The Neisseriacaee:
The family Neisseriaceae includes the genera Neisseria, Kingella, Eikenella, Simonsiella, Alysiella,and several unnamed species.General characters
Morphology
Members of the genus Neisseria are coccal gram negative organisms that are frequently occur in pairs called Diplococci with adjacent flat side give the coffee bean appearance it is approximately 0.8 μm in diameter non –motile and do not form spores.
Culture
All the spp of genus Neisseria inhabit mucous membrane surfaces of warm- blooded hosts. These organisms and most species grow optimally at 35 to 37 C. In 48 hours on enriched media (eg, Mueller-Hinton,modified Thayer-Martin), the pathogenic spp form convex, glistening, elevated, mucoid colonies 1–5 mm in diameter. Colonies are transparent or opaque, non-pigmented, and non-hemolytic.
The organism are aerobic and grow well in the presence of 5 % CO2 (Capnophilic) and grow best in moist environment. They have complex growth requirements.
Most neisseriae utilize carbohydrates, producing acid but not gas, and their carbohydrate fermentation patterns are a means of distinguishing them.
The neisseriae produce oxidase and give positive oxidase reactions; the oxidase test is a key test for identifying them.
Species of genus Neisseria
Non pathogenic
Neisseria cinerea
Neisseria flavescens
Neisseria lactamica
Neisseria mucosa
Neisseria ploysaccharea
Pathogenic Species
The genus includes
N. gonorrhoeae ( also called gonococcus (GC))
N. meningitides ( also called meningococcus).
Neisseria gonorrhoea:
Virulence factors :Lipooligosaccharide (LOS): is a major in vivo virulence factor that mediates damage to body tissues and elicits inflammatory response. The mo release outer membrane fragment called "blebs" during the period of rapid growth these blebs contain LOS.
Pili: pili and other surface proteins fine hair like projection that is important in the initial attachment of the mo to the mucosal surfaces. Pili also, inhibit phagocytosis of the mo and helps in the exchange of the genetic materials between the cells.
Outer membrane proteins:
Por I proteins (-PorA/PorB): the major outer membrane porin protein form channels for nutrients to pass into and waste product to exit the cell it also influence the intracellular killing of the mo by PMN.
Protein II (Opa for opacity) a group of protein that facilitate adherence to phagocytic and epithelial cells. Gonococcal colonies that express Opa protein are opaque on certain transparent media while Opa protein negative produces transparent colonies.
Protein III (reduction modified protein [RMP]) blocks the host serum bactericidial (IgG) action against the organism.
Iron repressible proteins: these are produced under condition of iron starvation or anaerobiosis.
IgA1 proteases which hydrolyze the IgA1 but not IgA2 at the hinge region.
Plasmid: plasmid born virulence of N gonorrhoea is mainly associated with antimicrobial resistance.
Epidemiology:
Human are the only natural host of N. gonorrhoea. Infection is most commonly transmitted sexually. The primary reservoir is the asymptomatic carrier. Gonorrhea is second to Chlamydia trachomatis in the number of sexually transmitted bacterial infection.
Clinical infections:
Gonorrhea has short incubation period of approximately 2-7 days.
In men acute urethritis usually with purulent discharge and dysuria. Asymptomatic infection is uncommon. Complication is ascending infection including prostaitis and epididymitis.
In women the endocervix is most common site of infection resulting in vaginal discharge, dysuria and lower abdominal pain and might cause pelvic inflammatory disesase.
50% of cases are asymptomatic.
Anorectal and oropharngeal infection occur more common in homosexual men but can also occur in women.
In new born ophthalmia neonatorum: it is blinding disease if not treated immediately. Eye infection may occur in adults.
Blood –borne dissemination of N. gonorrhoeae occur in less than 1% of all infection resulting in purulent arthritis rarely septicemia. Fever and rash on extremities may be present.
