Microbiological features and pathogenesis of peritonsillar abscesses.

Samples of pus aspirated from 53 peritonsillar abscesses were examined in detail for aerobic and anaerobic bacteria, and the microbiological results correlated with clinical data in 44 cases. In 45 samples (85%) cultures were positive: 7 yielded organisms consistent with an aerobic infection, mainly Lancefield group A beta-haemolytic streptococci (5/7), and 38 yielded organisms consistent with an anaerobic infection. The anaerobic infections were usually mixed, but in two cases Fusobacterium necrophorum was isolated in pure culture. Peptostreptococcus micros and Streptococcus milleri were the predominant isolates in this group. Direct Gram stain smear and gas-liquid chromatography were useful indicators of the type of infection present. Samples from ten patients (18.9%) grew one or more beta-lactamase-producing isolates. Of the 25 patients prescribed antibiotics by their general practitioners prior to admission, 18 received one or more beta-lactam antibiotics. Most cases of peritonsillar abscess were due to mixed anaerobic infections, Lancefield group A beta-haemolytic streptococci playing a central role in only a minority of cases. In light of these findings and the possibility of infection with beta-lactamase-producing isolates, it is suggested that the first-line antibiotic therapy in this group of patients should include a chemotherapeutic agent directed against anaerobic bacteria.