A mycolyl transferase mutant of Rhodococcus equi lacking capsule integrity is fully virulent.
Rhodococcus equi is a mucoid Gram-positive facultative intracellular pathogen which can cause severe bronchopneumonia in foals and AIDS patients. A polysaccharide capsule which gives R. equi a mucoid appearance has long been suspected to be a virulence factor. Here, we describe a transposome mutant in the gene fbpA of strain R. equi 103 causing absence of a capsular structure. FbpA is a chromosomal gene homologous to antigen 85 (Ag85) mycolyl chain transferase gene of Mycobacterium tuberculosis. The mutant multiplied normally in isolated macrophages, was able to establish the unusual R. equi-containing vacuole in macrophages, was cytotoxic for macrophages, and was virulent in a mouse model. Colonies had a dry appearance on nutrient agar and defective capsule structure. Surprisingly, fbpA mutants cured of the virulence-associated plasmid were found in a phagosome that was more alkaline than that of the corresponding wild-type bacteria, were more cytotoxic and even multiplied to some extent. This study suggests that the capsule is not an important virulence factor of R. equi and that it may even counteract virulence traits.
Institute for Cell Biology and Bonner Forum Biomedizin, University of Bonn, Ulrich-Haberland-Str. 61a, 53121 Bonn, Germany.
Tobias
T
Sydor
Kristine
K
von Bargen
Ulrike
U
Becken
Sabine
S
Spuerck
Vivian M
VM
Nicholson
John F
JF
Prescott
Albert
A
Haas
D000217:Acyltransferases / Q000235:genetics*; D000595:Amino Acid Sequence; D000818:Animals; D000831:Animals, Newborn; D016667:Bacterial Capsules; D001426:Bacterial Proteins / Q000235:genetics*; D001681:Biological Assay / Q000662:veterinary; D006734:Horse Diseases / Q000382:microbiology; D006736:Horses; D006801:Humans; D008264:Macrophages / Q000382:microbiology; D051379:Mice; D017348:Microscopy, Electron, Scanning Transmission / Q000662:veterinary; D008969:Molecular Sequence Data; D009154:Mutation; D011135:Polysaccharides, Bacterial; D016929:Rhodococcus equi / Q000201:enzymology* / Q000472:pathogenicity*; D016415:Sequence Alignment / Q000662:veterinary; D037521:Virulence Factors
D001426:Bacterial Proteins; D011135:Polysaccharides, Bacterial; D037521:Virulence Factors; D000217:Acyltransferases