Geoffrey McKay - Academia.edu (original) (raw)

Papers by Geoffrey McKay

Antimicrobial Agents and Chemotherapy, Oct 1, 2003

MexXY is an aminoglycoside-inducible multidrug transporter shown to contribute to intrinsic and a... more MexXY is an aminoglycoside-inducible multidrug transporter shown to contribute to intrinsic and acquired aminoglycoside resistance in laboratory isolates of Pseudomonas aeruginosa. To assess its contribution to aminoglycoside resistance in 14 clinical isolates demonstrating a panaminoglycoside resistance phenotype unlikely to be explained solely by aminoglycoside modification, expression of mexXY by these isolates was examined by reverse transcription-PCR. Elevated levels of mexXY expression were evident for most strains compared with those detected for an aminoglycoside-susceptible control strain, although there was no correlation between mexXY levels and the aminoglycoside MICs for the resistant strains, indicating that if MexXY was playing a role, other factors were also contributing. Deletion of mexXY from 9 of the 14 isolates resulted in enhanced susceptibilities to multiple aminoglycosides, confirming the contribution of this efflux system to the aminoglycoside resistance of these clinical isolates. Still, the impact of MexXY loss varied, with some strains clearly more or less dependent on MexXY for aminoglycoside resistance. Expression of mexXY also varied in these strains, with some showing high-level expression of the efflux genes independent of aminoglycoside exposure (aminoglycoside-independent hyperexpression) and others showing hyperexpression of the efflux genes that was to a greater or lesser degree aminoglycoside dependent. None of these strains carried mutations in mexZ, which encodes a negative regulator of mexXY expression, or in the mexZ-mexXY intergenic region. Thus, mexXY hyperexpression in aminoglycoside-resistant clinical isolates occurs via mutation in one or more as yet unidentified genes.

Bioactive surface coatings have retained the attention of researchers and physicians due to their... more Bioactive surface coatings have retained the attention of researchers and physicians due to their versatility and range of applications in orthopedics, particularly in infection prevention. Antibacterial metal nanoparticles (mNPs) are a promising therapeutic, with vast application opportunities on orthopedic implants. The current research aimed to construct a polyelectrolyte multilayer on a highly porous titanium implant using alternating thin film coatings of chitosan and alginate via the layer-by-layer (LbL) self-assembly technique, along with the incorporation of silver nanoparticles (AgNPs) or titanium dioxide nanoparticles (TiO2NPs), for antibacterial and osteoconductive activity. These mNPs were characterized for their physicochemical properties using quartz crystal microgravimetry with dissipation system, nanoparticle tracking analysis, scanning electron microscopy, and atomic force microscopy. Their cytotoxicity and osteogenic differentiation capabilities were assessed by Al...

HAL (Le Centre pour la Communication Scientifique Directe), Oct 26, 2020

ACS Applied Materials & Interfaces

ACS Biomaterials Science & Engineering

RSC Medicinal Chemistry, 2022

Optimized RpoN-based stapled peptides selectively bind promoter DNA sequence and inhibit virulenc... more Optimized RpoN-based stapled peptides selectively bind promoter DNA sequence and inhibit virulence of Pseudomonas aeruginosa in an in vivo model.

Infection and Immunity, Jun 1, 2003

A homologue of the algC gene, responsible for the production of a phosphoglucomutase (PGM) associ... more A homologue of the algC gene, responsible for the production of a phosphoglucomutase (PGM) associated with LPS and alginate biosynthesis in Pseudomonas aeruginosa, spgM, was cloned from Stenotrophomonas maltophilia. The spgM gene was shown to encode a bifunctional enzyme with both PGM and phosphomannomutase activities. Mutants lacking spgM produced less LPS than the SpgM ؉ parent strain and had a tendency for shorter O polysaccharide chains. No changes in LPS chemistry were obvious as a result of the loss of spgM. Significantly, however, spgM mutants displayed a modest increase in susceptibility to several antimicrobial agents and were completely avirulent in an animal model of infection. The latter finding may relate to the resultant serum sensitivity of spgM mutants which, unlike the wild-type parent strain, were rapidly killed by human serum. These data highlight the contribution made by LPS to the antimicrobial resistance and virulence of S. maltophilia. Stenotrophomonas maltophilia is a gram-negative bacterium that is an important cause of nosocomial infections (17, 34). It has emerged as an important opportunistic pathogen in immunodeficient patients, including transplant recipients (38), cancer patients (33), and AIDS sufferers (19). However, the most frequent site of infection remains the lungs (4, 9, 20). In many cases, treatment of S. maltophilia is problematic owing to its high level of intrinsic resistance to multiple classes of antibiotics (56). A number of factors, including multidrug efflux pumps (1, 3, 65) and outer membrane impermeability (13, 37), likely contribute to the intrinsic antibiotic resistance of S. maltophilia. A key component of the outer membrane is lipopolysaccharide (LPS), and changes in LPS structure have been correlated with changes in resistance to a variety of antimicrobial agents (reviewed in reference 41). Several groups have investigated LPS in S. maltophilia in an effort to assess its contribution to antimicrobial resistance in this organism (43-45, 60). S. maltophilia exhibits a temperature-dependent variation in susceptibility to several antibiotics, including aminoglycosides and polymyxin B (60), whose activities are known to be affected by LPS (44), but not quinolones, ␤-lactams, and chloramphenicol (44, 60). Temperature-dependent changes in outer membrane fluidity (44), LPS side-chain length (45) and, possibly, core phosphate content (43) appear to explain the temperature-dependent variation in aminoglycoside susceptibility, implicating LPS as a determinant of aminoglycoside resistance in this organism. Temperaturedependent changes in lipid A (44), outer membrane proteins (45), or 3-deoxy-D-manno-octulosonic acid (43) have not been observed.

