Neisseria
· The genus Neisseria are Gram-negative cocci and include two important human pathogens: N. gonorrhoeae (gonococcus) and N. meningitidis (meningococcus).
· None pathogenic or potentially pathogenic members of the genus are common commensals of the human upper respiratory tract. (grow on simple media and at RT and does not ferment sugars).
Neisseria gonorrhoeae
· Gram-negative cocci, usually in pairs (diplococci, kidney-shaped cocci or bean-shaped (cocci in pairs with adjacent sides flattened or concave)); aerobic; oxidase-positive; fastidious microbe (requiring humidity, 5-7% CO2 and complex media) optimal growth at 37˚C on complex media in air with 5% CO2. Ferment glucose but not maltose or sucrose.
Epidemiology
· Obligate human parasite.
· Human case, commonly asymptomatic females act as a source of infection.
· Infection is transmitted by sexual contact. (Ophthalmia by direct contact with infected birth canal).
Pathogenesis (the organism can survive intracellularly)
· Pili: mediate adherence to mucosal epithelium (to columnar cells of mucous membrane, of the anterior urethra in male, the urethra and cervix in the female). Pili undergo phase variation (on/off switch of pili production). Nonpiliation greatly reduces virulence. Pili also exhibit antigenic variation
· Capsule
· IgAse (produces an extracellular enzyme that degrades (cleave) IgA. Cleavage inactivate the antimicrobial property of this secretory immunoglobulin. (IgAse also found in H.I & Strepto)
· Beta lactamase (possesses a plasmid that codes for penicillinase production)
· Outer membrane protein (LOS) (lipooligosaccharide) (mediate invasiveness, and produce endotoxin)
Clinical disease
· Urethritis (in man is characterized by thick, yellow, purulent urethral discharge and dysuria develop after 2-7 days incubation period).
· Endocervicitis and urethritis (in women is characterized by a purelent vaginal discharge, frequent, painful urination and abdominal pain)
· Rectal infections (Proctitis (homosexual))
· Disseminated infection (septicaemia and arthritis)
· Infant eye infection (Ophthalmia neonatorum 2-5 days after birth), which is contracted during passage through the birth canal (conjunctivitis)
Laboratory Diagnosis
· Specimens collection (urethral discharge, cervical swab (high vaginal swab), rectum,
conjunctiva, throat, blood or synovial fluid)
· Transport to lab. (the organisms are fragile, and specimen should be plated immediately. Ideally, exudate is taken directly from the patient onto appropriate preheated, freshly prepared solid media and immediately placed in a carbon dioxide incubator)
· In lab:
. Registration
. Microscopy:
- Demonstration of characteristic Gram-negative intracellular diplococci in urethral discharge very successful in men (strong presumptive evidence of gonorrhoea), less satisfactory in women.
. Culture: requires an enriched medium (chocolate agar) Thayer-Martin or chocolate agar incubated in a moist aerobic atmosphere
containing 5-10% CO2 at 35-37˚C
Thayer-Martin contains vancomycin (or lincomycin; few strains are inhibited by vancomycin), colistin, nystatin and trimethoprim
. Reading the plate: small, grey glistening colonies
. Biochemical identification:
Gram-negative diplococci, Oxidase-positive
Carbohydrate utilization test: Produce acid from glucose but not maltose or sucrose
. Antibiotic susceptibility testing
Treatment
Cephalosporins (ceftriaxone or cefuroxime)
Neisseria meningitidis
· Gram-negative cocci, usually in pairs (diplococci, kidney-shaped cocci or bean-shaped (cocci in pairs with adjacent sides flattened or concave)); aerobic; oxidase-positive; fastidious microbe (requiring humidity, 5-7% CO2 and complex media) optimal growth at 37˚C on complex media in air with 5% CO2. Ferment glucose and maltose.
(there are 13 serogroups A,B,C….; most infections are caused by the B & Y serogroup)
Epidemiology
· Obligate human parasite.
· Colonize the upper respiratory tract (10-25% of normal people).
