Interaction of virulent and non-virulent Rhodococcus equi human isolates with phagocytes, fibroblast- and epithelial-derived cells.
Rhodococcus equi is a facultative, intracellular, Gram-positive coccobacillus, increasingly reported in pneumonia of AIDS-infected patients. We investigated killing resistance properties of human R. equi virulent and avirulent human strains. Avirulent beta-lactam-susceptible strains had lower intracellular colony forming units after 45 min incubation in murine macrophages J774 and human monocyte-macrophage TPH-1 than those of virulent strains. Only virulent beta-lactam-resistant strains persisted within macrophages for at least 18 min only. A beta-lactam-resistant mutant was obtained from a beta-lactam-susceptible strain after selection in a penicillin G-containing culture medium. This mutant strain, like the natural virulent strains, persisted within macrophages, harboured cell-associated appendages, produced phage-like particles and induced, after its intravenous inoculation, a chronic infection in BALB/c nude mice. Supernatant culture of virulent strains transferred partial macrophage-killing resistance properties to avirulent strains. The same supernatant was toxic for L-929, HeLa and Vero cell cultures. These supernatant effects were heat-inactivated, trypsin-inactivated and did not seem to be linked to phage-like particle presence. These data argue that virulence, beta-lactam-resistance, and macrophage-killing resistance are associated in human R. equi isolates. Moreover, only virulent strains produced uncharacterized toxic factors.
Nordmann
P
P
Laboratoire de Microbiologie, Hôpital Raymond Poincaré, Faculté de Médecine Paris-Ouest, Université Paris 5, Garches, France.
Zinzendorf
N
N
Keller
M
M
Lair
I
I
Ronco
E
E
Guenounou
M
M
D000818:Animals; D001435:Bacteriophages / Q000502:physiology; D002460:Cell Line; D017077:Culture Media, Conditioned / Q000633:toxicity; D004847:Epithelial Cells; D004848:Epithelium / Q000382:microbiology; D005260:Female; D005347:Fibroblasts / Q000382:microbiology; D006801:Humans; D008264:Macrophages / Q000276:immunology / Q000382:microbiology*; D051379:Mice; D008807:Mice, Inbred BALB C; D008819:Mice, Nude; D016929:Rhodococcus equi / Q000276:immunology / Q000472:pathogenicity* / Q000821:virology; D014774:Virulence / Q000502:physiology
D017077:Culture Media, Conditioned