From external auditory canal microbiome to myringotomy techniques

The aims of this thesis were to increase the understanding of external auditory canal bacteria both in healthy and diseased ears, using novel methods and to investigate the tympanostomy treatment and compare surgical techniques used in tympanostomy tube insertions. This thesis is composed of four studies. Studies I and II examined the external auditory canal microbiome, whereas Study I was a pilot studying microbiome research methods. We found our “swab sampling” to be effective. Study I showed that the predominant bacteria of the healthy external auditory canal are Staphylococcus auricularis, Cutibacterium acnes, Alloiococcus otitidis, and Corynebacterium otitis. In Study II, microbiome samples from hearing aid users and asymptomatic volunteers were compared. The results showed that the long-term use of hearing aids lowers the bacterial diversity of the external auditory canal microbiome. The composition of microbes in hearing aid users was found to be mostly similar to that of asymptomatic control subjects, and pathogenic (infection-causing) bacterial findings were rare. Study III investigated the causative pathogens of acute otitis externa and auricular erysipelas, and their antimicrobial susceptibility testing results. The most frequent pathogens were Pseudomonas aeruginosa and Staphylococcus aureus. In auricular erysipelas associated cases, S. aureus dominated. Streptococci and P. aeruginosa were also frequent. Lowered antimicrobial susceptibility was rare and no multi-resistant bacteria were noted. In Study IV, ears with middle ear effusion received tympanostomy tube treatment, either using incisional myringotomy, CO2 laser myringotomy, or radiofrequency myringotomy. Patients were treated and had follow-up visits at Päijät-Häme Central Hospital until their tube extrusion. Special emphasis was placed on myringosclerosis formation and tympanometric testing. CO2 laser and radiofrequency proved to be safe myringotomy alternatives to the traditional incisional myringotomy. Myringosclerosis formation correlated with the severity of the middle ear ventilation problems and CO2 laser showed a tendency for less myringosclerosis formation. This thesis presents novel and important information regarding external auditory canal microbes and pathogens. This information can be utilized in clinical work and may contribute to the design and development of new treatment methods. In addition, we received valuable information about tympanostomy tubes, helping clinicians in planning and monitoring tympanostomy tube treatment.