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NBME 22 Answers

nbme22/Block 1/Question#48 (34.4 difficulty score)
A 1-year-old boy is found to have an ...
Staphylococcus aureus🔍

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submitted by thirdaid(8),

Phagocytes need to produce hydrogen peroxide from oxygen to be able to undergo the oxidative burst that will kill bacteria.

Hydrogen peroxide can come from:

  • A reaction catalyzed by NADPH oxidase (missing in Chronic Granulomatous Disease)
  • Production of hydrogen peroxide by own infecting bacteria

Hydrogen peroxide can be degraded by catalase in catalase-positive organisms. Without hydrogen peroxide there is no creation of hydroxyl halide radicals and no destruction of the pathogen.

There are two catalase positive organisms in the answers: E. coli and S. aureus. We are more commonly in contact with S. aureus and it is the more common pathogen so that's the answer.

submitted by rogeliogs(8),
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shiT tieunQos tsi uotba ioryesaprrt tbrus

itasPten ithw PDHAN nhnioecciidcc=ryef touamroulgasn deeassi )(CDG

Evne ghhout tntipeas hiwt DCG natc' kmea repSexui,od tehy acn use it romf teh atsacbire nad rtevocn it ot cbelha OHCL dan likl eht aascrebi.t

BTU aitraescb htwi leatacsa eysnzem iuzteralne hreti nwo rpouedxsei nda staht hwy teh CDG netpiat cn'ta ikll

latCasae etoviips :etrbcsaia .S useuar - sligAelrups

thomasburton  I thought E.coli was catalase positive too? Why can that not be correct? +6  
mb10  (FA 186) Catalase (+) microbes, especially S aureus +4  
makinallkindzofgainz  @thomasburton - because First Aid said so, so suck it +1  

submitted by rogeliogs(8),
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sihT netuosiQ tsi abtuo teaysriporr bstur

isntPtae tiwh APHDN fccyeic=ncnoiiderh tualgsonoaumr sdaeesi G)(DC

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saataeCl ispoievt: .S userau - rgsllieusAp

submitted by hello(259),
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psaele eplh -- fI pcavlsieiettaso-a aciretab iulztraene rieht nwo spee,rdoxui hyw stn'i ti teh aesc orf teelcas-atosivpia beitarca to snfiecntoi in oveey?ren

I'm nto idnrnngautesd het cneonoitcn to AHPDN eoiasxd fycein.cdei

hello  to cause** infections in everyone +  
bmd12  Bc everyone isn't NADPH deficient, meaning they can produce their own superoxide without needing to rely on the superoxide produced by the bacteria. +1  
bmd12  so even if catalase positive organisms neutralize their own superoxide, our body is producing its own and not relying on the ones produced by bacteria. You only begin to rely on the superoxide produced by bacteria if you are NADPH deficient. +  

submitted by atstillisafraud(157),
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nuoesQit is kginas atbuo aepecsdnuatl romgassin fecigtnni CDG ietn.ptsa .lEcio is soal Cna oenyna pnxead no ?hsit

keycompany  Step pneumonia is the most common pathogenic organism in CGD, and the most common cause of pneumonia, otitis media, meningits, and sepsis. While CGD are at an increased risk of encapsulated E. coli infections, however, they are at MOST risk for S. pneumo. This is kind of just a memorization fact that you need to know about S. pneumo. +  
keycompany  Sorry english is clearly not my shit, but you get the point +  
biliarytree220  CGD is susceptible against catalase-positive organisms (FA 109), of which S. aureus is the one to look out for. It's not about encapsulated organisms, like I had it confused in my head. +6  
.ooo.   You are completely right about E.Coli being encapsulated and is also a CAT+ organism and patients with CGD would have an increased risk of infection for both S. Aureus and E. Coli. How you narrow down the two is the most common infections are S. Aureus and Aspergillus (FA 109 like mentioned above) and also using the pneumonic "Cats Need PLACESS to Belch their Hairballs" (FA 128) Nocardia, Pseudomonas, Listeria, Aspergillus, Candida, E.Coli, Staphylococci, Serratia, B cepacia, H pylori +7  

submitted by usmleuser007(337),
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:Noet teh qsnosteui astted rrseraopyit" rt"bsu tusngggsei an URT c.nintfeoi

)1 tshi lesru uto yitgnhan tub iotpseryarr cinnfeoti (non rep nniioft:ce E. c,ilo E. uema)fic

2) PGD6 cefyiciend rmoe ublessceipt to cealatsa etpvisio nrsi smago -- tsih lesur uto ll(a tersp ingsmosar)

3) tLfe tihw H. znfuneaeli ;am&p .aprthS uuersa BOH(T are aslaeatc ptei)svoi

4) dlesEutnpaac gsomarni era smto gnrcocnine ewhn ehter si a.sianepl

imnotarobotbut  Respiratory burst has nothing to do with a respiratory infection. It describes the process of phagocytosing a bacteria and using NADPH oxidase/ROS to lyse it +4  
belleng  Aspergillus is still in the running, it is catalase positive as well...but not a choice +