Microbiology of otitis externa in the secondary care in United Kingdom and antimicrobial sensitivity

Introduction Otitis externa is one of the most common conditions seen in the otolaryngology clinics. There are no recently published studies that have looked at the causative pathogens of the otitis externa seen in secondary care in the United Kingdom and their antimicrobial sensitivities. We present results of a prospective study to determine the current bacteriology of the condition. Methods Swabs were taken from the external auditory canals of the patients who presented to the otolaryngology emergency clinic with symptoms of otitis externa. These were analysed using microscopy, culture and sensitivity testing in one laboratory. The samples were cultured on blood agar, chocolate agar, Sabouraud agar, fastidious anaerobes agar with neomycin and staph/strep agar. Antimicrobial sensitivities of isolated pathogens were tested on iso-sensitest and blood agars using the BSAC disc diffusion template program. Results The most commonly identified pathogen was Pseudomonas aeruginosa (45.1%), followed by Staphylococcus aureus (9%), anaerobes (6.3%), β haemolytic Streptococcus group G (2.8%), β haemolytic Streptococcus group A (1.4%), Streptococcus pneumoniae (0.7%), methicillin resistant S. aureus (0.7%), Candida species (9.7%), Aspergillus species (4.2%) and Absidia corymbifera (0.7%). One hundred percent resistance of Pseudomonas isolates to neomycin, chloramphenicol, trimethoprim and amoxicillin was observed while most were sensitive to ciprofloxacin (100%), polymixin B (100%) and gentamicin (98.5%). S. aureus isolates were sensitive to gentamicin and flucloxacillin (100%). 92.3% were sensitive to neomycin and chloramphenicol. Resistance to penicillin and amoxicillin is observed. All isolates anaerobes were sensitive to metronidazole. Conclusion Polymixin B, gentamicin or ciprofloxacin topical preparations should be used as first line treatment of otitis externa. If the infection does not settle swab results should be used to guide further treatment.