pseudogenes differed from the ancestral sequence by zero to two positions within a 1.5 kb stretch suggests that the silencing event happened approximately 2000-11,000 years ago. Divergence of H. aegyptius and H. influenzae biogroup aegyptius occurred subsequent to this genetic event. The loss of Hap protein expression may be one of the genetic events that facilitated exploitation of the conjunctivae as a new niche.

Genomic analysis of the F3031 Brazilian purpuric fever clone of Haemophilus influenzae biogroup aegyptius by PCR-based subtractive hybridization

PCR-based subtractive genome hybridization produced clones harboring inserts present in Brazilian purpuric fever (BPF) prototype strain F3031 but absent in noninvasive Haemophilus influenzae biogroup aegyptius isolate F1947. Some of these inserts have no matches in the GenBank database, while others are similar to genes encoding either known or hypothetical proteins. One insert represents a 2.3-kb locus with similarity to a Thermotoga maritima hypothetical protein, while another is part of a 7.6-kb locus that contains predicted genes encoding hypothetical, phage-related, and carotovoricin Er-like proteins. The presence of DNA related to these loci is variable among BPF isolates and nontypeable H. influenzae strains, while neither of them was detected in strains of types a to f. The data indicate that BPF-causing strain F3031 harbors unique chromosomal regions, most of which appear to be acquired from unrelated microbial sources.

Characterization of P1-deficient isogenic mutant of Haemophilus influenzae biogroup aegyptius associated with Brazilian purpuric fever

Haemophilus influenzae biogroup aegyptius (formerly H. aegyptius) is the etiologic agent of Brazilian purpuric fever (BPF). A surface-exposed epitope on the outer membrane protein P1 is present on most strains of H. influenzae biogroup aegyptius associated with BPF but is absent in almost all non-disease associated strains. The role of the outer membrane protein P1 in the pathogenesis of this disease was evaluated by utilizing an isogenic P1-deficient mutant. We compared the ability of the wild type and P1 isogenic mutant to grow under various conditions. The P1-deficient strain grew at a similar rate to the wild type in both complex and chemically defined medium. The P1-deficient mutant also had a similar growth rate to the wild type under anaerobic conditions. Anaerobic growth, however, resulted in up-regulation of the P1 protein in the wild type strain. Three assays were used to examine the pathophysiologic role of the P1 protein in BPF: 1) serum resistance; 2) sustained bacteremia in the infant rat model; and 3) the human microvascular endothelial cell (HMEC) cytotoxicity assay. Both the mutant and wild-type strains were resistant to killing in 95% normal human serum. The P1-deficient strain was also as virulent as the wild type in both the infant rat model of bacteremia and in the HMEC-1 tissue culture model. These results demonstrate that serum resistance, sustained bacteremia in the infant rat, and cytotoxicity of HMEC cells occur in the absence of P1. The P1 protein is not essential for the pathogenic potential identified by these assays. However, these results demonstrate that an anaerobic environment is a potent physiologic regulator of P1 protein expression. The impact of anaerobiosis on protein expression and pathogenesis will require further investigations.

Comparative analysis of immunoglobulin A1 protease activity among bacteria representing different genera, species, and strains

Immunoglobulin A1 (IgA1) proteases cleaving human IgA1 in the hinge region are produced constitutively by a number of pathogens, including Haemophilus influenzae, Neisseria meningitidis, Neisseria gonorrhoeae, and Streptococcus pneumoniae, as well as by some members of the resident oropharyngeal flora. Whereas IgA1 proteases have been shown to interfere with the functions of IgA antibodies in vitro, the exact role of these enzymes in the relationship of bacteria to a human host capable of responding with enzyme-neutralizing antibodies is not clear. Conceivably, the role of IgA1 proteases may depend on the quantity of IgA1 protease generated as well as on the balance between secreted and cell-associated forms of the enzyme. Therefore, we have compared levels of IgA1 protease activity in cultures of 38 bacterial strains representing different genera and species as well as strains of different pathogenic potential. Wide variation in activity generation rate was found overall and within some species. High activity was not an exclusive property of bacteria with documented pathogenicity. Almost all activity of H. influenzae, N. meningitidis, and N. gonorrhoeae strains was present in the supernatant. In contrast, large proportions of the activity in Streptococcus, Prevotella, and Capnocytophaga species was cell associated at early stationary phase, suggesting that the enzyme may play the role of a surface antigen. Partial release of cell-associated activity occurred during stationary phase. Within some taxa, the degree of activity variation correlated with degree of antigenic diversity of the enzyme as determined previously. This finding may indicate that the variation observed is of biological significance.