Virulence factors of Haemophilus ducreyi

We investigated the susceptibility of virulent and avirulent strains of Haemophilus ducreyi to the bactericidal activity of normal human serum and to phagocytosis and killing by human polymorphonuclear leukocytes (PMNL). Strains were defined as virulent if intradermal inoculation into a rabbit produced a typical necrotic lesion. Nonvirulent strains produced no cutaneous lesions in rabbits. Virulent strains were resistant to the complement-mediated lethal action of normal human and rabbit sera, whereas avirulent strains were susceptible (greater than 95% kill, 60 min). Virulent strains were relatively resistant to phagocytosis and killing by human PMNL, in contrast to the avirulent strains. In past studies polymyxin resistance has been correlated with virulence in H. ducreyi. In our studies, polymyxin resistance could not be correlated with virulence, since polymyxin-sensitive mutants obtained from polymyxin-resistant parent strains remained virulent for rabbits and resistant to bactericidal action of normal serum and phagocytosis and killing by human PMNL. Similarly, polymyxin-resistant mutants obtained from polymyxin-sensitive parent strains remained avirulent for rabbits and susceptible to bactericidal action of normal serum and PMNL. The acquisition of polymyxin resistance was accompanied by the loss of a 47,000-molecular-weight protein. The association of serum resistance and resistance to phagocytosis and killing by human PMNL with virulent strains, as defined by the rabbit intradermal test, suggests that these factors may mediate the pathogenicity of H. ducreyi.     

Haemophilus ducreyi SapA Contributes to Cathelicidin Resistance and Virulence in Humans

