The pathogenic Neisseria species are capable of utilizing transferrin as their sole source of iron. A neisserial transferrin receptor has been identified and its characteristics defined; however, the biochemical identities of proteins which are required for transferrin receptor function have not yet been determined. We The ability of many human pathogens to cause infection is dependent in part on their ability to acquire iron from their host. Unlike the members of the family Enterobacteriaceae, the pathogenic Neisseria species do not produce and secrete soluble siderophores to compete with host iron-binding proteins such as transferrin (Tf) and lactoferrin (Lf), but instead can acquire iron directly from these proteins (32, 33). Utilization requires direct contact between Tf and the cell membrane (1,30,53), which implies the presence of specific receptors for these iron-binding proteins. Recent evidence suggests that other human pathogens such as Haemophilus influenzae and Bordetella pertussis also possess specific receptors for Tf (43,48).Tf receptor function has been characterized in the pathogenic Neisseria species (8,27,50,58). Tf utilization and binding is iron repressible (27,50,53,60)

The method of shuttle mutagenesis has been extended to Neisseria gonorrhoeae. We have constructed a defective mini-Tn3 derivative that encodes chloramphenicol resistance in both N. gonorrhoeae and Escherichia coli and selected for mutations in the chloramphenicol resistance gene that express higher levels of antibiotic resistance in N. gonorrhoeae. Isogenic N. gonorrhoeae strains that differ only in pilin expression were constructed and used to test the effect of pilin null mutations on DNA transformation competence.

We recently identified a set of mammalian cell receptors for Neisseria gonorrhoeae that are glycolipids.These receptors, lactosylceramide Glc(J81-1)Cerj, gangliotriosylceramide [GalNAc(Pl14)Gal(P14)Glc(P81-1)Cer], and gangliotetraosylceramide [Gal(f31-3)GalNAc(131-4)Gal(P14)Glc(,81-1)CerJ, were shown to be specifically bound by a gonococcal outer membrane protein distinct from pilin and protein II. Here we report the isolation of the gene encoding the gangliotetraosylceramide-binding adhesin from a N. gonorrhoeae MSl1 gene bank in Escherichia coli. Transposon mutagenesis studies in E. coli indicate that the adhesin is a protein with a molecular mass of 36,000 Da. The gene encoding the 36-kDa protein is duplicated in MS11 since two transposon insertiohs were required to abolish expression ofthe gene in this bacterium. This protein is present on the surface of the gonococcus and is not associated with the pilus.The binding of a pathogen to host cells is an important step in most infectious processes. The host cell receptors for several bacterial pathogens have been identified. For example, Escherichia coli strains causing urinary tract infections bind to a digalactoside moiety present in glycolipids (1, 2), and type 1 fimbriated E. coli, also implicated in urinary tract infections, bind to mannose residues in glycoproteins (3). In E. coli strains binding digalactoside, attachment to eukaryotic cells is independent of pilin, the major subunit of the pilus (4). In contrast, attachment of type 1 fimbriated E. coli is dependent on piliation (5). Recent work on digalactosidebinding E. coli demonstrated the presence of a minor protein at the tip of the pilus that binds to the receptor (6). The mannose-binding adhesin on type 1 fimbriae was shown to be present at the tip and along the sides of the pilus fiber (7,8). In addition to these pilus-associated adhesins, a nonpilus-associated surface adhesin responsible for mannoseresistant hemagglutination has been reported in uropathogenic E. coli KS52 (9).Pili have been shown to be important in the attachment of Neisseria gonorrhoeae to human epithelial cells and erythrocytes (10-12). However, recent in vitro studies indicated that both piliated (P+) and nonpiliated (P-) gonococci adhered to and were internalized by tissue culture cells with equal efficiency (13). We recently identified a set ofglycolipid receptors on epithelial cells that are recognized by both P+ and P-N. gonorrhoeae. They share lactose as their core sugar. Two of these, lactosylceramide [LacCer; Gal(, bound to LacCer with a lower affinity in vitro (14). Binding to these receptors was observed to be independent of pilin and protein II expression.A detailed characterization of the gonococcal surface adhesin, which recognizes the glycolipid receptor on host cells, is necessary for an understanding of the attachment process. For this purpose, we developed a thin-layer plate overlay assay for isolating the N. gonorrhoeae gene encoding the GgO4-binding adhesin from a pool of E. coli recombinants. Express...

The pigmented enterobacterium Serratia marcescens, an opportunistic pathogen, shows a striking variation of its red color. Different strains differ greatly both in color and in the frequency with which they produce color variants. Within a strain, the variations occur at constant rates and are reversible. During an investigation of this phenomenon we observed that variation of a 39-kilodalton protein in S. marcescens 274 is closely associated with color variation. Using antibodies to this protein we identified it as being a component of the bacterial flagella. Variation of surface proteins often provides an organism with alternate offense-defense strategies for survival in a challenging environment. The pigment, in association with flagella, may provide such a function for S. marcescens.