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Corynebacterium diphtheriae
Corynebacteria are Gram-positive, catalase positive, non-sporeforming, non-motile, rod-shaped bacteria that are straight or slightly
curved. Metachromatic granules are usually present representing stored
phosphate regions. Their size falls 6 2-micrometers in length and 0.5
micrometers in diameter. The bacteria group together in a characteristic
way, which has been described as the form of a "V", "palisades", or
"Chinese letters". They are aerobic or facultatively anaerobic,
chemoorganotrophs, with a 51–65% genomic G:C content. They are
pleomorphic through their life cycle.
The most notable human infection is diphtheria, caused by
Corynebacterium diphtheriae. It is an acute and contagious infection
characterized by pseudomembranes of dead epithelial cells, white
blood cells, red blood cells, and fibrin that form around the tonsils and
back of the throat. It is an uncommon illness that tends to occur in
Four subspecies are recognized: C. diphtheriae mitis, C. diphtheriae
intermedius, C. diphtheriae gravis, and C. diphtheriae belfanti. The
four subspecies differ slightly in their colonial morphology and
biochemical properties such as the ability to metabolize certain nutrients,
but all may be toxigenic (and therefore cause diphtheria) or nontoxigenic. Unusually, the diphtheria toxin gene is actually encoded by a
bacteriophage which is found in toxigenic strains, not on the bacterial
chromosome itself.
For primary isolation, a variety of media may be used: Loeffler agar,
Mueller-Miller tellurite agar, or Tinsdale tellurite agar. Sterile cottontipped applicators are used to swab the pharyngeal tonsils or their beds.
Calcium alginate swabs may be inserted through both nares to collect
nasopharyngeal samples for culture. Following initial isolation, C
diphtheriae may be identified as mitis, intermedius, or gravis biotype on
the basis of carbohydrate fermentation patterns and hemolysis on sheep
blood agar plates . The toxigenicity of C diphtheriae strains is determined
by a variety of in vitro and in vivo tests. The most common in vitro assay
for toxigenicity is the Elek immunodiffusion test.
C. diphtheriae can grow on media with sheep blood with or without
beta-hemolysis. Tinsdale agar (TIN) is used for the primary isolation
and identification of Corynebacterium diphtheriae. The medium
differentiates between C. diphtheriae and diphtheroids found in the upper
respiratory tract. This differentiation was based on the ability of C.
diphtheriae to produce black (or brown) colonies, surrounded by a
brown/black halo. The dark halo is due to the production of H2S from
cystine, interacting with the tellurite salt.
Listeria monocytogenes
L. monocytogenes is a non-fastidious bacterium growing well on
commonly used cultivation media. On blood agar it forms small colonies
about 1-2 mm in diameter after 24 hours of cultivation. Colonies are βhemolytic but many strains of L.monocytogenes produce only narrow
zones of hemolysis that frequently do not extend much beyond the edge
of the colonies. In appearance, they may resemble colonies of
Enterococci or some Corynebacteria.
L. monocytogenes is gram-positive and rod-shaped. Listeria are
known to be the bacteria responsible for listeriosis, They are able to grow
in temperatures ranging from 4°C (39°F), the temperature of a
refrigerator, to 37°C (99°F), the body's internal temperature. Furthermore,
listerosis's deadliness can be partially attributed to the infection's ability
to spread to the nervous system and cause meningitis. Finally, Listeria
has a particularly high occurrence rate in newborns because of its ability
to infect the fetus by penetrating the endothelial layer of the placenta.
Vegetables can become contaminated from the soil, and animals can also
be carriers. Listeria has been found in uncooked meats, uncooked
vegetables, unpasteurized milk, foods made from unpasteurized milk, and
processed foods. Listeria is killed by pasteurization and cooking.
Listeriosis is a serious infection caused by eating
foods contaminated with the bacterium Listeria
 This disease affects primarily pregnant women,
newborn, and adults with weakened immune
 This bacterium is too small to be seen without a
Listeria spp.
Schema of intracellular life cycle of pathogenic Listeria
Propionibacterium species are part of the normal bacterial flora that
colonize the skin, conjunctiva, oropharynx, and gastrointestinal tract.
These non-spore-forming, anaerobic, gram-positive bacilli are frequent
contaminants of specimens of blood and other sterile body fluids and
have been generally considered to play little or no pathogenic role in
Propionibacterium acnes and other Propionibacterium species have,
been recovered with or without other aerobic or anaerobic organisms as
etiologic agents of multiple infection sites Some P. acnes strains possess
synergistic capabilities with facultative and aerobic bacteria. The possible
role of P. acnes in the pathogenesis of acne vulgaris was suggested. In
addition to its ability to elaborate enzymes such as lipase, protease, and
hyaluronidase, and on its ability to activate the complement system and
enhance chemotactic activity of neutrophils.
Actinomyces (from Greek "actis" ray, beam and "mykes" mucus,
fungus) is a genus of the actinobacteria class of bacteria. They are all
Gram-positive. Actinomyces are facultatively anaerobic (except A.
meyeri, a strict anaerobe). All species grow best under anaerobic
conditions. Actinomyces species do not form endospores, and, while
individual bacteria are rod-shaped, Actinomyces colonies form funguslike branched networks of hyphae. The aspect of these colonies initially
led to the incorrect assumption that the organism was a fungus and to the
name "Actinomyces" or ray fungus.
Many Actinomyces species are opportunistic pathogens of humans
and other mammals, particularly in the oral cavity. In rare cases, these
bacteria can cause actinomycosis, a disease characterized by the
formation of abscesses in the mouth, lungs, or the gastrointestinal tract.
Actinomycosis is most frequently caused by Actinomyces israelii. A.
israelii may also cause endocarditis, though the resulting symptoms may
be similar to those resulting from infections by other bacterial species.
Actinomycetes are Gram-positive organisms. This means they have
a thicker layer of peptidoglycan in their cell wall than Gramnegative bacteria.
Actinomycetes contain a cell wall. Flagella grows in and on the
substrate. Another internal structure is thallus (a tissue like mass
that grows in cultures). One more internal structure is mycelium
(tangled mass of hyphae that is found in nature). Actinomycetes
can be identified by their branching growth pattern that results in
large threadlike structures. These filaments may break apart to
form rods or spheroidal shapes, called bacillus. Some
actinomycetes can form spores.
Actinomycetes reproduce by spores. One form of reproduction is
Hyphal growth is followed by fragmentation and release of spores.
Another form of reproduction is Conidia is when spores produce
asexually on aerial fillaments.
Actinomycetes produce Streptomycin which is an antibiotic that
prodeces... Spectinomycin, Neomycin, Tetracyclines,
Chamydias, Rickettsias etc., Nystatin, Erythromycin, Legionella,
and Chloramphenicol.