Haemophilus ducreyi is an extracellular pathogen of human epithelial surfaces that resists human antimicrobial peptides (APs). The organism''s genome contains homologs of genes sensitive to antimicrobial peptides (sap operon) in nontypeable Haemophilus influenzae. In this study, we characterized the sap-containing loci of H. ducreyi 35000HP and demonstrated that sapA is expressed in broth cultures and H. ducreyi-infected tissue; sapA is also conserved among both class I and class II H. ducreyi strains. We constructed a nonpolar sapA mutant of H. ducreyi 35000HP, designated 35000HPsapA, and compared the percent survival of wild-type 35000HP and 35000HPsapA exposed to several human APs, including α-defensins, β-defensins, and the cathelicidin LL-37. Unlike an H. influenzae sapA mutant, strain 35000HPsapA was not more susceptible to defensins than strain 35000HP was. However, we observed a significant decrease in the survival of strain 35000HPsapA after exposure to LL-37, which was complemented by introducing sapA in trans. Thus, the Sap transporter plays a role in resistance of H. ducreyi to LL-37. We next compared mutant strain 35000HPsapA with strain 35000HP for their ability to cause disease in human volunteers. Although both strains caused papules to form at similar rates, the pustule formation rate at sites inoculated with 35000HPsapA was significantly lower than that of sites inoculated with 35000HP (33.3% versus 66.7%; P = 0.007). Together, these data establish that SapA acts as a virulence factor and as one mechanism for H. ducreyi to resist killing by antimicrobial peptides. To our knowledge, this is the first demonstration that an antimicrobial peptide resistance mechanism contributes to bacterial virulence in humans.Haemophilus ducreyi is the causative agent of chancroid, a genital ulcer disease that facilitates both the transmission and acquisition of HIV-1 (4, 45). An obligate human pathogen, H. ducreyi infects epithelial surfaces and primarily remains localized in the skin (49). During experimental human infection, polymorphonuclear leukocytes (PMNs) and macrophages are rapidly recruited to the bacterial entry site. The organism colocalizes with PMNs and macrophages throughout disease but remains extracellular (8, 10).As part of the innate immune system''s response to infection, PMNs, macrophages, and epithelial cells secrete antimicrobial peptides (APs). Most APs are small, cationic peptides that are secreted into the extracellular milieu and have both bactericidal and chemotactic properties (26). Cationic APs are attracted to the anionic bacterial cell membrane where they lyse the bacterial cell. Some APs specifically recruit macrophages, PMNs, T cells, and immature dendritic cells to the site of bacterial infection, serving as a bridge between innate and adaptive immunity (39, 40, 53).In humans, the best-studied APs include the family of defensins, which are subdivided by structure into α- and β-defensins, and one human cathelicidin, LL-37. Defensins are cysteine- and arginine-rich β-sheet peptides that range from 29 to 47 amino acids in length (29). Defensins form three intramolecular disulfide bonds via six invariant cysteine residues. Both the positions of the cysteines and the pattern of disulfide bonding differ between the α- and β-defensins (17, 29). In contrast, cathelicidin LL-37 is devoid of cysteines and forms an α-helix (20).H. ducreyi encounters several cellular sources of APs during human infection: keratinocytes constitutively express human β-defensin 1 (HBD-1) and upregulate expression of HBD-2, HBD-3, and LL-37 in response to inflammation (22, 23, 30, 54); PMNs secrete preformed α-defensins, including human neutrophil peptide 1 (HNP-1), HNP-2, HNP-3, and HNP-4, as well as HBD-4 and LL-37 during infection (16, 50); and macrophages secrete HBD-1, HBD-2, and LL-37 in response to inflammatory mediators (15, 31). Vaginal epithelial cells also constitutively express the α-defensin human defensin 5 (HD-5) (43). Dual staining for H. ducreyi and HNP-1, HNP-2, and HNP-3 demonstrate that H. ducreyi is exposed to APs at the papular, pustular, and ulcerative stages of disease (10; C. A. Townsend and M. E. Bauer, unpublished data). H. ducreyi resists the bactericidal effects of several human APs, including those predicted to be at the site of infection; this resistance has been observed in representative members of two phenotypic H. ducreyi classes (38, 51). The mechanism(s) by which H. ducreyi evades AP-mediated killing is unknown.Bacterial pathogens have evolved many mechanisms to resist killing by APs, including enzymatic inactivation of APs, electrostatic repulsion by the addition of positively charged residues on the surface, and expression of transporters that remove APs before they can attack the cell membrane (27). To identify putative AP resistance factors in H. ducreyi, we examined the H. ducreyi genome (http://stdgen.northwestern.edu) for evidence of homology with previously described resistance strategies in other bacteria. Using a BLASTP search, we found that the H. ducreyi genome included homologs of the previously described transporter genes sensitive to antimicrobial peptides (sap genes) (3). The sap genes encode the Sap influx pump, which confers resistance to APs in several Gram-negative pathogens, including Salmonella enterica serovar Typhimurium, nontypeable Haemophilus influenzae, Proteus mirabilis, and Erwinia chrysanthemi (32, 35, 36, 41).The Sap transporter consists of five proteins: SapB and SapC are permease proteins that form a pore in the bacterial inner membrane, SapD and SapF function as ATPase subunits of the transporter, and SapA is a periplasmic solute binding protein (34, 41). The nontypeable H. influenzae SapA protein has been shown to directly bind APs, including both LL-37 and HBD-3 (34). Once an AP enters the periplasm, SapA is thought to shuttle the AP to the SapBCDF channel, where the AP is transported into the cytoplasm, bypassing direct interaction between the AP and the cytoplasmic membrane, which would be the lethal event in AP attack (34, 41). Once in the cytoplasm, the fate of the AP is unknown, but presumably, it is degraded and its amino acids are recycled.Sap transporters take up a variety of APs; among human APs tested, the S. enterica serovar Typhimurium Sap transporter confers resistance to crude extracts of human PMNs, and the nontypeable H. influenzae Sap transporter confers resistance to LL-37 and HBD-3 (19, 34, 35). Further, the nontypeable H. influenzae SapA protein has been shown to directly bind APs, including both LL-37 and HBD-3 (34).Because Sap transporters protect other pathogens from APs, we hypothesized that the putative H. ducreyi Sap transporter system would confer resistance against APs and that the loss of the periplasmic component SapA would result in increased susceptibility to APs in vitro and loss of virulence in vivo. Herein, we describe the construction of an isogenic sapA insertion-deletion mutant to test this hypothesis and to define a mechanism for AP resistance of H. ducreyi.     

