Lecture 4: Atypical bacteria

Question 1

Mycoplasmataceae features

Answer 1

• Mycoplasma pneumoniae, M. genitalium, M. hominis, U. Urealyticum
• smallest known free-living organisms (0.15 to 0.30 microns, size of poxvirus)
• minimal set of organelles (growth & replication)
• lack cell wall (entire life)
• no synthesis of peptidoglycan (stain pink -ve Gram)
• resistant: penicillin, cycloserine & lysozyme
• reproduction: cell elongates (filament), coccoid form from filament (binary fission), released by fragmentation
• cytoplasmic membrane contains sterols
• smallest genome capable of self reproduction
• growth on agar: diphasic colonies (“fried eggs”) all except M. pneumoniae
• unique attachment organelle: tapered tip + P1 adhesin; destruction: H2O2 & oxygen radical; M. pneumoniae; M. genitalium

Question 2

Rickettsiaeceae features

Answer 2

• Genera: Rickettsia & Orientia
• obligate intracell pathogens not cultivated on agar; can only be cultured on eukaryotic cells including: cell culture, embryonated eggs, susceptible animals
• spread to humans by ticks, life, fleas, mites
• small: 0.3 to 0.5 microns
• long rod/coccobacillary shaped (pleomorphic)
• closely related to Gram -ve
• Diaminopimelic acid
• some possess capsules ex. R. prowazeki

Question 3

Anaplasmataceae & Coxiella features

Answer 3

• small obligate intracell pathogens
• zoonotic

Question 4

Chlamydiaceae features

Answer 4

• 2 Genera: Chlamydia (C. trachomatis) & Chlamydophilia (C. psittaci, C. pneumoniae)
• 2 ecological groups

A. infect humans only C. trahomatis: Trachoma, inclusion conjunctivitis & lymphogranuloma venereum

B. zoonotic infections (birds to humans) C. pneumoniae, C. psittaci

• small obligate intracell pathogens
• do not generate ATP (no detectable flavoproteins or cyt)
• developmental forms (2)
  1. Elementary Body (EB): non-replicating, infectious, possess cell wall, adapted for extracell survival, induce endocytosis, metabolically inactive
  2. Reticulate Body (RB)/ Initial Body (IB): replicating, non-infectious, larger, adapted for intracell growth, does not induce endocytosis, metabolically active, see cell wall in reticulate form

Note: Elementary bodies develop into reticulate bodies after entry into host cell. RB grows & divides by binary fission. W/in 1 to 2 d, RB reorganises back to EB and host cell liberates EB.