The Pseudomonas aeruginosa genome: how do we use it to develop strategies for the treatment of patients with cystic fibrosis and Pseudomonas infections?

Chronic Pseudomonas aeruginosa infection in cystic fibrosis airway disease: metabolic changes that unravel novel drug targets

The cystic fibrosis (CF) airways have an incompletely characterized defect in innate defense that eventually leads to bacterial infection and airway inflammation. Persistent Pseudomonas aerugionsa infection resulting from defective innate immunity and a bacterial phenotypic switch to a more intractable mucoid form inside the airway are now well established as important components of CF pathogenesis. Broad-based factors leading to chronic infection will be discussed with respect to: bacterial virulence in the context of biofilm formation, quorum sensing machinery and alginate overproduction, and failure of innate lung immunity in CF airways. In addition, a controversial question as to whether inflammation or infection comes first during CF airway disease will be addressed. Finally, a new hypothesis, that P. aeruginosa thrives as biofilms within the thickened anaerobic mucus layers, will be developed.

Structural and antimicrobial properties of human pre-elafin/trappin-2 and derived peptides against Pseudomonas aeruginosa

Background

Pre-elafin/trappin-2 is a human innate defense molecule initially described as a potent inhibitor of neutrophil elastase. The full-length protein as well as the N-terminal "cementoin" and C-terminal "elafin" domains were also shown to possess broad antimicrobial activity, namely against the opportunistic pathogen P. aeruginosa. The mode of action of these peptides has, however, yet to be fully elucidated. Both domains of pre-elafin/trappin-2 are polycationic, but only the structure of the elafin domain is currently known. The aim of the present study was to determine the secondary structures of the cementoin domain and to characterize the antibacterial properties of these peptides against P. aeruginosa.

Results

We show here that the cementoin domain adopts an α-helical conformation both by circular dichroism and nuclear magnetic resonance analyses in the presence of membrane mimetics, a characteristic shared with a large number of linear polycationic antimicrobial peptides. However, pre-elafin/trappin-2 and its domains display only weak lytic properties, as assessed by scanning electron micrography, outer and inner membrane depolarization studies with P. aeruginosa and leakage of liposome-entrapped calcein. Confocal microscopy of fluorescein-labeled pre-elafin/trappin-2 suggests that this protein possesses the ability to translocate across membranes. This correlates with the finding that pre-elafin/trappin-2 and elafin bind to DNA in vitro and attenuate the expression of some P. aeruginosa virulence factors, namely the biofilm formation and the secretion of pyoverdine.

Conclusions

The N-terminal cementoin domain adopts α-helical secondary structures in a membrane mimetic environment, which is common in antimicrobial peptides. However, unlike numerous linear polycationic antimicrobial peptides, membrane disruption does not appear to be the main function of either cementoin, elafin or full-length pre-elafin/trappin-2 against P. aeruginosa. Our results rather suggest that pre-elafin/trappin-2 and elafin, but not cementoin, possess the ability to modulate the expression of some P.aeruginosa virulence factors, possibly through acting on intracellular targets.

Human pre-elafin inhibits a Pseudomonas aeruginosa-secreted peptidase and prevents its proliferation in complex media

Pseudomonas aeruginosa is a life-threatening opportunist human pathogen frequently associated with lung inflammatory diseases, namely, cystic fibrosis. Like other species, this gram-negative bacteria is increasingly drug resistant. During the past decade, intensive research efforts have been focused on the identification of natural innate defense molecules with broad antimicrobial activities, collectively known as antimicrobial peptides. Human pre-elafin, best characterized as a potent inhibitor of neutrophil elastase with anti-inflammatory properties, was also shown to possess antimicrobial activity against both gram-positive and gram-negative bacteria, including P. aeruginosa. Its mode of action was, however, not known. Using full-length pre-elafin, each domain separately, and mutated variants of pre-elafin with attenuated antipeptidase activity toward neutrophil elastase, we report here that both pre-elafin domains contribute, through distinct mechanisms, to its antibacterial activity against Pseudomonas aeruginosa. Most importantly, we demonstrate that the whey acidic protein (WAP) domain specifically inhibits a secreted peptidase with the characteristics of arginyl peptidase (protease IV). This is the first demonstration that a human WAP-motif protein inhibits a secreted peptidase to prevent bacterial growth in vitro. Since several WAP-motif proteins from various species demonstrate antimicrobial function with variable activities toward bacterial species, we suggest that this mechanism may be more common than initially anticipated.

The intensive care unit as a research laboratory: developing strategies to prevent antimicrobial resistance

OBJECTIVE

To assemble the available clinical data on the prevention of antimicrobial resistance in the intensive care unit (ICU) setting.

DATA SOURCE

A MEDLINE database search and references from identified articles were employed to obtain the literature relating to the prevention of antimicrobial resistance in the ICU.

CONCLUSIONS

The ICU presents a unique environment for the conduct of clinical research. The closed physical space with centralized patient management and efficient data recovery allows important clinical questions to be evaluated in a timely manner. Antimicrobial resistance has emerged as an important determinant of mortality for patients in the ICU. Additionally, there is currently a limited pipeline of new agents for the treatment of emerging bacteria with new resistance genes that pose an increasing threat to the ICU patient. Effective strategies for the prevention of antimicrobial resistance within ICUs are available and should be implemented aggressively. These strategies can be divided into non-pharmacologic infection- control strategies (e.g., routine hand hygiene, infection-specific prevention protocols) and antibiotic management strategies (e.g., shorter courses of appropriate antibiotics, narrowing of the antimicrobial spectrum on the basis of culture results). Additional studies conducted in ICUs are needed urgently to identify the optimal approaches for the management of antibiotics in order to balance the need for efficacy with the ability to minimize resistance.

Strategies to prevent antimicrobial resistance in the intensive care unit

OBJECTIVE

To assemble the available clinical data for the prevention of antimicrobial resistance into practical recommendations for clinicians.

DATA SOURCE

A Medline database and references from identified articles were employed to perform a literature search relating to the prevention of antimicrobial resistance.

CONCLUSIONS

Antimicrobial resistance has emerged as an important determinant of mortality for patients in the intensive care unit. This is largely due to the increasing presence of pathogenic microorganisms with resistance to existing antimicrobial agents, resulting in the administration of inappropriate treatment. Effective strategies for the prevention of antimicrobial resistance within intensive care units are available and should be aggressively implemented. These strategies can be divided into nonpharmacologic infection control strategies (e.g., routine hand hygiene, implementation of infection-specific prevention protocols) and antibiotic management strategies (e.g., shorter courses of appropriate antibiotic treatment, narrowing of antimicrobial spectrum based on culture results). Increasing current efforts aimed at the prevention of antimicrobial resistance is especially important given the limited availability of new antimicrobial drug classes for the foreseeable future.