Carbon Storage Regulator A Contributes to the Virulence of Haemophilus ducreyi in Humans by Multiple Mechanisms

The carbon storage regulator A (CsrA) controls a wide variety of bacterial processes, including metabolism, adherence, stress responses, and virulence. Haemophilus ducreyi, the causative agent of chancroid, harbors a homolog of csrA. Here, we generated an unmarked, in-frame deletion mutant of csrA to assess its contribution to H. ducreyi pathogenesis. In human inoculation experiments, the csrA mutant was partially attenuated for pustule formation compared to its parent. Deletion of csrA resulted in decreased adherence of H. ducreyi to human foreskin fibroblasts (HFF); Flp1 and Flp2, the determinants of H. ducreyi adherence to HFF cells, were downregulated in the csrA mutant. Compared to its parent, the csrA mutant had a significantly reduced ability to tolerate oxidative stress and heat shock. The enhanced sensitivity of the mutant to oxidative stress was more pronounced in bacteria grown to stationary phase compared to that in bacteria grown to mid-log phase. The csrA mutant also had a significant survival defect within human macrophages when the bacteria were grown to stationary phase but not to mid-log phase. Complementation in trans partially or fully restored the mutant phenotypes. These data suggest that CsrA contributes to virulence by multiple mechanisms and that these contributions may be more profound in bacterial cell populations that are not rapidly dividing in the human host.     

Chancroid and Haemophilus ducreyi.

Haemophilus ducreyi is the causative agent of chancroid, one of the genital ulcerative diseases. H. ducreyi is the major cause of genital ulcer disease in Africa and Southeast Asia and is of increasing concern in the United States. Definitive diagnosis of chancroid requires the isolation and identification of H. ducreyi, but isolation of this organism is difficult and the available medium is not optimal for all strains. Fluorescent antibody and serologic tests are of limited value. In general, our knowledge of this organism is rather limited, and indeed, recent studies have questioned the placement of H. ducreyi in the genus Haemophilus. H. ducreyi has relatively few biochemical activities, and epidemiologic studies are limited because there are limited phenotypic markers available for strain typing. Specific virulence factors of H. ducreyi have yet to be identified. Antimicrobial resistance in H. ducreyi is of special concern, as this organism has acquired both gram-negative and gram-positive resistance determinants. In addition, some of these determinants can be mobilized and transferred to other Haemophilus species or to Neisseria gonorrhoeae.     

Isolation and cultivation of Haemophilus ducreyi

A useful method for isolating and recognizing Haemophilus ducreyi from chancres and buboes of male patients is presented. A total of 41 clinical isolates of H. ducreyi were recovered from 33 patients over an 8-year period, and the experience with the 15 most recent isolates is presented in detail. Chocolate agar supplemented with 1% Iso VitaleX and 5% sheep blood agar were prepared, using Trypticase soy and Mueller-Hinton Agar bases, and incubation conditions included ambient, capneic, and anaerobic environments. Mueller-Hinton agar was clearly superior over Trypticase soy agar for isolation of H. ducreyi, although there was little difference between 5% sheep blood and supplemented chocolate agar. Growth in ambient air and under anaerobiasis was poor or lacking, whereas growth in 5 to 7% CO2 was good to luxuriant. Heat-inactivated and fresh (unheated)human blood clot tubes also were used for selective isolation. Although the rates of isolation from the two types of clot tube were not significantly different, unheated clot tubes were superior to heated clot tubes because of reduced level of contaminants. Gram stain characteristics taken from blood clot tubes and solid media, cellular and colonial morphology of the bacilli, and lack of oxidase, catalase, and biochemical activity except nitrate reductase were determinant factors. The results of this study demonstrated that successful isolation of H. ducreyi can be achieved with a minimal amount of resources and expertise.     

Enzymic activity of Haemophilus ducreyi

The enzymic activity of 29 Haemophilus ducreyi strains on 28 substrates is described. The results are compared with those of seven other authors. There is agreement only about the presence of alkaline phosphatase and arginine aminopeptidase and the lack of glycosidases. Possible reasons for the contradictions in the eight reports are discussed.     

