neisseria - prac. microbiology

Neisseria

General Characters of the Genus

1. Gram-negative diplococci

2. Aerobic

3. Oxidase positive (the key test of the genus)

The genus includes:

Many commensals

Two important human pathogens:

1. Neisseria gonorrhoeae (gonococci)2. Neisseria meningitidis ( meningococci)

N. gonorrhoeae

. Morphology

. Culture characters:

- Enriched media: Chocolate agar - Selective media: Modified Thayer Martin (Chocolate agar + antibiotics)

. 5-10% CO2

Virulence Factors:

• Pili• Outer membrane proteins• LOS• IgA protease

Diseases caused by N. gonorrehoeae

1. Gonorrhoeae : sexually transmitted disease (STD) Men: acute urethritis prostate, bladder & epididymis Women: cervicitis endometritis & salpingitis(PID)

2. Neonatal conjunctivitis3. Vulvo-vaginitis4. Oral infection

Gonorrhoeae

Urethral discharge Cervical Discharge

Neonatal Conjunctivitis

Laboratory Diagnosis of Gonococcal Infections

A. Specimen: Urethral /Cervical Discharge / pharyngeal swabs

B. Gram-stained smear

In men: Intracellular Gram-negative diplococci (diagnostic)

In women: Less sensitive

C. Cultivation:

D. Identification:

Identification at the genus level

Gram –ve diplococci Oxidase +ve

Identification at the species level

• Glucose utilization

• Nucleic acid probeGlucose Maltose

N. meningitidis

• Morphology: same + capsule

• Culture characters: 1. It grows on chocolate & MTM 2. It can also grow on blood agar

• Biochemical reactions: . Oxidase positive. . Utilization of glucose and maltose

(acid only)

Glucose Maltose

Virulence factors:

1. Polysaccharide Capsule is the most important at

least 13 serogroups , the most common A, B, C, Y,

and W135.

All highly immunogenic EXCEPT B.

2. LOS

3. Pili

4. IgA protease.

Diseases caused by N. meningitidis

N. meningitidis in the nasopharynx in 5- 30%

1. Meningitis

2. Meningococcemia

Skin rash

Laboratory diagnosis of Meningococcal Meningitis

Medical emergency

1. Specimen:

• CSF

• Blood

• Nasopharyngeal swab

2. Direct Detection:A. Gram-stained smear

B. Direct Meningococcal Antigen Detection in CSF by:

Latex Agglutination

Report: within one hour to direct the antimicrobial therapy.

Definitive diagnosis by culture is essential to apply the infection control measures

3. Cultivation:(CSF/ Nasopharyngeal swab)

Blood culture technique

(1)

(2) (3)

4. Identification:

Identification to the genus level

Identification to the species level

• Sugar utilization

• Antigen detection: by latex agglutination or

immunofluorescence

• Nucleic acid probe

Glucose Maltose

Meningococcal Vaccine

• Capsular polysaccharide vaccine (A,C,W135,Y)

• Protein conjugate vaccine: Capsular polysaccharide vaccine + protein for young children

• Given to groups at risk

Chemoprophylaxis

• Close contacts• Doctors 2 days oral Rifampin Or One injection Ceftriaxone

Review Questions

1. All of the following are characters of the genus Neisseria EXCEPT:

a. Gram negative coccib. Arranged in pairsc. Aerobicd. Oxidase negativee. Sugar fermentation identifies the species

2. All of the following are true about N. gonorrhea EXCEPT:

a. Can live intracellular b. Oxidase positivec. Produces acid only from glucose d. Can grow on nutrient agare. Causes sexually transmitted diseases

3. The following selective medium is used to isolate N. gonorrhea:

a. Chocolate agarb. Blood agarc. MacConkey’s mediumd. Mannitol salt agare. Modified Thayer-Martin medium

4. Culture of pathogenic Neisseria should be incubated :

a. In humid atmosphere at 22 °Cb. In 5-10 % CO2

c. Anaerobicallyd. Microaerophilicallye. 2-4 weeks

5. N. meningitidis may be detected in all of the following specimens EXCEPT:

a. CSFb. Bloodc. Stoolsd. Nasopharyngeal swab

Thank you