George G Zhanel

University of Manitoba, Winnipeg, Manitoba, Canada

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Publications (358)1391.44 Total impact

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    ABSTRACT: The use of adjuvants that rescue antibiotics against multidrug-resistant (MDR) pathogens is a promising combination strategy for overcoming bacterial resistance. While the combination of β-lactam antibiotics and β-lactamase inhibitors has been successful in restoring antibacterial efficacy in MDR bacteria, the use of adjuvants to restore fluoroquinolone efficacy in MDR Gram-negative pathogens has been challenging. We describe tobramycin-ciprofloxacin hybrid adjuvants that rescue the activity of fluoroquinolone antibiotics against MDR and extremely drug-resistant Pseudomonas aeruginosa isolates in vitro and enhance fluoroquinolone efficacy in vivo. Structure-activity studies reveal that the presence of both tobramycin and ciprofloxacin, which are separated by a C12 tether, is critical for the function of the adjuvant. Mechanistic studies indicate that the antibacterial modes of ciprofloxacin are retained while the role of tobramycin is limited to destabilization of the outer membrane in the hybrid.
    Angewandte Chemie International Edition in English 11/2015; DOI:10.1002/ange.201508330 · 13.45 Impact Factor

  • Angewandte Chemie International Edition in English 11/2015; DOI:10.1002/anie.201508330 · 13.45 Impact Factor
  • Amrita Bharat · Irene Martin · George G. Zhanel · Michael R. Mulvey ·
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    ABSTRACT: Antimicrobial resistant Neisseria gonorrhoeae is a major concern to public health due to decreased susceptibility to frontline antimicrobials. To find agents that are active against N. gonorrhoeae, we tested antimicrobials alone or in combination by Etest gradient strips. The potencies (as assessed by minimum inhibitory concentrations) of twenty-five antimicrobials were evaluated against nine reference strains of N. gonorrhoeae (WHO F, G, K, L, M, N, O, P and ATCC 49226). Potency was greatest for netilmicin, quinupristin-dalfopristin, ceftriaxone, ertapenem and piperacillin-tazobactam. Combinations of azithromycin, moxifloxacin, or gentamicin with ceftriaxone, doripenem, or aztreonam were tested against reference isolates and the fractional inhibitory concentration index (FICI) was calculated. All nine combinations resulted in indifference (>0.5 FICI ≤ 4). Combinations with FICI < 1 were further evaluated in nine clinical isolates which supported the finding of indifference. No antagonism was observed in any of the combinations tested. This is the first report in which the six combinations of azithromycin, moxifloxacin or gentamcin in combination with doripenem or aztreonam were tested in N. gonorrhoeae. These data on antimicrobials with higher potency and combinations that did not show antagonism can help to guide larger scale susceptibility studies for antimicrobial resistant N. gonorrhoeae.
    Journal of Infection and Chemotherapy 11/2015; DOI:10.1016/j.jiac.2015.10.002 · 1.49 Impact Factor
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    James A. Karlowsky · Kim Nichol · George G. Zhanel ·
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    ABSTRACT: Telavancin is a semisynthetic lipoglycopeptide derivative of vancomycin. Telavancin has a dual mechanism of antibacterial action, disrupting peptidoglycan synthesis and cell membrane function. In 2014, the Clinical and Laboratory Standards Institute (CLSI) revised the antimicrobial susceptibility testing method for telavancin, resulting in minimum inhibitory concentration (MIC) determinations that are more accurate and reproducible and demonstrate greater in vitro potency than shown with the previous testing method. The CLSI testing method changes coincided with revised telavancin MIC interpretive break point criteria for susceptibility approved by the US Food and Drug Administration for Staphylococcus aureus (≤0.12 µg/mL), Streptococcus pyogenes (≤0.12 µg/mL), Streptococcus agalactiae (≤0.12 µg/mL), Streptococcus anginosus group (≤0.06 µg/mL), and Enterococcus faecalis (vancomycin susceptible, ≤0.25 µg/mL). Telavancin is equally potent against methicillin-susceptible S. aureus (MSSA) and methicillin-resistant S. aureus (MRSA). It demonstrates activity against isolates of heterogeneous vancomycin-intermediate S. aureus and vancomycin-intermediate S. aureus but is poorly active against vancomycin-resistant S. aureus. It also demonstrates potent activity against Staphylococcus epidermidis and Streptococcus spp. (MIC90 ≤0.03 µg/mL). Thus far, it has not been possible to select for high-level telavancin resistance in the laboratory using serially passaged clinical isolates of MRSA and MSSA. © The Author 2015. Published by Oxford University Press on behalf of the Infectious Diseases Society of America. All rights reserved. For Permissions, please e-mail:
    Clinical Infectious Diseases 09/2015; 61(suppl 2). DOI:10.1093/cid/civ534 · 8.89 Impact Factor
  • Ronald Domalaon · George G Zhanel · Frank Schweizer ·
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    ABSTRACT: Antimicrobial peptides have recently garnered significant attention as an emerging source of potential antibiotics, due to the swift emergence of multidrug-resistant bacteria and a dwindling antibiotic pipeline. The vast majority of antimicrobial peptides are long, comprised of more than 10 amino acids, resulting in significant production costs for their synthesis while simultaneously displaying metabolic instability and relatively poor pharmacological profiles. To counter these problems, efforts have been shifted to shorter molecules and the development of new peptidomimetic approaches. In this paper, we review promising short, naturally-isolated or synthetic, antimicrobial peptides, along with their mimics, and discuss their merits as potential antibacterial agents.
