Bacteriophage susceptibility of the Mycobacterium fortuitum complex and the correlation to biochemical characteristics

The increasing awareness of human infections caused by the organisms in the Mycobacterium fortuitum complex, particularly in nosocomial infections, emphasizes the need to subdivide the species of this complex for epidemiological investigations. Biochemical characteristics were determined for 154 strains of these organisms in the arylsulphatase, nitrate reduction, iron uptake, and salt tolerance tests, and the utilization of sodium citrate, mannitol, and inositol as the sole source of carbon. The results for the various subspecies and biovars conformed to the expected results obtained with the respective reference strains. These biochemical test results were correlated to bacteriophage susceptibility patterns. A group of twelve mycobacteriophages, including three newly isolated for this study, were tested against the 154 strains. Susceptibility to lysis by at least one phage was found for 72.2% of the bacterial strains. M. fortuitum strains were more susceptible to the mycobacteriophages (79.5%) than were the M. chelonae strains (64.8%). Among the biotypes, 76.4% of the M. fortuitum biovar fortuitum strains, 88.0% of the M. fortuitum biovar peregrinum strains, 71.4% of the M. fortuitum 3rd biovar strains, 60.9% of the M. chelonae subsp. chelonae strains, and 70.0% of the M. chelonae subsp. abscessus strains were found to be phage susceptible. There was no consistent phage susceptibility pattern for a given biotype; each subgroup exhibited a sufficient diversity of lytic patterns to indicate that phage typing may be a practical tool to recognize strains for epidemiological studies. The results further indicate that within each particular biotype not all of the mycobacteriophages were appropriate and their number could be limited. The results strongly indicate that biochemical characterization and phage typing can provide evidence for a common source of contamination as the cause of mycobacterial infections. The findings in this study merit further investigations to establish a standardized phage typing system for the organisms of the M. fortuitum complex.

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