Pseudomonas aeruginosaIncreases Formation of Multidrug-Tolerant Persister Cells in Response to Quorum-Sensing Signaling Molecules

Abstract

Bacterial persister cells constitute a small portion of a culture which is tolerant to killing by lethal doses of bactericidal antibiotics. These phenotypic variants are formed in numerous bacterial species, including those with clinical relevance like the opportunistic pathogen Pseudomonas aeruginosa. Although persisters are believed to contribute to difficulties in the treatment of many infectious diseases, the underlying mechanisms affecting persister formation are not well understood. Here we show that even though P. aeruginosa cultures have a significantly smaller fraction of multidrug-tolerant persister cells than cultures of Escherichia coli or Staphylococcus aureus, they can increase persister numbers in response to quorum-sensing-related signaling molecules. The phenazine pyocyanin (and the closely related molecule paraquat) and the acyl-homoserine lactone 3-OC12-HSL significantly increased the persister numbers in logarithmic P. aeruginosa PAO1 or PA14 cultures but not in E. coli or S. aureus cultures.Over the last 50 years, Pseudomonas aeruginosa has emerged as a major cause of nosocomial infections in immunocompromised patients, including those relying on mechanical ventilation and suffering from neutropenia or severe burns, and is perhaps most well known as the agent primarily responsible for the decline in lung function leading to death in cystic fibrosis (CF) patients (8,14,16,23,38). P. aeruginosa possesses a multiplicity of virulence factors that are elicited upon access to susceptible individuals, including various toxins, secretion systems, siderophores, surface appendages, endotoxin (lipopolysaccharide [LPS]), alginate, and phenazines. These can generate acute toxicity/injury, leading P. aeruginosa to be labeled as the "hyena" of the bacterial world (15). Treatment of infections by P. aeruginosa is hindered by its high level of intrinsic resistance to antibiotics due primarily to a combination of the impermeable outer membrane and a number of broad-spectrum efflux pumps (50, 51). P. aeruginosa is also thought to enter into a biofilm mode of growth in CF lung infections (36,48,63), contributing both to pathogenicity/colonization and resistance to therapeutic intervention.In P. aeruginosa, global regulation, mediated by at least 3 quorum-sensing (QS) systems, controls population behaviors and synthesis of the majority of these pathogenicity factors (59, 66). This bacterium possesses two N-acyl-homoserine lactone (HSL)-mediated quorum-sensing systems, las and rhl (26,43,46,47), and a Pseudomonas quinolone signal (PQS) system mediated by 2-heptyl-3-hydroxy-4-quinolone (49). In the HSL-mediated systems, the HSL synthases LasI and RhlI are responsible for the synthesis of the autoinducers N-(3-oxododecanoyl)-L-HSL (3-OC12-HSL) and N-butyryl-L-HSL (C4-HSL), respectively. Expressions of the lasI and rhl genes are regulated by the transcriptional activators LasR and RhlR in response to their cognate HSL signal molecules. Among the numerous cellular and secreted virulence factors in P. aeruginosa whose...

Exogenous Pyocyanin Alters <i>Pseudomonas aeruginosa</i> Susceptibility to Ciprofloxacin

“…Persister cells constitute a small portion of a culture which is tolerant to killing by lethal doses of bactericidal antibiotics. The phenazine pyocyanin was recently shown to significantly increase the persister numbers in logarithmic P. aeruginosa PAO-1 or PA14 cultures (Moker et al, 2010). Although persister cells are believed to contribute to difficulties in treatment, the underlying mechanisms affecting persister formation are not well understood (Moker et al, 2010).…”

“…Pyocyanin was shown to have no significant growth inhibitory effects of its own at 100 µM. Exogenous addition of pyocyanin produced a decrease in susceptibility of both strains tested at concentrations well in excess of the MIC that may be associated with an increase in the persister cell population (Moker et al, 2010). Persister cells constitute a small portion of a culture which is tolerant to killing by lethal doses of bactericidal antibiotics.…”

Starvation- and antibiotics-induced formation of persister cells in Pseudomonas aeruginosa

“…Other mechanisms such as the development of swarming colonies, the stringent response, i.e. response to nutrient limitation, and the formation of multiresistant subpopulation of persistent cells contribute to the multidrug-resistant phenotype [21][22][23] . Furthermore, P. aeruginosa is versatile in the development or acquisition of new mechanisms of resistance to antibiotic treatment.…”

“…9 ) and quorum-sensing-related signaling molecule acyl-homoserine lactone 3-OC12-HSL and phenazine pyocyanin 10 , were found to be required for persister formation. It is noteworthy that persisters occur in biofilms and planktonic cultures.…”

“…The main advantage of the existence of two cell death pathways appears to be to permit survival of a small part of the bacterial population which may revert to normal growing cells 14,16 . Persister cells have been reported to be more numerous in stationary than in exponential P. aeruginosa cultures isolated by ciprofloxacin 10 . The aim of the present study was to investigate the formation of persister cells in P. aeruginosa stationary vs. exponential cultures using different bactericidal antibiotics.…”