Cell wall deficient bacteria


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Cell wall deficient bacteria

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