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Characterization of clonal strains of Pseudomonas aeruginosa isolated from cystic fibrosis patients in Ontario, Canada

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Pseudomonas aeruginosa is an opportunistic pathogen that can form biofilms in the lungs and airways of cystic fibrosis (CF) patients, resulting in chronic endobronchial infection. Two clonal strains of P. aeruginosa, named type A and type B, have recently been identified and have been found to infect more than 20% of CF patients in Ontario, Canada. In this study, 4 type A and 4 type B isolates retrieved from 8 CF patients in Ontario, Canada, were characterized. All 8 isolates grew well in rich medium and formed biofilms in vitro. Antibiotic resistance profiles of bacteria grown in biofilms and planktonic culture were studied via minimal bactericidal concentration assays for tobramycin, gentamicin, and ciprofloxacin. Compared to laboratory strains of P. aeruginosa, all 8 isolates showed increased resistance to all antibiotics studied in both biofilm and planktonic assays. Gene expression analysis of mexX, representing the MexXY-OprM efflux pump, and mexA, representing MexAB-OprM, revealed that these genes were up-regulated in the 8 clinical isolates. These results suggest clonal type A and type B isolates of P. aeruginosa isolated from CF patients in Ontario, Canada, show a multidrug resistance pattern that can be partially explained as being due to the increased expression of common antibiotic efflux systems.

Pseudomonas aeruginosa est un pathogène opportuniste qui peut former des biofilms dans les poumons et les voies respiratoires des patients atteints de fibrose kystique (FK), résultant en une infection chronique endobronchique. Deux souches clonales de P. aeruginosa appelées « type A » et « type B » identifiées récemment infectent plus de 20 % des patients FK en Ontario, Canada. Dans cette étude, 4 isolats du type A et 4 isolats du type B trouvés chez 8 patients FK ontariens ont été caractérisés. Les 8 isolats croissaient bien en milieu riche et formaient des biofilms in vitro. Les profils de résistance aux antibiotiques des bactéries cultivées en biofilm ou en culture planctonique ont été étudiés à l’aide d’un dosage de concentration bactéricide minimale de la tobramycine, de la gentamycine et du ciprofloxacin. Comparativement aux souches de laboratoire de P. aeruginosa, les 8 isolats montraient une résistance accrue à tous les antibiotiques étudiés, tant en biofilm qu’en culture planctonique. L’analyse de l’expression génique de mexX, représentant de la pompe d’efflux MexXY-OprM, et de mexA, représentant MexAB-OprM, a révélé que l’expression de ces gènes était plus élevée dans les 8 isolats cliniques. Ces résultats suggèrent que les isolats clonaux de type A et de type B de P. aeruginosa isolés de patients FK en Ontario, Canada, montrent un patron de multirésistance aux médicaments qui peut être partiellement expliqué par l’augmentation de l’expression des systèmes communs d’efflux d’antibiotiques.

Document Type: Research Article

Publication date: July 1, 2010

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  • Published since 1954, this monthly journal contains new research in the field of microbiology including applied microbiology and biotechnology; microbial structure and function; fungi and other eucaryotic protists; infection and immunity; microbial ecology; physiology, metabolism and enzymology; and virology, genetics, and molecular biology. It also publishes review articles and notes on an occasional basis, contributed by recognized scientists worldwide.
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