Microbiology of infected poison ivy dermatitis

We report the aerobic and anaerobic microbiology of secondarily infected poison ivy dermatitis. The study involved retrospective review of clinical and microbiology laboratory records of patients with secondarily infected poison ivy lesions. Bacterial growth was noted in 33 specimens. Aerobic or facultative anaerobic bacteria only were present in 18 (55%) patients, anaerobic bacteria only in seven (21%), and mixed anaerobic-aerobic bacteria in eight (24%). Forty-five isolates were recovered (1.4 per specimen): 27 aerobic or facultative anaerobic bacteria, and 18 strict anaerobes. The predominant aerobic and facultative anaerobic bacteria were Staphylococcus aureus (13 isolates) and group A beta-haemolytic streptococci (six). The predominant anaerobes were Peptostreptococcus spp. (seven isolates), pigmented Prevotella and Porphyromonas spp. (four) and Fusobacterium spp. (two). Single bacterial isolates were recovered in 18 (55%) patients, eight of which were S. aureus. Nineteen of the organisms isolated from 16 (48%) patients produced the enzyme beta-lactamase. Organisms that resided in the mucous membranes close to the lesions predominated in those infections. Enteric gram-negative rods and Bacteroides fragilis group predominated in leg and buttock lesions. Group A beta-haemolytic streptococci, pigmented Prevotella and Porphyromonas and Fusobacterium spp. were most frequently recovered from lesions of the finger, face and neck. The polymicrobial aetiology of secondarily infected poison ivy lesions, and the association of bacterial flora with the anatomical site of the lesions, are demonstrated.