Severe acute otitis media caused by mucoid Streptococcus pyogenes in a previously healthy adult

Streptococcus (S.) pyogenes is well recognized as the most common pathogen causing pharyngotonsillitis in school-age children. In Japan, mucoid Streptococcus pneumoniae is well known as a causative agent of severe acute otitis media (AOM); however, mucoid S. pyogenes has rarely been reported. To the best of our knowledge, this is the first report of an AOM patient caused by mucoid S. pyogenes in Japan. A 36-year-old previously healthy female was referred to our hospital with suspicion of cerebrospinal otorrhea due to increasing otalgia accompanied by headache following myringotomy. Bacterial cultures of middle ear secretions were performed, and mucoid-form colonies surrounded by zones of complete β-hemolysis were produced on sheep's blood agar. Antigen-agglutination test results were positive for S. pyogenes, and thus the patient received treatment with panipenem-betamipron 2.0 g/day for 10 days, which resolved nearly all symptoms. The bacteriological features of this strain were then investigated. The M-protein genotype encoded by the emm gene, the major virulence factor of S. pyogenes, was determined to be emm75. Generally, S. pyogenes forms colonies having non-mucoid matt appearances based on β-hemolysis of sheep's blood agar. The mucoid phenotype results from abundant production of hyaluronic acid capsular polysaccharide, a key virulence determinant. emm75 is common in noninvasive, but less common in invasive disease. In conclusion, mucoid S. pyogenes can cause severe infection even in previously healthy persons. Emergence of mucoid S. pyogenes and drug resistance trends should be monitored in the future.