Mycoplasma , Rickettsia, Chlamydia

• Mycoplasma and Ureaplasma general characteristics

  • Cell wall deficient organisms
  • Small (0.2 – 0.8 µm) and highly pleomorphic
  • Requires sterols for membrane function and growth
  • Are aerobic and have fastidious growth requirements
  • Designated as PPO or PPLO organism
  • Part of the microbial flora of humans mainly in the oropharynx, upper respiratory tract, and genitourinary tract
• Mycoplasma species

  • Mycoplasma genitalium
  • M. pirum
  • M. penetrans
  • M. fermentans
  • M. pneumonia
  • M. hominis
  • Ureaplasma urealyticum
• Culture medium for Mycoplasma

  Beef-heart infusion broth/agar supplemented with horse serum, yeast extract and nucleic acid
• Mycoplasma pneumoniae

  • Small, highly pleomorphic organism
  • Bulbous enlargement with a differentiated tip structure
  • Adhesion factor
  • Penetration factor
  • Causes Primary Atypical Pneumonia (PAP)
• Mycoplasma pneumoniae laboratory diagnosis

  • Serologic tests (ELISA, CF, and PCR)
  • Culture (Highly selective medium with glucose and penicillin & thallium, Mulberry-colony, Fried-egg appearance, Confirmatory - Overlaying colonies with 0.5% guinea pig erythrocytes in a phosphate-buffered saline)
• Ureaplasma urealyticum


  • Genital mycoplasma
  • Metabolizes urea with the production of ammonia
  • Causes nongonococcal urethritis in males
• Ureaplasma urealyticum laboratory diagnosis

  • Culture (Blood should be collected without anticoagulant, Swab specimens are collected without disinfectant, analgesics or lubricant, Highly selective medium with incorporated urea, Dark brownish clumps w/ urease production colonies)
• Mycoplasma hominis


  • Genital mycoplasma
  • Causes postpartum fever
  • Unique ability to utilize arginine in the culture medium
• Mycoplasma hominis laboratory diagnosis

  • Culture (Swab specimens, Highly selective medium with arginine, Fried-egg appearance colony)
• Additional Culture Media for Isolation of Mycoplasmas

  • Mycoplasma pneumoniae (SP-4 biphasic medium, SP-4 biphasic medium with glucose, PPLO agar or broth, PPLO agar with yeast extract and horse serum, Modified New York City medium)
  • Ureaplasma urealyticum (A7 or A8 agar, New York City medium, Modified New York City medium, SP-4 with glucose agar with urea, Ureaplasma 10C agar)
  • Mycoplasma hominis (A7 or A8 agar, New York City medium, Modified New York City medium, SP-4 with glucose agar with arginine)
• General characteristics of Chlamydiae

  • Obligate intracellular organisms
  • Possess a cell wall but cell lacks peptidoglycan layer
  • Produces endotoxin-like lipopolysaccharide antigen
  • Undergoes a developmental cycle intracellularly
• Comparison of Elementary body and Reticulate body

  • Elementary body (Size: 0.2 – 0.3 µ, Infectivity to host: Infectious, Metabolic activity: Inactive, Trypsin digestion: Resistant, Projections & rosettes: Few)
  • Reticulate body (Size: 1 µ, Infectivity to host: Non-infectious, Metabolic activity: Active, replicating stage, Trypsin digestion: Sensitive, Projections & rosettes: More)
• Diseases caused by Chlamydia trachomatis

  • Endemic/ocular trachoma (Cause of preventable blindness, Strains A, B, Ba, & C)
  • Lymphogranuloma venereum (LGV) (Characterized by three stages, Diagnosis through isolation of specific strain from bubo pus and Frei's test, Caused by strains L1 – L3)
  • Oculogenital infections (Acute inclusion conjunctivitis, Urethritis, cervicitis, bartholinitis, proctitis, salpingitis, epididymitis & acute urethral syndrome, Caused by strains D – K)
  • Perinatal infections (Inclusion conjunctivitis, Neonatal pneumonia)
• Chlamydia trachomatis laboratory diagnosis

  • Organism recovered from infected areas
  • Culture (McCoy, HeLa , and monkey kidney cells, Swab specimens should be placed in transport media)
  • Antibiotic sensitivity testing (Sulfonamide sensitive)
• Chlamydophila psittaci

  • Endemic pathogen of all bird specie
  • Transmission is by inhalation of aerosols
  • Causes psittacosis
• Chlamydophila psittaci laboratory diagnosis

  • Serologic methods (CF and indirect microimmunofluorescence)
  • Antibiotic sensitivity testing (Sulfonamide resistant)
• Chlamydophila pneumoniae


