Mycoplasmas
A group of the smallest organisms that can be
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);
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.
BIOLOGICAL FEATURES
Motility: Motile by possible release and
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:
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
These organisms are
a frequent cell culture contaminant
The organisms have limited biosynthetic abilities;
they require cholesterol for their cell membrane and
can generate energy via the breakdown of arginine
Ureaplasma
requires urea to produce an
GENETICS
These bacteria have the smallest
genome of any prokaryote ( about 20%
that of
E. coli
) and the lowest G C
Resistance
Sensitive to osmotic presssure
Transmission
M. pneumoniae
is spread by close
contact via aerosolized droplets
and thus is most easily spread in
confined populations (
e.g.
,
PATHOGENESIS
Adherence factors - The P1 Adhesin localizes at
tips of 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
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
Clinical Findings
U. urealyticum
,
M.hominis, M.genitalium
are responsible for one form of
nongonococcal urethritis.
M. hominis
is associated with
HOST DEFENSES
Host defenses are not well
EPIDEMIOLOGY
Mycoplasma
affect a specific age distribution
(5-9 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).
Antibody titers in
different age
groups.
Anti-mycoplasma
pneumoniae
Microbiological
diagnosis
GIT
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Specimens: throat swab, sputum, genital 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.
GIT
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MIT
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Theantibodies 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,
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 0.5-1.0mm)
Low turbidity in liquid
