Mycobacterium chelonei masquerading as Corynebacterium in a case of infectious keratitis: a diagnostic dilemma

The diagnosis of Mycobacterium keratitis can often be missed both clinically and microbiologically and this report highlights one such case.

Review of medical and microbiological records.

We report a case of Mycobacterium keratitis in a 25-year-old man that was misdiagnosed as Corynebacterium keratitis at initial presentation. Presence of partially stained and beaded bacilli in a Gram-stained smear of repeat corneal scrapings raised the suspicion of an unusual organism. Ziehl-Neelsen staining of the decolorized Gram-stained smear and subculture on Löwenstein-Jensen medium helped us to establish the diagnosis.

A high degree of suspicion needs to be maintained, especially in cases in which (a) there is a history of corneal trauma involving a foreign body, (b) the Gram-stained smear of corneal scrapings shows a paucity of organisms and the presence of partially stained and beaded bacilli in the presence of confluent growth of colonies resembling those of Corynebacterium, and (c) a typical corneal feature like "cracked windshield" stromal lesion is seen, to avoid such a misdiagnosis. Inclusion of a Löwenstein-Jensen culture at the initial presentation, especially when the clinical presentation is atypical, as seen in this case, will lead to an early diagnosis.