    Current topics in medicinal chemistry 09/2015; · 3.40 Impact Factor
  • George G Zhanel · Kevin D Wolter · James A Karlowsky ·

    Journal of Antimicrobial Chemotherapy 08/2015; DOI:10.1093/jac/dkv234 · 5.31 Impact Factor
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    M. De Silva · C. Ning · S. Ghanbar · G. Zhanel · S. Logsetty · S. Liu · A. Kumar ·
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    ABSTRACT: Pseudomonas aeruginosa is well known for causing hospital-acquired infections that are often difficult to treat because of its high intrinsic and acquired resistance to antibiotics. Resistance-nodulation-division (RND) efflux pumps are the major contributors to the intrinsic multidrug resistance (MDR) in this organism. Various biocides used in hospital settings have been shown to select for RND-pump-overexpressing mutants of P. aeruginosa that show cross-resistance to clinically relevant antibiotics. Therefore, finding biocides that do not select for multidrug-resistant mutants is important in controlling the spread of bacteria such as P. aeruginosa. To evaluate the potential of a novel quaternary ammonium compound and its N-chloramine derivative in selecting for MDR mutants of P. aeruginosa. P. aeruginosa PA01 was cultured in the presence of increasing concentrations of the quaternary ammonium compound and its N-chloramine derivative respectively, and one mutant each selected. Susceptibility of the mutants to both compounds as well as antibiotics was tested. Susceptibility of P. aeruginosa strains with deletions in RND pumps was also tested for both compounds to determine whether they are a substrate of these pumps. Expression of mexB, mexD, and mexY genes in the mutants was analysed using quantitative reverse transcriptase-polymerase chain reaction to determine whether the compounds can select for pump-overexpressing mutants. We show that whereas both compounds can be pumped by the MexCD-OprJ pump, they neither select for mutants that overexpress RND pumps nor for mutants that display cross-resistance to antibiotics. These compounds are promising candidates to be used as disinfectants in hospital settings. Copyright © 2015 The Healthcare Infection Society. Published by Elsevier Ltd. All rights reserved.
    The Journal of hospital infection 06/2015; 91(1). DOI:10.1016/j.jhin.2015.05.009 · 2.54 Impact Factor
  • Borna Mehrad · Nina M Clark · George G Zhanel · Joseph P Lynch ·
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    ABSTRACT: Aerobic gram-negative bacilli, including the family of Enterobacteriaceae and non-lactose fermenting bacteria such as Pseudomonas and Acinetobacter species, are major causes of hospital-acquired infections. The rate of antibiotic resistance among these pathogens has accelerated dramatically in recent years and has reached pandemic scale. It is no longer uncommon to encounter gram-negative infections that are untreatable using conventional antibiotics in hospitalized patients. In this review, we provide a summary of the major classes of gram-negative bacilli and their key mechanisms of antimicrobial resistance, discuss approaches to the treatment of these difficult infections, and outline methods to slow the further spread of resistance mechanisms.
