Structural and functional modulation of gonococcal surface proteins

Bacterial cell wall research in Tübingen: a brief historical account

Research in Tübingen on bacterial cell walls began in 1951 and continues to this day. The studies over the decades reflect the development in the field, which was strongly influenced by the design of suitable biochemical and genetic methods used to unravel the highly complex envelope structure. At the beginning of this period, improper crude extraction and solubilization methods were employed in an attempt to isolate pure components. Nevertheless, progress was steady and culminated in major insights into the structure and function of individual cell wall components and the cell wall as a whole. The "cell wall" has various definitions. In this short overview, the term includes the cell wall of gram-positive bacteria in the strict sense, and also the outer membrane, the murein (peptidoglycan) and the outer membrane of gram-negative bacteria and the cytoplasmic membranes.

Phenotypic variants of meningococci and their potential in phagocytic interactions: the influence of opacity proteins, pili, PilC and surface sialic acids

In previous studies we have examined the roles of meningococcal surface structures (capsule, lipopolysaccharides, pili and opacity proteins: Opa and Opc) in bacterial interactions with human epithelial, endothelial and mononuclear phagocytic cells. In the current investigations, using defined derivatives of a serogroup A strain C751 and a serogroup B strain MC58, we studied the roles of these structures with human polymorphonuclear phagocytes (PMN). In addition, we examined the potential influence of the pilus-associated protein, PilC, previously known to affect epithelial cell interactions. The data show, that, as with monocytes, opacity proteins affect bacterial interactions with PMN and require surface sialic acids (on capsule and LPS) to be down-modulated in order to function. Also, in contrast to their role in human epithelial and endothelial adherence, neither pili nor PilC expression had any effect on phagocytic cell interactions with respect to induction of chemiluminescence as well as phagocytic killing. Examination of the relative influence of Opa and Opc indicated that Opa proteins are more effective than Opc in PMN interactions whereas the reverse was the case with monocytes. These results suggest that Opa and Opc mediate interactions with phagocytic cells via distinct mechanisms. Observations presented here and reported previously collectively show that the structural requirements of meningococci for interacting with phagocytes, in the absence of opsonins, are present in the phenotype which is often isolated from the nasopharynx (asialylated, piliated, Opa/Opc+) whereas the phenotype prevalent in the blood (sialyted, piliated, Opa/Opc+) retains the ability to adhere to endothelial cells (via pili) but appears to be refractory to interactions with phagocytic cells.

Interaction of pathogenic Neisseria with host defenses. What happens in vivo?

N. gonorrhoeae initiates infection by adhering to and invading columnar epithelial cells. Over time these activities often induce inflammation, with the influx of neutrophils and serum into the urethral lumen, cervical os, conjunctiva, and the like. At least some of these infected niches contain CMP-NANA (cytidine monophospho-N-acetyl neuraminic acid, also called CMP-sialic), contain sialylated gonococci, and are relatively or strictly anaerobic due to neutrophil and gonococcal metabolism and to the site of disease, that is, the peritoneal cavity. Gonococci thus encounter environmental conditions, reagents, and substrates in the human body that are not normally present in vitro. Knapp and Clark were the first to successfully grow gonococci anaerobically in an easily reproducible system, allowing researchers to begin to investigate in vitro the effects of anaerobiosis on gonococcal virulence traits. As a result of a series of elegant and in depth studies, Smith and Parsons and their colleagues showed that growth in CMP-NANA confers on the gonococcus a high degree of phenotypic (readily reversible) serum resistance and that CMP-NANA is available in vivo at sites of gonococcal infection and disease; gonococci become covalently coated with sialic acid and they become serum resistant (reviewed in refs. 8-10). Given that gonococci growing in the absence of oxygen or in the presence of CMP-NANA probably more closely resemble gonococci growing inside the human host, we studied several possible virulence traits of gonococci cultivated under these conditions. We first observed that anaerobic growth (in the absence of CMP-NANA) increases gonococcal resistance to killing by low (but not high) concentrations of normal human serum. We also asked whether anaerobic growth affected gonococcal association with host cells. Contrary to the effects on serum killing, anaerobic growth (in the absence of CMP-NANA) does not appear to affect the ability of gonococci (expressing certain adhesive outer membrane proteins called Opa proteins) to bind to and enter human epithelial cell lines or to bind to or resist killing by human neutrophils. The results from studies investigating the modulatory role of CMP-NANA were more striking. Growth in CMP-NANA dramatically inhibits the adherence of Opa+ gonococci to human neutrophils. It does not, however, appear to significantly decrease their sensitivity to phagocytic killing or to in vitro killing by lysosomal contents (aqueous extracts of human neutrophil granules).(ABSTRACT TRUNCATED AT 400 WORDS)

Dynamics of the bacterial genome: deletions and integrations as mechanisms of bacterial virulence modulation

Bacterial virulence is a multifactorial phenomenon, arising from the coordinate action of special abilities of the infectious agents, termed as virulence factors, which is crucial for the infectious process. The genetic determinants encoding those factors are termed virulence associated genes, which can be located on the bacterial chromosome or on extrachromosomal elements (plasmids). Various examples have repeatedly demonstrated that bacterial genome dynamics contributes to virulence modulation. Strikingly, a reduced in vivo virulence of the pathogens was shown to be due to the spontaneous loss of virulence associated genes. The deletion events can involve chromosomal as well as plasmid regions. Also integration of plasmids into the chromosome are considered as dynamic events. The new genetic location of the formerly plasmid encoded virulence associated genes can result in an alteration of virulence expression.

