What is Neisseria?
Neisseria is a large genus of commensal
They colonize the mucosal surfaces of
Of the 11 species that colonize
humans, only two are pathogens.
• N. meningitidis
• N. gonorrhoeae
Shape and Arrangement:All are diplococcal
N. elongata and N.
Present in pairs or
All species are oxidase
positive except N.
elongata which are
Culturing:Most species grow optimally
at temperatures ranging
between 35 to 37 C
Growth is usually stimulated
by carbon dioxide and
They grow on chocolate agar
and Thayer-Martin agar.
Importance:Pathogenic bacteria causes diseases,some which
are followings:N. gonorrhoeae causes gonorrhea disease.
N. meningitidis one of the most common
causes of bacterial meningitis.
N. meningitidis is causative agent of
What is Rickettsia?
Rickettsia is a genus of gram-negative,
coccoid-shaped or rod shaped bacteria.
Rickettsia is divided into three catagories:Spotted fever group
Scrub typhus group
History:Rickettsias are named after their discoverer, the American
pathologist Harold Taylor Ricketts, who died of typhus in
Mexico after confirming the infectious agent of that
Shape and or rod-shaped bacteria
coccoid-shaped size:cocci (0.1 μm in diameter)
thread like rods (1–4 μm long)
they can produce ATP &
being obligate intracellular
parasites, they require a
living host cell to survive
Culturing:Rickettsia cannot live in artificial nutrient environments
and is grown either in tissue or embryo cultures
(typically, chicken embryos are used).
Transmission:Transmitted by arthropod vectors
(lice, fleas, ticks, mites); thus, humans are accidental
Mechanism of attack:invades the endothelial cells that line the
pathogen causes changes in the host cell
cytoskeleton that induces phagocytosis
they are able to avoid lysosomal fusion
oxidative burst by escaping from the
phagosome into the cytoplasm where they
multiply and spread
Causes many diseases
Significance:R.prowazekii causes louse-borne
typhus, carried by lice.
Flea, or murine typhus is caused by R.
mooseri, is transmitted from rodents to
people by fleas.
African tick typhus, are transmitted by
ticks from animal hosts to people.
Mite-borne rickettsial infections include
rickettsialpox, caused by Rickettsia akari
What is Chlamydias?
Chlamydia is a genus of
bacteria that are obligate
Chlamydia infections are the
most common bacterial
sexually transmitted diseases
in humans and are the leading
cause of infectious blindness
Chlamydia species:The four Chlamydia species includes:1. Chlamydia trachomatis (a human pathogen)
2. Chlamydia suis (affects only swine)
3. Chlamydia pecorum (infects ruminants,koalas and
4. Chlamydia muridarum (affects only mice and
Characteristics:characteristics intermediate between bacteria
obligate intracellular parasites of people and
they are capable of independent reproduction
they do not synthesize ATP
life cycle lasts from 24 to 48 hours
Shape & size:coccoid or rod shape
size is about 0.3μm
Transmission:Chlamydia infection is a common sexually transmitted
infection (STI) in humans caused by the bacterium
Significance:Chlamydia trachomatis, and Chlamydophila, which
includes Chlamydophila pneumoniae and
Chlamydophila psittaci are susceptible to antibiotic
Chlamydia is a common infectious cause of genital and
eye diseases in humans.
Study of chlamydia could open the way to new
treatments and the development of a vaccine for this
sexually transmitted disease.
What are Facultative anaerobes?
A facultative anaerobe is an organism that makes ATP
by aerobic respiration if oxygen is present, but is
capable of switching to fermentation or anaerobic
respiration if oxygen is absent.
Characters of Enterobacteriaceae: All Enterobacteriaceae
Ferment glucose with acid production
Reduce nitrates into nitrites
All enterobacteria have peritrichous flagella.
Motile except Shigella and Klebsiella
Non-capsulated except Klebsiella
Classification based on lactose fermentation:1.
Lactose fermenters:Escherichia coli
Late lactose fermenters:Shigella sonnei
Para colons etc
Non lactose fermenters:Salmonella
Culturing:There are several selective and differential
media used to
isolate and distinguish between LF & LNF
The most important media are:
Eosin Methylene Blue (EMB) agar
Salmonella Shigella (SS) agar
Triple Sugar Iron (TSI) agar
Growth of E.coli on nutrient agar,blood
Surface antigens: O and K
O antigen – somatic lipopolysaccharide surface O
antigen has endotoxic activity, protects the bacteria
from phagocytosis and bactericidal effects of
K antigen – affords protection against phagocytosis
and antibacterial factors in normal serum.
Importance:Salmonella species that cause intestinal disease known
Klebsiella species, the causes of pneumonia,intestinal
disease, and other infections
Yersinia pestis, the cause of plague
Escherichia coli is also a member of this group,which
used for experimental work.