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The field of chlamydial genetics has seen major advances over the past 5 years. We can now generate targeted mutants, carry out large-scale chemical mutagenesis for forward and reverse genetic approaches, express foreign and recombinant genes using various shuttle vectors, and we are positioned to begin generating conditional lethal mutants by combining inducible promoter systems with chemical or targeted mutagenesis. The latter approach may prove to be vital for studying many chlamydial genes that may be essential due to the reduced genomes and obligate intracellular lifestyle of these pathogens ( 17 ). Alternative approaches available for studying essential genes in Chlamydia include regulated overexpression of wild-type genes or dominant-negative mutant genes along with further development of antisense RNA approaches described by Mishra et al. ( 79 ). In addition, validation of fluorescent protein expression in C. trachomatis coupled with detection of fluorescent EBs via flow cytometry (or enumeration in plaque assay) should allow for optimization of transformation procedures as new methods of mutagenesis are explored ( 44 ). Along this line, transformation via electroporation as utilized by Binet and Maurelli (and the method of choice for transformation in other obligate, intracellular bacteria) is worth revisiting to assess efficiency versus chemical transformation ( 43 ). Collectively, the currently available tools have provided important insights into chlamydial pathogenesis that could not have been ascertained as recently as 4 years ago, such as elucidating the function of the secreted protease, CPAF (chlamydial protease-like activity factor) ( 80 ).

However, the chlamydial field still lacks numerous genetic methods available for other bacterial pathogens. Major needs include methods for allelic exchange and identification of broad-host-range plasmids to allow for complementation and/or expression of recombinant genes without loss or alteration of native cryptic plasmids as well as use of a single shuttle plasmid across species/strains. Another major limitation is the absence of transposon mutagenesis systems for both random mutagenesis and targeted delivery of genes to the chromosome as exemplified by the Tn 7 platform ( 81 , 82 ). For many of these approaches, we can look to other obligate intracellular bacteria for inspiration ( Table 2 ). A plethora of tools are available for manipulating Coxiella burnetii , the majority of which were established after the development of axenic growth conditions for the bacterium ( Rico hat Black Maison Michel Cheap Websites Sale Explore C2IXDBV
). Axenic growth conditions would likely yield similar fruit for Chlamydia ( 84 ). In addition, transposon mutagenesis has been successfully employed in Rickettsia spp., E. chaffeensis , Anaplasma spp., and C. burnetii prior to establishment of axenic growth conditions supporting the feasibility of transposon mutagenesis for Chlamydia ( Table 2 ). While it remains impossible to predict the future, it seems clear that in regard to chlamydial genetics, it will be bright.

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Article Text

Research report
bacteria in shower aerosols increase the risk of Pontiac fever among older people in retirement homes


Background: 828 elderly subjects residing in nursing homes were followed up during 4 months to ascertain incidence of symptoms associated with Pontiac fever (PF) in a non-epidemic setting.

Methods: The exposure situation was inhalation of bacteria while showering. An audit of the hot water system in all institutions allowed ascribing each subject to a water quality area wherefrom one shower was sampled for assays at the end of the follow-up period. were detected in water and aerosols using the culture (CFU, colony forming units) and in situ hybridization (FISH) techniques.

Results: Among 32 Pontiac-like episodes, 29 cases complied with the operational definition of PF elaborated for this study. Incidence density was 0.11 case/person–year (95% CI 0.07 to 0.15). Water concentrations greater than 10 5 FISH/l and 10 Clearance Wholesale Price Rylan Guipure Cottonlace Maxi Dress White Miguelina Free Shipping Excellent With Mastercard Online Cheap Free Shipping Release Dates 7ijThA
CFU/l were associated with an increased risk of PF (respectively RR 2.23, p = 0.05 and RR 2.39, p = 0.11, with significant dose–response patterns: p for trend <0.04). The condition also seems associated with aerosol concentrations above 10 Deals Womens NonPadded Wired Bra Cotonella Buy Cheap Enjoy New Online ThgvSmPn
FISH/l of air. A significantly higher risk of Pontiac-like episodes (RR 6.24, 95% CI 2.12 to 18.38) was seen for elderly subjects receiving corticosteroid therapy.

Conclusion: The water and threshold values identified in this research could be used to inform guidance measures aimed at protecting institutionalised older people from Legionnaires’ disease. Immunosuppressive therapy in the same population group can significantly enhance susceptibility to bacteria.


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Funding: This study was funded by AFSSET (French Agency for Environmental and Occupational Health Security) (Grant number: RD-2002-015 and RD-2003-009), the French Ministry of Health and Veolia Environnement. Magali Deloge-Abarkan was recipient of a doctoral scholarship from ADEME and EDF. These funding sources were not involved in the study design, in the collection, analysis and interpretation of the data, or in the decision to submit the paper for publication.

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