Transcellular passage of Neisseria gonorrhoeae involves pilus phase variation.

Piliated and nonpiliated Neisseria gonorrhoeae organisms were added on top of confluent layers of HEC-1-B cells, each maintained on a microporous Transwell-COL membrane. The bacteria released into the lower chamber were characterized with respect to the following virulence determinants: pili, which mediate adherence to target host cells; PilE, the major pilus subunit protein; and PilC, which is involved in pilus biogenesis and adherence. Even if >99% of the added bacteria of N. gonorrhoeae MS11 were piliated, bacteria recovered on the other side of the cell layer were predominantly nonpiliated. The recovered clones still expressed unassembled PilE protein, but 50% had lost PilC production. Nonpiliated gonococci, in which the 5' end of pilE had been deleted, were released in reduced numbers, and piliated recA bacteria added to the cell layer were not released at all, at time points when piliated recA+ clones were found at high numbers in the lower chamber. Our data indicate that bacteria producing unassembled PilE protein are selected for during passage through an epithelial cell layer. The finding that the pilE gene sequence was altered in the transmigrants suggests that pilin sequence variation is involved in the transcellular passage of N. gonorrhoeae.

Helicobacter pylori adhesin binding fucosylated histo-blood group antigens revealed by retagging.

The bacterium Helicobacter pylori is the causative agent for peptic ulcer disease. Bacterial adherence to the human gastric epithelial lining is mediated by the fucosylated Lewis b (Leb) histo-blood group antigen. The Leb-binding adhesin, BabA, was purified by receptor activity-directed affinity tagging. The bacterial Leb-binding phenotype was associated with the presence of the cag pathogenicity island among clinical isolates of H. pylori. A vaccine strategy based on the BabA adhesin might serve as a means to target the virulent type I strains of H. pylori.

Surface localization of Helicobacter pylori urease and a heat shock protein homolog requires bacterial autolysis.

Helicobacter pylori is a gram-negative bacterium which causes chronic gastritis and is associated with peptic ulcer disease, gastric carcinoma, and gastric lymphoma. The bacterium is characterized by potent urease activity, thought to be located on the outer membrane, which is essential for survival at low pH. The purpose of the present study was to investigate mechanisms whereby urease and HspB, a GroEL homolog, become surface associated in vitro. Urease, HspB, and catalase were located almost exclusively within the cytoplasm in fresh log-phase cultures assessed by cryo- immunoelectron microscopy. In contrast, significant amounts of surface-associated antigen were observed in older or subcultured preparations concomitantly with the appearance of significant amounts of extracellular antigen, amorphous debris, and membrane fragments. By use of a variety of biochemical methods, a significant fraction of urease and HspB was associated with the outer membrane in subcultured preparations of H. pylori. Taken together, these results strongly suggest that H. pylori cells undergo spontaneous autolysis during culture and that urease and HspB become surface associated only concomitant with bacterial autolysis. By comparing enzyme sensitivity to flurofamide (a potent, poorly diffusible urease inhibitor) in whole cells with that in deliberately lysed cells, we show that both extracellular and intracellular urease molecules are active enzymatically. Autolysis of H. pylori is an important phenomenon to recognize since it likely exerts significant effects on the behavior of H. pylori. Furthermore, the surface properties of H. pylori must be unique in promoting adsorption of cytoplasmic proteins.

The Gal(alpha 1-4)Gal-specific tip adhesin of Escherichia coli P-fimbriae is needed for pyelonephritis to occur in the normal urinary tract.

Nonobstructive acute pyelonephritis in humans is most often caused by P-fimbriated Escherichia coli. P-fimbriae are heteropolymeric fibers carrying a Gal(alpha 1-4)Gal-specific PapG adhesin at its distal end. The pyelonephritic strain DS17 expresses P-fimbriae from a single gene cluster. A mutant strain, DS17-8, which expresses P-fimbriae tacking the PapG adhesin, was constructed by allelic replacement introducing a 1-bp deletion early in the papG gene. In cynomolgus monkeys, DS17 and DS17-8 were equally able to cause bladder infection, whereas only the wild-type strain DS17 could cause pyelonephritis as monitored by bacteriological, functional, and histopathological criteria. Since DS17, but not DS17-8, adheres to renal tissue, these data underscore the critical role of microbial adherence to host tissues in infectious disease and strongly suggest that the PapG tip adhesin of P-fimbriae is essential in the pathogenesis of human kidney infection.

The amino-terminal domain of the P-pilus adhesin determines receptor specificity.

Pyelonephritic isolates of Escherichia coli commonly express P-pili, which mediate bacterial attachment to glycolipids on epithelial cell surfaces. Three classes of P-pili have been defined, based on varying specificity for galabiose-containing glycolipids. Variation in adhesive capacity is correlated with a shift in preferred host, suggesting that host tropism depends largely on detailed specificity for the globoseries glycolipids. In this study we examined the importance of the PapG adhesin in determining receptor specificity. Translational fusions were constructed between the amino-terminus of the PapG adhesin from each of the three pilus classes and a reporter protein. The binding specificity of the purified fusion proteins in vitro was identical to that seen with whole bacteria. Adherence of intact bacteria to cultured kidney cells was markedly reduced by a monoclonal antibody specific for the Class III adhesin (previously denoted PrsG), confirming the importance of the amino-terminus of PapG in mediating attachment to a receptor when presented on the eukaryotic cell surface. These results suggest that the detailed receptor specificity resides solely within the amino-terminus of the PapG adhesin and is independent of the complex pilus architecture.

