Rapidly Progressive Pasteurella multocida Soft-Tissue Infection After a Cat Bite: Diagnosis by Culture and MALDI-TOF Mass Spectrometry: A Case Report

Abstract

Background:

Pasteurella multocida is a Gram-negative coccobacillus that lives in the mouth and upper airway of cats and dogs. It causes soft-tissue infection after bites and scratches. The infection can progress within hours. The organism can also be missed in the laboratory because it is small and pleomorphic.

Case presentation:

A 57-year-old man with hypertension and coronary artery disease was bitten on the left forearm by a cat. He received tetanus toxoid and rabies post-exposure prophylaxis and was discharged. He returned within 24 hours with throbbing pain and intermittent fever. Examination showed a 3-cm fluctuant swelling over the posterior forearm with warm, tender, red skin. He had no known immune deficiency disorders and was hemodynamically stable. No regional lymphadenopathy was found. Incision and drainage under local anesthesia released about 3 mL of pus. Oral amoxicillin-clavulanate and linezolid were started empirically. A Gram-stained smear of the pus showed small, pleomorphic Gram-negative coccobacilli. Culture produced convex, greyish, non-hemolytic colonies on blood and chocolate agar and no growth on MacConkey agar. MALDI-TOF mass spectrometry identified the isolate as P. multocida. Disk diffusion testing showed susceptibility to penicillin, ampicillin, amoxicillin-clavulanate, chloramphenicol, trimethoprim-sulfamethoxazole and levofloxacin. Linezolid was stopped and amoxicillin-clavulanate was continued alone. At follow-up, the cellulitis had resolved and the wound showed healthy granulation tissue.

Conclusion:

P. multocida should be suspected in any rapidly progressive soft-tissue infection after a cat bite. Culture followed by MALDI-TOF MS enabled species-level identification after overnight incubation. Susceptibility results then allow the empirical regimen to be narrowed to a single agent. A history of animal contact should always be sought.