Pathogens in Dog and Cat Bites


Source: Talan DA, et al. Bacteriologic analysis for infected dog and cat bites. N Engl J Med 1999;340:85-92.

This prospective case series was conducted at 18 different emergency departments in the United States as part of the Emergency Medicine Animal Bite Infection Study Group. The purpose of the study was to better define the bacteria responsible for infections of dog and cat bites. Only patients who met well-defined criteria for infection were enrolled.

Results were analyzed from 50 patients with infected dog bites and 57 patients with infected cat bites. A mix of both aerobes and anaerobes were isolated from 56% of all wounds, aerobes alone from 36%, anaerobes alone from only 1%, and 7% of cultures had no growth. Pasteurella species were the most common pathogens in both dog bites (50%) and cat bites (75%). (Pasteurella canis was the most common isolate in dog bites; Pasteurella multocida was the most common in cat bites). Streptococci, staphylococci, moraxella, corynebacterium, and neisseria were the next most common isolates. The predominate anaerobes were fusobacterium, bacteroides, porphyromonas, and prevotella species.

Comment by Stephanie Abbuhl, MD

The findings from this study emphasize the importance of the pasteurella species in both dog and cat bite infections. Although more common in cat bites, pasteurella species were isolated from 50% of dog bites, contradicting the impression that this is an uncommon pathogen in dog bites.

When empirical therapy for dog and cat bites is indicated, it should be directed against pasteurella, streptococci, staphylococci, and anaerobes. Unfortunately, many of the antibiotics typically used for routine skin and soft tissue infections, such as the anti-staphylococcal penicillins, first generation cephalosporins, clindamycin and erythromycin, are not very active against pasteurella. Pasteurella species are usually susceptible to ampicillin, penicillin, second- and third-generation cephalosporins, doxycycline, trimethoprim-sulfamethoxozole, fluoroquinolones, clarithromycin, and azithromycin. In addition, many species isolated from infected bites, including staphylococci and most anaerobes, are b-lactamase producers.

Given the constraints above, the following choices for empirical therapy are suggested: a combination of a b-lactamase antibiotic and a b-lactamase inhibitor (amoxicillin with clavulanic acid po or ampicillin with sulbactam IV), a second-generation cephalosporin with anaerobic activity (cefoxitin IM or IV), or combination therapy with either penicillin and a first-generation cephalosporin, or clindamycin and a fluoroquinolone. Azithromycin has shown some promise in vitro, with activity against common aerobic and anaerobic isolates from bite wounds.