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{{WBRQuestion
{{WBRQuestion
|QuestionAuthor={{Rim}}
|QuestionAuthor={{YD}} (Reviewed by Serge Korjian)
|ExamType=USMLE Step 1
|ExamType=USMLE Step 1
|MainCategory=Microbiology
|MainCategory=Microbiology
Line 8: Line 8:
|MainCategory=Microbiology
|MainCategory=Microbiology
|SubCategory=General Principles
|SubCategory=General Principles
|MainCategory=Microbiology
|MainCategory=Microbiology
|MainCategory=Microbiology
|MainCategory=Microbiology
|MainCategory=Microbiology
Line 20: Line 21:
|MainCategory=Microbiology
|MainCategory=Microbiology
|SubCategory=General Principles
|SubCategory=General Principles
|Prompt=In an experiment, a researcher grows bacteria in cultures that are colonized in uninfected asymptomatic 50 volunteers. Using appropriate technique, he notes the growth of the bacteria shown in the image below in approximately 30% of his subjects. Which of the following is most likely the site of colonization of the cultured organism?
|Prompt=In an experiment, a researcher obtains swab samples from 50 asymptomatic volunteers to detect the possible bacterial species that colonize uninfected individuals. He isolates several species and records his findings. Despite a significant similarily between recovered species, the growth of the bacteria shown in the image below was noted in approximately 25% of his subjects. Which of the following is most likely the site of colonization of the cultured organism?


[[Image:WBR0846.jpg|500px]]
[[Image:WBR0846.jpg|500px]]
|Explanation=The image shown above is that of Staphylococcus aureus. S. aureus appears as gram-positive (violet color on gram-stain) cocci (circular shape) that are organized in clusters that resemble grapes. In fact, the Greek word "staphyle" means "grape". Staphylococcus aureus classically colonizes the anterior nares. Approximately 30-50% of individuals carry S. aureus in the anterior nares and are completely healthy. Other sites of S. aureus are also possible, such as in the throat.
|Explanation=The image shown above is that of ''Staphylococcus aureus''. ''S. aureus'' is a gram-positive (violet color on gram-stain) coccus (circular shape) organized in clusters that resemble grapes. In fact, the Greek word "staphyle" means "grape". Staphylococcus aureus classically colonizes the anterior nares. Approximately 30-50% of individuals carry S. aureus in the anterior nares and are completely healthy. Other sites of S. aureus are also possible, such as in the throat.  
 
Educational Objective:
Staphylococcus aureus are gram-positive cocci that are arranged in clusters. The classical site of primary colonization is the anterior nares.
 
Reference:
Hu L, Umeda A, Kondo S, et al. Typing of Staphylococcus aureus colonising human nasal carriers by pulsed-field gel electrophoresis. J Med Microbiol. 1995; 42(2):127-32.
|AnswerA=Rectum
|AnswerA=Rectum
|AnswerAExp=Several organisms, such as lactobacilli, can colonize the rectum.
|AnswerAExp=Several organisms, such as Lactobacilli, can colonize the rectum.
|AnswerB=Oral cavity
|AnswerB=Oral cavity
|AnswerBExp=Anaerobes, such as Actinomyces israelii colonize the oral cavity.
|AnswerBExp=Anaerobes, such as ''Actinomyces israelii'' colonize the oral cavity.
|AnswerC=Vagina
|AnswerC=Vagina
|AnswerCExp=Several organisms, such as lactobacilli, can colonize the vagina.
|AnswerCExp=Several organisms, such as Lactobacilli, can colonize the vagina.
|AnswerD=Anterior nares
|AnswerD=Anterior nares
|AnswerDExp=Staphylococcus aureus colonizes the anterior nares.
|AnswerDExp=''Staphylococcus aureus'' colonizes the anterior nares.
|AnswerE=Nasopharynx
|AnswerE=Nasopharynx
|AnswerEExp=Several bacteria can colonize the nasopharynx, such as Neisseria species, H. influenzae type B, M. catarrhalis, and S. pneumoniae.
|AnswerEExp=Several bacteria can colonize the nasopharynx, such as Neisseria species, ''H. influenzae'' type B, ''M. catarrhalis'', and ''S. pneumoniae''.
|EducationalObjectives=''Staphylococcus aureus'' are gram-positive cocci that are arranged in clusters. The classical site of primary colonization is the anterior nares.
|References=Hu L, Umeda A, Kondo S, et al. Typing of Staphylococcus aureus colonising human nasal carriers by pulsed-field gel electrophoresis. J Med Microbiol. 1995; 42(2):127-32.
|RightAnswer=D
|RightAnswer=D
|WBRKeyword=staphylococcus, staphylococcal, anterior, nares, colonization, primary, site, culture, swab, grape, cluster, gram, positive, violet, stain, cocci, coccus
|WBRKeyword=Staphylococcus, Staphylococcal, Anterior nares, Colonization, Culture, Swab, Gram-positive, Cocci, Coccus
|Approved=No
|Approved=Yes
}}
}}

