Biofilm formation by the human pathogen Neisseria meningitidis was analyzed. Biofilm-forming meningococcal strains were identified and quantitated by crystal violet staining. Laser scanning confocal microscopy of the meningococcal biofilm revealed variable layers up to 90 m in thickness. A total of 39 meningococcal isolates were studied; 23 were nasopharyngeal-carriage isolates, and 16 were invasive-disease isolates. Thirty percent of carriage isolates and 12.5% of invasive-disease isolates formed biofilms proficiently on a polystyrene surface. Generally, the strains that formed biofilms showed high-level cell surface hydrophobicity, characteristic of strains lacking a capsule. The inhibitory role of capsule in biofilm formation was further confirmed by comparing the biofilm-forming capabilities of a serogroup B wild-type strain of a disease-associated isolate to those of its capsule-deficient mutant (ctrA). Some strains of meningococci form biofilms, and this process is likely important in menigococcal colonization.Bacterial biofilms are sessile bacterial communities that adhere to each other and solid surfaces and are enclosed in an exopolysaccharide matrix (6). Biofilms are the predominant communities of many bacterial species in numerous ecosystems. Formation of biofilms involves participation of the extracellular-matrix and cellular-surface molecules, including membrane proteins. Biofilm formation also requires considerable bacterial energy and resources. The formation of biofilms begins with the attachment of the planktonic cells to a suitable surface, followed by replication and spreading. Eventually, the biofilms mature to differentiated forms. Exopolysaccharides play a key role in the establishment of biofilm architecture (6).In clinical settings, bacteria in biofilms are less susceptible to antimicrobial agents and host immune responses, thereby becoming persistent colonizers or sources of chronic infections (8). Bacteria are released from biofilms as individual planktonic cells or as a result of the sloughing of the biofilms. While many biofilms form on abiotic surfaces such as medical devices, some also develop on living tissues, as in the case of endocarditis or cystic fibrosis (8).Studies of biofilm formation by the Neisseria species are very limited, and most of those species examined have been oral commensals (4,20,24,26,38). Biofilm formation by Neisseria meningitidis, an etiologic agent of epidemic sepsis and bacterial meningitis, has not been documented. Meningococci are isolated from 5 to 10% of the normal population, and the colonization of the human nasopharyngeal mucosal surface by meningococci is the first step of the host-parasite interaction.Successful meningococcal colonization requires initial attachment facilitated by pili and subsequent interaction of other secondary-surface molecules with the host mucosal surface (12,31,36,43).In this study, the formation of the biofilms by N. meningitidis was assessed. In addition, the roles of the bacterial-surface molecules (pilus, capsule, and ...

Several genetic systems that allow the use of iron-protoporphyrin IX (heme) have been described for the pathogenic bacterium Neisseria meningitidis. However, many questions about the process of heme acquisition and utilization remain to be answered. To isolate and analyze unidentified genes that play a role in heme iron uptake and utilization, a Himar1 transposon mutant library was screened in N. meningitidis serogroup A strain IR4162. One locus identified by transposon mutagenesis conferred protection against heme toxicity. A mutant with a deletion in a gene termed ght (gene of hydrophobic agent tolerance) within this locus was susceptible to heme and other hydrophobic agents compared to the parental strain. Transcriptional analysis indicated that ght is cotranscribed with an upstream open reading frame NMA2149. Uncharacterized orthologues of ght were identified in many other gram-negative bacteria. We present genetic evidence for the importance of ght in resistance to hydrophobic agents and its potential role in interaction with other hydrophobic agent resistance mechanisms within N. meningitidis.

It has been proposed that increased phase variation frequencies in Neisseria meningitidis augment transmissibility and invasiveness. A Himar1 mariner transposon mutant library was constructed in serogroup A N. meningitidis and screened for clones with increased phase variation frequencies. Insertions increasing the frequency of slippage events within mononucleotide repeat tracts were identified in three known phase variation-modulating genes (mutS, mutL, and uvrD), as well as six additional loci (pilP, fbpA, fbpB, NMA1233, and two intergenic regions). The implications of these insertion mutations are discussed.

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