Rapidly growing mycobacteria: clinical and microbiologic studies of 115 cases

We analyzed clinical and microbiologic features of 115 cases involving rapidly growing mycobacteria (RGM) isolated at the University of Texas M.D. Anderson Cancer Center, Houston (2000-2005) and identified by 16S ribosomal RNA gene sequencing analysis. At least 15 RGM species were included: Mycobacterium abscessus (43 strains [37.4%]), Mycobacterium fortuitum complex (33 strains [28.7%]), and Mycobacterium mucogenicum (28 strains [24.3%]) most common, accounting for 90.4%. Most M abscessus (32/43) were isolated from respiratory sources, whereas most M mucogenicum (24/28) were from blood cultures. Antimicrobial susceptibility tests showed that M abscessus was the most resistant species; M mucogenicum was most susceptible. From blood and catheter sources, 46 strains (40.0%) were isolated; 44 represented bacteremia or catheter-related infections. These infections typically manifested high fever (mean temperature, 38.9 degrees C), with a high number of RGM colonies cultured. All infections resolved with catheter removal and antibiotic therapy. Six strains (M abscessus and M fortuitum only) were from skin, soft tissue, and wound infections. There were 59 strains from respiratory sources, and 28 of these represented definitive to probable infections. Prior lung injuries and coisolation of other pathogenic organisms were common. Overall, 78 RGM strains (67.8%) caused true to probable infections without direct deaths.