Rickettsia: The rickettssia are a diverse collection of obligate intracellular Gram-negative bacteria found in ticks, lice, fleas, mites, chiggers, and mammals. Spirochetes: Spirochetes are long and slender bacteria, usually only a fraction of a micron in diameter but 5 to 250 microns long.

1. Name – Soumyadip Mukherjee
Subject – Pharmaceutical
Microbiology

2. CONTENTS
 RICKETTSIA
 Clinical Manifestations
 Structure, Classification, and Antigenic Types
 Pathogenesis
 Host Defences
 Epidemiology
 Diagnosi
 Controls
 SPIROCHETE Bacteria
 References

3. RICKETTSIA

4. RICKETTSIA
The rickettssia are a diverse collection of obligate
intracellular Gram-negative bacteria found in ticks,
lice, fleas, mites, chiggers, and mammals. They
include the genera Rickettsiae, Ehrlichia, Orientia,
and Coxiella. These zoonotic pathogens cause
infections that disseminate in the blood to many
organs.

5. Clinical Manifestations
Rickettsia species cause Rocky Mountain spotted
fever, rickettsialpox, other spotted fevers, epidemic
typhus, and murine typhus. Orientia (formerly
Rickettsia) tsutsugamushi causes scrub typhus.
Patients present with febrile exanthems and
visceral involvement; symptoms may include
nausea, vomiting, abdominal pain, encephalitis,
hypotension, acute renal failure, and respiratory
distress.

6. Structure, Classification, and
Antigenic Types
Rickettsia species are small, Gram-negative bacilli
that are obligate intracellular parasites of
eukaryotic cells. This genus consists of two
antigenically defined groups: spotted fever group
and typhus group, which are related; scrub typhus
rickettsiae differ in lacking lipopolysaccharide,
peptidoglycan, and a slime layer, and belong in the
separate, although related, genus Orientia.

8. Pathogenesis
Rickettsia and Orientia species are transmitted by the
bite of infected ticks or mites or by the feces of
infected lice or fleas. From the portal of entry in
the skin, rickettsiae spread via the bloodstream to
infect the endothelium and sometimes the vascular
smooth muscle cells. Rickettsia species enter their
target cells, multiply by binary fission in the
cytosol, and damage heavily parasitized cells
directly.

9. Host Defences
T-lymphocyte-mediated immune mechanisms and
cytokines, including gamma interferon and tumor
necrosis factor alpha, play a more important role
than antibodies.
Epidemiology
The geographic distribution of these zoonoses is
determined by that of the infected arthropod,
which for most rickettsial species is the reservoir
host.

10. Diagnosis
Rickettsioses are difficult to diagnose both clinically
and in the laboratory. Cultivation requires viable
eukaryotic host cells, such as antibiotic-free cell
cultures, embryonated eggs, and susceptible
animals. Confirmation of the diagnosis requires
comparison of acute- and convalescent-phase
serum antibody titers.
Control
Rickettsia species are susceptible to the broad-
spectrum antibiotics, doxycycline, tetracycline, and
chloramphenicol. Prevention of exposure to infected
arthropods offers some protection. A vaccine exists
for epidemic typhus but is not readily available.

11. SPIROCHETE BACTERIA

12. SPIROCHETE Bacteria
Spirochetes are long and slender bacteria, usually
only a fraction of a micron in diameter but 5 to 250
microns long. They are tightly coiled, and so look
like miniature springs or telephone cords.
Members of this group are also unusual among
bacteria for the arrangement of axial filaments,
which are otherwise similar to bacterial flagella.
These filaments run along the outside of the
protoplasm, but inside an outer sheath; they enable
the bacterium to move by rotating in place.

13.  Spirochaetes are a genetically and morphologically distinct
group of bacteria.
 Spirochaetes are thin spiral‐shaped or wave‐like bacteria that
are highly motile.
 Endoflagella/periplasmic flagella provide spirochaetes with
their characteristic corkscrew‐like motility.
 Spirochaetes differ from typical Gram‐negative bacteria at the
ultrastructural level.
 Spirochaetes are chemo‐organotrophic, grow in diverse
conditions and are comprised of both pathogenic and
nonpathogenic members.
 Complete genome sequencing has allowed for the
characterisation and differentiation of spirochaetes at the
genetic level.
 Medically important spirochaetes belong to the three
genera Borrelia, Leptospira and Treponema.

15. Evolutionary relationships among representatives of
Spirochaetales. The evolutionary history was inferred
using the Neighbor‐Joining method. The percentage
of replicate trees in which the associated taxa
clustered together in the bootstrap test (1000
replicates) is shown next to the branches
(Felsenstein, ). The tree is drawn to scale, with branch
lengths computed using the p‐distance method (Nei
and Kumar, ). The analysis involved 37 nucleotide
sequences. All ambiguous positions were removed for
each sequence pair. There were a total of 1492
positions in the final dataset. Evolutionary analyses
were conducted in MEGA5 Tamura et al.

17. The T. pallidum cell envelope architecture. The space between
the outer and cytoplasmic membranes increases from
approximately 23 nm to approximately 49 nm in regions
containing the periplasmic flagella (a and c). The periplasmic
flagella (blue line) remain closely associated with the cell
cylinder following removal of the outer membrane through
repeated centrifugation (b and d). The 4 nm lipid bilayer
composition of the cytoplasmic membrane is visible in higher
magnification views (e and g). The locations of the cytoplasmic
filaments (red line), lipoprotein layer (purple circles) and
peptidoglycan (orange line) are indicated (e). a, b and e are
longitudinal views, while c and d are the cross‐section views.
Most membrane proteins (coloured in orange) are anchored to
the cytoplasmic membrane (CM) just underneath the thin layer
of peptidoglycan (PG). A model of the T. pallidum cell envelope
is shown in (f). Rare outer membrane proteins (coloured in
purple) are exposed on the outer membrane (OM).
Reproduced with permission from Liu et al. ().

18. References
Links & Books :
 https://www.ncbi.nlm.nih.gov/books/NBK7624/
 McDade JE. Natural history of Rickettsia
rickettsii. Annu Rev Microbiol. 1986;40:287.
 https://www.britannica.com/science/spirochete
 http://www.els.net/WileyCDA/ElsArticle/refId-
a0000466.html
 https://onlinelibrary.wiley.com/doi/abs/10.1002/9780470
015902.a0000466.pub3