MALDI-TOF mass spectrometry reveals a highly complex bacterial profile of otitis media with effusion

With conventional microbiological methods, a significant proportion of middle ear effusion (MEE) proves to be sterile. Accurate molecular biological techniques have been used to identify only pathogenic bacteria. Matrix assisted laser desorption and ionization time-of-flight mass spectrometry (MALDI-TOF MS) is an adequate tool for the precise and simultaneous identification of a wide range of bacterial species from a small sample. The aim of this study was to explore the use of MALDI-TOF MS in revealing the frequency and complexity of bacterial flora in MEE in otitis media with effusion (OME).

MEEs from 40 children with chronic otitis media with effusion were examined for 2000 pathogenic, facultative pathogenic and nonpathogenic bacterial species using MALDI-TOF MS. Two middle ear samples from children who underwent cochlear implantation with healthy middle ear were also examined in the same way.

No bacteria were found in healthy control samples and 92% of OME samples were positive for at least one bacterium. In 52% of the samples more than one bacterium was identified. In total 39 bacterial species were found in the middle ear samples. Of the positive samples 19% contained those pathogens which were previously thought to contribute OME.

MALDI-TOF MS is a suitable tool for identifying a wide range of bacterial species in MEE. Results show that bacterial flora of MEE in OME is more diverse and abundant than it was formerly thought. This previously unreported bacterial invasion may help to obtain proper understanding and therapy of OME.