Growth of Neisseria gonorrhoeae in CMP-N-acetylneuraminic acid inhibits nonopsonic (opacity-associated outer membrane protein-mediated) interactions with human neutrophils

Gonococci possessing certain opacity-associated (Opa) outer membrane proteins adhere to and are phagocytosed by human neutrophils in the absence of serum. Recently, it has been shown that serum-sensitive strains of Neisseria gonorrhoeae possessing the appropriate lipooligosaccharide phenotype become serum resistant when grown in the presence of CMP-N-acetylneuraminic acid (CMP-NANA) because of sialylation of their lipooligosaccharide. We investigated whether such sialylation affects nonopsonic (antibody- and complement-independent) interactions of gonococci with human neutrophils in vitro. We grew Opa+ gonococci in the presence of up to 50 micrograms of CMP-NANA per ml, incubated them with neutrophils in vitro, and measured their abilities to adhere to neutrophils, stimulate neutrophil luminol-dependent chemiluminescence (LDCL), and be phagocytically killed by neutrophils. Growth in CMP-NANA dramatically inhibited (in a dose-dependent manner) the ability of Opa+ gonococci to adhere to neutrophils and stimulate neutrophil LDCL. Growth of Opa+ gonococci in 50 micrograms of CMP-NANA per ml appeared to delay, but did not inhibit, their killing by neutrophils. Sialidase treatment of sialylated Opa+ gonococci, i.e., gonococci grown with CMP-NANA, totally restored their abilities to adhere to neutrophils and stimulate neutrophil LDCL. Opa- gonococci grown in the presence of 50 micrograms of CMP-NANA per ml and opsonized with fresh human serum bound to neutrophils only about 30% less efficiently than did Opa- gonococci grown without CMP-NANA and opsonized. The results of our studies show that sialylated Opa+ gonococci have dramatically reduced nonopsonic interactions with neutrophils. Some gonococcal strains may resist killing by human neutrophils in vivo by such a mechanism.

Prevalence of gene sequences coding for hypervariable regions of Opa (protein II) in Neisseria gonorrhoeae

Opas (protein IIs) are a family of surface-exposed proteins of Neisseria gonorrhoeae. Each strain of N. gonorrhoeae has multiple (10-11) genes encoding for Opas. Identifiable elements in opa genes include the coding repeat within the signal sequence, conserve 5' and 3' regions, and hypervariable regions (HV1 and HV2) located within the structural gene. N. gonorrhoeae strains appear to have many biological properties in common that are either HV-region-mediated or associated with the presence of specific HV regions, suggesting that HV regions could be found in many clinical isolates. Oligonucleotides from three source strains representing three conserved regions of opa, 12 HV1 regions, and 14 HV2 regions were used by dot blot analysis to probe 120 clinical isolates of N. gonorrhoeae. The probe for the coding repeat hybridized to all 120 strains, the 3' conserved-region probe reacted with 98% of the strains, and the 5' conserved-region probe with 90% of the strains. Nine HV1 probes hybridized to 3.3-39.2% of the strains, and 13 of the HV2 probes hybridized to 1.7-25% of the isolates. Analysis of the number of probes that hybridized to each of the isolates showed that 19% did not hybridize with any of the HV1 probes and 25% did not hybridize with any of the HV2 probes. Approximately three-quarters of the isolates hybridized with one, two or three of the HV1 probes or one, two or three of the HV2 probes; 89% of the isolates hybridized to least one HV1 or one HV2 probe. The data indicate that some genes encoding HV regions of N. gonorrhoeae Opa proteins are widely distributed in nature.

Virulence determinants of Escherichia coli O6 extraintestinal isolates analysed by Southern hybridizations and DNA long range mapping techniques

A total of 16 Escherichia coli O6 strains isolated from cases of extraintestinal infections were analysed for the genetic presence and phenotypic expression of fimbrial adhesins (P, S/FIC, type 1), aerobactin and hemolysin. In addition restriction fragment length polymorphisms (RFLPs) of Xbal-cleaved genomic DNA of seven selected strains, separated by orthogonal field alternation gel electrophoresis (OFAGE) were determined and virulence-associated DNA probes were used for Southern hybridization studies of the Xbal-cleaved genomic DNAs. The virulence characteristics and hybridization patterns obtained differed between the various isolates. In three isolates hemolysin genes and P fimbrial determinants were located on the same Xbal fragments. Furthermore, multiple copies of FIC determinants (foc) could be detected in two strains. Our data show that the new technique of pulse field electrophoresis together with Southern hybridization represents a powerful tool for the genetic analysis of pathogenic bacteria.

Opa (protein II) influences gonococcal organization in colonies, surface appearance, size and attachment to human fallopian tube tissues

Opa-expressing variants of Neisseria gonorrhoeae strain F62-SF and an Opa- variant, all non-piliated, were examined for differences in the interaction of the bacteria within colonies and in attachment to and damage of human fallopian tube mucosa. Expression of certain Opas was associated with the formation of transparent colonies where the bacteria were tightly packed and evenly spaced within the colonies. Expression of other Opas was associated with the formation of opaque colonies where the gonococci were less tightly packed and were unevenly spaced. Distinct differences in the size of the gonococci and in their surface characteristics were dependent upon the Opa being expressed. Certain Opas were associated with gonococci that had significantly larger cross-sectional areas and bigger perimeters. Scanning electron microscopy showed that OpaC- and OpaD-containing variants yielded greater mucosal damage than OpaB-containing and Opa- variants with the least damage caused by the OpaA-containing variant (clumped bacteria from dark opaque friable colonies). The mucosal damage after 60 min incubation included shortening and decreased numbers of microvilli on non-ciliated cells and invagination and sloughing of ciliated cells. Differences in the interactions of gonococci within colonies and in attachment to fallopian tube mucosa and damage to the mucosal cells occurred with different Opa-expressing variants of N. gonorrhoeae strain F62-SF.