Review Question - QID 218806

This patient who was bitten by a stray cat and has a wound culture positive for a gram-negative coccobacillus was most likely infected by Pasteurella multocida.

Pasteurella multocida is a facultative anaerobic encapsulated gram-negative coccobacillus that can cause cellulitis at the site of inoculation. The most common mechanism by which patients are infected by this organism is a cat bite though bites from other animals may also carry the organism. Patients will present with a wound with signs of cellulitis such as purulence, surrounding erythema, and edema. More extensive infection can result in systemic symptoms such as fever and chills as well as osteomyelitis. Selective culture results for this organism include catalase positivity, oxidase positivity, and growth on 5% sheep blood. The treatment for this condition is amoxicillin/clavulanate. Patients without symptoms who have deep puncture wounds from a cat bite should also receive antibiotic prophylaxis with extended spectrum penicillins in order to treat a possible polymicrobial source.

Adler et al. present a case of Pasteurella multocida resulting in septic shock. They found that this patient was originally misdiagnosed with a urinary tract infection but was later discovered to have a cat bite. They recommend keeping this organism in mind in patients with strange soft tissue wounds.

Incorrect Answers:
Answer 1: Brucella melitensis is also a gram-negative coccobacillus that is associated with animals; however, patients are most commonly infected by ingesting contaminated foods. This organism results in undulant fever with headache, arthralgia, and chills.

Answer 2: Francisella tularensis is also a gram-negative coccobacillus that is associated with animal bites. The hosts for this organism are ticks, rabbits, and deer flies. This organism causes ulceroglandular disease.

Answer 4: Pseudomonas aeruginosa is a gram-negative bacillus that can cause osteomyelitis in patients that experience puncture wounds through a shoe or clothing. This organism causes skin and soft tissue infections as well as pneumonia and systemic disease.

Answer 5: Staphylococcus aureus is the most common cause of skin and soft tissue infections; however, these organisms are gram-positive cocci that organize in clusters.

Bullet Summary:
Pasteurella multocida is a gram-negative coccobacillus that can cause soft tissue infections after infected cat bites.