Variations of plasmid content in Rickettsia felis.
BACKGROUND
Since its first detection, characterization of R. felis has been a matter of debate, mostly due to the contamination of an initial R. felis culture by R. typhi. However, the first stable culture of R. felis allowed its precise phenotypic and genotypic characterization, and demonstrated that this species belonged to the spotted fever group rickettsiae. Later, its genome sequence revealed the presence of two forms of the same plasmid, physically confirmed by biological data. In a recent article, Gillespie et al. (PLoS One. 2007;2(3):e266.) used a bioinformatic approach to refute the presence of the second plasmid form, and proposed the creation of a specific phylogenetic group for R. felis.


RESULTS
In the present report, we, and five independent international laboratories confirmed unambiguously by PCR the presence of two plasmid forms in R. felis strain URRWXCal(2) (T), but observed that the plasmid content of this species, from none to 2 plasmid forms, may depend on the culture passage history of the studied strain. We also demonstrated that R. felis does not cultivate in Vero cells at 37 degrees C but generates plaques at 30 degrees C. Finally, using a phylogenetic study based on 667 concatenated core genes, we demonstrated the position of R. felis within the spotted fever group.


CONCLUSIONS
We demonstrated that R. felis, which unambiguously belongs to the spotted fever group rickettsiae, may contain up to two plasmid forms but this plasmid content is unstable.
Unité des rickettsies, IFR 48, CNRS-IRD UMR 6236, Faculté de médecine, Université de la Méditerranée, Marseille, France.
Pierre-Edouard
PE
Fournier
Lokmane
L
Belghazi
Catherine
C
Robert
Khalid
K
Elkarkouri
Allen L
AL
Richards
Gilbert
G
Greub
François
F
Collyn
Motohiko
M
Ogawa
Arantxa
A
Portillo
Jose A
JA
Oteo
Anna
A
Psaroulaki
Idir
I
Bitam
Didier
D
Raoult
D001483:Base Sequence; D017931:DNA Primers; D010802:Phylogeny; D010957:Plasmids; D016133:Polymerase Chain Reaction; D041161:Rickettsia felis / Q000145:classification / Q000235:genetics*
D017931:DNA Primers