Neisseria-Steinauer

Question 1

What are the characteristics of Neisseria?

Answer 1

1. Gram(-)
2. Nonmotile, non-sporeforming.
3. Diplococci
4. Oxidase positive (due to cytochrome C)
5. Catalase positive
6. Over-competent: can uptake DNA from the environment (transformation).
7. Obligate aerobes

Question 2

What are the Neisseria species associated with humans? What are their characteristics? Like what they cause, transmission, population etc.

Answer 2

1. N. gonorrhoeae
   •Local infection, sexually transmitted, can be disseminated.
   •Infects: mucosa of gential tract, oropharyngeal and rectal.
   •Most men get the symptoms. 50% of women do.
   •Ages from 15-19 for women, 20-24 for men.
2. N. meningitides
   •Can result in meningitis and bacteremia.
   •Found in oral pharynx.
   •Respiratory transmission.
   •Usually infects kids 6 months - 2 years or people in crowded conditions (around 20 years old (college dorms)). Due to delay of competent immune system.

Question 3

What is this structure of Neisseria capsule (which strain has it?) and outer membrane? What are the outer membrane proteins and what do they do?

Answer 3

1. Capsule (only in meningitidis)
   •Used in serotyping.
   •Is antiphagocytic.
   •Have a vaccine based on the capsule (not for all serotypes though).
2. Outer Membrane
   •Pili: long extensions for attachment.
   •LOS: missing the O-polysaccharide antigen. Mimics host cell glycosphingolipids for evasion. Also plays a role in adhesion.
3. Outer membrane proteins: opacity proteins (change characteristic of how colonies look in culture, opaque or not as well as in adherence) and porins (involved in channels for nutrients and invasion into epithelial cells.

Question 4

What is the course of infection for Meningitidis?

Answer 4

• Part of normal flora.
• Transmission via airborne respiratory droplets that colonize the membranes of the nasopharynx.
• Can get infection of the blood stream and CNS (disseminate).Can invade into the cells, multiply and get out thru submucosa and then go to blood stream.
• Can get a rash (due to blood infection).

Question 5

What is the course of infection for Gonorrhoeae?

Answer 5

•Transmission via sexual contact.
•Attached to epithelial cells → go intracellular, divide → exit into submucosa → stay localized once in submucosa (due to no capsule).
•Can live in neutrophils.
•Localized to: gential tract, rectal and oropharyngeal.
•Results in purulent discharge and irritation.
•Chronic: fibrosis.
•Dissemination: rare but can lead to pustules and arthritis.
•Four types of reactions:
1. Gonorrhoea
2. Pelvic inflammatory disease (PID)
3. Disseminated gonococcal infection (septic arthritis)
4. Ophtalmia neonatorum (infection of the eyes in a newborn and happens when going thru birth canal)

Question 6

What are the Neisseria virulence factors associated with adhesion and invasion?

Answer 6

1. Pili, outer membrane proteins, LOS.

2. Invasion via receptor mediated invasion and outer membrane proteins (Opa and porin).

Question 7

What are the Neisseria virulence factors associated with evasion of the host immune system (6)?

Answer 7

1. Avoidance of phagocytosis-Meningococcus are better at evading and getting into blood stream.
2. Antigenic variation-Sequential switching of genes, Change in outer surface antigens (for pili, Opa and LOS), Programmed rearrangements and recombination among these genes.
3. Phase variation-On-off switch of genes, For capsule and Opa.
4. Mimicry: LOS mimics glycosphingolipids.
5. IgA protease-Degrades IgA1 (specifically the Fab arms from Fc region)
6. Penicillin resistance:
   oLow-Level: due to chromosomal mutation in gene for Penicillin-binding protein (PBP).
   oHigh-level: plasmid-mediated transmissible. Due to penicillinase (beta-lactamase). More common in gonococci.

Question 8

What specimen is used to ID Neisseria?

Answer 8

1. Meningococcus-Cerebrospinal fluid, Blood
2. Gonococcus-Swab of cervical or urethral discharge, Anal/rectal, Oropharyngeal
   •Swab and put in transport medium (these bacteria are sensitive to drying). Then gram stained.

Question 9

How is Neisseria ID’d by microscopy?

Answer 9

• Gram(-) diplococcic.

* Will see high numbers of neutrophils.

Question 10

What are Neisseria’s culture requirements?

Answer 10

1. Fastidious-N. gonorrhoeae
2. Sensitive to drying-Transport medium containing a carbon dioxide source.
3. Special media-Sensitive to trace metals and fatty acids in ordinary media
4. Typically use chocolate agar (blood agar that is heated to 80 degree C)
5. Selective media Thayer-Martin medium: chocolate agar containing vancomycin, colistin, nystatin and sometimes trimethoprim.

Question 11

What biochemical tests are used to ID Neisseria? What methods distinguish between N. Meningitidis and N. gonorrhoeae?

Answer 11

1. Oxidase positive (so indicator will change color → purple)
2. Catalase positive (Bubbles!)
3. Sugar utilization test used to determine which type of Neisseria.
   •Glucose, lactose, maltose and sucrose tested.
   •Positive test produces an acid which results in a color change.
   •Meningitidis uses both glucose and maltose.
   •Gonorrhea only uses glucose.
4. Also look for Deoxyribonuclease or DNase.
   •Present in N. gonorrhoeae.

Question 12

What is used to diagnose Neisseria?

Answer 12

Cerebral spinal fluid, blood, skin lesions
•Gram negative diplococci: presumptive diagnosis
•Chocolate agar/Thayer martin medium
•Oxidase positive/ catalase positive
•Carbohydrate utilization (determine type of Neisseria)
•Immunologic tests

Question 13

What Neisseria strains are found in normal flora?

Answer 13

N. lactamica, N. sicca, N.flavescens, N.mucosa, and N. subflava
Typically commensals of oropharynx, but can become pathogenic.