Gram -ve Cocci; Chlamydia, Mycoplasmas, Treponemes and STDs

Question 1

Describe the Gram stain appearance of Neisseria gonorrhoeae.

Answer 1

Pink, diplococci

Question 2

Why is N. gonorrhoeae a significant STD?

Answer 2

Rates of infection are increasing and high in 20-29 year olds, especially men. Also has high Aboriginal:Non-Aboriginal rate ratio of 18:1.

Question 3

Is N. gonorrhoeae antibiotic resistant?

Answer 3

Yes - used to be sensitive to penicillin, now mostly resistant except rural WA. There is increasing resistance to ceftriaxone (the recommended first-line treatment).

Question 4

Name the important chlamydias.

Answer 4

Chlamydia trachomatis
Chlamydophila pneumoniae
Chlaydophila asittaci

Question 5

What health problems do different serovars of C. trachomatis cause?

Answer 5

Urethritis
Cervicitis
LGV - lymphogranuloma venereum
Ocular trachoma

Question 6

What is the nature of C. psittaci infection?

Answer 6

Pneumonic illness with prominent systemic symptoms:

• Abrupt onset of fever
• Malaise
• Myalgia
• Dry cough
• Pronounced headache
• Sweats and rigors

Question 7

What type of infection does C. pneumoniae cause?

Answer 7

Respiratory - mainly lower tract infection

• 5% bronchitis and 10% community acquired cases
• highest incidence in elderly
• associated w/ pharyngitis or sinusitis

Question 8

Can treponemes be Gram stained? Why?

Answer 8

No - it’s extremely thin

Question 9

Explain how dark ground microscopy works.

Answer 9

Applied in both light or electron microscopy where the unscattered beam is excluded, therefore showing the organism.

Question 10

What is the cause of syphilis?

Answer 10

Treponema pallidum

• Morphology: spiral
• Obligate intracellular pathogen (requires a host)

Question 11

What is the duration and clinical features of primary syphilis?

Answer 11

3-10 weeks

• Chancre at site of inoculation (painless ulcer, raised firm edges)
• Infectious

Question 12

What is the duration and clinical features of secondary syphilis?

Answer 12

3-6 weeks

• Begins with skin rash (palms/soles)
• Condyloma lata (warty lesion in moist areas, highly infectious)
• Alopecia
• Mucous patches (highly infectious)

Question 13

What is the duration and clinical features of tertiary syphilis?

Answer 13

Years to decades (about 25% of untreated cases)
3 possible forms:
(1) CNS - most common; damage to neurons of the cerebrum/spinal cord –> progressive dementia, sensory ataxia, pain and pupillary abnormalities. Destruction of spinal cord dorsal columns can also leave sufferers with a unique gait.
(2) Cardiovascular - small vessel vasculitis –> heart failure
(3) Gummatous - least common; granulomatous lesions of skin, bones or viscera

Question 14

What is the main difference between mycoplasmas and other bacteria?

Answer 14

Mycoplasma are very small, and have no peptidoglycan in their cell envelopes.

Question 15

How do we manage antibiotics for mycoplasma bacteria? (couldn’t find answer on micromodule but it’s a learning outcome)

Answer 15

Erythromycin, clarithromycin and azithromycin

Question 16

What is the role of M. pneumoniae in human respiratory disease?

Answer 16

It causes tracheobronchitis, bronchiolitis and pneumonia. Pharyngitis and otitis media may accompany disease.
It’s a common cause of community acquired pneumonia, especially in young people - “walking pneumonia”

Question 17

What are the genital mycoplasmas, and what do they cause?

Answer 17

Mycoplasma hominis: PID, postpartum and postabortal fever
Ureaplasma urealyticum: urethritis, adverse pregnancy outcomes, postpartum and postabortal fever
Mycoplasma genitalium: cervicitis and PID

Question 18

When does primary syphilis start following exposure? What about secondary?

Answer 18

Primary - 9-90 days after exposure

Secondary - 6 weeks to 6 months after exposure

Question 19

If a woman has syphilis and falls pregnant, how does risk of transmission change, depending on which stage she is in?

Answer 19

If she’s in 1st or 2nd, 60-90% risk of transmission
Early latent - 40% transmission
Late latent -

Question 20

Why can Chlamydia and Mycoplasma not be seen on a gram stain?

Answer 20

Both lack peptidoglycan in their cell walls

Question 21

What does N.gonorrhoeae infection cause?

Answer 21

Uncomplicated: asymptomatic, urethritis, cervicitis, PID and disseminated disease
Complicated: rectal infection, epididymitis and infertility in females