    Chest 05/2015; 147(5):1413-21. DOI:10.1378/chest.14-2171 · 7.48 Impact Factor
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    ABSTRACT: The goal of this study was to characterize Streptococcus pneumoniae demonstrating MDR (resistant to three or more antimicrobial classes) or XDR (resistant to five or more classes) phenotypes, collected from Canada during the CANWARD 2007-13 study. From 2007 to 2013 inclusive, S. pneumoniae isolates were collected as a part of the CANWARD surveillance study. MDR and XDR isolates were subjected to PFGE, MLST, molecular detection of pneumococcal pili and macrolide resistance determinants mef(A/E) and erm(B), sequencing of PBPs 1A, 2B and 2X and comparison with Pneumococcal Molecular Epidemiology Network (PMEN) clones. Of 2129 S. pneumoniae isolates collected during the CANWARD 2007-13 study, 61 (2.9%) were found to be MDR. Of these MDR isolates, 43 (70.5%) were XDR. The most common serotypes for both MDR and XDR S. pneumoniae were 19A and 19F. Twenty-nine of 61 isolates (48%) demonstrated resistance to clarithromycin, clindamycin, doxycycline, penicillin and trimethoprim/sulfamethoxazole. All isolates possessed at least one macrolide resistance determinant and mutations in PBPs 1A, 2B and 2X. The most common clone was piliated, XDR ST320, an internationally circulating double-locus variant of Taiwan(19F)-14 (ST236). Though the rate of MDR S. pneumoniae has remained relatively stable since 2007, XDR strains have emerged in Canada. These strains are virulent, possess resistance determinants and are related to international clones. © The Author 2015. Published by Oxford University Press on behalf of the British Society for Antimicrobial Chemotherapy. All rights reserved. For Permissions, please e-mail:
    Journal of Antimicrobial Chemotherapy 04/2015; 70(8). DOI:10.1093/jac/dkv107 · 5.31 Impact Factor
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    ABSTRACT: Of 1927 Enterococcus spp. isolated across Canada from 2007-2013, inclusive, 4.2% (80) were identified as VRE. VRE infections tripled in Canadian hospitals from 1.8% to 6.0% (p=0.03). All VRE were E. faecium, with 90% possessing vanA. The prevalence of vanB decreased from 37.5% in 2007 to 0% in 2013 (p<0.05). VRE were multi-drug resistant but 70.6%, 86.3% and 100% were susceptible to doxycycline, linezolid and daptomycin, respectively. Copyright © 2015, American Society for Microbiology. All Rights Reserved.
    Antimicrobial Agents and Chemotherapy 04/2015; 59(7). DOI:10.1128/AAC.00384-15 · 4.48 Impact Factor
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    ABSTRACT: This work examined Escherichia coli O157:H7 strain 02-0304 for putative genes responsible for sinigrin hydrolysis. Sinigrin is a glucosinolate present in Oriental mustard (Brassica juncea), and its hydrolysis is mediated in plants by the enzyme myrosinase. Sinigrin hydrolysis by plant or bacterial myrosinase yields allyl isothiocyanate (AITC) which is bactericidal. In silico analysis using public databases found sequence similarity between plant myrosinase and enzymes encoded by genes from β-glucosidase families in E. coli O157:H7. Specifically, 6-phospho-β-glucosidase encoded by the genes bglA and ascB (family 1), and chbF (family 4) present in E. coli O157:H7 showed the highest similarity. Polymerase chain reaction (PCR) confirmed the presence of bglA, ascB, and chbF in the clinical E. coli strain tested. Disruption of these genes in wild-type E. coli O157:H7 strain 02-0304 using lambda-red replacement created single and double mutants. The relative importance of each gene in the hydrolysis of sinigrin by E. coli O157:H7 was also assessed by comparing gene expression and sinigrin degradation rates among the E. coli O157:H7 wild-type strain and its mutants. The results suggested that the genes bglA and ascB play a substantial role in the degradation of sinigrin by E. coli O157:H7 strain 02-0304. Copyright © 2015. Published by Elsevier B.V.
    International journal of food microbiology 04/2015; 205:105-111. DOI:10.1016/j.ijfoodmicro.2015.04.008 · 3.08 Impact Factor
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    ABSTRACT: Amphiphilic aminoglycosides (AAGs) are an emerging source of antibacterials to combat infections caused by antibiotic-resistant bacteria. Mode-of-action studies indicate that AAGs predominately target bacterial membranes, thereby leading to depolarization and increased permeability. To assess whether AAGs also induce host-directed immunomodulatory responses, we determined the AAG-dependent induction of cytokines in macrophages in the absence or presence of lipopolysaccharide (LPS). Our results show for the first time that AAGs can boost the innate immune response, specifically the recruitment of immune cells such as neutrophils required for the resolution of infections. Moreover, AAGs can selectively control inflammatory responses induced in the presence of endotoxins to prevent septic shock. In conclusion, our study demonstrates that AAGs possess multifunctional properties that combine direct antibacterial activity with host-directed clearance effects reminiscent of those of host-defense peptides. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    Angewandte Chemie International Edition 04/2015; 54(21). DOI:10.1002/anie.201500598 · 11.26 Impact Factor
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    ABSTRACT: Amphiphilic aminoglycosides (AAGs) are an emerging source of antibacterials to combat infections caused by antibiotic-resistant bacteria. Mode-of-action studies indicate that AAGs predominately target bacterial membranes, thereby leading to depolarization and increased permeability. To assess whether AAGs also induce host-directed immunomodulatory responses, we determined the AAG-dependent induction of cytokines in macrophages in the absence or presence of lipopolysaccharide (LPS). Our results show for the first time that AAGs can boost the innate immune response, specifically the recruitment of immune cells such as neutrophils required for the resolution of infections. Moreover, AAGs can selectively control inflammatory responses induced in the presence of endotoxins to prevent septic shock. In conclusion, our study demonstrates that AAGs possess multifunctional properties that combine direct antibacterial activity with host-directed clearance effects reminiscent of those of host-defense peptides.
