The end of the reign of a "master regulator''? A defect in function of the LasR quorum sensing regulator is a common feature of Pseudomonas aeruginosa isolates.

Pseudomonas aeruginosa, a bacterium causing infections in immunocompromised individuals, regulates several of its virulence functions using three interlinked quorum sensing (QS) systems (las, rhl, and pqs). Despite its presumed importance in regulating virulence, dysfunction of the las system regulator LasR occurs frequently in strains isolated from various environments, including clinical infections. This newfound abundance of LasR-defective strains calls into question existing hypotheses regarding their selection. Indeed, current assumptions concerning factors driving the emergence of LasR-deficient isolates and the role of LasR in the QS hierarchy must be reconsidered. Here, we propose that LasR is not the primary master regulator of QS in all P. aeruginosa genetic backgrounds, even though it remains ecologically significant. We also revisit and complement current knowledge on the ecology of LasR-dependent QS in P. aeruginosa, discuss the hypotheses explaining the putative adaptive benefits of selecting against LasR function, and consider the implications of this renewed understanding.

Pseudomonas aeruginosa Strains from Both Clinical and Environmental Origins Readily Adopt a Stable Small-Colony-Variant Phenotype Resulting from Single Mutations in c-di-GMP Pathways.

A subpopulation of small-colony variants (SCVs) is a frequently observed feature of Pseudomonas aeruginosa isolates obtained from colonized cystic fibrosis lungs. Since most SCVs have until now been isolated from clinical samples, it remains unclear how widespread the ability of P. aeruginosa strains to develop this phenotype is and what the genetic mechanism(s) behind the emergence of SCVs are according to the origin of the isolate. In the present work, we investigated the ability of 22 P. aeruginosa isolates from various environmental origins to spontaneously adopt an SCV-like smaller alternative morphotype distinguishable from that of the ancestral parent strain under laboratory culture conditions. We found that all the P. aeruginosa strains tested could adopt an SCV phenotype, regardless of their origin. Whole-genome sequencing of SCVs obtained from clinical and environmental sources revealed single mutations exclusively in two distinct c-di-GMP signaling pathways, the Wsp and YfiBNR pathways. We conclude that the ability to switch to an SCV phenotype is a conserved feature of P. aeruginosa and results from the acquisition of a stable genetic mutation, regardless of the origin of the strain. IMPORTANCE P. aeruginosa is an opportunistic pathogen that thrives in many environments. It poses a significant health concern, notably because this bacterium is the most prevalent pathogen found in the lungs of people with cystic fibrosis. In infected hosts, its persistence is considered related to the emergence of an alternative small-colony-variant (SCV) phenotype. By reporting the distribution of P. aeruginosa SCVs in various nonclinical environments and the involvement of c-di-GMP in SCV emergence from both clinical and environmental strains, this work contributes to understanding a conserved adaptation mechanism used by P. aeruginosa to adapt readily in all environments. Hindering this adaptation strategy could help control persistent infection by P. aeruginosa.

Characterization of chemical exposures in hairdressing salons.

Workers in hairdressing salons are exposed to several hundred chemicals, of which a few are possibly detrimental to pregnant workers or their fetuses. In Quebec, a government program provides protective reassignment for exposed pregnant workers. This study was set up to assist public health physicians by describing the exposure levels for ingredients that were measurable (i.e., airborne), selected from a list of possibly detrimental hairdressing ingredients. Twenty-six salons were sampled in Montreal, Canada, between June 1996 and December 1997. At the time of sampling, information on certain work conditions (e.g., chemical services offered, number of clients, average CO(2) level during the day) was also noted. Fifty percent of the salons provided additional services other than hairdressing, such as manicures, pedicures, or beauty treatments. Almost half of the salons were quite small, with less than 5 employees. Average temperature ranged between 17 and 26 degrees C, relative humidity between 18 and 59 percent and average CO(2) concentrations from 583 to 4301 mg/m(3). Duration of samples varied between 15 minutes and 8 hours. The most prevalent chemicals were alcohols: ethanol, at an average personal concentration of 39.9 mg/m(3), and isopropanol at an average personal concentration of 3.1 mg/m(3). Acetone, toluene, and acetates, all related to manicure services, were also measured in small quantities. An empirical mathematical model brought in evidence that CO(2) levels explained 46 percent of variation in the concentration of ethanol; when number of permanent waves done during the day and relative humidity and temperature were added, the resulting model explained 68 percent of the variations in ethanol. Thus, although the measured concentrations of chemicals were fairly low in this study, it appears possible that on very busy days, especially if other chemical services are performed in the salon, the total mixture of airborne chemicals could reach significant concentrations.