What are the general features of Neisseriae (gram reaction, aeration, shape/morphology, motility, capsulation, other structures?)
- Gonococci: unencapsulated
- Meningococci: encapsulated in samples
What are the two Neisseria species responsible for disease in humans? Name of disease?
- Neisseria gonorrhoeae (gonococcus): gonorrhea
- Neisseria meningitidis (meningococcus): meningitis
Where is N. gonorrhoeae typically found within clinical samples?
Inside polymorphonuclear leukocytes (granulocytes)
How is N. gonorrhoeae transmitted? Why?
- During sexual contact (often)
- From infected birth canal (infrequent)
- *highly sensitive to dehydration
What are the virulence factors in N. gonorrhoeae w/ description?
- Pili: enhance attachment to mucosa and resist phagocytosis (only pilated species are virulent)
- Antigentic variation - expression of varied pilin molecules over time via pilin gene recombination
- Lipooligosaccharide (LOS): similar to LPS, but is highly branched, and has an absence of repeating O-antigen subunits
- Outer membrane proteins:
- OMP I and III - Make a porin complex in the outer membrane
- OMP II (opacity protein) - make colonies less translucent, mediates attachment to mucosa (with pili), and undergoes extensive antigenic variation
- IgA protease: cleaves IgA1 (immunolgobulin)
Where does N. gonorrhoeae typically colonize and what are its symptoms? (general)
- Mucosa of the genitourinary tract or rectum
- Typically causes localized infection with pus production immediately (acute infection)
- May lead to tissue invasion, chronic inflammation, and fibrosis
- Females are often asymptomatic and act as reservoirs for infection (chronic infection)
What are the potential disease states caused by N. gonorrhoeae with a brief description/symptoms?
- Genitourinary tract infections:
- males - yellow, purulent urethral discharge. Painful urination.
- females - greenish-yellow cervical discharge. Intermenstrual bleeding. Infertility occurs in ~20% of women (tubal scarring).
- Rectal infections: constipation, painful defecation, purulent discharge
- Pharyngitis: purulent exudate, may mimic mild viral sore throat
- Opthalmia neonatorum: infection of conjuntival sac at birth. Could lead to blindness.
- Disseminated infection: Septicemia is rare, but may result in fever, painful, purulent arthritis, and small pustules on the skin.
What is the most common cause of septic arthritis in adults? Children?
- Adults: gonococcal infection
- Children: S. aureus
Describe the laboratory identification for N. gonorrhoeae (general, culture conditions, and tests)
- Male - finding of neutrophils containing gram-negative diplocci in smear from urethral exudate (not specific)
- Female - positive culture is required to diagnose.
- Culturing conditions: aerobic conditions with CO2 present. Cultures plated promptly for sample integrity.
- Thayer-Martin medium (choc. agar+antibiotics) selects for gonococci.
- All Neisseria are oxidase-positive
- N. gonorrhoeae ferments glucose only
Describe the treatment of N. gonorrhoeae
- >20% of isolates are resistant to penicillin, tetracylcine, cefotoxin, and spectinomycin
- Most strains respond to 3rd generation cephalosporins
When are meningitis outbreaks most common? Why?
- Winter and early spring due to close contact between individuals (schools, institutions, barracks)
- Transmitted through respiratory droplets
What are the virulence factors in N. meningitidis w/ description?
- Capsule: antiphagocytic (most important)
- Pili: allow attachment to the nasopharyngeal mucosa (exists as normal flora for 5-15%)
How are N. meningitidis strains categorized? What are the important types?
- Serogroup: based on the LOS and capsule
- Most infections caused by serogroups A,B,C,W, and Y
- Serogroup A: responsible for massive epidemics (meningitis belt)
- Serogroup B: most common in the US
Describe the epidemiology of N. meningitidis (transmission, risk factors, hosts, and susceptible targets)
- Transmission via inhalation of respiratory droplets (asymptomatic carrier or presymptom patient)
- Risk factors: recent upper-respiratory tract infection, smoking, and complement deficiency
- Humans are the only natural host
- Incidence is highest amongst infants <1 year
What are the potential disease states caused by N. meningitidis with a brief description/symptoms?
- Initially colonizes nasopharynx (asymptomatic)
- In young children organism penetrates epitehlia and spreads through blood (meningococcemia) causing meningitis and/or fulminating septicemia
- purulent meningitis: crosses blood-brain barrier, infects meninges, induces inflammatory response
- fulminating meningococcemia: rapidly moving septicemia w/o meningitis. LOS causes skin hemorrhages, vomiting, diarrhea, circulatory collapse, and death within 10-12 hours (FAST)
- Not severe: fever and nonspecific symptoms
Describe the laboratory identification of N. meningitidis (general, culture conditions, and tests)
- Appears of gram-negative diplococci in association with granulocytes under light microscope (from CSF)
- Carriers detected by swabbing the nasopharynx
- Culture conditions: chocolate agar (non-selective + blood) w/ increased CO2. Usually cultured from CSF or blood (should be sterile ∴ selective media unneccessary.
- Thayer-Martin medium required for nasopharyngeal swab
- All Neisseria are oxidase-positive
- Ferments glucose AND maltose
- Rapid latex agglutination tests can ID serogroups
What is the treatment for N. meningitidis
- Medical emergency - antibiotic treatment CANNOT await definitive diagnosis
- High fever, headache, and rash indicative of meningococcal infection are treated immediately.
- Previous used penicillin G or ampicillin in large intravenous dose, but now use other antibiotics
Describe the prevention of N. meningitidis
- MCV4 vaccine: tetravalent vaccine for serogroups A, C, W-135, and Y conjucated to diptheria toxoid which increases effectiveness (limited to ages 11-55)
- Prophylaxis: rifampin for family members of an infected individual eliminates carrier state