Medical MCQ - A truck driver was involved in a serious accident and received second and third degree burns over his body. He was placed in the burn unit and, on his twelfth day of his admission, developed a wound infection with a bluish-green exudate. Treatment with chloramphenicol and tetracycline was unsuccessful. A gram-negative, motile organism was isolated that was oxidase-positive, did not ferment lactose, sucrose, or glucose, but grew on MacConkey's agar and produced a fruity aroma on that medium. Which of the following organisms was most likely isolated?

A truck driver was involved in a serious accident and received second and third degree burns over his body. He was placed in the burn unit and, on his twelfth day of his admission, developed a wound infection with a bluish-green exudate. Treatment with chloramphenicol and tetracycline was unsuccessful. A gram-negative, motile organism was isolated that was oxidase-positive, did not ferment lactose, sucrose, or glucose, but grew on MacConkey’s agar and produced a fruity aroma on that medium. Which of the following organisms was most likely isolated?

Candida albicans

Clostridium perfringens

Escherichia coli

Pseudomonas aeruginosa

Question Category:

Microbiology

Correct Answer:

Pseudomonas aeruginosa

Description:

Pseudomonas aeruginosa is a very common oppounist in burn patients, in whom it classically causes secondary wound infections and septicemia. It may also cause cystitis in patients with urinary catheters and pneumonia in patients with cystic fibrosis. The organism is found in water and usually gains access to the body this source, as a contaminant in the water used in respirators or in water baths, etc. used to cleanse wounds. This organism is a non-fermenter, that is, it does not metabolize sugars by classic pathways. It produces a blue-green, water-soluble pigment (pyocyanin), and has a fruity odor when growing on laboratory media. It has a propensity for developing antibiotic resistance; current therapy employs the synergistic combination of an aminoglycoside, such as amikacin, with a cell wall synthesis inhibitor (carbenicillin, ticarcillin, or piperacillin). Candida albicans is a normal flora yeast that will appear as very large, gram- positive, spherical-to-ovoid organisms with budding daughter cells in Gram-stained preparations. Candidiasis is an oppounistic infection in individuals with a compromised immune system. The fungus usually causes mucocutaneous lesions, but in severely compromised individuals like AIDS patients, systemic disease may occur. Oral candidiasis appears as creamy, white patches of exudate that can be scraped off an inflamed tongue or buccal mucosa. Clostridium perfringens is a gram-positive, spore-forming, anaerobic rod. It is a common cause of gas gangrene when it is introduced into a wound. The organism produces a variety of toxins and enzymes that enable it to destroy muscle tissue and spread through the soft tissues of the body. Escherichia coli is a lactose-fermenting, gram-negative rod commonly seen as normal flora of the intestine of man. It is the most common cause of pyelonephritis, and sepsis in patients with indwelling urinary catheters. It is also the major cause of traveler's diarrhea with watery stools and is a very impoant pathogen in neonates, who become infected during passage through the bih canal. Ref: Brooks G.F. (2013). Chapter 16. Pseudomonads, Acinetobacters, and Uncommon Gram-Negative Bacteria. In G.F. Brooks (Ed), Jawetz, Melnick, & Adelberg's Medical Microbiology, 26e.

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