Micro Ch 14
Neisseriae: Gonococcus and Meningococcus
Key Concepts
 Pathogens: Neisseria gonorrhoeae (gonococcus) and Neisseria meningitides (meningococcus); both Gramdiplococci that don’t have niche outside human host
 Encounter: may be carried asymptomatically in genital tract (gonococcus) or nasopharynx (meningococcus)
 Entry: N. gonorrhoeae is STD and can lead to PID in women and epididymitis in men; N. meningitides spread
from person to person by respiratory droplets (causes septicemia and meningitis)
 Spread and Multiplication: both microbes colonize mucosa by means of pilus and replicate there
o Gonococci produce IgA protease as protection against Ig surveillance on mucosal epithelium
o Surface structures of both pathogens can undergo phase variation and antigenic variation, enabling
them to avoid immune detection
o Both can enter bloodstream; only meningococci produces capsule that protects from neutrophil attack
o Some gonococci serum resistant and can spread in blood
 Damage: localized gonococcal infection can damage GU epithelium, cause urethral discharge of pus, and lead to
urinary pain; meningococcal septicemia can cause disseminated intravascular coagulation and meningitis
 Diagnosis: characteristic Gram stain from genital tract or CSF diagnostic; Neisseria species require chocolate agar
o CSF and blood cultures used to diagnose meningococcal infection
o PCR-based identification widely used for screening
 Treatment and Prevention: both require antibiotics; resistance is concern w/gonococci
o Meningococcal vaccine – mixture of all capsule types except serogroup B
 Vaccines against serogroup B meningococcus target protein antigens
Biology
 Tubal scarring w/gonococcal PID can lead to ectopic pregnancy and/or infertility
 Rarely, localized gonococcal infection can invade bloodstream and cause acute dermatitis-arthritis-tenosynovitis
(inflammation of tendons) syndrome called disseminated gonococcal infection (DGI)
 Complement membrane attack complex of late complement components can lyse most neisseriae
 Meningococci shed large amounts of outer membrane material; membrane blebs contain LPS (endotoxin; also
called lipooligosaccharide, or LOS, because Neisseria lacks O antigen)
o LPS induces release into bloodstream or CSF of TNF-α (elicits systemic signs of meningococcemia,
disseminated intravascular coagulation (DIC), and shock)
 Neisseria are facultative anaerobes that can use nitrite as electron acceptor to grow anaerobically
o Fragile; may not survive for long outside human hosts; only source of infection is a person (not object)
o When initially cultured, grow best in atmosphere w/increased CO2 (candle jar); needs chocolate agar
o Certain strains can cause uncomplicated cervicitis or urethritis, PID, or DGI
Encounter and Entry
 Prevalence of asymptomatic carriage greater among women
 Case-contact tracing – test all known sexual contacts of patient
 Once gonococci introduced into vagina or urethral mucosa of either gender, they attach to epithelial cells of
distal urethra or cervix and multiply
o Gonococci possess pili, surface proteins, and LOS that help them attach to host cells
 Pili and gonococcal surface proteins immunodominant (well recognized by immune system); also highly variable
in structure, so they are ineffective targets; antibodies don’t protect
 Gonococci may or may not be taken up by neutrophils, depending on type of outer membrane proteins they
express; some outer membrane proteins (colony Opa proteins) help them get engulfed by neutrophils
o Gonococci lacking Opa proteins commonly associated w/PID, DGI, and arthritis
Alteration of Gene Expression by DNA Rearrangements
 In some cases, evasion of specific host immune responses involves antigenic variation (results in changes in
composition or structure of predominant surface molecules)
o Genetic rearrangements take place randomly and at high frequency in bacterial population; new
variants selected for and emerge by virtue of escape from antibody-mediated immune mechanisms
o In gonorrhea, repertoire of new antigenic types so great that protective immunity rarely develops
 In microbes, antigenic variation can result from reassortment and recombination of duplicated gene segments
(analogous to way Ig made)
 Gonococcal chromosome contains single copy of complete pilin gene (structural protein polymerized to form
pili); pile gene; chromosome contains 10-15 copies of variant-encoding pilin genes, all truncated at 5’ ends and
lacking transcriptional promoter elements, as well as sequences specifying N-terminus part of pilin (pilS loci)
o Antigenic variation occurs when genetic info from nonfunctional alleles transferred to complete pilin
gene locus by homologous recombination
o Diversification higher because small stretches of pilS sequence can be recombined into expression locus
resulting in chimeric pilin types – occurs through gene conversion (pilS alleles act as donors of new
genetic info but are not altered themselves)
