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One well in the center of the
Petri dish with antitoxin and 6 surrounding wells if positive for specific toxin will
produce precipitin lines in possibly 24 hourse. Sometimes paper disks are used rather than
wells cut out with a testtube. Small dishes of 4.5 cm take 3 ml of agar, and disks or
wells can be 9 mm apart. Gram stain and culture results.
These bacteria are clubshaped or irregular grampositive rods
that often display Chinese letters, because of snapping fission. With a throat swab,
inoculate blood agar with 5 % sheep blood or other and incubate at 37 ° C for 18-36
hours. Corynebacterium diphteriae forms 1-2 mm grey colonies. Two recommended agars
are a) Tellurite cysteine agar with brain-heart infusion and sheep blood with cysteine,
and b) Tinsdale agar as enriched peptone or with Loeffler’s agar. C. diphtheriae is
a) catalase +, b) glucose +, c) urease -, d) maltose +, e) nitrate reductase +, f) sucrose
-, g) mannitol -, h) starch + and i) hemolysis variable. Laboratory diagnosis depends most
of Elek-Ouchterlony toxigenicity test. |
