[Assessment of the invasiveness of rapidly-growing nonpigmented mycobacteria with the fibroblast microcolony assay].
OBJECTIVE
The invasive capacity of rapidly-growing nonpigmented mycobacteria strains was evaluated by means of a fibroblast microcolony assay and related to the colony phenotype on Middlebrook 7H11 and to the clinical significance of the isolates.


METHODS
Twenty-nine strains [Mycobacterium chelonae (8), M. fortuitum (6), M. peregrinum (5), M. abscessus (5), M. mucogenicum (4) and M. septicum (1)], proceeding from a bacterial collection and clinical isolates, were evaluated. The smooth or rough phenotype of the colonies was assessed in Middlebrook 7H11 medium. Intracellular invasiveness was determined by the fibroblast-microcolony assay described by Shepard. Quantitative culture characteristics were compared with Student's t-test, and qualitative characteristics with Fisher's exact test.


RESULTS
No significant differences were found between colonies with different phenotypes or strains having a different clinical significance, except for two strains of Mycobacterium chelonae isolated from cases of catheter-related bacteremia, which showed elongated microcolonies. M. fortuitum and M. peregrinum strains showed larger microcolonies than M. chelonae, M. abscessus and M. mucogenicum, and displayed a fluffy appearance, while the latter two strains showed rounded colonies.


CONCLUSIONS
Very few strains of mycobacteria had invasive capacity and the majority of strains isolated from human infections do not show this characteristic; hence this trait is not essential for mycobacteria to cause infection in humans.
Esteban
Jaime
J
Departamento de Microbiología Clínica, Fundación Jiménez Díaz-UTE, Madrid, España. jesteban@fjd.es
Gadea
Ignacio
I
Zamora
Nieves
N
Ortiz
Alberto
A
Fernández-Roblas
Ricardo
R
D001431:Bacteriological Techniques / Q000706:statistics & numerical data; D002478:Cells, Cultured / Q000382:microbiology; D003470:Culture Media / Q000494:pharmacology; D005347:Fibroblasts / Q000382:microbiology*; D006801:Humans; D009170:Nontuberculous Mycobacteria / Q000254:growth & development* / Q000472:pathogenicity; D010641:Phenotype; D013045:Species Specificity; D014774:Virulence
D003470:Culture Media