Mim Lecture 20

Front 1

20.1

Neisseria

Back 1

- free-living bacteria: grow by themselves w/o help of living cells
- gram negative diplococci, 'coffee bean' shaped
- aerobic
- oxidase +, grown on chocolate agar. Oxidase reagent added, and Neisseria oxidizes it, turning the colonies black.
- can oxidize certain sugars. Can be used to distinguish b/w species of neisseria.
- fastidious, must grow on rich media w/ some CO2, body temperature

- neisseria gonorrhoeae and neisseria meningitidis

Front 2

20.2

isolation of pathogenic Neisseria

Back 2

- Sterile sites (CSF, Blood) -> chocolate agar
- mucosal surfaces -> Thayer-Martin (TM) agar; chocolate agar + antibiotic colistin and antifungal drug nystatin

Front 3

20.3

neisseria gonorrhoeae: virulence factors

Back 3

- pilin, Por (porin) protein, Opa (opacity) protein

Front 4

20.4

Pathogenesis of Gonorrhoeae

Back 4

4 main stages within 72 hours
1. attachment to epithelial waall
i. distant/loose attachment: adherence mediated by pili
ii. close attachment: mediated by Opa protein for firm attachment after distant attachment. Opa protein is part of the outer membrane
2. Ingestion into cell
- endocytosis
3. Transport to basement membrane and multiplication of the organism during transport
4. exocytosis and dissemination into bloodstream (mostly in females)

Front 5

20.5

How does Neisseria evade host defenses and prevent reinfection?

2 mechanisms: 1st one (pili)

Back 5

- antigenic variation in pili
- pili protein is known as Pilin, consists of protein repeats.
- Pilin mediates loose adherence in pathogenesis

- expression gene is pilE; it has the promoter and complete coding sequences for pilin.
- pilS is the silent gene, lacks promoter
- gene loci can undergo homologous recombination (switching minicassettes) and a new pilE variant is formed, where the previously silent sequences can now be expressed under the new promoter
- the new strain, now very different from the original, can now slip past the immune system
- happens after primary infection, or even many times during infection

Front 6

20.6

structure of the N. gonorrhoeae pilin protein

Back 6

- in the structure of N. Gonorrhoeae pilin protein, the variable minicassette regions are interspersed with the highly conserved spacers.
- a hydrophobic constant region serve as sites for homologous integration of minicassettes.
- hypervariable immunodominant region is important for variation

Front 7

20.7

How does Neisseria evade host defenses and prevent reinfection?

2 mechanisms: 2nd one (Opa)

Back 7

- phase variation of Opa through slipped stranded DNA mispairing (reinfection)
- because of the coding repeats (CTTCT) during DNA replication, strand sliippage and subsequent mispairing -> deletion or addition of nucleotide repeats -> frameshift mutation -> truncated protin
- in time the mistake is corrected and the OPA protein is made again.
- many OPA proteins so during the course of the infection, they are of/on -> confusing the immune system.

Front 8

20.8

diagnosis of pharyngitis

Back 8

- gram stain would be useless b/c there are many non-pathogenic Neisseria species in the oral cavity
- postive gram stain = more significant in males because there are no normal floras that resemble Neisseria.
- but in women, there are gram negative diplococci in the normal flora.

Front 9

20.9

basic diagnostic steps are:

Back 9

1. direct examination of stained sample. Neutrophils containing gram negative diplococci = good indicator of Neisseria
2. Culturing and isolating the organism. TM agar is used for mucosal samples while CAP is used for CSF/blood (sterile sites) samples. If specimen is from competing microorganisms -> selective media must be used.
3. After colonies appear, the oxidase and sugar tests can be conducted to confirm organism

Front 10

20.10

N. Meningitidis and capsule

Back 10

- has a polysaccaride capsule
- protect the bacteria from antibody-mediated phagocytosis

Front 11

20.11

Chlamydiae

Back 11

- obligate, intracellular pathogens (will not grow on agar media and can only be grown in the lab by infecting living cells)
- #1 pathogen = chlamydia trachomatis

Front 12

20.12

chlamydiae life cycle and types

Back 12

- very unique infectious life cycle
- 2 cell types (only bacterium that has this):
elementary body
reticulate form
- induce own phagocytosis
- travels with other STDs (such as gonorrhea). G travels faster than Chlyamydia, so drugs that are used to treat G must also be able to treat Chlamydia
- no host immunity, so reinfection is common

Front 13

20.13

elementary body

Back 13

- do not replicate in nature
- about 0.3 um
- rigid cell wall
- cells are infectious
- extracellular
- not capable of cell division

Front 14

20.14

reticular form

Back 14

- 0.5 - 1 um
fragile cell wall
- cells are not intracellular
- undergo cell division

Front 15

20.15

C. Trachomatis

Back 15

- leading cause of urethritis in the US, eye infections also, more in developing countries

Front 16

20.16

Treponema pallidium

Back 16

- bacteria responsible for syphilis
- spirochete
- non-stainable b/c it is so slender and small
- very susceptible to disinfectant, heat and drying. Will not live long outside a human host
- cannot be grown in vitro
- great imitator: symptoms mimic other diseases

Front 17

20.17

treponema disease cycle

Back 17

1. incubation period - multiply locally or disseminate into the bloodstream. no visible symptoms
2. 1st degree syphilis - if organism stayed local: local ulceration lesion (chancre) can appear. This will later heal in the asymptomaptic period after this primary stage. Organism that circulate to the bloodstream localized around blood vessels. 50% proceed to 2nd degree
3. 2nd degree: in tissue: cause s systemic response: rash, inflmmation of mucosal membranes etc. 2/3 patients will proceed to latent syphilis and skin lesions that contain infectious organisms
4. latent syphilis - residual bacteria (not eliminated by IR during primary and secondary stages) in spleen and lymph nodes. Lead to more proliferation during the following asymptomatic period. 1/3 patient will have go on to 3rd degree
5. 3rd degree: mediated by a systemic IR. A lot of tissue destruction, though disease is not contagious anymore.