Molecular epidemiology of Mycobacterium abscessus, with focus on cystic fibrosis

Abstract

Mycobacterium abscessus has been isolated increasingly often from the respiratory tracts of cystic fibrosis (CF) patients. It is not known whether these organisms are transmitted from person to person or acquired from environmental sources. Here, colony morphology and pulsed-field gel electrophoresis (PFGE) pattern were examined for 71 isolates of M. abscessus derived from 14 CF patients, three non-CF patients with chronic respiratory M. abscessus infection or colonization, one patient with mastoiditis, and four patients with infected wounds, as well as for six isolates identified as environmental contaminants in various clinical specimens. Contaminants and wound isolates mainly exhibited smooth colony morphology, while a rough colony phenotype was significantly associated with chronic airway colonization (P=0.014). Rough strains may exhibit increased airway-colonizing capacity, the cause of which remains to be determined. Examination by PFGE of consecutive isolates from the same patient showed that they all represented a single strain, even in cases where both smooth and rough isolates were present. When PFGE patterns were compared, it was shown that 24 patients had unique strains, while four patients harbored strains indistinguishable by PFGE. Two of these were siblings with CF. The other two patients, one of whom had CF, had not had contact with each other or with the siblings. Our results show that most patients colonized by M. abscessus in the airways have unique strains, indicating that these strains derive from the environment and that patient-to-patient transmission rarely occurs.

FIG. 1.

Colony morphology of M. abscessus after 5 days of incubation on horse blood agar at 37°C. The same magnification was used for both images. (Left) Type strain CCUG 20993 with smooth colonies. (Right) Strain with rough colonies from a CF patient. Images were obtained with a Nikon Coolpix 4300 and Adobe Photoshop Elements 2.0.

FIG. 2.

PFGE analysis of AseI-digested DNA from 29 M. abscessus isolates. Relationships among isolates from 28 Swedish patients and type strain ATCC 19977 are shown in a similarity dendrogram constructed after calculation of the similarity matrix with the Jaccard algorithm (optimization, 1.20%; position tolerance, 1.2% to 1.2%; (minimum height > 0.0%; minimum > 0.0%) and clustering according to UPGMA. CF-Göteborg, isolates obtained from CF patients in the Västra Götaland region; CF-Stockholm, isolates obtained from CF patients in the Stockholm/Uppsala area; non-CF-Göteborg, isolates from other patients with lung infection/colonization from the Västra Götaland region; non-CF-Stockholm, isolates from a patient with mastoiditis in the Stockholm area; tsunami wound, isolate from Swedish tsunami victim (strain obtained in Thailand); transient colonizer, isolate found on a single occasion in a clinical specimen followed by a negative sample and/or lack of associated clinical conditions, suggesting that the isolate was an environmental contaminant.

FIG. 3.

PFGE analyses of cluster A after AseI and XbaI digestion of DNA. (A) AseI PFGE gel corresponding to the dendrogram in panel B. Lanes 1, 6, and 11, reference strain S. aureus NCTC 8325 (not shown in dendrogram). Lane 2, patient 3, isolate 05*1230; lane 3, patient 6, isolate 05*2299; lane 4, patient 10, isolate 05*2316; lane 5, patient 1, isolate 01*5153; lane 7, patient 1, isolate 03*4569; lane 8, patient 2, isolate 04*2226; lane 9, patient 20, isolate 02*1284; lane 10, patient 11, isolate 01* 1526. (B and C) AseI (B) and XbaI (C) PFGE patterns presented as similarity dendrograms and schematic views of bands analyzed. *, isolate 01*5153; **, isolate 03*4569.