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Old 09-17-2011
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Eye Pleomorphic gram-negative bacilli grown from the eye discharge

A 16-year-old girl presents to her physician complaining of redness and a yellowish discharge from her left eye for the past 2 days. She reports minimal crusting upon awakening in the morning, and denies eye pain or previous trauma. Upon examination, there is diffuse conjunctival hyperemia associated with a mucoid discharge. The pupils dilate normally, although there is mild photophobia in the affected eye. Gram stain of the exudate shows pleomorphic, gram-negative bacilli. To culture this organism with whole-blood agar, which of the following must be used?

A. Antibiotics to inhibit normal flora
B. Cold temperature
C. Egg-yolk cholesterol
D. Reduced oxygen tension
E. Staphylococcus aureus

Source Kaplan Step 1 Qbank
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Old 09-17-2011
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pleomorphic, gram-negative bacilli, that wud be Hemophilus, so
E. Staphylococcus aureus.
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yep, s. aureus
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E. Staph aureus
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Yeap, i think its Staph, because it provide the NAD factor ( V) for the haemophilus can use it to destroy the hydrogen peroxide in the media.

Just a review note, Haemophilus use NAD ( V ) and X ( Hematin ) which is require for him to grow up, when we culture it in a media with staph it provide the NAD which help to lyse the hydrogen peroxide, but when Haemophilus is grow in a media with strep it produce hydrogen peroxide which inhibit his growth.

Another Bug that require NAD is Ricketsia, which require NAD and CoA =)...
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Old 09-17-2011
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Quote:
Originally Posted by rulz View Post
Yeap, i think its Staph, because it provide the NAD factor ( V) for the haemophilus can use it to destroy the hydrogen peroxide in the media.

Just a review note, Haemophilus use NAD ( V ) and X ( Hematin ) which is require for him to grow up, when we culture it in a media with staph it provide the NAD which help to lyse the hydrogen peroxide, but when Haemophilus is grow in a media with strep it produce hydrogen peroxide which inhibit his growth.

Another Bug that require NAD is Ricketsia, which require NAD and CoA =)...
not all staph only staph aureus is beta hemolytic so setellite phenomenon seen only with that. . .
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E > stap. aures
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The correct answer is E. The patient is suffering from conjunctivitis caused by Hemophilus, a fastidious organism requiring factors V (nicotinamide adenine dinucleotide) and X (hematin), which must be released from whole-blood preparations to be accessible to the organism. This can be done by gentle heating, which lyses the red blood cells, or by co-culture withStaphylococcus aureus, which is beta-hemolytic and lyses the red blood cells to provide the factors Hemophilus needs for growth. This is called the satellite phenomenon.
Antibiotics (choice A) would not be necessary since, with proper culture techniques, no normal flora should be available to confuse the diagnosis from this site.
Cold temperature (choice B) would not be necessary because Hemophilus grows at normal body temperature. Listeria is the genus commonly mentioned for which a cold temperature is necessary.
Cholesterol (choice C) is necessary for the growth of Mycobacteria, but not Hemophilus.
Low oxygen tension (choice D) is necessary for the growth of the microaerophiles (such as Campylobacter, Helicobacter, andBorrelia), but is not a condition for growth of Hemophilus.
MedEssentials (2nd Ed.): pp. 274
First Aid (2008): pp. 146
Hemophilus influenzaecan cause conjunctivitis, identified by Gram stain (shows gram-negative pleomorphic rods).
Hemophilus influenzaerequires factors X and V: growth on chocolate agar
Satellite phenomenon: growth when co-cultured withStaphylococcus aureus, which lyses blood cells and releases factors V and X from whole-blood preparations
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