Mucoidy, Quorum Sensing, Mismatch Repair and Antibiotic Resistance in Pseudomonas aeruginosa from Cystic Fibrosis Chronic Airways Infections

Abstract

Survival of Pseudomonas aeruginosa in cystic fibrosis (CF) chronic infections is based on a genetic adaptation process consisting of mutations in specific genes, which can produce advantageous phenotypic switches and ensure its persistence in the lung. Among these, mutations inactivating the regulators MucA (alginate biosynthesis), LasR (quorum sensing) and MexZ (multidrug-efflux pump MexXY) are the most frequently observed, with those inactivating the DNA mismatch repair system (MRS) being also highly prevalent in P. aeruginosa CF isolates, leading to hypermutator phenotypes that could contribute to this adaptive mutagenesis by virtue of an increased mutation rate. Here, we characterized the mutations found in the mucA, lasR, mexZ and MRS genes in P. aeruginosa isolates obtained from Argentinean CF patients, and analyzed the potential association of mucA, lasR and mexZ mutagenesis with MRS-deficiency and antibiotic resistance. Thus, 38 isolates from 26 chronically infected CF patients were characterized for their phenotypic traits, PFGE genotypic patterns, mutations in the mucA, lasR, mexZ, mutS and mutL gene coding sequences and antibiotic resistance profiles. The most frequently mutated gene was mexZ (79%), followed by mucA (63%) and lasR (39%) as well as a high prevalence (42%) of hypermutators being observed due to loss-of-function mutations in mutL (60%) followed by mutS (40%). Interestingly, mutational spectra were particular to each gene, suggesting that several mechanisms are responsible for mutations during chronic infection. However, no link could be established between hypermutability and mutagenesis in mucA, lasR and mexZ, indicating that MRS-deficiency was not involved in the acquisition of these mutations. Finally, although inactivation of mucA, lasR and mexZ has been previously shown to confer resistance/tolerance to antibiotics, only mutations in MRS genes could be related to an antibiotic resistance increase. These results help to unravel the mutational dynamics that lead to the adaptation of P. aeruginosa to the CF lung.

Chronic pulmonary pseudomonal infection in patients with cystic fibrosis: A model for early phase symbiotic evolution

“…Longitudinal bacterial culture following patient disease progression suggests that a gradual decrease in bacterial diversity is associated with an increase in patient age and advanced pulmonary disease (Cox et al, 2010). Transmission of CF airway adapted strains, for example, a hyper-mucoid Pa, has never been reported (Aaron et al, 2004(Aaron et al, , 2010Feliziani et al, 2010;Furukawa et al, 2006;Hogardt et al, 2007;Oliver & Mena, 2010).…”

“…Strains that arise from a founder clone in the same airway show phenotypic dissociation (2-6 phenotypes per specimen) and carry quorum-sensing lasR mutations, as well as noncytotoxic variants with lesions in T3SS (type three secretion system) ExoS and PopD. Most importantly, the accumulation of lossof-function mutations in DNA mismatch repair genes, such as mutS, mutL, and uvrD, has been recognized for its effect on niche-adapted Pa strains with relaxed DNA replication fidelity, and collectively labeled as ''anti-mutator deficient'' properties (Barth & Pitt, 1995a;Dacheux et al, 2000Dacheux et al, , 2001Feliziani et al, 2010;Furukawa et al, 2006;Heurlier et al, 2005;Hogardt et al, 2007;Irvin et al, 1981;Oberhardt et al, 2010;Rau et al, 2010;Roy-Burman et al, 2001;Smith et al, 2006;Thomas et al, 2000;Vendeville et al, 2005;Zierdt & Schmidt 1964). Recently, terms such as ''cheater cells'' and ''easy riders'' have been used to describe this functional heterogeneity and isogenic interdependency (Xavier et al, 2011).…”

“…As early as 9 days post colonization in acutely ill patients, subpopulations of clinical Pa isolates defective in QS emerged with mutations in the autoinducer lasR (Kohler et al, 2009;Winstanley & Fothergill, 2009). QS-deficient lasR mutants have been detected in a significant proportion (30-63%) of CF Pa isolates (Feliziani et al, 2010;Hoffman et al, 2009). Moreover, isolates of Pa defective in lasR, lasI, and/or rhlI have been shown to be much less virulent than QS-positive strains in animal models (Willcox et al, 2008;Wu et al, 2001).…”

Resistance suppression by high-intensity, short-duration aminoglycoside exposure against hypermutable and non-hypermutablePseudomonas aeruginosa

“…5,19,20 It provides bacteria with an advantage through the ability to adapt quickly to stressful and fluctuating environments via rapidly gaining or enhancing resistance mechanisms. 15,21,22 Two pharmacokinetic/pharmacodynamic indices are most commonly used as predictors for bacterial killing by aminoglycosides, being the fAUC/MIC and the fC max /MIC.…”

Pseudomonas Aeruginosa AmpR Transcriptional Regulatory Network

“…Higher mutation rates are the driving force for the P. aeruginosa population heterogeneity in the CF lung (578)(579)(580). Specifically, mutations in mucA and lasR arise early in the colonization process, followed by mutations in anti-mutator genes such as mutS, mutT, mutY and mutM (581 Supplementary information for Chapter 5, Table 3), indicating negative AmpR regulation.…”