Nutrient Availability as a Mechanism for Selection of Antibiotic Tolerant Pseudomonas aeruginosa within the CF Airway

Abstract

Microbes are subjected to selective pressures during chronic infections of host tissues. Pseudomonas aeruginosa isolates with inactivating mutations in the transcriptional regulator LasR are frequently selected within the airways of people with cystic fibrosis (CF), and infection with these isolates has been associated with poorer lung function outcomes. The mechanisms underlying selection for lasR mutation are unknown but have been postulated to involve the abundance of specific nutrients within CF airway secretions. We characterized lasR mutant P. aeruginosa strains and isolates to identify conditions found in CF airways that select for growth of lasR mutants. Relative to wild-type P. aeruginosa, lasR mutants exhibited a dramatic metabolic shift, including decreased oxygen consumption and increased nitrate utilization, that is predicted to confer increased fitness within the nutrient conditions known to occur in CF airways. This metabolic shift exhibited by lasR mutants conferred resistance to two antibiotics used frequently in CF care, tobramycin and ciprofloxacin, even under oxygen-dependent growth conditions, yet selection for these mutants in vitro did not require preceding antibiotic exposure. The selection for loss of LasR function in vivo, and the associated adverse clinical impact, could be due to increased bacterial growth in the oxygen-poor and nitrate-rich CF airway, and from the resulting resistance to therapeutic antibiotics. The metabolic similarities among diverse chronic infection-adapted bacteria suggest a common mode of adaptation and antibiotic resistance during chronic infection that is primarily driven by bacterial metabolic shifts in response to nutrient availability within host tissues.

Evolution and diversification of Pseudomonas aeruginosa in the paranasal sinuses of cystic fibrosis children have implications for chronic lung infection

“…Several of the mutations and phenotypes that we have observed among sinus isolates, evolved in parallel in the different patients, including those conferring loss of motility and quorum sensing signals (virulence), alginate overproduction, antibiotic resistance and increased biofilm formation (SCVs). (Cabral et al, 1987;Mahenthiralingam et al, 1994;Haussler et al, 1999;Smith et al, 2006;D'Argenio et al, 2007;Starkey et al, 2009;Hoffman et al, 2010). Most of them are generally thought to be beneficial also in the lung environment through the development of resistance to host defenses and antibiotics or to optimized utilization of available nutrients.…”

“…Nutrient availability may also explain, in combination with antibiotic treatment, the selection of the lasR mutant population found in the left side of the sinuses of patient B22. Recent findings have shown that lasR mutants exhibit a dramatic metabolic shift with decreased oxygen and increased nitrate utilization and in addition they display increased resistance to antibiotics such as ciprofloxacin and tobramycin (Hoffman et al, 2010). Therefore, the lasR mutation is also likely to confer increased fitness in the sinuses.…”

“…Many characteristics of chronically infecting strains are consistently selected in different CF patients, suggesting that adaptation occurs with conserved patterns of evolution (Nguyen and Singh, 2006;Smith et al, 2006;Yang et al, 2011). These characteristics include enhanced antibiotic resistance, changes in nutrient utilization, overproduction of the mucoid exopolysaccharide alginate, reduction in growth rate and loss of O-antigen, motility, type III secretion and quorum sensing (Lam et al, 1980;Hancock et al, 1983;Mahenthiralingam et al, 1994;Dacheux et al, 2001;D'Argenio et al, 2007;Yang et al, 2008;Hoffman et al, 2010). In addition, the initial infecting strains of P. aeruginosa often diversify into subpopulations with distinct colony morphologies (Wahba and Darrell, 1965;Thomassen et al, 1979).…”

Anaerobiosis-Induced Loss of Cytotoxicity Is Due to Inactivation of Quorum Sensing in Pseudomonas aeruginosa

“…However, recent genetic studies using diverse P. aeruginosa clinical isolates reported that adaptive mutations in the lasR gene occur spontaneously in the course of chronic airway infection in CF (9,12,19,42). Phenotype on April 7, 2019 by guest http://iai.asm.org/ changes conferred on P. aeruginosa by these mutations include (i) facilitated growth on amino acids present in relatively large quantities in CF airways (1,12), (ii) an efficient shift to an anaerobic mode of growth using nitrate over oxygen (20), and (iii) elevated antibiotic resistance (12,20). Therefore, frequent identification of lasR mutants suggests that P. aeruginosa may acquire the mutation to increase its survival fitness in a harsh host environment at the expense of its ability to regulate QS-mediated virulence properties.…”

Metabolite transfer with the fermentation product 2,3-butanediol enhances virulence by Pseudomonas aeruginosa

“…Owing to the oxygen-limited conditions within the thick biofilms in CF airways (Hoffman et al, 2010;Guss et al, 2011), fermentation products, which are either from bacterial metabolism or hostgenerated via neutrophil metabolism, are found in the sputum of CF patients (Palmer et al, 2007;Bensel et al, 2010). Many bacteria in the CF airway microbiome, such as E. aerogenes, Klebsiella pneumoniae, Staphylococcus aureus, Serratia marcescens, Streptococcus sp.…”