As I stumbled through this question:

A 16-year-old female patient presented to her family physician with a complaint of an abnormal vaginal discharge and pruritus (itching). The patient denied having sexual activity and recently completed a course of doxycycline for the treatment of her acne. An examination of a Gram-stained vaginal smear revealed the presence of gram-positive oval cells about 4–8 μm in diameter. Her vaginitis is caused by which of the following agents? (A) Bacterium (B) Virus (C) Protozoa (D) Fungus (E) Prion

I noticed that in order to answer such question, one possible way is to know the diameter range of each pathological group because gram stain can be positive in both fungi and bacteria and so is gram negative.

I have googled and searched but found no such information; all i found was about largest bacteria in general (not pathogenic bacteria) and same for fungi.

It would be extremely useful to know the following diameter range of:

  • pathogenic gram-positive bacteria
  • pathogenic gram-negative bacteria
  • pathogenic fungi
  • pathogenic viruses

P.S. by pathogenic i mean pathogenic to Humans

  • I think you should search for side effects of doxycycline treatment to ànswer this question. It causes vaginal yeast infection. – user237650 May 19 at 8:18
  • 1
    Yes @Mesentery, I figured that out later. But still, knowing the diameters of pathogen groups will give extra hints and help in excluding other options even if one doesn’t know/recall side effects of drugs or whatsoever. I really hope that someone will answer this question :) – user13798 May 19 at 8:41
  • As for bacteria (most common sizes): cocci ~ 1 um in diameter; rods ~ 1 x 2 to 5 um: filamentous bacteria ~ 1 x 10 (or more) um. – Martin Klvana May 21 at 15:55

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