Characteristics of Haemophilus ducreyi in culture

Growth on different media and the influence of culture conditions were studied on 19 recently isolated strains of Haemophilus ducreyi, none of which had more than four passages on artificial media. The results were compared with 10 laboratory strains, which had an unknown number of passages in vitro. For all strains, growth was best on 30% rabbit blood agar and on Bieling agar. The laboratory strains showed a tendency to grow better on chocolate agar than did the fresh isolates. Of 19 fresh clinical isolates, 12 were CO2 dependent, and 2 needed extra moisture for growth. From the 10 laboratory strains, only one needed CO2 and none needed extra moisture. All 29 strains grew under anaerobic conditions. Of the 19 fresh clinical isolates, 12 grew at 22 degrees C, but only 2 of the 10 laboratory strains grew at this temperature. The laboratory strains grew better than the fresh isolates at 37 degrees C, and the optimal pH for all strains was pH 6.5 to 7.0. All strains showed starch aggregation.     

Target Cell Range of Haemophilus ducreyi Hemolysin and Its Involvement in Invasion of Human Epithelial Cells

Haemophilus ducreyi, the causative agent of chancroid, produces a hemolysin, whose role in virulence is not well defined. To assess the possible role of hemolysin in pathogenesis, we evaluated its target cell range by using wild-type H. ducreyi 35000, nonhemolytic mutants with the hemolysin structural gene deleted, and isogenic strains expressing different amounts of hemolytic activity. The cytotoxicity of the various cell types was assessed by quantitating the release of lactate dehydrogenase into culture supernatants as a measure of cell lysis. In these experiments, human foreskin fibroblasts, human foreskin epithelial cells, and, to a lesser extent, HEp-2 cells were lysed by H. ducreyi hemolysin. Hemolysin also lysed human blood mononuclear cells and immune system cell lines including U937 macrophage-like cells, T lymphocytes, and B lymphocytes. In contrast, human polymorphonuclear leukocytes were not sensitive to hemolysin under the conditions tested. We also analyzed the effect of hemolysin on invasion of human epithelial cells and found that H. ducreyi strains expressing cloned hemolysin genes showed a 10-fold increase in invasion compared to the control strain. These data support the hypothesis that the H. ducreyi hemolysin is important in the pathogenesis of chancroid and may contribute to ulcer formation, invasion of epithelial cells, and evasion of the immune response.     

Selenium and the growth of Haemophilus ducreyi.

One of the growth media in current use for Haemophilus ducreyi comprises Mueller Hinton agar, chocolatised horse blood, serum and IsoVitalex (BBL). For a better understanding of growth factors, attempts were made to simplify this complex medium. The horse blood was replaced by haemin (200 micrograms/ml), the serum by albumin (0.2%), and IsoVitalex was substituted only by L-glutamine 0.01%. Most of the strains grew, but when selenium ions were added in a concentration of 3.25 x 10(-3) micrograms/ml, growth was stimulated and became more luxuriant than growth on conventional media.     

Identification of Haemophilus ducreyi in the clinical laboratory

Some of the characteristics of 42 clinical isolates of Haemophilus ducreyi are reported. Only six of the 42 strains were able to grow on horse-blood agar. All strains gave a positive oxidase test with tetramethyl-p-phenylenediamine and a negative result with dimethyl-p-phenylenediamine. All of 15 test strains were negative in the porphyrin test. Tests for haemin requirement were inconclusive because of difficulties encountered in obtaining growth on a basal medium.     

Characterization of a Haemophilus ducreyi Mutant Deficient in Expression of Cytolethal Distending Toxin

Haemophilus ducreyi expresses a soluble cytolethal distending toxin (CDT) that kills HeLa, HEp-2, and other human epithelial cells in vitro. H. ducreyi CDT activity is encoded by a three-gene cluster (cdtABC), and antibody to the cdtC gene product can neutralize CDT activity in vitro (L. D. Cope, S. R. Lumbley, J. L. Latimer, J. Klesney-Tait, M. K. Stevens, L. S. Johnson, M. Purven, R. S. Munson, Jr., T. Lagergard, J. D. Radolf, and E. J. Hansen, Proc. Natl. Acad. Sci. USA 94:4056-4061, 1997). Culture supernatant fluid from a recombinant Escherichia coli strain containing the H. ducreyi cdtABC gene cluster readily killed both HeLa cells and HaCaT keratinocytes and had a modest inhibitory effect on the growth of human foreskin fibroblasts. Insertional inactivation of the cdtC gene in this recombinant E. coli strain eliminated the ability of this strain to kill HeLa cells and HaCaT keratinocytes. This mutated H. ducreyi cdtABC gene cluster was used to construct an isogenic H. ducreyi cdtC mutant. Monoclonal antibodies against the H. ducreyi CdtA, CdtB, and CdtC proteins were used to characterize protein expression by this cdtC mutant. Culture supernatant fluid from this H. ducreyi cdtC mutant did not detectably affect any of the human cells used in this study. The presence of the wild-type H. ducreyi cdtC gene in trans in this H. ducreyi mutant restored its ability to express a CDT that killed both HeLa cells and HaCaT keratinocytes. The isogenic H. ducreyi cdtC mutant was shown to be as virulent as its wild-type parent strain in the temperature-dependent rabbit model for experimental chancroid. Lack of expression of the H. ducreyi CdtC protein also did not affect the ability of this H. ducreyi mutant to survive in the skin of rabbits.     

