Environmentally Endemic Pseudomonas aeruginosa Strains with Mutations in lasR Are Associated with Increased Disease Severity in Corneal Ulcers

Abstract

The LasR transcription factor is an important regulator of quorum sensing in P. aeruginosa and positively controls multiple virulence-associated pathways. The emergence of strains with lasR loss-of-function alleles in chronic disease is well described and is thought to represent a specific adaptation to the host environment. However, the prevalence and virulence of these strains in acute infections remain unclear. This report describes observations revealing that lasR mutants were common among isolates from a large, multicenter clinical study of keratitis and were associated with worse clinical outcomes than LasR-intact strains despite reduced production of LasR-regulated factors. Additionally, these lasR mutants were closely related strains or clones, as determined by molecular analysis. Because bacterial keratitis is community acquired, these data indicate infection by endemic, LasR-deficient strains in the environment. These results suggest that the conventional paradigm regarding the role for LasR-mediated regulation of virulence is more complex than previously appreciated.

Candida albicans and Pseudomonas aeruginosa Interact To Enhance Virulence of Mucosal Infection in Transparent Zebrafish

“…Taken together, our results indicate that C. albicans enhances the ability of P. aeruginosa to colonize the site of infection without enhancing bacterial virulence, or that coinfection requires only a low threshold for P. aeruginosa burden to enhance mortality, either of which would be consistent with the LasR-independent ability of P. aeruginosa to promote virulence in our model. Depending on the context, infections with LasR-defective P. aeruginosa can be more virulent in mice and humans (68)(69)(70)(71)(72). Interestingly, coculture of ΔlasR mutants with C. albicans restores some bacterial virulence gene expression, suggesting that interactions between these two common human commensals enhance pathogenesis (19).…”

Pseudomonas aeruginosa lasRmutant fitness in microoxia is supported by an Anr-regulated oxygen-binding hemerythrin

“…We previously reported that Δ lasR mutants in laboratory strains PA14 and PAO1 as well as in diverse clinical isolates had higher activity of the transcription factor Anr than their LasR+ counterparts under microoxic conditions (16, 19). To determine if Anr activity contributes to the higher fitness of lasR mutant strains, we developed an assay for the assessment of fitness in colony biofilms grown under microoxic conditions (0.2%; 2.5 µM O 2 ).…”

“…Mhr protein levels were 2.8-fold higher in the Δ lasR mutant than in the wild type ( Figures 2D ). We also analyzed Mhr levels in a clinical isolate from a corneal eye infection (262K) that was a natural lasR mutant (16) and a 262K derivative in which the native allele was replaced with the PA14 allele, as well is two clinical isolates from the same subject with CF with one isolate bearing a lasR mutation. We found that in the two clinical isolate backgrounds, the lasR mutant in each pair had significantly more Mhr than the corresponding LasR+ strain ( Figures 2E-F ).…”

“…In many different contexts, the gene that encodes one of the key transcriptional regulators involved in QS, lasR , frequently sustains loss-of-function mutations. LasR-defective (LasR-) strains of P. aeruginosa are commonly isolated from the lungs of individuals with CF (10-12) and other pulmonary diseases (13, 14), implanted device infections (5, 15), acute corneal ulcers (16), and the environment (16).…”

“…Several factors may lead to the selection for P. aeruginosa lasR mutants and their observed fitness relative to their wild-type counterparts including the advantages of social cheating (17, 18) and enhanced growth on specific carbon and nitrogen sources (9). In addition, both laboratory strains and clinical isolates with mutations in lasR display higher expression of the Anr regulon in microoxic environments than their lasR -intact counterparts (16, 19). Anr and its homologs have been well-characterized as oxygen-sensitive transcription factors (20-22).…”