title: Mycobacterium gilvum illustrates size-correlated relationships between mycobacteria and Acanthamoeba polyphaga.
abstract: Mycobacteria are isolated from soil and water environments, where free-living amoebae live. Free-living amoebae are bactericidal, yet some rapidly growing mycobacteria are amoeba-resistant organisms that survive in the amoebal trophozoites and cysts. Such a capacity has not been studied for the environmental rapidly growing organism Mycobacterium gilvum. We investigated the ability of M. gilvum to survive in the trophozoites of Acanthamoeba polyphaga strain Linc-AP1 by using optical and electron microscopy and culture-based microbial enumerations in the presence of negative controls. We observed that 29% of A. polyphaga cells were infected by M. gilvum mycobacteria by 6 h postinfection. Surviving M. gilvum mycobacteria did not multiply and did not kill the amoebal trophozoites during a 5-day coculture. Extensive electron microscopy observations indicated that M. gilvum measured 1.4 ± 0.5 μm and failed to find M. gilvum organisms in the amoebal cysts. Further experimental study of two other rapidly growing mycobacteria, Mycobacterium rhodesiae and Mycobacterium thermoresistibile, indicated that both measured <2 μm and exhibited the same amoeba-mycobacterium relationships as M. gilvum. In general, we observed that mycobacteria measuring <2 μm do not significantly grow within and do not kill amoebal trophozoites, in contrast to mycobacteria measuring >2 μm (P < 0.05). The mechanisms underlying such an observation remain to be determined.
authors.affiliation: Aix Marseille Université, Marseille, France.
authors.forename: Otmane
authors.initials: O
authors.lastname: Lamrabet
authors.forename: Michel
authors.initials: M
authors.lastname: Drancourt
mesh_terms: D000048:Acanthamoeba / Q000166:cytology* / Q000382:microbiology*; D058491:Bacterial Load; D002470:Cell Survival; D050296:Microbial Viability; D008853:Microscopy; D009170:Nontuberculous Mycobacteria / Q000166:cytology* / Q000502:physiology*