Genus Mycoplasma

Question 1

Classification

Answer 1

Family: Mycoplasmataceae

GENUS

Mycoplasma

SPECIES

M.pneumoniae occur in young adults, especially in military recruits living in close quarters

Question 2

Morphology

Answer 2

• smallest free-living organisms
  (Can pass through sterilisation filters)
• lack cell wall (enclosed by lipid bilayer containing sterols)
• due to the absence of cell wall, they are: plastic, pleomorphic and neither rods or cocci
• not seen on Gram-stained smear due to the lack of cell wall

Question 3

Growth characteristics

Answer 3

• facultatively anaerobic (except M.pneumoniae > strict aerobe)
• fastidious (require complex media for growth > including sterols)
• grows slowly by binary fission
• doubling time can be as long as 16 hours, extended incubation needed

Question 4

Virulence factors

Answer 4

No exotoxins produced

Non endotoxin because there is no cell wall

Produces hydrogen peroxide, which may damage the respiratory tract

Question 5

Disease

Answer 5

“Atypical” pneumonia = walking pneumonia

• called so, due to inability to isolate or culture the microorganism
• X-ray appears much worse than the patient appears physically
  > Shows “patchy” (reticulonodular) infiltrate

Question 6

Microbiological diagnosis

Answer 6

Gram stain not useful

Can be cultured on special bacteriological media but takes at least 10 days to grow, which is too long to be clinically useful
> Eton’s agar
(Fried egg colonies - colonies have granular appearance)

Positive cold-agglutinin test is presumptive evidence
> clumping of RBCs in cold temperatures by IgM cold agglutinins

Complement fixation test for antibodies to Mycoplasma pneumonia is more specific

Question 7

Treatment and prevention

Answer 7

• Macrolides (erythromycin)
• Tetracycline can also be used

No cell wall —> so they are resistant to penicillins, cephalosporins and vancomycin etc.

Prevention: no vaccine