Question

multiple choice question
which of the following would be clinically significant in determining presence of an infection?

• absence of microbes in blood
• isolation of small numbers of e. coli from a urine sample
• presence of a few colonies of mycobacterium tuberculosis in a sputum culture
• isolation of staphylococcus species from the skin

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Explanation:

• Absence of microbes in blood is normal (blood is sterile in healthy state, so this doesn't indicate infection).
• Small numbers of E. coli in urine may be contamination or normal flora (not always indicative of infection).
• Staphylococcus on skin is normal flora (skin has resident microbes, so isolation here isn't indicative of infection).
• Mycobacterium tuberculosis in sputum culture: M. tuberculosis causes tuberculosis, and its presence in sputum (a site where it shouldn't be normally) is clinically significant for TB infection.

Answer:

C. presence of a few colonies of Mycobacterium tuberculosis in a sputum culture