Histologic sections revealed fibrovascular and adipose tissue with granulation tissue and focal prominent acute inflammation.(Images 01, 02, 03 and 04) Gram stain showed numerous gram positive rods (Images 05 and 06) Acid fast stain revealed several groups of rarely beaded acid fast rods (Images 07 and 08)
Aerobic cultures showed rare coagulase negative staphylococcus. Gram positive rods grew on 5% sheep blood agar after four days (Image 09). The gram positive rods were acid fast positive. Growth of buff colored, nonphotochromogenic, rounded, smooth colonies without filamentous extensions was noted on Lowenstein-Jensen agar at 28oC in four days (Images 10 and 11). Subculture onto Lowenstein-Jensen agar with 5% NaCl and MacConkey agar without Crystal Violet showed growth in 5 days. Growth on tap water agar after 48 hours at 28oC lacked aerial hyphae and showed morphology typical of mycobacterial species. The 3-day arylsulfatase test was positive. The nitrate reduction and iron uptake tests were negative. The organism was identified as Mycobacterium abscessus (formerly M. chelonae subsp. abscessus).
Drug susceptibility testing was performed at the University of Texas Health Center Department of Microbiology (Richard J. Wallace, Jr., M.D.). The following results were obtained: