Gram Negative Bacilli Growing in Colistin Agar! - USMLE Forums
USMLE Forums Logo
USMLE Forums         Your Reliable USMLE Online Community     Members     Posts
Home
USMLE Articles
USMLE News
USMLE Polls
USMLE Books
USMLE Apps
Go Back   USMLE Forums > USMLE Step 1 Forum

USMLE Step 1 Forum USMLE Step 1 Discussion Forum: Let's talk about anything related to USMLE Step 1 exam


Reply
 
Thread Tools Search this Thread Display Modes
  #1  
Old 01-06-2012
USMLE Forums Addict
 
Steps History: Not yet
Posts: 191
Threads: 96
Thanked 271 Times in 97 Posts
Reputation: 281
Bacteria Gram Negative Bacilli Growing in Colistin Agar!

A 17-year-old girl with cystic fibrosis has a slight increase in her frequent cough and production of mucoid sputum. A sputum specimen is obtained and plated on routine culture media. The predominant growths are gram-negative bacilli that form very mucoid colonies after 48 hours of incubation. These bacilli are oxidase-positive, grow at 42C, and have a grape-like odor.
The sputum also is plated on a colistin-containing agar. After 72 hours of incubation, the colistin-containing agar grows gram-negative bacilli that are oxidase-positive but are otherwise difficult to identify. This microorganism is of major concern. It is sent to a reference laboratory so that molecular methods can be used to identify or rule out which of the following?
A. Pseudomonas aeruginosa
B. Burkholderia cepacia
C. Haemophilus influenzae
D. Pseudomonas putida
E. Burkholderia pseudomallei
Reply With Quote Quick reply to this message
The above post was thanked by:
1TA2B (01-09-2012), ab_baby (01-09-2012), Abdulaziz (01-08-2012), fahadalam (01-09-2012), jinni (01-06-2012), sabs_49 (01-25-2012)



  #2  
Old 01-06-2012
USMLE Forums Master
 
Steps History: 1+CK+CS
Posts: 851
Threads: 88
Thanked 710 Times in 380 Posts
Reputation: 720
Default

Ans.A Pseudomonas aeruginosa
Reply With Quote Quick reply to this message
  #3  
Old 01-06-2012
USMLE Forums Master
 
Steps History: 1+CK+CS+3
Posts: 791
Threads: 76
Thanked 673 Times in 317 Posts
Reputation: 691
Default

Quote:
Originally Posted by step_enhancer View Post
Ans.A Pseudomonas aeruginosa
i was almost confirmed of P.aeruginosa but this colistin containing agar?????
what does the second part signify?????
Reply With Quote Quick reply to this message
 
  #4  
Old 01-06-2012
USMLE Forums Addict
 
Steps History: Not yet
Posts: 108
Threads: 15
Thanked 23 Times in 14 Posts
Reputation: 33
Default

A. Pseudomonas aeruginosa
Reply With Quote Quick reply to this message
  #5  
Old 01-06-2012
USMLE Forums Master
 
Steps History: 1+CK+CS
Posts: 851
Threads: 88
Thanked 710 Times in 380 Posts
Reputation: 720
Default

Quote:
Originally Posted by anomali View Post
i was almost confirmed of P.aeruginosa but this colistin containing agar?????
what does the second part signify?????
i don know what colistin agar is but i know gram negative bacilli oxidase positive got to be P.aerognosa + cystic fibrosis lung infx i think its a give away . but lets see what is the answer. . . .
Reply With Quote Quick reply to this message
  #6  
Old 01-06-2012
USMLE Forums Addict
 
Steps History: Not yet
Posts: 191
Threads: 8
Thanked 121 Times in 76 Posts
Reputation: 131
Default

I think its E. Burkholderia pseudomallei causing Meliodosis. Its can be grown on Colistin containing medium. Pseudomonas can not grow in it. But I am not sure if Burkhoderia is oxidase positive or not
Reply With Quote Quick reply to this message
  #7  
Old 01-06-2012
USMLE Forums Veteran
 
Steps History: Not yet
Posts: 281
Threads: 74
Thanked 132 Times in 69 Posts
Reputation: 142
Default

I think its B cepaciae
Reply With Quote Quick reply to this message
  #8  
Old 01-06-2012
USMLE Forums Scout
 
Steps History: 1+CK+CS
Posts: 93
Threads: 15
Thanked 45 Times in 25 Posts
Reputation: 45
Default

Quote:
Originally Posted by mohitkmc View Post
I think its E. Burkholderia pseudomallei causing Meliodosis.Its can be grown on Colistin containing medium.Pseudomonas can not grow in it.But I am not sure if Burkhoderia is oxidase positive or not
Well Burkholderia used to be considered a part of the Pseudomonas genus..
If it is very similar to Pseudo than it should have the same features I'm assuming..

