FYBSc-Microbiology SIWS College Mumbai University

1. Rickettsia

2. General features
• Tiny, non-motile, Gram Negative bacteria
• Pleomorphic in nature
• Obligate bacteria
• Not able to grow on an artificial media, but not
virus
• Associated with arthropods which act as the
vectors( lice, tick, mite, flea) to transmit the
diseases to vertebrates
• Are able to multiply in cells of blood in vertebrate
• (in cytoplasm or nucleus)

3. General features
• Diseases caused are-Rocky Mountain Spotted
Fever (tick), typhus fever (lice), rickettsia pox (
mites)scrub typhus (mites)
• Can be cultured in-
a. Embryonated egg (yolk sac membrane)
b. Tissue cell culture.

4. Difference between rickettsia and Virus
Property Rickettsia /typical
bacteria
chlamydia Virus
DNA/RNA both both any one
Multiplication by binary
fission
yes yes no
Cell wall with muramic
acid
yes yes no
ribosome yes yes no
Metabolically active
enzymes
yes yes no
Inhibition by antibacterial
enzymes
yes yes no
ATP synthesis yes No no

5. Chlamydia
Obligatory parasite

6. General features
• Obligatory bacteria
• Two morphological forms- elementary body (EB)
and reticulate body (RB)
• EB-extracellular and RB- intracellular
• Unable to make ATP (also called energy parasite)
• Can be grown in tissue culture (yolk sac
membrane, tissue culture-HeLa, Mc Coy
• Has characteristic developmental cycle

7. Reproduction

9. Mycoplasmas
• Bacteria, facultative anaerobe, obligate anaerobe
• Can be grown on an artificial medium
• Lacking cell wall so cell membrane is the outer
most
• Cells have plasticity so show many shapes ranging
from spheres to branching filaments
• Lysed very easily by osmotic shock due to lack of
cell wall
• Not killed by penicillin since cell wall is not there
(penicillin acts on cell wall)

10. • They have genome that are about one fifth-to one-
half the size of other bacteria capable of growing
on an artificial media
• Have limited biosynthetic abilities
• Colonies on agar are tiny and require an aid of low
power microscope to observe them
• The colonies are embedded in to agar and has a
characteristic fried-egg appearance

12. Fried egg appearance