Clinical Microbiology

Bacterial Isolate
Gram positive rods
Possible organisms on the gram stain, L.Monocytogenes,
L.Ivanovii, Corynebacterium sp.
Listeria monocytogenes
On SBA L.monocytogenes grow as
small, round, smooth, and
translucent. Beta hemolysis. Grow
in chocolate. Identification tests for
the organism include catalase,
motility, Esculin hydrolysis, and
6.5% NaCl are positive. If incubated
at room Umbrella motility viewed.
Disease associated with
L.monocytogenes cause food
poisoning if contaminated cheese,
chicken, ice cream, and hot dogs
consumed. In pregnant women it is
responsible for spontaneous
abortion and stillborn neonates.
Infection of the neonates is
extremely serious and fatality rate is
about 50% for newborn.
Gram positive cocci in pairs
Possible organisms on gram stain under microscope,
S.Pneumoniae, S.Bovis, S.mitans
Streptococcus pneumoniae
On SBA the colony appearance is
dark alpha hemolytic, mucoid
appearance, dime shape, and
translucent colony. Identification
test is Catalase-negative, Optichin
disk-positive, bile solubile and
quellung reaction is positive.
Disease associated are Pneumonia,
sinusitis, bacterial, meningitis, otitis
media, and arthritis. Most frequently
isolate in children under age of
3years with recurrent otitis media
and the number one cause of
bacterial pneumonia in elderly
persons and in patients with
underlying disease.
Gram positive Cocci in clusters
Possible organisms on the gram stain, S.Aureus,S. Saprophyticus
S. aureus
On SBA it is beta hemolytic, creamy,
buttery looking colony. Identification
tests include Catalase and Coagulase
tests both of which are positive for this
organism. Diseases caused by S.
aureus include cutaneous infections
like folliculiti ,carbuncles, impetigo
and toxic induced diseases such as
food poisoning, scalded skin
syndrome, and toxic shock syndrome.
Gram positive Cocci in chains
Possible organisms on gram stain under microscope,
S.Pyogenes, S.Agalactiae, Entercoccus spp.
Streptococuss pyogenes
On SBA S.pyogenes grow as
small, transparent, smooth and
beta hemolysis. Identification
test for the organism is Catalasenegative. Bacitrain and PYR are
sensitive and positive. Common
disease associated are
pharyngitis is the most common,
impetigo, erysiples, cellulites,
scarlet fever, rheumatic fever,
acute glomerulonephritis,
streptococcal TSS, and
necrotizing fasciitis.
Gram Negative Rod
Possible organisms on gram stain under microscope, E.Coli,
K.Pnemoniae, C.freundii
Escherichia coli
On SBA some are beta hemolysis and
some non hemolysis. Large and gray
colony. Some ferment lactose.
Identification tests include Oxidase is
Positive and the tubes test, TSI-A/A
without H2S production. LIA is
Neg/Pos. Most of E.coli are motile
and all are Indole positive. Citerate is
Negative for this test. Disease
associated with the presence of this
organism such as GI tract pathogens
like Enteropathogenic,
enterotoxigenic, enteroinvasive,
enterohemorragic, and HUS are
common infection in GI. UT Infection
is mostly caused by this organism.
Septicemia and Meningitis are also
caused by E.coli.

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