  • TWAR strain (Taiwan Acute Respiratory)
  • Transmission is through aerosol via respiratory route
• Chlamydophila pneumoniae laboratory diagnosis

  • Culture (HeLa cells and Hep-2 cells)
  • Antibiotic sensitivity testing (Tetracycline and erythromycin)
• Differential Characteristics among Chlamydiae

  • C. trachomatis (Host range: Humans, EB morphology: Round, Inclusion morphology: Round, vacuolar, Glycogen-containing inclusion: Yes, Plasmid DNA: Yes, Susceptibility to sulfonamides: Yes)
  • C. psittaci (Host range: Birds, lower mammals, humans, EB morphology: Round, Inclusion morphology: Variable, dense, Glycogen-containing inclusion: No, Plasmid DNA: Yes, Susceptibility to sulfonamides: No)
  • C. pneumoniae (Host range: Humans, EB morphology: Pear-shaped, Inclusion morphology: Round, dense, Glycogen-containing inclusion: No, Plasmid DNA: No, Susceptibility to sulfonamides: No)
• General characteristics of Rickettsia, Orientia, and Ehrlichia

  • Obligate intracellular organisms
  • Highly pleomorphic and multiplies in the cytoplasm of host cell
  • Insect vectors are reservoir for human disease
  • Spectrum of diseases
• Diseases caused by Rickettsia and Orientia

  • Spotted Fever Group (Rickettsial pox, Mediterranean spotted fever, Indian tick typhus, Kenya tick typhus, Rocky Mountain Spotted Fever (RMSF))
  • Typhus Group (Epidemic typhus, Brill-Zinsser disease, Murine typhus)
  • Scrub Typhus Group (Scrub typhus)
• Diseases caused by Ehrlichia

  • HME (Human monocytic ehrlichiosis, caused by Ehrlichia chaffeensis)
  • HGE (Human granulocytic ehrlichiosis, caused by E. phagocytophila group)
  • Sennetsu fever (caused by E. sennetsu)
• Laboratory diagnosis of Rickettsia, Orientia, and Ehrlichia

  • Biopsy of skin tissue
  • PCR
  • Giemsa or Diff-Quick stained peripheral blood buffy-coat smear
  • Serologic tests (IFA, indirect immuperoxidase assay, latex agglutination, EIA, line blot, CF, western blotting, microimmunofluorescence blot test)
  • Weil-Felix test
• Rickettsia and Orientia


  • No known developmental cycle
  • Infection cycle inside host cell (Organism deposited in bloodstream, Induces phagocytosis, Replicates in the cytoplasm of host cell, Cell death and ruptures releasing morula)
• Ehrlichia


  • Undergoes developmental cycle in the host cell (Elementary bodies, Initial bodies, Morulae)
  • Causes ehrlichiosis
• Coxiella burnetii


  • Resistant to various chemical and physical agents
  • Extracellular organism
  • Exists in two antigenic states
  • Cattles, sheep, and goats are the animal reservoir
  • Causes Q fever
• Coxiella burnetii laboratory diagnosis

  • Serologic method (IFA)
• Weil-Felix Reaction


  • Brill-Zinsser (OX-19: V, OX-2: V, OX-K: -)
  • Epidemic typhus (OX-19: +, OX-2: V, OX-K: -)
  • Murine typhus (OX-19: +, OX-2: V, OX-K: -)
  • Rickettsial pox (OX-19: -, OX-2: -, OX-K: -)
  • RMSF (OX-19: +, OX-2: +, OX-K: -)
  • Scrub typhus (OX-19: -, OX-2: -, OX-K: V)
  • Q fever (OX-19: -, OX-2: -, OX-K: -)
  • Ehrlichiosis (OX-19: -, OX-2: -, OX-K: -)
• Mycoplasmas have small genomes (0.6-1.5 Mb)
• Mycoplasmas can cause pneumonia, arthritis, meningitis, and genital tract infection
• Mycoplasmas have no cell wall so they cannot be stained with Gram stain or treated with penicillin
• Mycoplasma possess a small genome and limited metabolic capabilities.
• Mycoplasma cells are surrounded by a cell membrane composed of lipids.
• Mycoplasmas lack cell walls
• Mycoplasmas are the smallest free-living organisms
• Mycoplasmas are the smallest bacteria
• Mycoplasma lack a cell wall, making them unique among bacteria.
• Mycoplasmas lack peptidoglycan layer
• Mycoplasmas can be grown on artificial media without serum supplementation
• Mycoplasmas do not form colonies on agar plates but grow well in liquid media