Microbiology-Ulcerative STDs

Question 1

What will the lab say if you ask for a syphilis culture?

Answer 1

Did you ever go to medical school? You can’t culture syphilis.

Question 2

What bacteria causes chancroid?

Answer 2

Haemophilus ducreyi

Question 3

A patient presents with a ragged genital ulcer with marked swelling and tenderness. Inguinal lymph nodes are enlarged and tender. What are you looking for in the lab if you suspect chancroid?

Answer 3

Gram negative small rods that require X and V in warm chocolate agar w/10% CO2 to grow. This is characteristic of all haemophilus bacterium. Herpes culture and syphilis antibody tests will be negative.

Question 4

What differentiates chancroid from syphilis?

Answer 4

Chancroid has painful ulcerations and painful lymphadenopathy.

Question 5

Organisms that are spiral-shaped, have corkscrew motility, don’t gram stain and grow slowly or not at all in vitro.

Answer 5

Spirochetes. Note that it is a gram-negative organism despite not having LPS.

Question 6

What are the pathogenic spirochetes?

Answer 6

Treponema (pallidium + carateum): morphologically identical, same serologic response in humans and susceptible to penicillin. Borrelia and Leptospira are zoonotic infections.

Question 7

What methods can be used to visualize microbial infection causing syphilis?

Answer 7

Treponemes are too thin to see microscopically. They can be visualized by dark field microscopy, direct fluorescent Ab to T. pallidum or silver staining.

Question 8

Visualization of borrelia spirochetes

Answer 8

Giemsa or Wright stain

Question 9

Visualization of leptospires

Answer 9

Darkfield microscopy or silver stain

Question 10

How can syphilis be transmitted?

Answer 10

Sexually and in utero

Question 11

Greatest source of syphilis

Answer 11

MSM

Question 12

Why is T. pallidum so infectious?

Answer 12

The 50% infectious dose for humans is < 100 organisms. They infect mucous membranes easily especially if there are small cuts or abrasions.

Question 13

Why is T. pallidum infection a risk factor for HIV?

Answer 13

Ulcerations allow for easier transmission of HIV

Question 14

Primary syphilis lesions

Answer 14

Chancre: PAINLESS ulcer with a clean hard base that develops within 2-10 weeks at the primary site of infection. It heals spontaneously but systemic infection persists asymptomatically.

Question 15

Secondary syphilis lesions

Answer 15

Appear 2-10 weeks after disappearance of chancre: papulosquamous rash on palms/soles, mucous patches on mouth and warty genital lesions (condylomata kata). These resolve and infection continues asymptomatically.

Question 16

Latent syphilis

Answer 16

Early latency = < 1 year. Late latency = > 1 year.

Question 17

Tertiary syphilis

Answer 17

1/3 of patient will develop aortitis, neurosyphilis, meningovascular syphilis, tabes dorsalis, general paresis, optic atrophy and late benign syphilis years after infection.

Question 18

Easy routine tests for syphilis

Answer 18

Non-trepnemal tests. Measures the anti-phospholipid respond (anti-cardiolipin) which are not specific to the organism. Note that other diseases like lupus and malaria can cause a positive test. This is more of a screening test.

Question 19

Treponemal tests for syphilis

Answer 19

Serum absorbs anti-treponemal antibody specific for t. pallidum.

Question 20

Drug of choice for T. pallidum

Answer 20

Penicillin G

Question 21

In pregnancy the risk of transmission to the fetus is highest during which stages of syphilis?

Answer 21

Primary and secondary stages. This is when bacteremia is most likely to occur and crossing of the placenta is a high risk.