Ear swabs are collected for the diagnosis of otitis externa only. They are not useful in the diagnosis of otitis media as the tympanic membrane (ear drum) separates the middle ear from the ear canal.
Otitis externa is a bacterial infection of the external auditory canal usually caused by Pseudomonas aeruginosa, Staphylococcus aureus, Streptococcus pneumoniae, Group A streptococcus or fungus / yeast. Polymicrobial infections are not unusual.
Direct Examination
Gram stain
Culture
| Media | Incubation |
| Blood Agar (BA) | CO2, 35°C x 48 hours |
| MacConkey Agar (MAC) | O2, 35°C x 48 hours |
| Chocolate Agar (CHOC) | CO2, 35°C x 48 hours |
If fungus is requested, add:
| Sabouraud’s Heart Infusion Agar (SABHI) | O2, 30°C x 4 weeks |
| SABHI with Chloramphenicol (SABHI-C) | O2, 30°C x 4 weeks |
For specimens from neonates only, identify and report Group B streptococcus.
For other organisms, a significant result is determined by the presence of a moderate to heavy growth of an organism which correlates with the predominant organism on the Gram stain. The Gram stain should also show >1+ pus cells. Full identification is required for all significant organisms except yeasts.
Gram stain
Report with quantitation the presence of pus cells and organisms.
Culture
Negative Report
“Normal skin flora” or “No growth”.
Positive Report
Quantitate all significant isolates with appropriate susceptibilities. If normal flora is also present, report with quantitation.
H.D. Isenberg, 2004. Wound Cultures – Wound and Soft Tissue Cultures, p. 3.13.1.1 – 3.13.1.16. In Clinical Microbiology Procedures Handbook, 2nd Edition, Vol 1 ASM Press, Washington, D.C.
H.D. Isenberg. 2004. Otitis Cultures p. 3.11.5.1 – 3.11.5.6. In Clinical Microbiology Procedures Handbook, 2nd Edition, Vol 1 ASM Press, Washington, D.C.