Corynebacterium amycolatum: An Unexpected Pathogen in the Ear.

Non-diphtheritic Corynebacteria are now being increasingly recognised as the causative agents of various infections. Among these organisms, Corynebacterium amycolatum is the most frequently isolated one. It has been isolated from urine, pus, catheter tips, blood, prostatic secretion, cerebrospinal fluid and sputum. However, to the best of our knowledge, there are no reports on its role in ear infections. Here, we present 12 cases of ear infection with C.amycolatum. A high index of suspicion is necessary for identification of these gram positive bacilli as they resemble other Corynebacterium species on gram stain. They have metachromatic granules which can be demonstrated by Albert's stain and form characteristic dry, flat colonies on blood agar. These organisms are frequently resistant to ceftriaxone and imipenem. In our study, among the 12 isolates, eight isolates were resistant to ceftriaxone and four to imipenem and two were intermediately susceptible to ceftriaxone although all the 12 strains were uniformly susceptible to vancomycin. All the isolates were negative for toxA and toxB genes by PCR. Genomic sequencing of two isolates confirmed them as C.amycolatum. C.amycolatum is a relatively rare cause of pyogenic ear infections. As it demonstrates more antibiotic resistance than other similar organisms, careful identification with antibiotic susceptibility testing is required in managing these infections.