    Angewandte Chemie 04/2015; DOI:10.1002/ange.201500598
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    ABSTRACT: The mechanism of aminoglycoside resistance among 338 gentamicin non-susceptible gram-negative bacteria (207 Enterobacteriaceae and 131 Pseudomonas aeruginosa) was assessed, and the in vitro activity of ceftazidime-avibactam versus these isolates was determined. Aminoglycoside modifying enzymes (AMEs) were detected in 91.8% of Enterobacteriaceae and 13.7% of P. aeruginosa. A single strain of Klebsiella pneumoniae harbored a 16S rRNA methylase (ArmA). The ceftazidime-avibactam MIC90 was 0.5 μg/ml (MIC, ≤8 μg/ml, for 100% of isolates) and 16 μg/ml (MIC, ≤8 μg/ml, for 87.8% of isolates) versus the gentamicin non-susceptible Enterobacteriaceae and P. aeruginosa isolates, respectively. Copyright © 2015, American Society for Microbiology. All Rights Reserved.
    Antimicrobial Agents and Chemotherapy 03/2015; 59(6). DOI:10.1128/AAC.00364-15 · 4.48 Impact Factor
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    ABSTRACT: We investigated whether specific sequence types, and their shared virulence gene profiles, may be associated with both human and food animal reservoirs. A total of 600 Escherichia coli isolates were assembled from human (n=265) and food-animal (n=335) sources from overlapping geographic areas and time periods (2005-2010) in Canada. The entire collection was subjected to multilocus sequence typing and a subset of 286 E. coli isolates was subjected to an E. coli-specific virulence gene microarray. The most common sequence type (ST) was E. coli ST10, which was present in all human and food-animal sources, followed by ST69, ST73, ST95, ST117, and ST131. A core group of virulence genes was associated with all 10 common STs including artJ, ycfZ, csgA, csgE, fimA, fimH, gad, hlyE, ibeB, mviM, mviN, and ompA. STs 73, 92, and 95 exhibited the largest number of virulence genes, and all were exclusively identified from human infections. ST117 was found in both human and food-animal sources and shared virulence genes common in extraintestinal pathogenic E. coli lineages. Select groups of E. coli may be found in both human and food-animal reservoirs.
    Foodborne Pathogens and Disease 03/2015; 12(4). DOI:10.1089/fpd.2014.1860 · 1.91 Impact Factor
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    ABSTRACT: Serotype replacement in Streptococcus pneumoniae following the implementation of a new vaccine has been associated with the emergence of non-vaccine serotypes as prominent causes of invasive pneumococcal disease (IPD). The aim of this study was to characterize specific non-PCV-13 serotypes 15A, 22F, 33F and 35B from IPD, isolated in Canada post-PCV-13 introduction in 2010. Of 3802 IPD isolates collected from across Canada in 2011-13, 18.4% were found to be serotypes 15A, 22F, 33F and 35B. These 699 isolates were subjected to antimicrobial susceptibility testing, PFGE, MLST, molecular detection of pneumococcal pili and comparison with Pneumococcal Molecular Epidemiology Network (PMEN) clones. This study demonstrated clonal spread of specific STs, including MDR ST63 and its Sweden(15A)-25-related variants, the increasingly common ST433 and a variant of piliated, penicillin-non-susceptible ST558, related to PMEN clone Utah(35B)-24 (ST377). New STs of serotype 33F were identified. Several potential capsular switching events were identified within these serotypes. Non-PCV-13 serotype 22F is increasing in Canada through the rapid clonal expansion of ST433. Numerous new STs associated with serotype 33F indicate the potential divergence of the serotype. Serotypes 15A and 35B in Canada are related to international clones of S. pneumoniae. © The Author 2015. Published by Oxford University Press on behalf of the British Society for Antimicrobial Chemotherapy. All rights reserved. For Permissions, please e-mail:
    Journal of Antimicrobial Chemotherapy 03/2015; 70(7). DOI:10.1093/jac/dkv061 · 5.31 Impact Factor