· Infection is transmitted by respiratory droplet (nasopharyngeal secretions of cases and carriers act as a source of infection)
Pathogenesis (the organism can survive intracellularly)
· Capsule (capsular polysaccharide)
· IgAse (produces an extracellular enzyme that degrades (cleave) IgA. Cleavage inactivate the antimicrobial property of this secretory immunoglobulin. (IgAse also found in H.I & Strepto)
· Outer membrane protein (LPS) (mediate invasiveness, and produce endotoxin, causing extensive tissue necrosis, hemorrhage, circulatory collapse, intravascular coagulation and shock)
Clinical disease
· Meningitis
· Septicaemia
Laboratory Diagnosis
Specimens collection (CSF, skin lesion aspirate, blood)
· Transport to lab.
· In lab:
. Registration
. Microscopy: (centrifuge of CSF may be needed to concentrate organisms)
- Demonstration of characteristic Gram-negative intracellular diplococci
. Direct agglutination test
. Culture: chocolate agar incubated in a moist aerobic atmosphere
containing 5-10% CO2 at 35-37˚C
. Reading the plate: small, grey glistening colonies
. Biochemical identification:
Gram-negative diplococci, Oxidase-positive
Carbohydrate utilization test: Produce acid from glucose and maltose
. Antibiotic susceptibility testing
Treatment
Penicillin G or ceftriaxone or cefuroxime
Neisseria
· The genus Neisseria are Gram-negative cocci and include two important human pathogens: N. gonorrhoeae (gonococcus) and N. meningitidis (meningococcus).
· None pathogenic or potentially pathogenic members of the genus are common commensals of the human upper respiratory tract.
Neisseria gonorrhoeae
· Gram-negative cocci, usually in pairs (diplococci); aerobic; oxidase-positive; optimal growth at 37˚C on complex media in air with 5% CO2.
· Ferment glucose but not maltose or sucrose.
Epidemiology
· Obligate human parasite.
· Human case, commonly asymptomatic females act as a source of infection.
· Infection is transmitted by sexual contact.
Pathogenesis
· Pili: mediate adherence to mucosal epithelium
· Capsule
· IgAse
· Beta lactamase
· Outer membrane protein (LOS)
Clinical diseases
· Urethritis
· Cervicitis
· Rectal infections
· Disseminated infection (septicaemia and arthritis)
· Infant eye infection (Ophthalmia neonatorum)
Laboratory Diagnosis
· Specimens collection
· Transport to lab.
· In lab:
. Registration
. Microscopy:
- Demonstration of characteristic Gram-negative intracellular diplococci in urethral discharge very successful in men, less satisfactory in women.
. Culture: Thayer-Martin or chocolate agar incubated in a moist aerobic atmosphere
containing 5-10% CO2 at 35-37˚C
. Reading the plate: small, grey glistening colonies
. Biochemical identification:
Gram-negative diplococci, Oxidase-positive
Carbohydrate utilization test: Produce acid from glucose but not maltose or sucrose
. Antibiotic susceptibility testing
Treatment
Cephalosporins (ceftriaxone or cefuroxime)
Neisseria meningitidis
· Gram-negative cocci, usually in pairs (diplococci); aerobic; oxidase-positive; optimal growth at 37˚C on complex media in air with 5% CO2.
· Ferment glucose and maltose.
Epidemiology
· Obligate human parasite.
· Colonize the upper respiratory tract
· Infection is transmitted by respiratory
Pathogenesis
· Capsule
· IgAse
· Outer membrane protein (LPS)
Clinical disease
· Meningitis
· Septicaemia
Laboratory Diagnosis
· Specimens collection
· Transport to lab.
· In lab:
. Registration
. Microscopy:
- Demonstration of characteristic Gram-negative intracellular diplococci
. Direct agglutination test
. Culture: chocolate agar incubated in a moist aerobic atmosphere containing 5-10% CO2
at 35-37˚C
. Reading the plate: small, grey glistening colonies
. Biochemical identification:
Gram-negative diplococci, Oxidase-positive
Carbohydrate utilization test: Produce acid from glucose and maltose
. Antibiotic susceptibility testing
Treatment
Penicillin G or ceftriaxone or cefuroxime