A 24-year-old man comes to the emergency department with leg swelling. His dog, which is fully vaccinated and has lived with him for the past year, bit him on the left leg last night, leading to a break in the skin and bleeding. The patient irrigated the wound with bottled water and soap and managed his pain with acetaminophen. This morning, the wound area became warm, red, and swollen. On examination, temperature is 36.4 C (97.5 F). There is an open wound on the left leg, with surrounding erythema, warmth, and tenderness. No wound drainage or crepitus is present. The distal pulses are palpable. Wound cultures grow gram-negative coccobacilli; the culture has a mouse-like odor. Which of the following organisms is most likely responsible for this patient's current presentation?

Question

A 24-year-old man comes to the emergency department with leg swelling.  His dog, which is fully vaccinated and has lived with him for the past year, bit him on the left leg last night, leading to a break in the skin and bleeding.  The patient irrigated the wound with bottled water and soap and managed his pain with acetaminophen.  This morning, the wound area became warm, red, and swollen.  On examination, temperature is 36.4 C (97.5 F).  There is an open wound on the left leg, with surrounding erythema, warmth, and tenderness.  No wound drainage or crepitus is present.  The distal pulses are palpable.  Wound cultures grow gram-negative coccobacilli; the culture has a mouse-like odor.  Which of the following organisms is most likely responsible for this patient's current presentation?

Quizplus · Accepted Answer

11ec160b_380a_dca0_9249_ab40c6bea3aa_MD0001_00 This patient has a skin and soft-tissue infection (SSTI) that developed at the site of a dog bite relatively soon following the bite. Pasteurella multocida is an organism found in the mouths of dogs and is responsible for the majority of acute skin infections following a dog bite. Infection typically occurs within 24 hours of inoculation and has a characteristic mouse-like odor (indole-positive species). P multocida SSTI can also occur following a cat bite. Other organisms associated with dog bites include staphylococci, streptococci, and Capnocytophaga canimorsus. Management includes wound care and antibiotics (eg, amoxicillin-clavulanate). (Choice A) Bartonella henselae is associated with cat-scratch disease, which can develop following inoculation from an infected cat and presents with lymphadenopathy that is often self-limiting. It is not associated with dog bites. (Choices B and I) Campylobacter jejuni typically causes gastrointestinal (diarrheal) illness, and Proteus mirabilis is a common cause of urinary tract infection. (Choices C and E) Clostridium perfringens is an anaerobe that can cause necrotizing SSTI, which occurs most commonly after a traumatic wound and leads to myonecrosis and gas gangrene. Erysipelothrix rhusiopathiae is a gram-positive rod (not a gram-negative coccobacillus) that causes erysipeloid. (Choices D and G) Coxiella burnetii can cause Q fever, a mild form of pneumonia. Fusobacterium is part of the anaerobic oral flora potentially causing aspiration pneumonia or pharyngitis (Lemierre disease). (Choice F) Francisella tularensis causes tularemia, a zoonotic infection that can occur following contact with lagomorphs and rodents (eg, rabbits, beavers, squirrels). The presentation is variable (eg, severe febrile pulmonary infection, ulcerative disease at inoculation site). Educational objective: Pasteurella multocida is a cause of soft-tissue infection that develops within 24 hours following a dog or cat bite. Management includes wound care and antibiotics targeted against this organism. __________ References: Dog and cat bites. (http://www.ncbi.nlm.nih.gov/pubmed/25250997) Bite wounds and infection. (http://www.ncbi.nlm.nih.gov/pubmed/1562653)

A 24-Year-Old Man Comes to the Emergency Department with Leg