Outbreak of Infection with Mycobacterium abscessus: Is Sodium Dodecyl Sulfate-Polyacrylamide Gel Electrophoresis a Useful Technique for Epidemiological Typing?

We have read with interest the article by Zhibang et al. (12) about an outbreak of infections due to Mycobacterium abscessus. We believe, as the authors did, that the strains isolated from the different patients and the environmental samples were the same clone. Classical epidemiology data support this fact, as did conventional microbiology data and plasmid analysis (although only one plasmid was detected and no digestion with restriction enzymes or other studies were done to demonstrate the identity of the plasmids). However, we have some clarifications to make about the use of sodium dodecyl sulfate-polyacyrylamide gel electrophoresis (SDS-PAGE) of whole-cell proteins as an epidemiological marker in this case.

SDS-PAGE of whole-cell proteins is a technique that has been used for epidemiological typing in many cases (1, 3, 9, 11). However, in other cases, the stability of protein profiles made it a technique useful for characterization of bacterial isolates instead of epidemiological typing (5). In the case of rapidly growing mycobacteria, SDS-PAGE of whole-cell proteins has been used by several authors for characterization of the strains, even for taxonomic purposes (2, 6-8). In our experience (4), SDS-PAGE is a useful technique for characterization but not for epidemiology studies. In our study, intraspecies similarity showed Dice coefficients higher than 95%, with only one strain of Mycobacterium fortuitum with a six-band difference. However, interspecies similarity was always below 75%. The same profile could be found between different isolates of the same species from different origins without any relation between them, and identification of the species could be easily performed comparing the profile of the problem strain with the profile of the type strain, when both strains are analyzed in the same gel. Because of all these data, we think that SDS-PAGE is not a useful technique for determining the isogeny of isolates of rapidly growing mycobacteria. Other previously described techniques are more accurate in achieving this objective (10).