B. cepacia is resistant to Colistin/Polymyxin so I think that's the answer
Reply With Quote Quick reply to this message
  #9  
Old 01-06-2012
USMLE Forums Addict
 
Steps History: Step 1 Only
Posts: 177
Threads: 33
Thanked 86 Times in 16 Posts
Default

A.....I guess shud be the ans
Reply With Quote Quick reply to this message
  #10  
Old 01-06-2012
USMLE Forums Addict
 
Steps History: Not yet
Posts: 175
Threads: 18
Thanked 63 Times in 48 Posts
Reputation: 73
Default

B. Cepacia seems the answer
Cystic fibrosis and pneumonia clinches the diagnosis in its direction

@mohitkmc and Dr. Swagg
B.Cepacia and pseudomellei both are resistant to colistin and polymixin and oxidase positive.

Found similar qns in Kaptest
Reply With Quote Quick reply to this message
  #11  
Old 01-06-2012
USMLE Forums Scout
 
Steps History: 1+CK+CS
Posts: 93
Threads: 15
Thanked 45 Times in 25 Posts
Reputation: 45
Default

Where did these Burk ogranisms come from though? First time I ever heard of it was on UWorld.. It wasn't in Kaplan.. Don't think its in Clinical Micro MRS unless I missed them
Reply With Quote Quick reply to this message
  #12  
Old 01-07-2012
USMLE-Syndrome's Avatar
USMLE Forums Master
 
Steps History: ---
Posts: 1,203
Threads: 180
Thanked 1,254 Times in 441 Posts
Reputation: 1268
Default

A. Pseudomonas aeruginosa
Reply With Quote Quick reply to this message
  #13  
Old 01-07-2012
USMLE-Syndrome's Avatar
USMLE Forums Master
 
Steps History: ---
Posts: 1,203
Threads: 180
Thanked 1,254 Times in 441 Posts
Reputation: 1268
Default

plz the answer with explanation
Reply With Quote Quick reply to this message
  #14  
Old 01-08-2012
USMLE Forums Addict
 
Steps History: Not yet
Posts: 175
Threads: 18
Thanked 63 Times in 48 Posts
Reputation: 73
Default

Quote:
Originally Posted by Dr_Swagg View Post
Where did these Burk ogranisms come from though? First time I ever heard of it was on UWorld.. It wasn't in Kaplan.. Don't think its in Clinical Micro MRS unless I missed them
Actually similar qns was in kaplan Qbank with a good explanation differentiating the two which i have posted earlier.

BTW whats the answer
Reply With Quote Quick reply to this message
  #15  
Old 01-08-2012
USMLE Forums Scout
 
Steps History: 1+CK+CS
Posts: 90
Threads: 2
Thanked 68 Times in 30 Posts
Reputation: 78
Default

I wanna know the answer too..
Reply With Quote Quick reply to this message



  #16  
Old 01-08-2012
USMLE Forums Newbie
 
Steps History: Not yet
Posts: 9
Threads: 0
Thanked 3 Times in 1 Post
Reputation: 13
Default

The answer is P.aeroginosa
Reply With Quote Quick reply to this message
  #17  
Old 01-08-2012
USMLE Forums Scout
 
Steps History: Not yet
Posts: 23
Threads: 0
Thanked 5 Times in 5 Posts
Reputation: 15
Default

Pseudomonas a
Reply With Quote Quick reply to this message
  #18  
Old 01-09-2012
USMLE Forums Scout
 
Steps History: 1+CK+CS
Posts: 93
Threads: 15
Thanked 45 Times in 25 Posts
Reputation: 45
Default

Quote:
Originally Posted by jinni View Post
Actually similar qns was in kaplan Qbank with a good explanation differentiating the two which i have posted earlier.

BTW whats the answer
I meant they're not in the Kaplan Lecture Notes..
Reply With Quote Quick reply to this message
  #19  
Old 01-09-2012
USMLE Forums Scout
 
Steps History: Not yet
Posts: 15
Threads: 1
Thanked 7 Times in 3 Posts
Reputation: 17
Default Burkholderia cepacia

Pseudomonas aeruginosa The organism is G- / Oxidase + / aerobic and is known to produce grape like odor , and also produces a slime layer and test for growth at 42C is important as a taxonomic tool . A respiratory tract infection is a finger pointing toward aerobic organisms .

