Lipooligosaccharide-DeficientNeisseria meningitidisShows Altered Pilus-Associated Characteristics

Abstract

Molecular interaction between host mucosal surfaces and outer membrane components of microbes is crucial in the infection process. The outer membrane of pathogenic Neisseria contains surface molecules such as pili, PilC, and Opa and a monolayer of lipooligosaccharide (LOS), all of which are involved in the interaction with host cells. Pili mediate the initial attachment to human epithelial cells, which is followed by tight contact between bacteria and the eucaryotic cells, leading to bacterial invasion. To further examine the basis for bacterium-host cell contact, we constructed an LOS-deficient Neisseria meningitidis serogroup C mutant. LOS deficiency was without exception accompanied by altered colony opacity and morphology, which most likely represented an "on" switch for Opa540 expression, and by reduced levels of the iron-regulated proteins FetA and FbpA. We show here that LOS is essential for pilus-associated adherence but dispensable for fiber formation and twitching motility. The absence of attachment to epithelial cells could not be attributed to altered levels of piliation or defects in the pilus adhesion phenotype. Further, LOS mutants do not invade host cells and have lost the natural competence for genetic transformation.The mucosal epithelial cell barrier is the first physical defense encountered by bacteria upon contact with the human host. Immediately upon adherence of bacteria, the epithelial cells initiate a nonspecific or innate immune response by production of proinflammatory factors. The inflammatory response to bacterial infections plays an important role in detection and elimination of invading microorganisms. Various components of the bacterial cell wall such as peptidoglycan, lipoteichoic acid, lipoproteins, and lipopolysaccharide (LPS) are capable of activating the proinflammatory reaction. For gram-negative bacteria, LPS is the dominant trigger of the systemic inflammatory response. Recently, Toll-like receptors (TLRs) have been implicated in host responses to bacterial pathogens. Specifically, TLR4 mediates LPS responses whereas TLR2 plays a broader role in the recognition of a variety of bacteria and bacterial antigens (41). The host inflammatory response in meningococcal sepsis is generally believed to be induced by lipooligosaccharide (LOS).LOS of Neisseria meningitidis (meningococcus) is an endotoxin that is structurally distinct from LPS of enteric gramnegative bacteria (21, 33). Unlike most enteric LPSs, meningococcal LOS lacks O-antigen and possesses relatively short polysaccharides, only two to five sugar residues, attached to the meningococcal LOS inner core. LOS is an amphipathic molecule that consists of a hydrophilic carbohydrate portion and a hydrophobic lipid A portion that anchors the LOS to the outer membrane. Endotoxic shock is mediated by the lipid A portion of LOS and is characterized by activation of macrophages and production of a diverse array of cytokines, including those that act as chemoattractants for other leukocytes. Meningococcal septic shock is a direct r...

Roles of 3-Deoxy- d - manno -2-Octulosonic Acid Transferase from Moraxella catarrhalis in Lipooligosaccharide Biosynthesis and Virulence

“…Bacterial adherence to the surface of epithelial cells plays a critical role in colonization and is believed to be the first step in the pathogenesis of microbial infections. It has been reported that several LOSs from respiratory tract bacteria are associated with bacterial adherence (2,18,20,41,44). Fitzgerald et al showed that the bacterial adherence of M. catarrhalis might be mediated by carbohydrate moieties (12).…”

Identification of an outer membrane protein required for the transport of lipopolysaccharide to the bacterial cell surface

“…LPS is an essential OM component in E. coli, but not in Neisseria meningitidis, which can exist without LPS as demonstrated by the viability of lpxA mutants, in which the gene involved in the first step in LPS biosynthesis is disrupted (9,10). These lpxA mutants are completely devoid of LPS.…”

The LptD Chaperone LptE Is Not Directly Involved in Lipopolysaccharide Transport in Neisseria meningitidis

“…Apparently, the lpt mutations render the cells less competent. This is likely related to their low LPS content, because a meningococcal lpxA mutant, which does not produce any LPS, was also reported to be severely impaired in competence (29). Therefore, we created conditional strains by first introducing a plasmid containing the relevant gene under IPTG control in strain HB-1, followed by inactivation of the chromosomal gene copy in the presence of IPTG.…”