Learning Objectives: chronic otitis media culture strain.

Introduction: The perioperative prophylactic antibiotic of chronic otitis media (COM) surgery is selected based on the result of preoperative bacterial culture. Learning objectives: To investigate the changes of strains of middle ear through COM surgery, we conducted bacterial culture before, during, and after COM surgery. Method: We analyzed the medical records of 156 patients who received COM surgery at Daejeon St. Mary's Hospital from March 2012 to September 2015. Preoperative bacterial culture was conducted with otorrhea or swap of middle ear mucosa, intraoperative culture was conducted with granulation tissue in either the middle ear or mastoid cavity, and postoperative culture was selectively conducted when otorrhea was developed after surgery. Results: Sixty cases of tympanoplasty only and 96 cases of both tympanoplasty and mastoidectomy were performed for 111 cases of COM-without-cholesteatoma and 45 cases of COM-with-cholesteatoma. The growths of bacteria were observed in 71 patients (45.5%) of preoperative culture, in 21 patients (13.5%) of intraoperative culture, and in 7 patients (4.5%) of postoperative culture. Methicillin-resistant staphylococcus (MRSA) was identified most commonly in all of tests, and it was identified from 23 of 71 cases (32.4%), 11 of 21 cases (52.4%), and 5 of 7 cases (71.4%), respectively, and the percentage of MRSA was increased from the intraoperative to postoperative identification tests. In 23 cases of MRSA in preoperative tests, 6 cases showed MRSA also in intraoperative tests, and 3 cases showed MRSA in postoperative tests. Conclusions: The distribution of strains in middle ear was changed through COM surgery, and the percentage of resistant strains, in particular, MRSA was increased. But, the bacterial culture results of postoperative otorrhea showed lower agreement with that of preoperative or postoperative culture, and the re-identification of strains is needed.