 Phase variation – expression of particular gene product turned on or off at high frequency
o Turned off by inversion of DNA segment that has gene promoter (type I fimbriae expression in E. coli)
 In on state, promoter oriented so transcription of fimA can take place
 Also works in flagellar types of Salmonella and pilus expression in Gram- pathogens
o Turned off by short nucleotide repeats at 5’ ends of genes; repeats readily gained or lost as consequence
of strand misalignment during normal DNA replication and repair (slipped strand mispairing)
 Disrupts integrity of gene’s translational reading frame
 N. gonorrhoeae uses this mechanism to change expression of virulence-associated Opa proteins
 Multiple copies of complete opa genes scattered throughout genome, and each
contains repeats of CTCTT in 5’ end of reading frame; gain or loss alters translational
reading frame of gene and determines whether intact protein made
 Controls expression of gonococcal and meningococcal surface proteins and oscillates expression
of biosynthetic genes for gonococcal and meningococcal LOS, resulting in structural variability
o Slipped strand mispairing can disrupt gene expression when it occurs in promoter element of gene;
binding by RNA polymerase to initiate transcription requires precise positioning of enzyme onto DNA by
recognizing 2 elements spaced appropriately
 Spacing between elements may change due to slipped strand mispairing, reducing efficiency
with which RNA polymerase binds and amount of expression of that gene
Spread and Multiplication
 After colonizing mucosal cell surface, gonococci multiply rapidly and are shed into genital secretions
 Genital mucosal secretions contain 3 types of IgG and IgA1 and IgA2; IgG indicates leakage of antibody from
serum onto mucosal surface; IgA actively secreted into lumen of genital tract
o Gonococci produce extracellular protease that specifically cleaves IgA1 in hinge region; because Fc
region is portion recognized by phagocytes, less likely to be taken up by WBCs
 When gonococci exposed to fallopian tube sections
o Gonococci attach to microvilli of nonciliated cells
o Motility of ciliated cells slow and ultimately ceases; ciliary activity important in moving fertilized egg
from fallopian tube into uterus (also flushes mucus and bacteria from mucosal surfaces)
o Ciliated cells die and are selectively sloughed from epithelial surface; doesn’t require intact organisms
and can be elicited by gonococcal LPS or peptidoglycan fragments
o Through cascade of events initiated by gonococcus, microvilli of nonciliated cells (acting as pseudopodia)
engulf bacteria; gonococci internalized by parasite-directed endocytosis
o Gonococci transported to interior of cell in phagocytic vacuoles that coalesce; gonococci multiply in here
o Gonococci can be transported to base of nonciliated cells where bacteria-laden vacuoles fuse w/BM
o Phagocytic vacuoles discharge gonococci into subepithelial CT; from there, organisms cause local
inflammation or enter blood vessels to cause disseminated disease
 In primary cervical cells, pilus-mediated association w/CR3 may lead to stimulation of cellular uptake, which
induces series of downstream events, leading to epithelial cell colonization
o Pilus-CR3 association diminishes inflammatory response by cells (asymptomatic colonization)
Gonococci Damage

Gonococci don’t secrete exotoxins, so damage caused by LPS and other components of bacterial cell wall
(peptidoglycan); both LPS and peptidoglycan induce production of TNF-α (cause sloughing of ciliated cells from
fallopian tube mucosa) by human cells
 Nonciliated epithelial cells containing gonococci may lyse, releasing cellular tissue factors that mediate further
inflammation
o Inflammatory response in male urethra responsible for local Sx (dysuria and urethral discharge of pus)
 Urethral discharge tends to be more copious, thick, and greenish yellow; pain more intense
o Women can experience dysuria, dyspareunia, discharge, or genital discomfort
 Major targets for antibodies are LOS and protein I (on outer membrane)
o Gonococci become serum resistant when LOS altered by addition of terminal sialic acid; because sialic
acid negatively charged and surface component of cells, it may camouflage organisms and protect them
from antibodies responsible for serum killing
o Serum resistance in strains associated w/DGI occurs by binding both C4b-binding protein and factor H (2
negative regulators of complement activation)
 Serum-resistant strains more sensitivity to penicillin and have specific nutritional requirements
o Manifestations of DGI include pustular skin lesions w/surrounding red areola, tenosynovitis, and frank
infections of joints (suppurative arthritis)
o Despite appropriate diagnostic attempts, cultures of blood, joint fluid, or skin lesions sterile
 Gonococci may be present in numbers too low to be detectable in culture
 Nutritional requirements of organisms inhibit or not grow using normal culture conditions
