Cell wall deficient bacteria
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Cell wall deficient bacteria

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Cell wall deficient bacteria Cell wall deficient bacteria Presentation Transcript

  • Mycoplasma and Cell wall defective bacteria Dr Sabrina Moyo Department of Microbiology and Immunology
  • Mycoplasma
    • Smallest viable form in cell free media can pass pore of 200nm- 450nm
    • Due to their smallest size, originally thought to be viruses, but differ in
    • i)Division by binary fission
    • Ii)Growth on artificial cell free media
    • Iii)Contain both RNA and DNA
  • Classification
    • At least 15 spp are thouhgt to of human origin, but four spp are of medical importance
    • M.pneumoniae- pnuemoina
    • M.hominis- postpartum fever and uterine tube infections
    • Ureaplasma urealyticum-non gonococcal urethritis and lung disease in premature infants of LBW
    • M.genitalium- urethral infections
  • General characterisitcs
    • Smallest organisms that can be free living 125-250nm in size
    • Highly pleumorphic because of lack of rigid cell wall
    • Completely resistant to penicillin because of lack of cell wall
    • Can reproduce in cell free media, on agar produce colonies of fried egg appearance
    • Have affinity for mammalian cell membrane
  • General characterisitcs
    • Gram –ve , stain poorly with bacteria stain, but stain well with Giemsa
    • Bounded by triplle-layered unit membrane that contain sterol
    • Cannot be studied by usual bacteriologic methods because of the small size of their colonies and delicacy due to lack of rigid cell wall
    • Growht require addition of serum or cholestrol to the medium to produce sterols
  • Culture and growth characteristics
    • They are facultative anaerobes except for M.pneumoniae strict aerobe
    • Use glucose as energy source
    • Growth require sterol supllied by animal serum, Ureaplasma reqiure urea
    • May strains grow in heart infusion peptone broth with 2% agar pH 7.8 and animal serum or 30% ascitic acid added
  • Culture and growth characteristics
    • Grows better on H 2 and N 2 with 10% CO 2
    • most grow at 37 0 C Grow slowly generation time 1-6 hrs
    • After 2-6 days of incubation produce small colonies that have freid- egg appearance
    • M.pnuemoniae colonies do not have a thin halo; mullberry-shaped
  • Pathogenesis
    • Pathogenic Mycoplasma have polar tips structures-mediate adherence to host cells
    • Direct cytotoxicity through generation of hydrogen peroxide and superoxide radicals
    • Cell lysis-by antigen antibody reactions/ chemotaxis and action of mononuclear cellls
  • Medical importance
    • Part of normal flora of mouth, genitourinary tract especially females
    • i) atypical pneumonia
    • Incubation period 1-3 wks
    • M.pneumoniae- transmitted by infected respiratory secretions
    • Generally mild disease, asypmtomatic infection-serious pneumonitis
    • Complications-neorologic, hemolytic anaemia, skin lesions
  • Medical importance
    • ii) uterine tube infections(salpingitis and tubo-ovarian abscesses) 10%
    • post abortal or post partum fever(10%)
    • Occasionally arthritis
    • Can be caused by M.hominis
    • iii)non gonococcal urethritis,and lung disease in premature LBW
    • Can be caused by U.urealyticum or M.genitalium
  • Diagnosis
    • Specimen include, blood, sputum ,urethral exudates
    • Direct staining is of limited use
    • Culture
    • CF, titer of 1:64 support diagnosis
    • immunflorescence
  • Susceptibilty to chemical physical agents and antibiotics
    • Lack of cell wall make organisms susceptible to most disinfectants and antiseptics
    • Killed when held at 56oC for 30 minutes
    • Sensitive to antimicrobials that inhibit protein synthesis e.g tetracyline, erythromicin,chloramphenical
    • Resitant to antimicrobials acting on cell wall e.g penicillines, cephalosporins and vancomycin
  • Cell wall- defective bacteria
    • Mutant bacteria with defective cell walls
    • L-forms
    • Result from
    • i) Spontaneous mutation or
    • Ii) from effects of chemicals
    • Iii) Enzymes (lysozymes)
    • If they attack gram positive it destroy the cell wall and result to Protoplast
    • If they attack gram positive cell wall is not completely destroyed outer membrane remain form Spheroplast
    • Not genetically related to mycoplasmas
  • Cell wall- defective bacteria
    • Some are stable and can replicate as non rigid cell and produce colonies on solid media
    • Others are unstable and revert to parental form when cultured in media free of inhibitor of cell wall
    • Do not have sterols on their cell membrane
    • Can form cell wall under appropriate conditions
    • 15-30% gelatin or 2.5% agar in growth media enhance reversion of L-forms to parental form
    • Inhibitors of protein synthesis inhibits reversion of L-forms