Microbiology of nonbullous impetigo

Our objective was to establish the aerobic and anaerobic microbiology of nonbullous impetigo (NI) in children. We used a retrospective review of clinical microbiology laboratory and patients' records. Specimens were obtained from 40 patients with NI lesions and showed bacterial growth. Aerobic or facultative anaerobic bacteria only were present in 24 patients (60%), strict anaerobic bacteria only in 5 patients (12.5%), and mixed anaerobic-aerobic flora was present in 11 patients (27.5%). Sixty-four isolates were recovered (1.6 per specimen): 43 aerobic or facultative, and 21 anaerobic. The predominant aerobic and facultative bacteria were Staphylococcus aureus (29 isolates), Group A beta hemolytic streptococcus (GABHS) (13 isolates), and Escherichia coli (1 isolate). The predominant anaerobes were Peptostreptococcus spp. (12), pigmented Prevotella spp. (5), Fusobacterium spp. (2), and Bacteroides fragilis (1). Single bacterial isolates were recovered in 17 patients (42.5%), 13 of which were S. aureus. S. aureus alone or mixed with GABHS or Peptostreptococcus spp. were isolated from all body sites. Mixed flora of Peptostreptococcus spp. with Prevotella spp. or Fusobacterium spp. was mostly found in infections of the head and neck, while E. coli mixed with B. fragilis and Peptostreptococcus spp. were isolated from one infection of the buttocks area. Thirty-three organisms isolated from 32 patients (80%) produced the enzyme beta-lactamase. This study demonstrates the polymicrobial aerobic-anaerobic microbiology of NI lesions.