two pathogenic species of Neisseria infect only humans: N. meningitidis and N. gonorrhoeae - Ruchira S. Datta

N. meningitidis has 5-10% mortality rate. There exists an incompletely effective vaccine which the people where this is endemic cannot afford. - Ruchira S. Datta

Gonorrhoea has become resistant to almost all antibiotics now, so the CDC calls it a superbug. #LAMG10 - Ruchira S. Datta

asymptomatic carriage of N. meningitidis: 20-50% - Ruchira S. Datta

asymptomatic carriage of N. gonorrhaea: >5% - Ruchira S. Datta

wanted to study these asymptomatic commensals - Ruchira S. Datta

8 commensal Neisseria species (non-pathogenic) also isolated from humans - Ruchira S. Datta

tree shows commensal Neisseria came first, the two pathogens are relative newcomers - Ruchira S. Datta

170 Neisseria virulence genes; immune evasion, intracellular replication, capsule production - Ruchira S. Datta

many of these are present in commensal Neisseria species, which serve as reservoir of virulence genes - Ruchira S. Datta

Type 4 pilus: Wolfgang & Koomey, EMBO J 19:6408. Used for DNA uptake, attachment, motility - Ruchira S. Datta

assembly extrudes the pilus, and disassembly of pilin retracts the pilus - Ruchira S. Datta

N. gonorrhaea crawl on polyacrymalide pillars, pulling them w/ pili and bending them w/ mechanical force - Ruchira S. Datta

known Type IV pilus biogenesis genes - Ruchira S. Datta

DNA Uptake sequence (DUS) GCCGCCTGAA: Neisseria won't uptake DNA unless this sequence is present - Ruchira S. Datta

these are present in many Neisseria species. variant DUS GTCGTCTGAA used by a couple of species (N sicca and N mucosa), which also is effective for uptake. - Ruchira S. Datta

looked for evidence of horizontal gene transfer using Recombination Detection Program (RDPv3.8). detected recombination breakpoints in 53 of 69 vir genes, with >50% of these involving both commensal and pathogenic species - Ruchira S. Datta

phylogenetic method: make gene trees of the virulence genes, check whether they are topologically different from other gene trees and p-value significance. most disagree. - Ruchira S. Datta

virulence is a dynamic state: there may not be a genetic border separating pathogens and commensals - Ruchira S. Datta

Wu et al New Engl J Med vol 360 2009: Emergence of Ciprofloxacin resistant N meningiditis in N. America. This resistance gene came from a commensal Neisseria species present in throats of contacts. - Ruchira S. Datta

Type IV pili exhibit variation in the antigens they present. Silent copies of pilin genes combine with pilE (pil expression) - Ruchira S. Datta

Pilin antigenic variation occurs in vitro and in vivo, and is thought to be a strategy to evade immune recognition. - Ruchira S. Datta

cell pumps out DNA, autolysis releases the DNA, and the living cell takes up DNA via the Type IV pilus (Tfp) - Ruchira S. Datta

think the silent variant genes have a function, but don't know what - Ruchira S. Datta

commensals undergo limited pilin antigenic variation. how do they avoid our protective antibodies? - Ruchira S. Datta

retraction of the pili extends mechanical force into the cell, triggering many signaling events - Ruchira S. Datta

can trigger apoptotic cell death, which is pro-inflammatory - Ruchira S. Datta

but Tfp triggers anti-apoptotic pathways, activating ERK and preventing release of Cytochrome C and apoptosis - Ruchira S. Datta

Higashi et al showed this involvement in 2007 - Ruchira S. Datta

working hypothesis: Tfp was evolved by commensals to help them colonize silently, and this "cytoprotective" activity helps N. meningitidis and N. gonorrhoea infect asymptomatically - Ruchira S. Datta

differentiate commensal and pathogenic Tfp to look for pathogenic traits? e.g., host signaling - Ruchira S. Datta

Q: how to define commensal vs pathogenic, since many of the "pathogens" are carried asymptomatically? A: do have good tests for species identity. whether it's the cause of, e.g., septicemia, can only infer from lack of other bacteria - Ruchira S. Datta

Jonathan Eisen: any distance cutoff for uptake of the vir genes btw different species? A: haven't looked at that - Ruchira S. Datta