Pseudomonas putida : doesnt grow very well at 42 degrees

H. influenza even though G-/ Oxidase + and pleomorphic , there is little to speak about growth at 42 degrees and also the resistance to higher generation antibiotics is not known only toward B lactams .

Burkholderia cepacia is G-/ Slowly oxidase +/ catalase + & non lactose fermenting known to cause pneumonia is immunocompramised individuals and those with cystic fibrosis .Highly virulent and the treatment is usually with Isolation to begin with . These are known to be resistant to Aminoglycosides and polymyxin b and Oxidation-fermentation polymyxin-bacitracin-lactose (OFPBL) agar is used for culture to differentiate them form esp Pseudomonas .

Burkholderia pseudomallei : Gram-negative, bipolar, aerobic, motile rod-shaped
bacterium known to cause melioidosis and these are reported to grow at inconvenient temperatures of 40 degree and above.

I want to mention that I have referred text to answer this question and I want to extend my gratitude to the author of this question for helping me to understand a very challenging question, thank you sir .

Last edited by tabishnabil; 01-09-2012 at 02:07 AM. Reason: Incomplete text
Reply With Quote Quick reply to this message
The above post was thanked by:
ab_baby (01-09-2012), fahadalam (01-09-2012), jinni (01-09-2012)
  #20  
Old 01-09-2012
USMLE Forums Addict
 
Steps History: 1+CK+CS
Posts: 109
Threads: 2
Thanked 41 Times in 34 Posts
Reputation: 51
Default

so whats the answer? i know classically speaking CF patients are prone to p.aeruginosa (A)
Reply With Quote Quick reply to this message
  #21  
Old 01-09-2012
USMLE Forums Scout
 
Steps History: 1 + CS
Posts: 79
Threads: 19
Thanked 33 Times in 11 Posts
Reputation: 43
Correct Answer

B is d correct ans.
Reply With Quote Quick reply to this message
  #22  
Old 01-09-2012
USMLE Forums Newbie
 
Steps History: ---
Posts: 2
Threads: 1
Thanked 0 Times in 0 Posts
Reputation: 10
Correct Answer B cepacia

B. cepacia is an important human pathogen which most often causes pneumonia inimmunocompromised individuals with underlying lung disease (such as cystic fibrosis or chronic granulomatous disease)
Reply With Quote Quick reply to this message
  #23  
Old 01-09-2012
USMLE Forums Scout
 
Steps History: Not yet
Posts: 22
Threads: 2
Thanked 10 Times in 4 Posts
Reputation: 20
Default

Quote:
Originally Posted by indigo View Post
I think its B cepaciae
I concur, it's B. beautiful question! keep 'em coming!

Last edited by ab_baby; 01-09-2012 at 08:48 AM.
Reply With Quote Quick reply to this message
  #24  
Old 01-11-2012
USMLE Forums Addict
 
Steps History: Not yet
Posts: 191
Threads: 96
Thanked 271 Times in 97 Posts
Reputation: 281
Default

The prototypic species Burkholderia cepacia plus at least eight other species makeup the Burkholderia cepacia complex. Additional isolates cannot be assigned to these species based on molecular methods. Burkholderia gladioli is a closely related species. Thus, the classification of these bacteria is complex; their specific identification is difficult. These are environmental organisms able to grow in water, soil, plants, animals, and decaying vegetable materials. In hospitals, B cepacia has been isolated from a variety of water and environmental sources from which it can be transmitted to patients. People with CF, in particular, and those with chronic granulomatous disease are vulnerable to infection with bacteria in the B cepacia complex It is likely that B cepacia can be transmitted from one CF patient to another by close contact. They may have asymptomatic carriage, progressive deterioration over a period of months, or rapidly progressive deterioration with necrotizing pneumonia and bacteremia. Although a relative small percentage of CF patients become infected, the association with progressive disease makes B cepacia complex a major concern for these patients. A diagnosis of B cepacia infection in a CF patient may significantly alter the patient's life, because they may not be allowed association with other CF patients and they may be removed from eligibility for lung transplant.
B cepacia grows on most media used in culturing patients' specimens for gram-negative bacteria. Selective media containing colistin also can be used. B cepacia grows more slowly than enteric gram-negative rods, and it may take 3 days before colonies are visible. The B cepacia are oxidase-positive, lysine decarboxylase-positive, and produce acid from glucose, but differentiating B cepacia from other pseudomonads including Stenotrophomonas maltophilia requires a battery of biochemical tests and can be difficult. Submission of isolates to reference laboratories is recommended because of the prognostic implications of colonization in CF patients. In the United States, the CF Foundation supports a reference laboratory that uses phenotypic and genotypic methods to confirm the identity of organisms within the B cepacia complex. Susceptibility tests should be done on B cepacia complex isolates, though slow growth may make routine testing difficult. B cepacia complex from CF patients often are multidrug-resistant.
Reply With Quote Quick reply to this message
The above post was thanked by:
drortho (01-15-2012), fahadalam (01-11-2012), sabs_49 (01-25-2012)
  #25  
Old 03-15-2012
USMLE Forums Scout
 