Mechanisms of lung injury and repair

Journal of Biological Chemistry, Oct 1, 1997

Bacterial resistance to the aminoglycoside antibiotics is manifested primarily through the expres... more Bacterial resistance to the aminoglycoside antibiotics is manifested primarily through the expression of enzymes which covalently modify these drugs. One important mechanism of aminoglycoside modification is through ATP-dependent O-phosphorylation, catalyzed by a family of aminoglycoside kinases. The structure of one of these kinases, APH(3)-IIIa has recently been determined by x-ray crystallography, and the general fold is strikingly similar to eukaryotic protein kinases (Hon,

Antimicrobial Agents and Chemotherapy, Dec 1, 2010

Oritavancin is an investigational lipoglycopeptide in clinical development for the treatment of a... more Oritavancin is an investigational lipoglycopeptide in clinical development for the treatment of acute bacterial skin and skin structure infections. In this study, we demonstrate that oritavancin causes bacterial membrane depolarization and permeabilization leading to cell death of Gram-positive pathogens and that these effects are attributable to the 4-chlorobiphenylmethyl group of the molecule.

Chemistry & Biology, 1999

Background: Elacterial resistance to aminoglycoside antibiotics occurs primarily through the expr... more Background: Elacterial resistance to aminoglycoside antibiotics occurs primarily through the expression of modifying enzymes that covalently alter tl?e drugs by 0-phosphorylation, 0-adenylation or N-acetylation. Aminoglycoside phosphotransferases (APHs) catalyze the ATP-dependent phosphorylation of these antibiotics. Two particular enzymes in this class, APH(3')-llla and AAC(G')-APH(S"), are produced in gram-positive cocci and have been shown to phosphorylate aminoglycosides on their 3' and 2" hydroxyl groups, respectively. The three-dimensional structure of APH (3')sllla is strikingly similar to those of eukaryotic protein kinases (EPKs), and the observation, reported previously, that APH(3')-llla and AAC(G')-APH(2") are effectively inhibited by EPK inhibitors suggested the possibility that these aminoglycoside kinases might phosphorylate EPK substrates. Results: Our data demonstrate unequivocally that APHs can phosphorylate several EPK substrates and that this phosphorylation occurs exclusively on serine residues. Phosphorylation of Ser/Thr protein kinase substrates by APHs was considerably slower than phosphorylation of aminoglycosides under identical assay conditions, which is consistent with the primary biological roles of the enzymes. Conclusions: These results demonstrate a functional relationship between aminoglycoside and protein kinases, expanding on our previous observations of similarities in proiein structure, enzyme mechanism and sensitivity to inhibitors, and suggest an evolutionary link between APHs and EPKs.

