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