 In cases of tenosynovitis, fragments of murein or immune complexes consisting of gonococcal
antigens and host antibodies, rather than viable gonococci, deposited in synovial tissue and
causes local inflammation
 Repeated infections of urethra in men can lead to scarring and stricture of urethra
 Symptoms of cervicitis – cervical discharge, bleeding, and pain
 DGI occurs predominantly in women
 Prompt treatment decreases risk of ascending or disseminated infection and resulting sequelae
 When gonococci reach bloodstream in most individuals, they are killed by host defenses; even serum-resistant
strains don’t grow appreciably in circulation (may reach other organs)
Meningococci Damage
 More usual outcome of exposure is colonization of nasopharynx w/no local symptoms or systemic consequences
 Patients susceptible to meningococcemia or meningococcal meningitis deficient in bactericidal anticapsular
antibodies or in activity of complement cascade
 Individuals w/capsule-specific antibodies or antibodies directed at other surface components resist ability of
meningococcus to invade and multiply in bloodstream
 If not killed by bactericidal activity or phagocytes in bloodstream, meningococci multiply rapidly, reaching blood
titers among highest known for any bacterium
o Smear of buffy coat (layer containing WBCs when whole blood centrifuged) shows organisms
 Entry into human bloodstream can lead to systemic disease marked by purpura fulminans and DIC
w/generalized skin manifestations (petechiae and ecchymoses), meningitis, shock, and death
o Systemic signs direct result of ability of meningococcus to survive and multiply in bloodstream
o DIC accompanied by shock, fever, and other responses to endotoxin or other cell components medated
by cytokines (TNF-α and IL-1)
o Likelihood of death or neurologic damage proportional to levels of endotoxin and elevation in serum
and CSF of TNF-α concentrations
 Meningococcal disease effective prevented by vaccines containing capsular polysaccharide
o Capsule of serogroup B strains is homopolymer of sialic acid identical to human sialic acid polymers
Diagnosis
 Neutrophils containing Gram- diplococci in cervical or urethral secretions evidence of gonococcal infection
o Positive microscopic findings justify beginning antibiotic therapy before results of cultures known
o Gram stain of urethral exudate of men more sensitive than Gram stain of cervical exudate in women
 Cervical Gram stain may be negative, despite positive culture result

Positive Gram stain of cervical secretions confirmatory evidence of active gonorrhea in
symptomatic women; routine Gram stains of secretions from asymptomatic women not useful
 Findings of gonorrhea must be confirmed by culturing or using genetic probes
 2 reasons to culture: to be completely certain of identity of infecting microorganism and to obtain isolate for
antimicrobial susceptibility testing
 Nucleic acid-based detection tests increasingly used for purposes of screening asymptomatic patients at risk
 Grows on chocolate agar, Thayer-Martin medium, and Martin-Lewis medium (each contains antibiotics to inhibit
other bacterial species and yeasts found in genital tract)
o Specimens should always be cultured on chocolate agar w/antibiotics to inhibit normal microbiota
 All members of Neisseria possess cytochrome oxidase that can catalyze color change in presence of specific
reagent; if Gram- diplococcus is oxidase positive, it is Neisseria or close relative
o To determine N. gonorrhoeae from other species, microbio lab determines pattern of fermentation of
various sugars
 Gonococci utilize glucose, but not maltose or sucrose
 Meningococci utilize both glucose and maltose
Treatment
 Relatively high proportion of gonococci have plasmid that encodes β-lactamase; these cause serious locally
invasive diseases (PID and DGIs)
o Recommended initial therapy is β-lactamase-resistant cephalosporin (cefixime or ceftriaxone)
o Gonococci resistant to quinolones in SE Asia and North America
 Patients infected w/N. gonorrhoeae often coinfected w/Chlamydia trachomatis; treat them w/antichlamydial
agent as well (azithromycin or doxycycline)
o Infection w/N. gonorrhoeae is risk factor for HIV transmission; treatment for gonococcal infection
among some groups has led to concomitant decrease in rates of HIV transmission
 Treatment of meningococcal infection by IV antibiotics indicated
Prevention
 Repeat gonococcal infections common among individuals w/repeat exposures
 Prevention of meningococcal infections primarily approached w/treatment w/antibiotics (rifampin or
ciprofloxacin) of close contacts of cases and targeted mass vaccination in outbreak settings where indicated
o Polysaccharide conjugate vaccine (MCV4) for prevention of meningococcal disease resulting from
serogroups A, C, Y, and W-135 licensed for use in individuals age 2-55
o MenZBTM – vaccine for noncapsular antigens for serogroup B; targets outer membrane proteins; used
in New Zealand for individuals under age 20