Revision as of 22:18, 4 March 2015
Author [[PageAuthor::Yazan Daaboul, M.D. (Reviewed by Serge Korjian)]]
Exam Type ExamType::USMLE Step 1
Main Category MainCategory::Microbiology
Sub Category SubCategory::General Principles
Prompt [[Prompt::In an experiment, a researcher obtains swab samples from 50 asymptomatic volunteers to detect the possible bacterial species that colonize uninfected individuals. He isolates several species and records his findings. Despite a significant similarily between recovered species, the growth of the bacteria shown in the image below was noted in approximately 25% of his subjects. Which of the following is most likely the site of colonization of the cultured organism?

]]

Answer A AnswerA::Rectum
Answer A Explanation AnswerAExp::Several organisms, such as Lactobacilli, can colonize the rectum.
Answer B AnswerB::Oral cavity
Answer B Explanation AnswerBExp::Anaerobes, such as ''Actinomyces israelii'' colonize the oral cavity.
Answer C AnswerC::Vagina
Answer C Explanation AnswerCExp::Several organisms, such as Lactobacilli, can colonize the vagina.
Answer D AnswerD::Anterior nares
Answer D Explanation AnswerDExp::''Staphylococcus aureus'' colonizes the anterior nares.
Answer E AnswerE::Nasopharynx
Answer E Explanation AnswerEExp::Several bacteria can colonize the nasopharynx, such as Neisseria species, ''H. influenzae'' type B, ''M. catarrhalis'', and ''S. pneumoniae''.
Right Answer RightAnswer::D
Explanation [[Explanation::The image shown above is that of Staphylococcus aureus. S. aureus is a gram-positive (violet color on gram-stain) coccus (circular shape) organized in clusters that resemble grapes. In fact, the Greek word "staphyle" means "grape". Staphylococcus aureus classically colonizes the anterior nares. Approximately 30-50% of individuals carry S. aureus in the anterior nares and are completely healthy. Other sites of S. aureus are also possible, such as in the throat.

Educational Objective: Staphylococcus aureus are gram-positive cocci that are arranged in clusters. The classical site of primary colonization is the anterior nares.
References: Hu L, Umeda A, Kondo S, et al. Typing of Staphylococcus aureus colonising human nasal carriers by pulsed-field gel electrophoresis. J Med Microbiol. 1995; 42(2):127-32.]]

Approved Approved::Yes
Keyword WBRKeyword::Staphylococcus, WBRKeyword::Staphylococcal, WBRKeyword::Anterior nares, WBRKeyword::Colonization, WBRKeyword::Culture, WBRKeyword::Swab, WBRKeyword::Gram-positive, WBRKeyword::Cocci, WBRKeyword::Coccus
Linked Question Linked::
Order in Linked Questions LinkedOrder::
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