Journal of Antimicrobial Chemotherapy, Mar 13, 2003

Stenotrophomonas maltophilia is an emerging nosocomial pathogen that displays high-level intrinsi... more Stenotrophomonas maltophilia is an emerging nosocomial pathogen that displays high-level intrinsic resistance to multiple antibiotics including aminoglycosides. A gene [aac(6′)-Iz] encoding an aminoglycoside-modifying enzyme, AAC(6′)-Iz acetyltransferase, was recently cloned and sequenced in S. maltophilia, but its importance with respect to aminoglycoside resistance in this organism was not determined. Using a homologous gene replacement approach, mutants carrying unmarked chromosomal deletions of the aac(6′)-Iz gene were constructed in wild-type and in vitro-selected aminoglycoside-resistant S. maltophilia. AAC(6′)-Iz-deficient mutants derived from both wild-type and aminoglycoside-resistant strains displayed an increase in susceptibility to amikacin, netilmicin, sisomicin and tobramycin (4-to 32-fold decrease in MICs), known substrates for AAC(6′)-I enzymes. The cloned aac(6′)-Iz gene restored the aminoglycoside resistance of the aac(6′)-Iz mutants, and could also confer aminoglycoside resistance upon Escherichia coli. To assess the significance of the aac(6′)-Iz gene with respect to the aminoglycoside resistance of clinical strains, its distribution was assessed in 65 clinical isolates from two hospitals. Using PCR, Southern hybridization, RT-PCR and/or nucleotide sequencing, the aac(6′)-Iz gene was identified in 57% of the isolates. Susceptibility tests indicated a good correlation between the presence of the aac(6′)-Iz gene and the resistance to tobramycin, netilmicin and sisomicin in these strains. These results indicate that the aac(6′)-Iz gene is an important contributor to aminoglycoside resistance in clinical strains of S. maltophilia, particularly to tobramycin.

Journal of Experimental Medicine, 2021

The airway mucosal microenvironment is crucial for host defense against inhaled pathogens but rem... more The airway mucosal microenvironment is crucial for host defense against inhaled pathogens but remains poorly understood. We report here that the airway surface normally undergoes surprisingly large excursions in pH during breathing that can reach pH 9.0 during inhalation, making it the most alkaline fluid in the body. Transient alkalinization requires luminal bicarbonate and membrane-bound carbonic anhydrase 12 (CA12) and is antimicrobial. Luminal bicarbonate concentration and CA12 expression are both reduced in cystic fibrosis (CF), and mucus accumulation both buffers the pH and obstructs airflow, further suppressing the oscillations and bacterial-killing efficacy. Defective pH oscillations may compromise airway host defense in other respiratory diseases and explain CF-like airway infections in people with CA12 mutations.

PLOS Pathogens, 2021

Pseudomonas aeruginosa causes chronic airway infections, a major determinant of lung inflammation... more Pseudomonas aeruginosa causes chronic airway infections, a major determinant of lung inflammation and damage in cystic fibrosis (CF). Loss-of-function lasR mutants commonly arise during chronic CF infections, are associated with accelerated lung function decline in CF patients and induce exaggerated neutrophilic inflammation in model systems. In this study, we investigated how lasR mutants modulate airway epithelial membrane bound ICAM-1 (mICAM-1), a surface adhesion molecule, and determined its impact on neutrophilic inflammation in vitro and in vivo. We demonstrated that LasR-deficient strains induce increased mICAM-1 levels in airway epithelial cells compared to wild-type strains, an effect attributable to the loss of mICAM-1 degradation by LasR-regulated proteases and associated with enhanced neutrophil adhesion. In a subacute airway infection model, we also observed that lasR mutant-infected mice displayed greater airway epithelial ICAM-1 expression and increased neutrophilic p...

Antimicrobial Agents and Chemotherapy, 1996

The interactions of the aminoglycoside 3'-phosphotransferase IIIa with aminoglycoside antibio... more The interactions of the aminoglycoside 3'-phosphotransferase IIIa with aminoglycoside antibiotics lacking specific amino groups were examined by steady-state kinetic analyses. The results demonstrate that an amino group on C-1 and either an amino or a hydroxyl group at the 2' and 6' positions are important for detoxification of aminoglycosides by this enzyme.

Journal of Fungi, 2022

The mold Aspergillus fumigatus and bacterium Pseudomonas aeruginosa form biofilms in the airways ... more The mold Aspergillus fumigatus and bacterium Pseudomonas aeruginosa form biofilms in the airways of individuals with cystic fibrosis. Biofilm formation by A. fumigatus depends on the self-produced cationic exopolysaccharide galactosaminogalactan (GAG), while P. aeruginosa biofilms can contain the cationic exopolysaccharide Pel. GAG and Pel are rendered cationic by deacetylation mediated by either the secreted deacetylase Agd3 (A. fumigatus) or the periplasmic deacetylase PelA (P. aeruginosa). Given the similarities between these polymers, the potential for biofilm interactions between these organisms were investigated. P. aeruginosa were observed to adhere to A. fumigatus hyphae in a GAG-dependent manner and to GAG-coated coverslips of A. fumigatus biofilms. In biofilm adherence assays, incubation of P. aeruginosa with A. fumigatus culture supernatants containing de-N-acetylated GAG augmented the formation of adherent P. aeruginosa biofilms, increasing protection against killing by ...

Undergraduate research journal for the human sciences, 2014