Rickettsia

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 thediseases to vertebrates

• Are able to multiply in cells of blood in vertebrate• (in cytoplasm or nucleus)

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.

Difference between rickettsia and VirusProperty Rickettsia /typical

bacteriachlamydia Virus

DNA/RNA both both any oneMultiplication by binaryfission

yes yes no

Cell wall with muramicacid

yes yes no

ribosome yes yes noMetabolically activeenzymes

yes yes no

Inhibition by antibacterialenzymes

yes yes no

ATP synthesis yes No no

Chlamydia

Obligatory parasite

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

Reproduction

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)

• They have genome that are about one fifth-to one-half the size of other bacteria capable of growingon 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

Fried egg appearance