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Chapter 10: Normal Human Microbiota

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A 26-year-old woman visits her physician because of an unusual vaginal discharge. On examination, the physician observes a thin, homogeneous, white-gray discharge that adheres to the vaginal wall. The pH of the discharge is 5.5 (normal, <4.3). On Gram stain, many epithelial cells covered with gram-variable rods are seen. Bacterial vaginosis is diagnosed. Which one of the following normal genital flora microorganisms is greatly decreased in bacterial vaginosis?

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(A) Corynebacterium species

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(B) Staphylococcus epidermidis

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(C) Prevotella species

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(D) Candida albicans

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(E) Lactobacillus species

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Certain microorganisms are never considered to be members of the normal flora. They are always considered to be pathogens. Which one of the following organisms fits into that category?

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(A) Streptococcus pneumoniae

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(B) Escherichia coli

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(C) Mycobacterium tuberculosis

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(D) Staphylococcus aureus

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(E) Neisseria meningitidis

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A 9-year-old girl develops fever and severe pain on the right side of her throat. On examination, redness and swelling in the right peritonsillar area are seen. A peritonsillar abscess is diagnosed. The most likely organisms to be cultured from this abscess are

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(A) S aureus

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(B) S pneumoniae

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(C) Corynebacterium species and Prevotella melaninogenica

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(D) Normal oral nasal flora

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(E) Viridans streptococci and C albicans

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A 70-year-old man with a history of diverticulosis of the sigmoid colon experiences a sudden onset of severe left lower quadrant abdominal pain. Fever develops. The severe pain gradually subsides and is replaced by a constant aching pain and marked abdominal tenderness. A diagnosis of probable ruptured diverticulum is made, and the patient is taken to the operating room. The diagnosis of ruptured diverticulum is confirmed, and an abscess next to the sigmoid colon is found. The most likely bacteria to be found in the abscess are

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(A) Mixed normal gastrointestinal flora

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(B) Bacteroides fragilis alone

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(C) E coli alone

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(D) Clostridium perfringens alone

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(E) Enterococcus species alone

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Antimicrobial therapy can decrease the amount of susceptible bowel flora and allow proliferation of relatively resistant colonic bacteria. Which one of the following species can proliferate and produce a toxin that causes diarrhea?

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(A) Enterococcus species

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