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Old 09-14-2012
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Default Nbme block 3

A specimen from a patient's surgical wound is streaked for isolation on an agar plate. After overnight culture at 37C, the plate has bacterial growth as shown in the diagram. Which of the following labeled arrows points to a colony that is most likely to be a laboratory contaminant?
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also can anybody explain to me Qno.11
thanks in advance
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whats the answer?
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answer is D
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Old 09-14-2012
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i'm not sure abt my explanation...but, what i'm thinking is

generally ,bacteria grows all over the plate streaked of surgical wound....D is growing isolate from the streaked wound...so, i guess it's the fatal contaminant colony....
correct me if any one have other bettr explanations..thank you
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Default i found the answer somewhere else just posting it here

"STREAKING": is is a technique used to inoculate organism on agar plate.For this we use cotton swab or "Inoculant WIRE Loop" which is a wire that have very small loop at it's tip.


At first we sterilize and then dip this loop into sample that we have collected.Now we roll it on 1/4th of the agar plate(Just like u see in stem pic the region marked with "A").

Second Next we sterilize the loop again and this time we don't dip it in the collected sample rather we drag it over the FIRST 1/4th inoculated region which will pick up the organisms and spread it to the next 1/4th space on the agar plate.

Third Next we sterilize the loop again and this time we drag it over the SECOND 1/4th inoculated region which will pick up organisms and spread it to the next 1/4th space on the agar plate.

Fourth Next we reapeat the same previous step to spread on the last 1/4th space on the agar.

** Every time we repeat the streaking it picks up fewer and fewer organisms and in the end we end-up separating the "PURE COLONY OF SINGLE ORGANISM" as u see the colony that is marked with "D".Now in our second step of streaking we got Gray and White colonies but not the black one and again in the third step we just got Gray colonies which means the black one was not present at all in 2nd and 3rd 1/4th region of agar but showed up on the fourth step that tell us that it was contaminated as is also present in the first 1/4th streaked space.

http://video.google.com/videoplay?do...3448873922892#
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Last edited by usmlemydream; 09-14-2012 at 04:17 PM. Reason: xyz
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Old 03-14-2013
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Quote:
Originally Posted by usmlemydream View Post
"STREAKING": is is a technique used to inoculate organism on agar plate.For this we use cotton swab or "Inoculant WIRE Loop" which is a wire that have very small loop at it's tip.


At first we sterilize and then dip this loop into sample that we have collected.Now we roll it on 1/4th of the agar plate(Just like u see in stem pic the region marked with "A").

Second Next we sterilize the loop again and this time we don't dip it in the collected sample rather we drag it over the FIRST 1/4th inoculated region which will pick up the organisms and spread it to the next 1/4th space on the agar plate.

Third Next we sterilize the loop again and this time we drag it over the SECOND 1/4th inoculated region which will pick up organisms and spread it to the next 1/4th space on the agar plate.

Fourth Next we reapeat the same previous step to spread on the last 1/4th space on the agar.

** Every time we repeat the streaking it picks up fewer and fewer organisms and in the end we end-up separating the "PURE COLONY OF SINGLE ORGANISM" as u see the colony that is marked with "D".Now in our second step of streaking we got Gray and White colonies but not the black one and again in the third step we just got Gray colonies which means the black one was not present at all in 2nd and 3rd 1/4th region of agar but showed up on the fourth step that tell us that it was contaminated as is also present in the first 1/4th streaked space.

http://video.google.com/videoplay?do...3448873922892#
WOW, thanks man, awesome explanation.
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Old 08-25-2015
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@usmledream you explanation suggests answer as 'c'?
@ venky2600 your ans 'd'
offline answer key says answer 'd',Whats the exact answer? ne one from online or clearing the two diff ans?
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