Evaluation of a high-throughput repetitive-sequence-based PCR system for DNA fingerprinting of Mycobacterium tuberculosis and Mycobacterium avium complex strains

Abstract

Repetitive-sequence-based PCR (rep-PCR) is useful for generating DNA fingerprints of diverse bacterial and fungal species. Rep-PCR amplicon fingerprints represent genomic segments lying between repetitive sequences. A commercial system that electrophoretically separates rep-PCR amplicons on microfluidic chips, and provides computer-generated readouts of results has been adapted for use with Mycobacterium species. The ability of this system to type M. tuberculosis and M. avium complex (MAC) isolates was evaluated. M. tuberculosis strains (n = 56) were typed by spoligotyping with rep-PCR as a high-resolution adjunct. Results were compared with those generated by a standard approach of spoligotyping with IS6110-targeted restriction fragment length polymorphism (IS6110-RFLP) as the high-resolution adjunct. The sample included 11 epidemiologically and genotypically linked outbreak isolates and a population-based sample of 45 isolates from recent immigrants to Seattle, Wash., from the African Horn countries of Somalia, Eritrea, and Ethiopia. Twenty isolates exhibited unique spoligotypes and were not analyzed further. Of the 36 outbreak and African Horn isolates with nonunique spoligotypes, 23 fell into four clusters identified by IS6110-RFLP and rep-PCR, with 97% concordance observed between the two methods. Both approaches revealed extensive strain heterogeneity within the African Horn sample, consistent with a predominant pattern of reactivation of latent infections in this immigrant population. Rep-PCR exhibited 89% concordance with IS1245-RFLP typing of 28 M. avium subspecies avium strains. For M. tuberculosis as well as M. avium subspecies avium, the discriminative power of rep-PCR equaled or exceeded that of RFLP. Rep-PCR also generated DNA fingerprints from M. intracellulare (n = 8) and MAC(x) (n = 2) strains. It shows promise as a fast, unified method for high-throughput genotypic fingerprinting of multiple Mycobacterium species.

FIG. 1.

Rep-PCR analysis of 25 African Horn immigrant isolates and 11 Seattle outbreak isolates. A dendrogram (A) and gel-like images (E) were generated on coded DNA samples by Bacterial Barcodes, Inc. Correct strain identifications (B), spoligogroups (C), and IS6110-RFLP clusters (D), corresponding with nomenclature used in Table 1, were added by the authors. NT, not typeable by IS6110-RFLP. Strains without RFLP cluster designations had unique IS6110-RFLP patterns.

FIG. 2.

IS6110-RFLP patterns of the four major multistrain clusters of M. tuberculosis isolates in Fig. 1. The image was constructed from a single gel. Because some lanes exhibited stronger signals than others, a composite of long exposure and short exposure images was constructed. M. tuberculosis strain H37Ra patterns are shown on each end.

FIG. 3.

Rep-PCR analysis of M. avium subspecies avium samples. The dendrogram (A) and gel-like images (D) were generated on coded DNA samples by Bacterial Barcodes, Inc. Correct strain identifications (B) and IS1245-RFLP clusters (C) were added by the authors. Duplicate samples are marked with asterisks. NT, not typeable by IS1245-RFLP.

FIG. 4.

IS1245-RFLP patterns of the four major multistrain clusters of M. avium subspecies avium isolates in Fig. 3. The image was constructed from a single gel as in Fig. 2, except for the two lanes marked with asterisks. DNA from these two strains was incompletely digested in the main gel image of cluster B. Therefore, an image from a second gel was added to better document the similarity between these two strains.

FIG. 5.

Rep-PCR analysis of Mycobacterium intracellulare (MI) and MAC_X samples. The dendrogram (A) and gel-like images (D) were generated on coded DNA samples by Bacterial Barcodes, Inc. Correct strain identifications (B) and species (C) were added by the authors.