杜克雷嗜血杆菌血红蛋白受体和其部分蛋白片段的表达纯化及其多克隆抗体建立ELISA检测杜克雷嗜血杆菌的初步研究

目的:制备纯化杜克雷嗜血杆菌血红蛋白受体(HgbA)及其部分蛋白片段(HgbAF),免疫家兔获得rHgbA和rHgbAF特异性多克隆抗体,用于临床软下疳病原学诊断.方法:采用分子生物学技术克隆HgbA和HgbAF基因,诱导表达并纯化rHgbA和rHgbAF;用rHgbA和rHgbAF免疫家兔制备多克隆抗体,采用Western blot和ELISA方法测定抗体免疫活性;建立杜克雷嗜血杆菌HgbA双抗体夹心ELISA检测系统,对其敏感性、特异性进行初步评价.结果:成功克隆了目的基因,经诱导表达获得纯化杜克雷嗜血杆菌rHgbA及其部分重组蛋白片段;免疫家兔获得rHgbA和rHgbAF特异性抗血清,经饱和硫酸氨盐析后,Western blot实验结果显示其能与rHgbA和rHgbAF特异性结合;建立的杜克雷嗜血杆菌HgbA双抗体夹心ELISA,对杜克雷嗜血杆菌、流感嗜血杆菌及其他7种生殖器溃疡相关的细菌进行检测,发现除杜克雷嗜血杆菌呈现强阳性反应外,其余8种菌均为阴性结果,无交叉反应发生;上述ELISA检测纯化rHgbA灵敏度为1.56 ng/ml,杜克雷嗜血杆菌检测灵敏度为2×105 cfu/ml,脓汁模拟样本中杜克雷嗜血杆菌检测的灵敏度为1×106 cfu/ml.结论:成功制备了杜克雷嗜血杆菌血红蛋白受体及其部分蛋白片段,免疫家兔所获得的多克隆抗体能与杜克雷嗜血杆菌特异性结合,而与流感嗜血杆菌及其他7种生殖器溃疡相关的细菌无交叉反应,表明建立的ELISA具有较好的特异性.上述ELISA检测方法的敏感性水平不能满足临床所有标本中杜克雷嗜血杆菌的检测,有待于进一步提高,但该方法的建立具有潜在临床应用价值.     

Specificity of the immune response to Haemophilus ducreyi

The specificity of the antibody response toHaemophilus ducreyiin sera from patients attending a sexually transmitted disease clinic in South Africa has been studied using immunoblotting. Patients with chancroid were shown to have higher levels of IgG (mean 0.74, SD 0.34) toH. ducreyithan those with no history of chancroid (mean 0.34, SD 0.19). The pattern of the antibody specificity was highly variable between patients with culture proven chancroid but there was no observed strain specificity. In comparison, the patterns obtained using sera from patients without known exposure toH. ducreyishowed less variation between patients and were of less intensity at the dilution used. Sera from patients with chancroid recognised epitopes on proteins that varied in molecular weight between strains, particularly of 60–66kDa (10 of 36 patients) and 25–27kDa (8 of 36 patients). In addition epitopes were recognised on the GroEL and/or DnaK heat shock proteins in 13 of 36 sera tested. There was no apparent change in the epitopes recognised on proteins between the homologous and heterologous strains. Patterns of antibody specificity in sequential sera only varied in one of six patients tested.     

