Chlamydia and Mycoplasma

Question 1

Why “atypical bacteria”?

Answer 1

Chlamydias have intracellular phase in life cycle

Mycoplasma don’t possess cell wall

Question 2

Chlamydia life cycle

Answer 2

Obligate intracellular pathogen
Unable to produce ATP

Biphasic developmental cycle involving Elementary bodies (EB) and Reticulate bodies (RB)
- EB enter host cell –> differentiate into RB and replicate –> released as EB again

Question 3

Chlamydia trachomatis - serovars, transmission route and associated diseases

Answer 3

Major human pathogen (but not common in HK)

Ocular serovars A-C

• transmission: hand-eye, fomites, flies
• conjunctivitis, corneal scarring, trachoma

Oculogenital serovars D-K

• transmission: sexual, congenital
• non-gonococcal urethritis, cervicitis, acute proctitis, neonatal conjunctivitis

Lymphogranuloma venereum serovars L1-L3

• transmission: sexual
• submucosal and LN infections

Question 4

Trachoma - transmission, disease progression

Answer 4

A-C
Leading cause of PREVENTABLE BLINDNESS in resource poor countries

Transmitted by mucosal secretions (hand to eye) or fomites
Transmission also facilitated by “eye-seeking flies” Musca sorbens in resource poor countries

Disease:

• chronic keratoconjunctivitis caused by recurrent infection
• infection –> conjunctival inflammation –> follicle formation in eyelids –> eyelid scarring –> ingrown eyelashes –> corneal scarring –> blindness (cicatricial disease)

Active infection usually in children with subsequent scarring in adults

Question 5

Genital tract infections by C. trachomatis - manifestations

Answer 5

D-K
Sexually transmitted and perinatal infections

Women
- urethritis/cervicitis (PID)
- perihepatitis
- complicated pregnancy
==> perinatal infection of neonates --> inclusion conjunctivitis, pneumonia

Men

• urethritis
• proctitis
• epididymitis, prostatitis

Question 6

Genital tract infections by C. trachomatis - prevalence, diagnosis, treatment

Answer 6

Most common bacterial cause of STD (other causes e.g. gonorrhea, syphilis)

Higher risk in MSM

Most are asymptomatic

Diagnosis:

• FIRST CATCH URINE (from urethra) or swab of anatomical site
• -> PCR for chlamydia and gonorrhea

Treatment:
- Azithromycin and doxycycline

Question 7

Lymphogranuloma venereum - transmission, disease progression/ symptoms

Answer 7

L1-L3
Sexually transmitted

Extend from primary infective sites (small papule or ulcer on genital mucosa) to draining lymphatics and LNs

Secondary symptoms develop wks later with lymphangitis, LN necrosis and abscess (buboes)

Question 8

Chlamydophila pneumoniae - prevalence, transmission, incubation, disease presentation, diagnosis, treatment

Answer 8

Low prevalence - easily missed if not suspecting (not detected in conventional investigation of sputum)

Transmission: human-human by respiratory secretion
Incubation: 3-4 wks (atypical)

Disease:
- most are asymptomatic or only mild symptoms of fever, cough, SOB

Atypical pneumonia

• mild to life-threatening
• WITH EXTRAPULMONARY MANIFESTATIONS e.g. myocarditis, meningoencephalitis, reactive arthritis

Diagnosis:

• PCR based assays
• Serology (now rare due to cross reaction)

Treatment:
- Doxycycline or Azithromycin

Question 9

Chlamydophila psittaci - notifiable?, source, transmission, manifestations, diagnosis, treatment

Answer 9

Psittacosis - NOTIFIABLE DISEASE
Natural reservoir: birds

In birds:

• asymptomatic to fatal
• shed in urine, faeces, respiratory secretions

Human infections:

• Zoonotic from birds
• inhalation of dried bird droppings/secretions
• 5-14 days incubation
• asymptomatic, atypical pneumonia
• fevers, chills, myalgia, dry cough, chest pain, diarrhoea, headache, altered mental state

Diagnosis:

• PCR testing (with clinical suspicion)
• serology (4x increase Ab at least 4 wks apart; IgM titre >1:16)
• culture not routinely done as can’t grow on agar plates

Treatment
- doxycycline or azithromycin

Question 10

Mycoplasmas and Ureaplasmas - general features/size, colonial appearance

Answer 10

Lack cell wall

Smaller than conventional bacteria

• ureaplasma and M. hominis 0.2-0.3 mcm
• m. pneumonia 1-2 mcm in length and 0.1-0.2 mcm in width

Mycoplasmas “fried egg” colonial appearance (very small!!) – Diene’s stain to enhance contrast on agar

Question 11

Mycoplasma pneumoniae - transmission, clinical features, extra-pulmonary manifestations

Answer 11

Transmission: respiratory droplets
Incubation: 3 wks
Usually affect children and young adults

Clinical features

• asymptomatic
• INSIDIOUS onset fever/malaise/headache and NON-PRODUCTIVE cough +/- pleuritic chest pain and SOB
• CXR: MULTI-LOBAR involvement

Extra-pulmonary manifestations:

• haemolysis (cold agglutinin)
• skin (mild erythematous maculopapular or vesicular rash, Stevens-Johnson syndrome)
• CNS – encephalitis, aseptic meningitis, transverse myelitis
• CVS – myocarditis, pericarditis

Question 12

Mycoplasma pneumoniae - diagnosis, treatment

Answer 12

Diagnosis:

• detection of cold agglutinins in serum (previously)
• serology for 4x Ab or elevated IgM
• PCR GOLD STANDARD

Treatment
- Azithromycin (if susceptible; emerging macrolide resistance)
or
- Doxycycline

Question 13

M. hominis, M. genitalium & U. urealyticum clinical diseases

Answer 13

Genitourinary tract infections
- urethritis

Neonatal pneumonia
- after vaginal delivery from infected mother