Outcome of bacterial culture from mastoid granulations: is it relevant in chronic ear disease?

Abstract

Objective: To detect the presence of bacteria in mastoid granulations and compare its prevalence in both types of chronic suppurative otitis media (CSOM). To find out if stage of disease activity, age, duration of disease, and aditus patency relate to obtaining positive cultures.

Study design and setting: A prospective, parallel group study done at a tertiary care referral centre. Mastoid granulations from 79 patients with CSOM undergoing mastoidectomy were processed for anaerobic and aerobic bacteria.

Results: Aerobes were isolated from 57.55 per cent of the tubotympanic and 74.4 per cent of atticoantral disease (p = 0.18). Anaerobic cultures were positive in one case from each group. Monomicrobial growth was detected in 37.5 per cent of tubotympanic and 48.5 per cent of atticoantral disease. Polymicrobial growth occurred in 20 per cent and 25.6 per cent in the tubotympanic and atticoantral groups, respectively. The predominant aerobic isolate was coagulase negative Staphylococcus, followed by Pseudomonas aeruginosa, Staphylococcus aureus, non-fermenting Gram-negative bacteria, Enterobacter and Enterococcus, Proteus species, Citrobacter, non-pathogenic Neisseria, aerobic spore formers were grown only in atticoantral disease. A single isolate of Aspergillus was grown. Correlating the state of disease activity of the ears with positive mastoid granulation cultures, six out of the eight inactive ears were culture positive along with seven out of the nine active and 10 out of the 23 quiescent ears. Positive mastoid granulation cultures were obtained in 60 per cent of those with blocked aditus and 42.9 per cent with patent aditus.

Conclusion and significance: In this study, we found that mastoid granulations are not sterile but harbour polymicrobial pathogens. Positive cultures were obtained irrespective of stage of disease activity, age, duration of disease and aditus patency. The pattern of organisms cultured from safe and unsafe CSOM and also from ears in active, quiescent and inactive stages, were similar. These findings suggest that these organisms may be responsible for mastoid granulations. We also noted that positive cultures had no statistical correlation with aditus patency and duration of disease. We suggest further studies to evaluate the significance of asymptomatic mastoid granulations harbouring organisms and whether opening the mastoid antrum and achieving aditus patency, irrespective of the stage of disease activity, will help improve the long-term surgical outcome and also prevent recurrence of ear discharge.