1. Mycoplasmas and Cell Wall Defective Bacteria

2. Mycoplasmas smallest known free-living organisms
Due to their smallest size, originally thought to be viruses, but differ in
i) Contain both RNA and DNA
ii) Can synthesize proteins by their own enzymes
iii) Can multiply on their own

3. Classification For many years thought to be viruses
Nowdays classified as atypical bacteria because they lack the cell wall
At least 15 spp are thouhgt to be of human origin, only 4 spp are of medical importance
Spp.
Disease
M.pneumoniae
. atypical pnuemoina
M.hominis
. postpartum fever
. pelvic inflamatory diseases
Ureaplasma urealyticum
. non gonococcal urethritis
. lung diseases in premature infants of low birth weight (LBW)
M.genitalium
. Urethral infections

4. General characterisitcs
Smallest organisms that can be free living nm in size
Highly pleumorphic because of lack of rigid cell wall
Completely resistant to penicillin and cephalosporins 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

5. Morphology
Stain poorly with bacteria stain (gram stain), but stain well with Giemsa stain
They lack cell wall so:
Highly pleomprphic
Not stained with gram stain
Can’t be killed by penicillin
On Giemsa stain they appear as tiny pleomorphic cocci, short rods, short spirals, and sometimes as hollow ring forms. Their diameter ranges from 0.15 µ to 0.30 µ

6. Growth and Cultural Characteristics
Cannot be studied by usual bacteriologic methods because of the small size of their colonies and delicacy due to lack of rigid cell wall
Facultative anaerobes except for M.pneumoniae that are strict aerobe
Grows better on H2 and N2 with 10% CO2
Most grow at 370C. Generation time slow, 1-6 hrs

7. Use glucose as energy source
Many strains grow in heart infusion peptone broth with 2% agar, pH 7.8 and animal serum or 30% ascitic fluid added
Mycoplsama contain sterols in their cell membrane, so their growth requires the addition of serum or cholestrol to the medium to produce sterols, Ureaplasma reqiure urea

8. After 2-6 days of incubation, produce small colonies that have freid- egg appearance

9. 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

10. Medical importance
Part of normal flora of mouth, genitourinary tract especially females
i) Asymptomatic
Many infections due to Mycoplsmas are asymptomatic.

11. Medical importance
ii) Mycopasma pneumoniae and atypical pneumonia (walking pneumonia)
M.pneumoniae is a prominant cause of a typical pneumonia especially in persons 5-20 years of age
transmitted by infected respiratory secretions
Incubation period 1-3 wks
Generally mild disease, but can range from asypmtomatic infection-serious pneumonitis
Complications-neorologic, hemolytic anaemia, skin
lesions

12. Medical importance iii) Mycoplsma hominis
uterine tube infections (salpingitis and tubo-ovarian abscesses) 10%
post abortal or post partum fever(10%)
Occasionally arthritis

13. Medical importance IV) Ureaplasma urealyticum
Common in female genital tract
Attributed to some cases of non gonococcal urethritis in men
Associated with lung disease in premature LBW infants
Weak evidence correlates U.urealyticum to infertility

14. Medical importance V) Mycoplasma genitalium
Attributed to some cases of non acute and chronic non-gonococcal urethritis in men
In females, M.genitalium has been associated with cervicitis, endometritis salpingitis and infertility

15. Diagnosis Specimen include,
blood,sputum,nasopharyngial or urethral exudates
Direct staining is of limited use. For direct detection in clinical specimen :
. IF
. PCR
Culture is difficult and time consuming

16. Diagnosis Serology (most widely used)
Detection of IgM or rising titer of IgG by ELISA or
CFT (acute and convalescent phase sera are
necessary to demonstrate a fourfold rise in the CF
antibodies)
Cold agglutinins at a titer of 1/128 or higher =
acute infection (Heamoaglutination)

17. Cold agglutinins?
Positive in?
Specific?
Certain antigens on human red blood cells are identical to Mycplasma pneumonia antigens. So, antibodies to mycoplasma cross react with human red blood cells causing them to agglutinate at 4 degree but not at 37 degree
Positive in 50 % of cases
Not specific. Positive in other diseases like viral infections & malaria

18. Treatment
Lack of cell wall make organisms resitant to antimicrobials acting on cell wall e.g penicillines, cephalosporins and vancomycin
Sensitive to antimicrobials that inhibit protein synthesis e.g. tetracyline, erythromicin , azithromycin and chloramphenical

19. Other Cell wall- defective bacteria (L-forms bacteria)
First isolated in 1935 by Emmy Klienburger who named them L-forms (Lister Institute in London where she was working)
Don’t occur naturaly and not genetically related to mycoplasma
Usually result from
Spontaneous mutation
Effects of chemicals
Enzymes (lysozymes)
Antibiotic treatment

20. Other Cell wall- defective bacteria (L-forms bacteria)
Two types:
Protoplast (stable L-forms) usually derived from gram positive bacteria in which the cell wall is completely destroyed.They can’t be reverted to their original morphology.
Spheroplast (unstable L-forms) usually derived from gram negative bacteria in which cell wall is not completely destroyed; they retain some outer membrane material and can revert to their original morphology.
Their role in disease is uncertain; may be responsible for the recurance of the infection after antimicrobial treatment.

21. L Forms vs Mycoplasma
contain a rigid cell wall, at least at one stage of their life cycle
no sterols in their cytoplasmic membrane