Case II 012207

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UNIVERSITY OF COLORADO SCHOOL OF
MEDICINE DEPARTMENT OF PATHOLOGY RESIDENCY
TRAINING PROGRAM MICROBIOLOGY Case Studies Beta
Hemolytic Streptococci
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Gram-Positive Sepsis
The colonies appearing on the surface of the
sheep blood agar plate were recovered from each
of a pair of blood culture bottles obtained from
a 65 year-old man with low-grade fever, recent
weight loss and mild hypo-chromic anemia. The
gram stain features are illustrated in the right
frame. Based on the colony morphology and the
gram stain features, what presumptive
identification can be made? What confirmatory
tests should be performed? ANSWER
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Gram-Positive Sepsis
Latex Test
A latex agglutination test was performed. This
test employs polystyrene latex beads as the
carriers for the group of specific antisera,
which produces a flocculation of the latex
particles if the unknown isolate possesses the
complementary antigen. The latex panel
illustrated here reveals a fine granulation in
the Group D well (weak reaction).
What bacterial species should be considered? What
confirmatory tests might be performed?
ANSWER
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Gram-Positive Sepsis
In this case, the 6.5 NaCl (lack of growth in
left tube) was negative the bile esc-ulin
reaction (black pigment in the right tube) was
positive.
The hydrolysis of PYR is helpful in separating
Group D streptococci (negative) from the
Enterococci (positivesee photograph). Group A
streptococci are also PYR positive. The
evolution of a red color indicates the presence
of free beta-naphthalymide and a positive
test. The reaction in this case was neg.
ANSWER
WHAT IS THE MOST LIKELY GENUS ID?
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Septicemia API Assay
The API Rapid Strep System is used in the
identification of Streptococcus sp. This system
consists of 20 cupules containing modified
conventional and chromogenic substrates (see
photograph). Each cupule is inoculated with a
suspension of the unknown organism and incubated
for 4 hours. The positive and negative reactions
are converted into a biotype number using the
octal coding system. The profile number is
5240473 Streptococcus bovis. What comment
should be added to the report?
ANSWER
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Abbreviated Identification of Streptococcus bovis
Small, dry, gray-white, non or alpha hemolytic
colonies on sheep blood agar
Gram Positive Cocci in chains
Group D antigen in latex agglutination test
Bile Esculin positive
PYR Negative
No Growth in 6.5 NaCl
Set up commercial identification system (API 20 E
Biocode 5240473 keys out to)
STREPTOCOCCUS BOVIS (GROUP D)
QUIT
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Answer to Questions on Page 2
The colony morphology is non-specific. The
colonies are relatively small, entire, slightly
convex, and have a slight off-white yellow
pigmentation. Hemolysis is absent. The gram
stain, however, showing gram positive cocci in
chains, indicates that the isolate is a
streptococcus or possibly an enterococcus. The
relatively long length of the chains rules
against the latter. The lack of hemolysis makes
presumptive identification more difficult.
Several test options are open to establish an
identificationPYR, esculin hydrolysis, growth in
6.5 NaCl, or set up of a commercial kit system.
A first step might be to determine if the isolate
carries one of the Lancefield group antigens.
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Answer to Questions on Page 3
The latex agglutination test indicates that this
isolate is carrying the streptococcus Group D
antigen. The two possibilities include a Group D
streptococcus (Streptococcus bovis) or an
Enterococcus species. To separate these two
possibilities, tests to set up would include PYR,
esculin hydrolysis, and growth in 6.5 NaCl.
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Answer to Questions on Page 4
Following the legends for the images on this
page, the PYR reaction was read as negative, no
growth was observed in 6.5 NaCl and the black
pigment in the bile/esculin tube indicates that
esculin was hydrolyzed. These reactions are
characteristic of a Group D streptococcus.
Further testing is required to confirm this
presumptive identification.
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Answer to Questions on Page 5
The last step in the diagnosis and work-up of
this case is to append the report of
Streptococcus bovis with the comment Bacteremias
with Streptococcus bovis
are commonly associated with carcinoma of the
colon. Follow-up diagnostic procedures are
indicated. The more advanced age of the patient
makes this diagnosis a real possibility.
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