Case 56

1. Presented by Robert Kruse, MD, PhD and reviewed by Heba Mostafa, MBBCh, PhD

A young patient who emigrated from a country with a tropical climate, presented to the clinic with a chronic non-healing axillary ulcer. The lesion started as a pus filled blister. There was no associated insect bite and no pruritus or pain. The patient was treated with one course of clindamycin, without significant improvement. The family history is notable for TB infection, which was diagnosed by a "blood test." The family member had no respiratory symptoms and was treated with three drugs for 6 months. The patient denies cough, fever, night sweats or weight loss. The patient had a positive QuantiFERON Gold TB test and subsequently had a chest X-ray which showed mediastinal fullness concerning for bilateral hilar adenopathy and possible TB disease.
Physical examination revealed a 1 cm nodular, indurated lesion in the left axilla, with central fistula and minimal active drainage. A punch biopsy from the lesion was obtained.

Laboratory Results
Bacterial culture from the wound showed very light mixed skin flora with no polymorphonuclear leukocytes. Fungal culture showed no fungal organisms and no fungus was seen by calcofluor white stain. The auramine-rhodamine stain showed no acid fast bacilli. The automated broth culture was positive for growth of a mycobacterial species in 19 days. The Ziehl-Neelsen stain of the positive culture showed cording of numerous bacilli which had a beaded appearance. Species identification was attempted using 4 mycobacterial probes for the M. tuberculosis complex, the M. avium complex, M. kansasii and M. gordonae, all of which were negative. The mycobacterial strain was finally identified as M. decipiens by 16S rRNA sequencing.
Question: True or False?
It is not known if all strains of M. decipiens are intrinsically resistant to rifampicin.