Sequence changes in the pilus subunit lead to tropism variation of Neisseria gonorrhoeae to human tissue.

Pili of Neisseria gonorrhoeae are correlated with increased bacterial attachment to epithelial cells and undergo both phase and antigenic variation. Phase variation of gonococcal pili can be brought about by recombination events in the pilin structural gene, pilE, or by the on/off switch in expression of PilC, a pilus biogenesis protein for which two loci exist. We have studied the binding to epithelial cell lines and to fixed tissue sections of N. gonorrhoeae MS11 derivatives and mutants carrying structurally defined PilE and PilC proteins. In situ binding studies of N. gonorrhoeae to formalin-fixed tissue sections resulted in a binding pattern similar to that obtained using viable epithelial cell lines of different origin. Piliated gonococcal clones, containing different pilE sequences, varied dramatically from one another in their efficiencies at binding to corneal and conjunctival tissue, but bound equally well to cervical and endometrial tissues. Further, the binding data suggested that PilC expression by itself, i.e. without pili, cannot confer bacterial binding and that expression of either PilC1 or PilC2 does not confer different binding properties to the bacterial cells. Possible receptors for piliated gonococci were expressed in human tissues, such as cervix, endometrium, cornea, intestine, stomach, mid-brain and meninges, but not in human kidney. Pretreatment of the target tissues with Proteinase K decreased the gonococcal binding dramatically, whereas pretreatment with neuraminidase and meta-periodate, which cleave carbon-carbon linkages between vicinal hydroxyl groups in carbohydrates, did not affect attachment of gonococci. These data argue that pilus-dependent attachment of N. gonorrhoeae to human tissue may be mediated by a eukaryotic receptor having protein characteristics, and that the pilus subunit sequence may play an important role in the interaction with human cornea.

Pathological significance and molecular characterization of the vacuolating toxin gene of Helicobacter pylori.

Some strains of Helicobacter pylori are known to produce an extracellular cytotoxin that causes vacuolization in various mammalian cells. In this study, we found that concentrated culture supernatants from four Helicobacter strains isolated from patients infected with the bacterium, but having normal gastric mucosa, lacked cytotoxic activity. We also show that a higher percentage of strains isolated from patients with polymorphonuclear leukocyte infiltration of gastric mucosa are toxin positive (78%) versus those isolated from patients lacking such infiltration (33%). In addition to examining the relationship between pathology and cytotoxic activity, we used the previously published N-terminal sequence of the protein to clone and characterize vacA, the structural gene encoding the cytotoxin. Briefly, three oligonucleotides capable of encoding the first nine amino acids corresponding to the sense strand and four oligonucleotides corresponding to the noncoding strand of the last seven known amino acids of the cytotoxin protein were made. They were used in all 12 possible combinations in 12 different PCR reactions, with DNA from a cytotoxin-positive strain as template. In four combinations, the expected 69-bp fragment was seen. The sequence of this 69-bp fragment confirmed that it encoded the known N-terminal sequence of the cytotoxin. This gene is capable of encoding a 136-kDa protein with a 33-amino-acid signal peptide, whereas the purified cytotoxin is only 87 kDa, suggesting processing in the C-terminal region of the protein. A single copy of the vacA gene encodes the cytotoxin in H. pylori. Consequently, the insertion of a kanamycin resistance marker in the vacA gene produced an isogenic mutant lacking the cytotoxic activity. This mutant provides genetic evidence that vacA encodes the cytotoxin. Sequence analysis of the DNA adjacent to the vacA gene demonstrated that this gene is next to a putative cysteinyl tRNA synthetase gene. From the sequence arrangement, we predict that there are no other genes transcribed together with vacA. We also show that five of seven cytotoxin-negative strains examined still carry the sequences encoding it whereas the other two have suffered a deletion of the vacA gene. We further show that in at least one cytotoxin-negative but vacA-positive strain (MO19), there are variations in the length of the vacA gene that could explain the cytotoxin-negative phenotype in this strain.

Host-specificity of uropathogenic Escherichia coli depends on differences in binding specificity to Gal alpha 1-4Gal-containing isoreceptors.

Four G adhesins, cloned from uropathogenic Escherichia coli strains, were examined for binding to glycolipids and various eukaryotic cells. PapGAD110 and PapGIA2 showed virtually identical binding patterns to Gal alpha 1-4Gal-containing glycolipids, while PapGJ96 differed slightly and PrsGJ96 markedly with respect to the effect of neighbouring groups on the binding. Their hemagglutination patterns confirmed the existence of three receptor-binding specificities. While the PapG adhesins bound to uroepithelial cells from man (T24) but not to those from the dog (MDCK II), the reverse was true of PrsG. These binding patterns were largely explained by the absence or presence of appropriate glycolipid isoreceptors, although the inability of the PapG adhesins to bind MDCK II cells was attributed to an inappropriate presentation of their receptor epitopes. The high prevalence of PrsG-like specificities observed among wild-type dog uropathogenic E. coli isolates, together with the determined isoreceptor composition of human and dog kidney target tissues, suggest variation in receptor specificity as a mechanism for shifting host specificity, and that this variation has evolved in response to the topography of the host cellular receptors. The receptor-binding half proposed for the predicted amino acid sequences of the four G adhesins and the corresponding adhesin of one of the dog E. coli isolates varied considerably among the three receptor-binding groups of adhesins, but only little within each group.