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Journal of Bacteriology, December 2003, p. 7222-7230, Vol. 185, No. 24
0021-9193/03/$08.00+0 DOI: 10.1128/JB.185.24.7222-7230.2003
Copyright © 2003, American
Society for
Microbiology. All Rights Reserved.
Transcription of Quorum-Sensing System Genes in Clinical and Environmental Isolates of Pseudomonas aeruginosa
Ségolène Cabrol,1 Anne Olliver,1 Gerald B. Pier,2 Antoine Andremont,1 and Raymond Ruimy1*
INSERM
EMI 9933, Epidémiologie de la Résistance aux
Anti-infectieux, and AP-HP Groupe Hospitalier Bichat-Claude
Bernard, 75877 Paris Cedex 18,
France,1
Channing Laboratory,
Department of Medicine, Brigham and Women's Hospital,
Harvard Medical School, Boston, Massachusetts
021152
Received 1 September 2003/
Accepted 29 September 2003
Quorum
sensing (QS)-based transcriptional responses in Pseudomonas
aeruginosa have been defined on the basis of increases in
transcript levels of QS-controlled genes such as lasB and
aprA following the hierarchical transcriptional increases of
central controllers such as the lasR gene. These
increases occur at high bacterial concentrations such as
early-stationary-phase growth in vitro. However, the extent to which
the increases occur in a variety of clinical and environmental isolates
has not been determined nor is there extensive information on allelic
variation in lasR genes. An analysis of the sequences of the
lasR gene among 66 clinical and environmental isolates showed
that 81% have a sequence either identical to that of strain PAO1
or with a silent mutation, 15% have nucleotide changes resulting
in amino acid changes, and 5% have an insertion sequence in the
lasR gene. Using real-time PCR to quantify transcript levels
of lasR, lasB, and aprA in the early log and
early stationary phases among 35 isolates from bacteremia and pneumonia
cases and the environment, we found most (33 of 35) strains had
increases in lasR transcripts in early stationary phase but
with a very wide range of final transcript levels per cell. There was a
strong correlation (r2 = 0.84) between
early-log- and early-stationary-phase transcript levels in all strains,
but this finding remained true only for the 50% of strains above
the median level of lasR found in early log phase. There were
significant (P < 0.05) but weak-to-modest correlations
of lasR transcript levels with aprA (r2
= 0.2) and lasB (r2 = 0.5)
transcript levels, but again this correlation occurred only in the
50% of P. aeruginosa strains with the highest levels of
lasR transcripts in early stationary phase. There were no
differences in distribution of lasR alleles among the
bacteremia, pneumonia, or environmental isolates. Overall, only about
50% of P. aeruginosa strains from clinical and
environmental sources show a lasR-dependent increase in the
transcription of aprA and lasB genes, indicating that
for about 50% of clinical isolates this regulatory system may
not play a significant role in
pathogenesis.
* Corresponding
author. Mailing address: Groupe Hospitalier Bichat-Claude Bernard, 46
Rue Henri Huchard, 75877 Paris CEDEX 18, France. Phone: 33 1 40 25 85
05. Fax: 33 1 40 25 85 81. E-mail:
raymond.ruimy{at}bch.ap-hop-paris.fr.
Journal of Bacteriology, December 2003, p. 7222-7230, Vol. 185, No. 24
0021-9193/03/$08.00+0 DOI: 10.1128/JB.185.24.7222-7230.2003
Copyright © 2003, American
Society for
Microbiology. All Rights Reserved.
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Copyright © 2003 by the American Society for Microbiology. All rights reserved.