Details of Research Interests:
Mechanisms of antibiotic resistance in the opportunistic human pathogen Pseudomonas aeruginosa
P. aeruginosa is a Gram-negative opportunistic human pathogen associated with debilitating infections of immunocompromised individuals including those with HIV/AIDS cancer and severe burns, although it also causes less severe infections of healthy individuals (e.g., swimmers ear and hot tub folliculitis). A common nosocomial (i.e., hospital-acquired) pathogen linked to infections of the blood, lungs and urinary tract, particularly in very sick individuals (e.g., those in the ICU), P. aeruginosa is a major pulmonary pathogen in patients with cystic fibrosis and chronic obstructive pulmonary disease and a major cause of ventilator-associated pneumonias. Infections caused by P. aeruginosa have a high mortality rate, in part attributable to the organism’s intrinsically high resistance to many antimicrobials and the increased incidence of multidrug-resistant isolates in health care settings, both of which complicate antipseudomonal chemotherapy.
Patients with cystic fibrosis (CF) are susceptible to pulmonary infections caused by many microorganisms, particularly Pseudomonas aeruginosa, which infects 80% of CF patients. Such infections typically become chronic and lead to death, making P. aeruginosa lung infection the leading cause of mortality in CF. Historically, CF patients colonized with P. aeruginosa have been treated with a combination of antibiotics, bronchodilators and chest physiotherapy. β-lactams and/or aminoglycosides have been the antibiotics of choice though in recent years these have been augmented by the fluoroquinolones. Despite earlier concerns with toxicity, colistin is gaining favour, particularly in the treatment of multidrug-resistant P. aeruginosa infections. Still, aminoglycosides remain the most significant class of antibiotic used in the treatment of CF lung infections. Unfortunately, the need for ongoing and/or recurring treatment of chronic lung infections in CF patients contributes to the rise of antibiotic resistance in P. aeruginosa in the CF lung.
The classical mechanisms of antibiotic resistance involve drug inactivation, target alteration, drug impermeability and active efflux. P. aeruginosa is also intrinsically resistant to a variety of antibiotics by virtue of its low permeability outer membrane (OM), which interferes with entry of antimicrobials into the bacterial cell. Active drug efflux (i.e. export) appears to work synergistically with this low permeability to limit drug accumulation and promote resistance in P. aeruginosa. Indeed, numerous studies highlight the significance of chromosomally-encoded multidrug efflux systems in intrinsic as well as acquired multidrug resistance in P. aeruginosa.
1. Regulation and operation of multidrug efflux systems in P. aeruginosa. Four multidrug efflux systems (a.k.a. efflux pumps) known to contribute to antibiotic resistance in clinical isolates of P. aeruginosa have been identified and are being characterized in terms of a) how they operate in exporting antibiotics from the cell, and b) how their production is regulated (i.e., which genes control their expression), and c) what physiological/environmental ‘signals’ influence their production. Modern tools of molecular biology, including gene cloning/sequencing, site-directed mutagenesis, whole genome sequencing, DNA microarray analysis, RT-PCR, etc, are being used to study these. The ultimate goal is to devise ways of circumventing these efflux pumps so as to render P. aeruginosa more readily treatable with existing antibiotics.
2. Identification and characterization of aminoglycoside-resistance mechanisms in P. aeruginosa. Several genes that contribute to aminoglycoside resistance in P. aeruginosa have been identified and these are being characterized at the molecular level using modern tools of molecular biology as described above. The goal is to define those mechanisms that are most significant in the context of P. aeruginosa infection of the CF lung.