Characterization of Rough and Smooth Morphotypes of Mycobacterium abscessus Isolates from Clinical Specimens

Abstract

Mycobacterium abscessus, which consists of the two subspecies M. abscessus subspecies abscessus and M. abscessus subspecies bolletii, can produce rough or smooth colony morphologies. Here we analyzed 50 M. abscessus isolates cultured from the respiratory specimens of 34 patients, 28 (82%) of whom had cystic fibrosis (CF), with respect to their colony morphologies and antibiotic susceptibilities. The overall proportions of occurrences of the two morphotypes were similar, with specimens from 50% of the patients showing a rough and 38% showing a smooth morphotype. A total of 12% of the specimens from the patients showed both morphotypes simultaneously. At the subspecies level, the proportions of rough and smooth morphotypes differed substantially; 88% of rough morphotypes belonged to M. abscessus subspecies abscessus, and 85% of smooth morphotypes belonged M. abscessus subspecies bolletii. Inducible clarithromycin resistance due to the Erm(41) methylase, as well as high-level resistance to clarithromycin due to mutations within the rrl gene, occurred independently of the morphotype. The MIC 50 s of amikacin and cefoxitin were identical for the two morphotypes, whereas the MIC 50 s of tigecycline were 0.25 g/ml for the rough morphotype and 2.0 g/ml for the smooth morphotype. Our results show that the smooth morphotype was more dominant in respiratory specimens from CF patients than previously thought. With respect to resistance, colony morphology did not affect the susceptibility of Mycobacterium abscessus to the first-line antibiotics clarithromycin, amikacin, and cefoxitin.T he genus Mycobacterium contains more than 100 different species which belong either to the Mycobacterium tuberculosis complex or to the large group of nontuberculous mycobacteria (NTMs). M. abscessus is an NTM, and clinical studies have begun to shed light on its epidemiology. M. abscessus is involved in soft tissue infections and is a dominant respiratory pathogen in patients with cystic fibrosis (CF). It is the second-most-common NTM species isolated from CF patients in the United States and the most common NTM species isolated from CF patients in Europe (1-6). Fatal infections with M. abscessus have been reported, especially after lung transplantation (7). M. abscessus has been subdivided in type I and type II, which, together with Mycobacterium chelonae, share identical 16S rRNA genes but show differences within the hsp65 gene (8, 9). Based on multilocus sequence analysis of hsp65, rpoB, secA, and the 16S-23S internal transcribed spacer (ITS) region, M. abscessus was further subdivided into three species, M. abscessus (sensu stricto), M. bolletii, and M. massiliense (10, 11). Recently, uniting M. bolletii and M. massiliense as M. abscessus subspecies bolletii (the former type II) and separating that subspecies from M. abscessus subspecies abscessus (the former type I) have been proposed (12).M. abscessus colonies on agar plates grow with either a rough or a smooth morphology (13,14). M. abscessus can show cord formation when visualized mic...

Selection of Resistance to Clarithromycin in Mycobacterium abscessus Subspecies

“…massiliense, which are intrinsically clarithromycin susceptible (27,28). Failure of the treatment has been more often related to the acquisition of clarithromycin resistance due to rrl 2058 and 2059 mutations (16,18,29,30). Such acquired resistance occurred not only in M. abscessus subspecies with clarithromycin-susceptible erm (41) sequevars (18) but also in subspecies with clarithromycin-resistant erm (41) sequevars (29).…”

GenoType NTM-DR for Identifying Mycobacterium abscessus Subspecies and Determining Molecular Resistance

“…The two species share the same biochemical features, have highly similar 16S rRNA sequences, and are frequently summarized as the M. chelonae/abscessus complex (9). Results of the GenoType NTM-DR assay were compared with the results of sequencing the hsp65, erm(41), rrl, rrs, and 16S rRNA genes, which were obtained previously (10) or sequenced within this study as described in reference 10. Additionally, molecular resistance results of all M. abscessus isolates were compared with results of phenotypic resistance to clarithromycin and amikacin published by Rueger et al (10), who used the broth microdilution method in RAPMYCO Sensititre 96-well plates.…”

“…Results of the GenoType NTM-DR assay were compared with the results of sequencing the hsp65, erm(41), rrl, rrs, and 16S rRNA genes, which were obtained previously (10) or sequenced within this study as described in reference 10. Additionally, molecular resistance results of all M. abscessus isolates were compared with results of phenotypic resistance to clarithromycin and amikacin published by Rueger et al (10), who used the broth microdilution method in RAPMYCO Sensititre 96-well plates. According to the CLSI breakpoints, highlevel clarithromycin resistance was defined as an MIC of Ն8 g/ml on day 5, and inducible resistance was defined as an increase of the clarithromycin MIC from Յ2 g/ml on day 5 to Ն8 g/ml on day 14.…”

In Vitro Evaluation of Povidone-Iodine and Chlorhexidine against Outbreak and Nonoutbreak Strains of Mycobacterium abscessus Using Standard Quantitative Suspension and Carrier Testing

“…By the surface carrier test, TPE 101 also demonstrated high resistance to PI. The possible mechanisms for the enhanced CHX and PI resistance phenotype of this outbreak strain, such as decreased cell wall permeability or "rough colony" morphology, deserve further characterization by EM studies, as described above (32)(33)(34). Furthermore, TPE 101 was typed as ST48, differing by only 1 of 7 multilocus sequence type (MLST) loci (murC gene) from the globally successful clone ST23, and belonging to the same clonal complex 3 as ST23 (8).…”