Neutropenia Restores Virulence to an Attenuated Cu,Zn Superoxide Dismutase-Deficient Haemophilus ducreyi Strain in the Swine Model of Chancroid

Haemophilus ducreyi causes chancroid, a sexually transmitted cutaneous genital ulcer disease associated with increased heterosexual transmission of human immunodeficiency virus. H. ducreyi expresses a periplasmic copper-zinc superoxide dismutase (Cu, Zn SOD) that protects the bacterium from killing by exogenous superoxide in vitro. We hypothesized that the Cu,Zn SOD would protect H. ducreyi from immune cell killing, enhance survival, and affect ulcer development in vivo. In order to test this hypothesis and study the role of the Cu,Zn SOD in H. ducreyi pathogenesis, we compared a Cu,Zn SOD-deficient H. ducreyi strain to its isogenic wild-type parent with respect to survival and ulcer development in immunocompetent and immunosuppressed pigs. The Cu,Zn SOD-deficient strain was recovered from significantly fewer inoculated sites and in significantly lower numbers than the wild-type parent strain or a merodiploid (sodC+ sodC) strain after infection of immunocompetent pigs. In contrast, survival of the wild-type and Cu,Zn SOD-deficient strains was not significantly different in pigs that were rendered neutropenic by treatment with cyclophosphamide. Ulcer severity in pigs was not significantly different between sites inoculated with wild type and sites inoculated with Cu,Zn SOD-deficient H. ducreyi. Our data suggest that the periplasmic Cu,Zn SOD is an important virulence determinant in H. ducreyi, protecting the bacterium from host immune cell killing and contributing to survival and persistence in the host.     

Expression of peptidoglycan-associated lipoprotein is required for virulence in the human model of Haemophilus ducreyi infection

Haemophilus ducreyi expresses a peptidoglycan-associated lipoprotein (PAL) that exhibits extensive homology to Haemophilus influenzae protein 6. We constructed an isogenic PAL mutant (35000HP-SMS4) by the use of a suicide vector that contains lacZ as a counterselectable marker. H. ducreyi 35000HP-SMS4 and its parent, 35000HP, had similar growth rates in broth and similar lipooligosaccharide profiles. 35000HP-SMS4 formed smaller, more transparent colonies than 35000HP and, unlike its parent, was hypersensitive to antibiotics. Complementation of the mutant in trans restored the parental phenotypes. To test whether expression of PAL is required for virulence, nine human volunteers were experimentally infected. Each subject was inoculated with two doses (41 to 89 CFU) of live 35000HP and one dose of heat-killed bacteria on one arm and with three doses (ranging from 28 to 800 CFU) of live 35000HP-SMS4 on the other arm. Papules developed at similar rates at sites inoculated with the mutant or parent but were significantly smaller at mutant-inoculated sites than at parent-inoculated sites. The pustule formation rate was 72% (95% confidence interval [CI], 46.5 to 90.3%) at 18 parent sites and 11% (95% CI, 2.4 to 29.2%) at 27 mutant sites (P < 0.0001). The rates of recovery of H. ducreyi from surface cultures were 8% (n = 130; 95% CI, 4.3 to 14.6%) for parent-inoculated sites and 0% (n = 120; 95% CI, 0.0 to 2.5%) for mutant-inoculated sites (P < 0.001). H. ducreyi was recovered from six of seven biopsied parent-inoculated sites and from one of three biopsied mutant-inoculated sites. Confocal microscopy confirmed that the bacteria present in a mutant inoculation site pustule lacked a PAL-specific epitope. Although biosafety regulations precluded our testing the complemented mutant in humans, these results suggest that expression of PAL facilitates the ability of H. ducreyi to progress to the pustular stage of disease.     

Isolation and rapid identification of Haemophilus ducreyi.

During a 2-month period, 62 strains of Haemophilus ducreyi were isolated from 168 genital lesions and 2 lymph node aspirates. Of these strains, 22 were found on both chocolate agar and fetal bovine serum agar supplemented with vancomycin, 29 were found only on chocolate agar, and 9 were found only on fetal bovine serum agar. Two additional strains were isolated on sheep blood agar. All of these isolates were correctly identified with the RapID NH system (Innovative Diagnostic Systems, Inc., Decatur, Ga.) a new identification kit that has a database for Haemophilus, Neisseria, and other genera that include fastidious gram-negative bacilli.