Diagnosis:
Specimens: pus and secretions are taken from the urethra, cervix, rectum, conjunctiva, throat, or synovial fluid for culture and smear. Blood culture is necessary in systemic illnessSmears: gram stain of urethral or endocervical swabs reveal many diplococci inside the pus cells. Stained smears of the urethral exudate from men have a sensitivity of about 90% and a specificity of 99%. Stained smears of endocervical exudates have a sensitivity of about 50% and a specificity of about 95%.
Culture: A variety of enriched culture media used for isolation of GC include modified Thayer Martin (MTM), Martin Lewis (ML)., GC Lect media and New York City (NYC) media. Antibiotics are added to make the media more selective. Direct plating is important because GC is susceptible to drying. The culture is incubated 3-7 % CO2 (candle jar) at moist 35-37C for 24-72hr.
Identification is made by culture characteristics and colonies morphology, oxidase test (positive) and sugar utilization test.
The mo
GlucoseMaltose
Sucrose
N. gonorrohoea
+
-
-
N. meningitides
+
+
-
N mucosa
+
+
+
Immunological assay:
a. monoclonal Ab coagulation (antigonococcal Ab).
b. direct fluorescent Ab .
c. Gongen II test anti-por monoclonal Ab.
Nucleic acid assays: nucleic acid probe and PCR.
Treatment
Currently recommended antimicrobial agents are ceftriaxone, cefixime, ciprofloxacin, or oflaxacin.Neisseria meningitidis:
Virulence factors:
Capsule polysaccharide: The capsule renders the mo resistant to phagocytosis and enhances organism survival during bloodstream and CNS invasion. There are 13 different capsular poly saccharide most important are A, B, C, Y and W-135.
Pili : pili mediate attachment of mo to the epithelia lining of the nasopharynx.
Outer membrane protein.Por Aand PorB meningococcal porin protein result from the expression of two genes por Aand PorB.
Opa and Opc protein: class 5 OPa protein are found in the outer membrane of NM. It facilitate adherence to different cell. Opc function in mucosal adherence and invasion of endothelial cells.
Iron binding protein same as GC.
LOS same as GC.
IgA protease same as GC.
Plasmids: are uncommon in NM. However beta lactamases encoding plasmids from GC can be transferred to NM.
Clinical infection:
Humans are the only natural hosts for whom meningo-cocci are pathogenic. The nasopharynx is the portal of entry. From the nasopharynx, organisms may reach the bloodstream, producing bacteremia; the symptoms may be like those of an upper respiratory tract infection. Fulminant meningococcemia is more severe, with high fever and hemorrhagic rash; there may be disseminated intravascular coagulation and circulatory collapse (Waterhouse-Friderichsen syndrome).Meningitis is the most common complication of meningococcemia. It usually begins suddenly, with intense headache, vomiting, and stiff neck, and progresses to coma within a few hours.
Lab. Diagnosis:
Specimens include CSF, blood, nasopharngeal swab and rarely urogenital specimens. Incubated under CO2 (same as GC)
Gram stain of cytocentrifuged CSF ( intracellular gram negative diplococci) .
Culture on selective and non-selective media (SBA or CHOC).
oxidase , catalase and CHO fermentation.
Latex agglutination to detect group specific surface Ag of NM. They do not replace gram stain or culture.
Molecular methods: available but none present commerially
Treatment:
The DOC for treatment of NM meningitis is penicillin., but rifampicin or sulfonamide recommended as prophylaxis for close contact. Patient with meningococcemia is best treated with 3rd generation cephalosporins.
Meningococcal Vaccine :
The new meningococcal vaccine like previous quarivalent vaccine , contain polysaccharide antigens to serogroups A, C, Y, and W-135 conjugated to diphtheria toxoid protein , this conjugate vaccine is expected to provide long term immunity.This vaccine does not protect caused by group B , because group B polysaccharide is very poor immunogen in human.
It is recommended to be given to to students 11-12 years of age, those entering high school, military recruits, asplenic patients, traveler to area of epidemics, and Lab personnel.
Moraxella catarrhalis
Gram negative diplococcic commensal of the URT (nasopharynx).
It causes otitis media and sinusitis upper & lower respiratory infection.
catalase +ve, oxidase+ve and differentiated from Neisseria that it does not utilize sugars .