Steps History: 1+CK+CS+3
Posts: 15
Threads: 4
Thanked 7 Times in 4 Posts
Reputation: 17
Default

Slime layer, growth at 42 degree C and multi drug resistance and cytsic fibrosis(immunocompromised) ,all these characteristics are common between Burkholderia cepacia and psuedomonas auerginosa ,the BUZZWORD is GRAPE like odor which is a hallmark of psuedomonas .
ans : A( psuedomonas auerginosa)
Reply With Quote Quick reply to this message



  #26  
Old 03-15-2012
bunny's Avatar
Banned
 
Steps History: Not yet
Posts: 176
Threads: 34
Thanked 117 Times in 69 Posts
Reputation: 127
Default

A 17-year-old girl with cystic fibrosis has a slight increase in her frequent cough and production of mucoid sputum. A sputum specimen is obtained and plated on routine culture media. The predominant growths are gram-negative bacilli that form very mucoid colonies after 48 hours of incubation. These bacilli are oxidase-positive, grow at 42C, and have a grape-like odor.
The sputum also is plated on a colistin-containing agar. After 72 hours of incubation, the colistin-containing agar grows gram-negative bacilli that are oxidase-positive but are otherwise difficult to identify. This microorganism is of major concern. It is sent to a reference laboratory so that molecular methods can be used to identify or rule out which of the following?
A. Pseudomonas aeruginosa
B. Burkholderia cepacia
C. Haemophilus influenzae
D. Pseudomonas putida
E. Burkholderia pseudomallei

The colistin agar inhibit the growth of Enterobacteriaceae and Pseudomonas while they allow the growth of yeast, staphylococci, streptococci and pneumococci.

Sources:
  1. http://medicalopedia.org/reference/C...n-nalidix_agar
  2. Ellener, P.C., C.J. Stoessel, E. Drakeford, and F. Vassi 1966. A new culture medium for medical bacteriology. Am J. Clin Pathol. 45:502-504.
Reply With Quote Quick reply to this message



Reply

Tags
Microbiology-, Step-1-Questions

Quick Reply
Message:
Options

Register Now

In order to be able to post messages on the USMLE Forums forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.
User Name:
Password
Please enter a password for your user account. Note that passwords are case-sensitive.
Password:
Confirm Password:
Email Address
Please enter a valid email address for yourself.
Email Address:
Medical School
Choose "---" if you don't want to tell. AMG for US & Canadian medical schools. IMG for all other medical schools.
USMLE Steps History
What steps finished! Example: 1+CK+CS+3 = Passed Step 1, Step 2 CK, Step 2 CS, and Step 3.

Choose "---" if you don't want to tell.

Favorite USMLE Books
What USMLE books you really think are useful. Leave blank if you don't want to tell.
Location
Where you live. Leave blank if you don't want to tell.

Log-in

Human Verification

In order to verify that you are a human and not a spam bot, please enter the answer into the following box below based on the instructions contained in the graphic.



Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes


Similar Threads
Thread Thread Starter Forum Replies Last Post
Short gram negative rods in the CSF! menatallah Elgohary USMLE Step 1 Forum 6 09-19-2011 04:51 PM
gram-negative, nonfermenting rod that produced a greenish hue in the culture plates! menatallah Elgohary USMLE Step 1 Forum 8 09-18-2011 09:17 PM
Pleomorphic gram-negative bacilli grown from the eye discharge ricko335 USMLE Step 1 Forum 7 09-18-2011 03:19 AM
Oxidase-negative, Motile, Gram-negative Bacillus! rulz USMLE Step 1 Forum 8 07-31-2011 08:09 AM
Gram Negative non-fermenters rods in Urine! INCOGNITO USMLE Step 1 Forum 7 07-09-2011 11:01 AM

RSS Feed
Find Us on Facebook
vBulletin Security provided by vBSecurity v2.2.2 (Pro) - vBulletin Mods & Addons Copyright © 2017 DragonByte Technologies Ltd.

USMLE® & other trade marks belong to their respective owners, read full disclaimer
USMLE Forums created under Creative Commons 3.0 License. (2009-2014)