Mycoplasmas

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Mycoplasmas
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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)
• Spiroplasmataceae (can form spiral structure)

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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 Aerobes-anaerobes.

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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
  electrochemical gradient urea is converted to
  ammonia to produce ATP.

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GENETICS

• These bacteria have the smallest genome of any
  prokaryote ( about 20 that of E. coli) and the
  lowest G C content (about 24).

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Resistance

• Sensitive to osmotic presssure
• resistant to thallium acetate????in a
  concentration of 110000 which can inhibit
  bacteria

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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).

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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 infected
  from 2 - 5 years of age but disease is most
  common in children 5-15 years of age.

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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.

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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.

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HOST DEFENSES

• Host defenses are not well characterized but
  probably involve both humoral and cell mediated
  responses.

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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).
• U. urealyticum is sexually acquired.

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• 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 

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Acquired Pneumonia Caused by Mycoplasma
pneumoniae
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Microbiological diagnosis

• 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.
• PCR

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CONTROL

• Sanitary Avoidance of contacts, if possible.
• Immunological No single vaccine is available.
  Natural resistance follows infection.
• Chemotherapeutic Tetracycline, erythromycin or
  chloramphenicol are effective.

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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 medium High turbidity in liquid medium ,may adhere to the wall or bottom of the tube