Gram's stain of a positive blood culture is the clinician’s first indication of a possible causative infective organism and a guide to suitable antimicrobial therapy prior to cultural and phenotypic identification with susceptibility test results. Occasionally interpretation of a Gram's stain can be difficult or no organisms may be seen if there is a low bacterial load. We report such a case where a positive blood culture taken from the Hickman line of an immunocompromised patient flagged positive at five days incubation but no organisms were seen on Gram's stain. Upon sub culture, a slow growing Gram positive bacillus was isolated which was initially misidentified and reported as a diphtheroid species. The actual identity of this organism and further isolates was later elucidated as Mycobacterium mucogenicum, a rapidly growing nontuberculous mycobacterium (NTM).
- Blood culture
- Gram's stain