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8/13/2019 Genus Corynebacterium
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Genus Corynebacterium
8/13/2019 Genus Corynebacterium
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Corynebacterium diptheriae
• Diphtheria Bacteria
• Kleb Loeffler’s Bacillus
• Causes DIPTHERIA
• Pathognomonic sign of
diptheria :
PSEUDOMEMBRANE
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Biochemical Characteristics
• Nitrate Red (+), except var. mitis
• Urease (-)
•
Catalase (+)• Ferements glucose and maltose but not
sucrose
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Cultural Characteristics• Narrow zone of hemolysis on BAP
• CULTURE MEDIA FOR C. diptheriae
Potassium Tellurite Agar – for primary isolation; coloniesare gray black
Cystine Tellurite Blood Agar(CTBA) – preferred isolation
medium; gunmetal gray coloniesLoeffler’s Coagulated Serum –stimulates production of
metachromatic granules
PAI’s Coagulated Egg Medium – enhances pleomorphism
and granule formationTinsdale Medium
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Three Varieties of C. diptheriae
• GRAVIS – large, flat, dark gray colonies withirregular edges and radial striations
- ferments starch and glycogen
• MITIS - “fried egg appearance” on BAP
- on CTBA, colonies are black, convex, andmoist with bleach-like odor
- does not ferment starch and glycogen• INTERMEDIUS – small & black
- does not ferment glycogen and starch
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Toxigenecity Test
• In-vitro animal Inoculation test – uses guinea
pig
• ELEK Test – in vitro test
(+) result : line of precipitation
• SCHICK Test- susceptibility test to diptheria
- involves subcutaneous injection of C.diptheriae toxin
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Corynebacterium ulcerans
• Highly pleomorphic;
• More pleomorphic and with fewer
metachromatic granules than C. diptheriae
• Growth similar with that of C. diptheriae on
Tellurite agar
•
Grows well on Loeffler’s and PAI’s media • Diseases: mastitis in cattle, diptheria-like
infection in man
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Corynebacterium pseudotuberculosis
• Formerly known as C. ovix
• Disease : rare cause of lymphadenitis
following contact with infected livestock
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FAMILY ENTEROBACTERIOCEAE
• Lactose Fermenters
Escherichia coli
Klebsiella pneumoniaeEnterobacter aerogenes
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• Non-Lactose Fermenter
Salmonella
ShigellaProteus
Yersinea
• Late Lactose FermenterArizona
Citrobacter
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• Enterotoxigenic Escherichia coli (ETEC) - an
important cause of diarrhea in infants and
travelers in underdeveloped countries or
regions of poor sanitation
TWO TYPES OF ETEC Toxins
1. heat-labile enterotoxin (LT) -similar in
molecular size, sequence, antigenicity, and
function to the cholera toxin (Ctx)
2. heat stable toxin (ST) – of low molecular size
and resistant to boiling for 30 minutes
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• Enteropathogenic Escherichia coli (EPEC)
infection of the human small intestine induces
severe watery diarrhoea linked to a rather
weak inflammatory response
• EPEC's in vivo causes disruption of the
epithelial barrier function
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• Enterohemorrhagic Escherichia coli (E. coli
O157:H7 – causes hemorrhagic diarrhea, and
occasionally to kidney failure, especially inyoung children and elderly persons.
Transmission is via the fecal-oral route, and
most illness has been associated with eatingundercooked, contaminated ground beef or
ground pork
•
Produces verotoxin• Associated with HEMOLYTIC UREMIC
SYNDROME (HUS)
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Culture of OH157: H7
• Stool culture using SORBITOL McCONKEY
AGAR (SMAC)
• OH157 produces colorless colonies
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Enteroinvasive E. coli
• Toxin is similar to Shigella toxin
• Produces bloody diarrhea
•
There are no known animal reservoirs of EIEC.Hence the primary source for EIEC appears to
be infected humans.
• infective dose of Shigella is low (in the range
of 10 to few hundred cells), volunteer feeding
studies showed that at least 106 EIEC
organisms are required to cause illness in
healthy adults.
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• Unlike typical E. coli, EIEC are non-motile, do
not decarboxylate lysine and do not ferment
lactose. Pathogenicity of EIEC is primarily due
to its ability to invade and destroy colonic
tissue.
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• Enteroaggregative E. coli (EAEC)
The distinguishing feature of EAEC strains is
their ability to attach to tissue culture cells in
an aggregative manner. These strains are
associated with persistent diarrhea in young
children similar to ETEC
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• Uropathogenic E. coli (UPEC) cause 90% of the
urinary tract infections (UTI) in anatomically-
normal, unobstructed urinary tracts.
• P fimbria (or pyelonephritis-associated pili
[PAP])- The adhesin that has been most
closely associated with UPEC
• P fimbriae bind with D-galactose-D galactose
residue on RBC surface and on uroepithelial
cell surface
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Escherichia coli colonies on EMB (Left) and
McConkey Agar (Right)
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Enterobacter aerogenes on EMB (Left) and
McConkey (Right)
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Flagellar stain of a Salmonella Typhi. Salmonella can be
differentiated from Shigella on the bais of a motility test or a
flagellar stain. (CDC)
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Salmonella on EMB (Left)
and McConkey (Right)
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Table 1. Characteristics shared by most Salmonella
strains belonging to subspecies I
Lactose negative; acid and gas from glucose,
mannitol, maltose, and sorbitol; no Acid from
adonitol, sucrose, salicin, lactose
ONPG test negative (lactose negative)
IMVIC - + - + Gelatin hydrolysis negative
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• Lysine decarboxylase positive
Urease negative
Ornithine decarboxylase positive
H2S produced from thiosulfate Do not grow with KCN
Phenylalanine and tryptophan deaminase
negative Gelatin Hydrolysis negative
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• Salmonella sp. after 24
hours growth on XLD
agar. Xylose Lysine (XL)
agar supplementedwith sodium
thiosulfate, ferric
ammonium citrate, and
sodium deoxycholate,it is then termed XLD
agar (CDC)
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Colonial growth pattern displayed by Salmonella
Typhimurium cultured on a Hektoen enteric (HEA) (CDC)
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Shigella
•S. dysenteriae – Shiga’s bacillus
• S. flexneri – Strong’s bacillus
• S. boydi
• S. sonnei – Sonne Duval’s bacillus
Cultural Characteristics:
XLD- pink to red colonies
HEA – green to blue green colonies
SSA – colorless colonies
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Photomicrograph of Shigella from a stool sample
( phototaken from wikipedia)
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Swarming colonies of Proteus
on EMB
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