Preliminary Characterization of a Mycobacterium abscessus Mutant in Human and Murine Models of Infection

Abstract

The ability to persist in the host after the establishment of infection is an important virulence determinant for mycobacteria.Mycobacterium abscessus is a rapidly growing mycobacterial species which causes a variety of clinical syndromes in humans. We have obtained a rough, wild-type human clinical isolate of M. abscessus (M. abscessus-R) and a smooth, attenuated mutant(M. abscessus-S) which spontaneously dissociated from the clinical isolate. We have found that M. abscessus-R is able to persist and multiply in a murine pulmonary infection model in contrast to M. abscessus-S, which is rapidly cleared. To understand the basis for this difference, we characterized the behavior of these variants in human tissue culture models of infection. M. abscessus-R is able to persist and multiply in human monocytes, while M. abscessus-S is deficient in this ability. Both of these variants are phagocytized by human monocytes. M. abscessus-R resides in a phagosome typical for pathogenic mycobacteria with a tightly adherent phagosomal membrane. In contrast,M. abscessus-S resides in a “loose” phagosome with the phagosomal membrane separated from the bacterial cell wall. BothM. abscessus variants also have distinctive growth patterns in a recently described fibroblast-mycobacterium microcolony assay, with M. abscessus-R exhibiting growth characteristics similar to those previously reported for virulent M. tuberculosis and M. abscessus-S exhibiting growth characteristics similar to those previously reported for avirulentM. tuberculosis. In both the monocyte infection assay and the murine pulmonary infection model, numerous infected mononuclear phagocyte aggregates develop at sites of M. abscessus-Rinfection, but are absent with M. abscessus-S infection. We conclude that a mutation has occurred in the M. abscessus-Svariant which has altered the ability of this organism to persist and multiply in host cells and that this may be related to the phenotypic changes we have observed in our tissue culture models of infection.

The cell surface-exposed glycopeptidolipids confer a selective advantage to the smooth variants ofMycobacterium smegmatis in vitro

“…4). These data are in agreement with other reports on the role of glycopeptidolipids in the interactions with host cells (Byrd & Lyons, 1999;Catherinot et al, 2007), particularly with an early observation indicating that the loss of the surface-exposed glycopeptidolipids induced a very rapid internalization of rough GPL lo M. smegmatis cells by human macrophages (Etienne et al, 2002). Our data are also in agreement with the fact that glycopeptidolipids have an antiphagocytic activity (Villeneuve et al, 2003).…”

Animal model ofMycobacterium abscessuslung infection

“…The lung granulomas of GKO mice have a larger lymphocytic core, greater number of highly vacuolated foamy cells, increased thickening of the parenchymal walls, and more rapid progression of pathology than C57BL/6 or ob/ob mice. Similar pathology associated with M. abscessus infection in humans and SCID mice has been reported [13]. Increased granuloma size correlates with poorer disease outcome in animal models of tuberculosis [8,27,29] and human tuberculosis [43].…”

“…Byrd and Lyons [13] showed that in SCID mice, intratracheal inoculation of a rough virulent strain of M. abscessus produced a persistent infection in the lungs and spleens up to a study period of 28 days. More recently, Rottman and coworkers [9] showed that T cells, IFN-␥, and TNF-␣ were important in controlling disseminated M. abscessus infection in C57BL/6 mice.…”

Overexpression of proinflammatory TLR-2-signalling lipoproteins in hypervirulent mycobacterial variants

“…Severe, often fatal pulmonary M. abscessus infections have been linked to a morphological switch from smooth (S) to rough (R) colony types on agar plates (Sanguinetti et al, 2001;Jönsson et al, 2007;Catherinot et al, 2009). Hypervirulence of the R variant was first revealed in comparisons of an isogenic S/R pair (strain 390) in vivo in SCID mice and ex vivo in human monocytes (Byrd and Lyons, 1999). The 390 R variant is more virulent in mice than the 390 S variant, and multiplies more rapidly in human monocytes (Byrd and Lyons, 1999).…”