Mycoplasmas
Mycoplasmas
 A group of the smallest organisms that can be
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free-living in nature,
Pass bacterial filter and also grow on
laboratory media. More than 80 species,
belong to Mycoplasmatales of Mollicute. 3
families can be divided:
Mycoplasmataceae (require external
cholesterol during growth, contain
Mycoplasma and Ureplasma two genera);
Acholeplasmataceae (need not external
cholesterol during growth);
Spiroplasmataceae (can form spiral structure).
ORGANISM
 Genus: Mycoplasma, Ureaplasma
 Species:
 M. pneumoniae: Upper respiratory tract disease,
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tracheobronchitis, atypical pneumonia
M. hominis: Pyelonephritis, pelvic inflammatory disease,
postpartum fever
M. genitalium: Nongonococcl urethritis
M.penetraus,
U. urealyticum: Nongonococcl urethritis
Morphology
 The smallest among prokaryotic microganisms
with circular dsDNA, usually 0.2-0.3um in size;
lack of cell wall;
 Pleomorphic, spherical, short rod, filament;
Gram negative, but stained hardly, usually use
Giemsa stain.
Morphology
They can assume multiple shapes including round, pear
shaped and even filamentous.
"fried egg"
colonial
morphology.
BIOLOGICAL FEATURES
 Motility: Motile by possible release and
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reattachment of terminal cell organelle; no flagella
present; possess a protein attachment factor
termed P1 that interacts with a specific cellular
receptor and allows adherence to respiratory
epithelium.
Respiration-Fermentation: Aerobes-anaerobes.
Culture
 Most aerobic; require 10%-20% human or
animal serum added to basic nutrient media
except Acholeplasma; typical colony show
fried egg apperance.
 Many species are part of the normal flora
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These organisms are a frequent cell culture
contaminant
 The organisms have limited biosynthetic abilities;
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they require cholesterol for their cell membrane
and can generate energy via the breakdown of
arginine
Ureaplasma requires urea to produce an
electrochemical gradient; urea is converted to
ammonia to produce ATP.
GENETICS
 These bacteria have the smallest genome of
any prokaryote ( about 20% that of E. coli)
and the lowest G C content (about 24%).
Resistance
 Sensitive to osmotic presssure
 resistant to thallium acetate醋酸亚
铊 in a concentration of 1:10000
which can inhibit bacteria
Transmission
 M. pneumoniae is spread by close contact via
aerosolized droplets and thus is most easily spread in
confined populations (e.g., families, schools, army
barracks).
PATHOGENESIS
 Adherence factors - The P1 Adhesin localizes at tips of
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the bacterial cells and binds to sialic acid residues on
host epithelial cells.The nature of the adhesins in the
other species has not been established. Colonization of
the respiratory tract by M. pneumoniae results in the
cessation of ciliary movement.
Toxic Metabolic Products
Immunopathogenesis : most children are infected from 2
- 5 years of age but disease is most common in children
5-15 years of age.
Clinical Findings
M.pneumoniae
 primary atypical pneumonia.
 Incubation: 1-3 weeks
 This disease can range from subclinical to
bronchopneumonia, often with a gradual onset
and mild to moderate severity. A long
convalescence (4-6 weeks) and several
possible complications (CNS, cardiac) follow
acute disease.
Clinical Findings
 U. urealyticum, M.hominis, M.genitalium
are responsible for one form of
nongonococcal urethritis.
 M. hominis is associated with pyelonephritis, pelvic
inflammatory disease and post-partum fevers.
HOST DEFENSES
 Host defenses are not well characterized but
probably involve both humoral and cell
mediated responses.
EPIDEMIOLOGY
 Mycoplasma affect a specific age distribution (5-9
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year olds) and represent 8-15% of all pneumonias
in school age children.
Disease occurs worldwide, is endemic in some
areas and is spread by close personal contact
(schools, families).
U. urealyticum is sexually acquired.
 Antibody titers in
different age groups.
Anti-mycoplasma
pneumoniae
antibodies indicate
pneumonia caused by
this organism is
highest in the 5-15
year age group
Acquired Pneumonia Caused by Mycoplasma
pneumoniae
Microbiological diagnosis
 Specimens: throat swab, sputum, genital
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secretion, etc.
Microscopy - This is not particularly useful because of the
absence of a cell wall but it can be helpful in eliminating
other possible pathogens.
Culture - Sputum (usually scant) or throat washings must be
sent to the laboratory in special transport medium. It may
take 2 -3 weeks to get a positive identification. Culture is
essential for a definitive diagnosis.
Complement fixation test
Cold agglutinins - Approximately 34% - 68% of patients with
M. pneumoniae infection develop cold agglutinins.
ELISA - There is a new ELISA for IgM that has been used for
diagnosis of acute infection.
PCR
The antibodies of cold agglutinins arise before the
complement fixing antibodies and they decline faster
CONTROL
 Sanitary: Avoidance of contacts, if possible.
 Immunological: No single vaccine is
available. Natural resistance follows
infection.
 Chemotherapeutic:
Tetracycline,erythromycin or
chloramphenicol are effective.
Mycoplasma and L Form Bacteria
MYCOPLASMA
L-FORM BACTERIA
No genetic relationship with
bacteria
Relate to their parent
bacteria ,sometimes can
revert
Cholesterol for their cell
membrane
No cholesterol for their cell
membrane
Stable in ordinary medium
Need hyperosmotic solution
Grow slowly, colony small
(diameter 0.1-0.3mm)
Colony larger(diameter 0.51.0mm)
Low turbidity in liquid
medium
High turbidity in liquid
medium ,may adhere to the
wall or bottom of the tube