Mycoplasmas and Cell-Wall Defective Bacteria
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Transcript of Mycoplasmas and Cell-Wall Defective Bacteria
Mycoplasmas and Cell Wall-
Defective Bacteria
Margie S. Gayapa, M.D., DPSP
Genus Mycoplasma
Mycoplasma pneumoniaeMycoplasma hominisUreaplasma urealyticumMycoplasma genitalium
Smallest free-living bacteria (thus, they can
pass through some filters used to remove bacteria)
Smallest genome size (thus, they lack many metabolic pathways and require complex media for their isolation)
Mycoplasmas are facultative anaerobes, except for M. pneumoniae, which is a strict aerobe
Highly pleomorphic because they lack a rigid cell wall
Mycoplasma
Unlike bacteria: lack
of cell wall Unlike viruses: contain
both DNA and RNA and can replicate in cell-free media
Unlike both bacteria and viruses: sterol-containing cell membranes
Mycoplasma
Small, 125-250 nm in size Lack a rigid cell wall Resistant to penicillins, inhibited by
tetracyclines or erythromycin Can reproduce in cell free media; on agar,
the center of the whole colony is characteristically embedded beneath the surface
Growth is inhibited by specific antibody Have an affinity to mammalian cell
membranes
MycoplasmaCharacteristics (Jawetz)
Typical Organisms
Because of their small size, they cannot be studied by the usual bacteriologic methods
Morphology appears different according to the method of examination
Culture Culture requires a complex media with serum or
ascitic fluid, growth factors (yeast extract) and metabolic substrate (glucose or urea), incubated for 3-10 days at 37ºC with 5% CO2 or a special broth
MycoplasmaMorphology and Identification
Grow slowly by binary
fission and produce "fried egg" colonies on agar plates
M. pneumoniae – colonies have a granular appearance
Ureaplasma – extremely small colonies called T-strains (tiny strains)
MycoplasmaMorphology and Identification
Growth characteristics
All require sterols for growth and for membrane synthesis
Many utilize glucose for energy (except for Ureaplasma which require urea)
The three species can be differentiated by their ability to metabolize glucose (M. pneumoniae), arginine (M. hominis) or urea (U. urealyticum)
The fourth species M. genitalium is extremely difficult to culture
MycoplasmaMorphology and Identification
Species are classified by biochemical and
serologic features: Complement fixation tests = Antigens are
glycolipids Enzyme-linked immunosorbent assay (ELISA)
tests = Antigens are proteins
MycoplasmaAntigenic Structure
Flask-like or
filamentous shapes and specialized polar tip structures mediate adherence to host cells
Adherence factors: interactive proteins, adhesins, adherence-accessory proteins
Toxic metabolic products: peroxides, superoxides
MycoplasmaPathogenesis
MycoplasmaPathogenesis (M. pneumoniae)
Adherence protein P1 Adhesin located at the tips of the bacterial cells binds to sialic acid residues on host epithelial cells
Colonization of the respiratory tract by M. pneumoniae results in the cessation of ciliary movement development of a dry cough
Association of the mycoplasma and the host cells: - direct toxicity: toxic metabolic products of mycoplasma metabolism (hydrogen peroxide and superoxide) accumulate and damage host tissues - inhibition host cell catalase- cytolysis by Ag-Ab reaction or chemotaxis
Extracellular
pathogens to humans
Host-specific
Tetracyclines and erythromycin are effective
MycoplasmaInfection and Treatment
Mycoplasma
Mycoplasma Species considered as Human Pathogens
Organism Disease
M. pneumoniaeUpper respiratory tract disease, tracheobronchitis, atypical pneumonia
M. hominisPyelonephritis, pelvic inflammatory disease, postpartum fever
M. genitalium Non-gonococcal urethritis
U. urealyticum Non-gonococcal urethritis
Causes atypical or walking pneumonia Common in ages 5-20 years old Causes majority of community-acquired
pneumonia that do not require hospitalization Transmitted by means of respiratory secretions Incubation period: 1 to 3 weeks Generally, a mild disease characterized by
patchy, sometimes bilateral infiltrates, prolonged cough and extra-pulmonary manifestations
Mycoplasma pneumoniae
Extrapulmonary manifestations may or may not
involve respiratory symptoms and include the following: Dermatologic manifestations e.g. erythematous macular
and/or morbilliform rash, papulovesicular exanthem, erythema multiforme, Steven Johnsons Syndrome
Cardiac manifestations e.g. arrhythmia and/or ECG abnormalities (conduction defects), congestive failure, pericarditis, myocarditis, endocarditis
Neurologic manifestations e.g. encephalitis and meningoencephalitis, transverse myelitis, cerebral infarction
Musculoskeletal manifestations e.g. polyarthralgias, acute arthritis (monoarticular or migratory)
Hematologic manifestations e.g. immune hemolytic anemia, pancytopenia
Mycoplasma pneumoniae
Resolution of
pulmonary infiltration and clinical improvement occur slowly over 1-4 weeks
Most common pathologic findings are interstitial and peribronchial pnemonitis and necrotizing bronchiolitis
Mycoplasma pneumoniae
Culture - gold standard but not widely available Serology
A. Complement Fixation – good sensitivity and specificity, titers do not peak until 4-6 weeks after infection; detection of IgM in a titer >1:16 or a fourfold increase in IgG is suggestive of current infection
B. Cold agglutinins - Approximately 34% - 68% of patients with M. pneumoniae infection develop cold agglutinins anti-I. Cold agglutinins are antibodies that agglutinate human erythrocytes at 4ºC. These are not specific for M. pneumoniae infections, if present, a presumptive diagnosis can be made
Mycoplasma pneumoniaeLaboratory Tests
Mycoplasma pneumoniaeLaboratory Tests
C. Enzyme
immunoassays (EIA) D. ELISA for IgM used
for diagnosis of acute infection
Polymerase chain reaction (PCR) in reference laboratories
Mycoplasma pneumoniaeLaboratory Tests
Occasionally grows on blood agar Causes postpartum sepsis, salpingitis, tubo-
ovarian abscess, wound infections
Mycoplasma hominis
Rapid urea hydrolysis in broth Causes nongonococcal urethritis in men, acute
urethritis in women, neonatal pneumonia and chorioamnionitis
Ureaplasma urealyticum
Mycoplasma species with the smallest
genome Causes acute and chronic nongonococcal
urethritis, cervicitis, endometritis, salpingitis and infertility in women
Mycoplasma genitalium
L Phase Variants (L
Forms)
Named after the Lister Institute in London
where they were discovered, also lack cell walls Loss of cell wall maybe complete or partial
(defective cell wall), the parent organism may be gram positive or negative
Protoplasts – usually derived from G(+) organisms, osmotically fragile, with external surfaces free of cell wall constituents
Spheroplasts - usually derived from G(-) organisms, cell wall defective since they retain some outer membrane material
L Phase Variants
Like mycoplasmas, they are pleomorphic and
continue to reproduce Can arise through spontaneous mutations
or from treatments or effects of chemicals
Some are stable, while others are unstable and revert back to bacterial parental forms
Reversion is enhanced by growth in the presence of 15-30% gelatin or 2.5% agar; inhibited by inhibitors of protein synthesis
L Phase Variants
Brooks, GF et al. Jawetz Medical Microbiology.
25th ed. McGraw Hill-Co, 2004. Mais, D. Quick Compendium of Clinical
Pathology. Second edition. American Society of Clinical Pathology Press. 2008.
Jones, S. Clinical Laboratory Pearls. Lippincott Williams and Wilkins. 2001.
References