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Choc Information and Courses from MediaLab, Inc.

These are the MediaLab courses that cover Choc and links to relevant pages within the course.

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Preliminary Identification of the Primary Select Agents of Bioterrorism
Bacillus anthracis

Culture Characteristics:Growth may be noted as soon as eight hours after inoculation and occurs on most routine media, including sheep blood agar (SBA), chocolate agar (CHOC), and routine blood culture media Does not grow on MacConkey (MAC) agarColony Morphology on SBA at 35°C, 18-24 hours:Flat or slightly raised, gray to white with a "ground glass" appearance Described as "tenacious" or "sticky" like petroleum jelly, shown in the top image B. anthracis is NOT hemolytic, while B. cereus is hemolyticCharacteristic Features:After 18 hours of incubation on SBA at 35°C, the slightly undulate margin may show curling, displaying a so-called "Medusa head" or described as comma-shaped protrusions, shown in the lower image

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Yersinia pestis

Culture Characteristics: Growth at 22-25oC and at 35oC Organism prefers 25oC, so the colonies will grow faster at this temperature Growth occurs on most routine media, including sheep blood agar (SBA), chocolate agar (CHOC), MacConkey (MAC) agar, and routine blood culture media Non-lactose fermenter on MAC agar Growth is slower than other EnterobacteriaceaeColony Morphology on SBA at 35oC: At 24 hours, colonies are pinpoint and translucent with a gray-white color Colonies take on a yellow tint as they age, after 48-72 hours, referred to as a "hammered copper" appearance An irregular or "fried egg" appearance, shown in the lower image, can also be seen at 48-72 hours Characeristic Features: Growth at 22-25oC is a hallmark feature of this organism

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Francisella tularensis

Culture Characteristics: Slow growing and fastidious Growth of visible colonies on agar may require two to five days Growth is stimulated by CO2 Will grow initially on sheep's blood agar (SBA), but growth is poor or absent on subculture Prefers cystein-enriched media such as chocolate (CHOC), Thayer-Martin (TM), buffered charcoal-yeast extract (BCYE), and thioglycollate (THIO) Growth is slow in broth, so blood cultures should be held up to three weeks if F. tularensis is suspectedColony Morphology on SBA at 35oC: Can grow poorly or not at all on SBA Tiny, pin-point, translucent colonies after 18-24 hours Difficult to see individual colonies in growth that is less than 24 hours Gray-white, opaque colonies less than 1 mm after 48 hours No hemolysisColony Morphology on CHOC at 35oC: Pin-point, gray-white, opaque growth after 24 hours 1-2 mm, gray-white, smooth, shiny growth after 48 hours Individual colonies exhibit mature growth at 3 days in CO2 environment and have a greenish appearance

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Brucella species

Culture Characteristics: Slow growth on sheep blood agar (SBA) and chocolate (CHOC) Growth in commercial blood culture systems, but may require extended incubation Enriched atmosphere with CO2may enhance growth of some strains If Brucella is expected or suspected, extend incubation up to seven days Colony Morphology on SBA at 35oC: Visible growth may take 48-72 hours Small, convex, and glistening Non-hemolytic

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Burkholderia species

Culture Characteristics: B. pseudomallei grows on sheep blood agar (SBA), chocolate (CHOC) agar, and MacConkey (MAC) agar B. mallei grows on very slowly on SBA and CHOC, but little or no growth on MAC Colony Morphology on SBA at 35oC: B. mallei: Smooth, gray, translucent colonies at 48 hours as displayed in the top, right image B. pseudomallei: Smooth, creamy, white colonies at 24 hours as displayed in the lower image on the right B. pseudomallei: May become dry and wrinkled as shown in the image below, often with a purplish hue at 48-72 hours Colony Morphology on MAC at 35oC: B. pseudomallei: Pink colonies at 24-48 hours (may be colorless at 48 hours) B.mallei: No growth or light pink colonies at 72 hours B. pseudomallei on CHOC at 72h image courtesy of CDC

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Which of the following organisms display the characteristic "Medusa head" on sheep blood agar (SBA) after 18 hours of incubation at 35°C?View Page
Francisella tularensis

Any isolate with the following features should be immediately referred to your LRN reference laboratory: Gram stain shows tiny, weak staining, gram-negative coccobacilli Gray-white, opaque colonies on sheep blood agar (SBA) and chocolate (CHOC) agar a at 48 hours Slow growth in broth (up to three weeks) Oxidase negative Urea negative

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