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    ABSTRACT: Tedizolid phosphate is a novel oxazolidinone prodrug (converted to the active form tedizolid by phosphatases in vivo) that has been developed and recently approved (June 2014) by the United States FDA for the treatment of acute bacterial skin and skin structure infections (ABSSSIs) caused by susceptible Gram-positive pathogens, including methicillin-resistant Staphylococcus aureus (MRSA). Tedizolid is an oxazolidinone, but differs from other oxazolidinones by possessing a modified side chain at the C-5 position of the oxazolidinone nucleus which confers activity against certain linezolid-resistant pathogens and has an optimized C- and D-ring system that improves potency through additional binding site interactions. The mechanism of action of tedizolid is similar to other oxazolidinones and occurs through inhibition of bacterial protein synthesis by binding to 23S ribosomal RNA (rRNA) of the 50S subunit of the ribosome. As with other oxazolidinones, the spontaneous frequency of resistance development to tedizolid is low. Tedizolid is four- to eightfold more potent in vivo than linezolid against all species of staphylococci, enterococci, and streptococci, including drug-resistant phenotypes such as MRSA and vancomycin-resistant enterococci (VRE) and linezolid-resistant phenotypes. Importantly, tedizolid demonstrates activity against linezolid-resistant bacterial strains harboring the horizontally transmissible cfr gene, in the absence of certain ribosomal mutations conferring reduced oxazolidinone susceptibility. With its half-life of approximately 12 h, tedizolid is dosed once daily. It demonstrates linear pharmacokinetics, has a high oral bioavailability of approximately 90 %, and is primarily excreted by the liver as an inactive, non-circulating sulphate conjugate. Tedizolid does not require dosage adjustment in patients with any degree of renal dysfunction or hepatic dysfunction. Studies in animals have demonstrated that the pharmacodynamic parameter most closely associated with the efficacy of tedizolid is fAUC0-24h/MIC. In non-neutropenic animals, a dose-response enhancement was observed with tedizolid and lower exposures were required compared to neutropenic cohorts. Two Phase III clinical trials have demonstrated non-inferiority of a once-daily tedizolid 200 mg dose for 6-10 days versus twice-daily 600 mg linezolid for the treatment of ABSSSIs. Both trials used the primary endpoint of early clinical response at 48-72 h; however, one trial compared oral formulations while the other initiated therapy with the parenteral formulation and allowed oral sequential therapy following initial clinical response. Throughout its development, tedizolid has demonstrated that it is well tolerated and animal studies have shown a lower propensity for neuropathies with long-term use than its predecessor linezolid. Data from the two completed Phase III clinical trials demonstrated that the studied tedizolid regimen (200 mg once daily for 6 days) had significantly less impact on hematologic parameters as well as significantly less gastrointestinal treatment-emergent adverse effects (TEAEs) than its comparator linezolid. As with linezolid, tedizolid is a weak, reversible MAO inhibitor; however, a murine head twitch model validated to assess serotonergic activity reported no increase in the number of head twitches with tedizolid even at doses that exceeded the C max in humans by up to 25-fold. Tyramine and pseudoephedrine challenge studies in humans have also reported no meaningful MAO-related interactions with tedizolid. With its enhanced in vitro activity against a broad-spectrum of Gram-positive aerobic bacteria, convenient once-daily dosing, a short 6-day course of therapy, availability of both oral and intravenous routes of administration, and an adverse effect profile that appears to be more favorable than linezolid, tedizolid is an attractive agent for use in both the hospital and community settings. Tedizolid is currently undergoing additional Phase III clinical trials for the treatment of hospital-acquired bacterial pneumonia (HABP) and ventilated nosocomial pneumonia (VNP).
    Drugs 02/2015; 75(3). DOI:10.1007/s40265-015-0352-7 · 4.34 Impact Factor
  • Musarrat Jahan · George G Zhanel · Richard Sparling · Richard A Holley ·
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    ABSTRACT: Enterococcus species are part of the normal intestinal flora of a large number of mammals including humans and consequently, they can be used as indicators of faecal contamination in food and water for human consumption. Their presence in large numbers in foods may indicate a lapse in sanitation and their ability to serve as a genetic reservoir of transferable antibiotic resistance is of concern. In the present study, Enterococcus spp., isolated from commercially fermented meat and human clinical specimen were studied to determine genetic relationships. SmaI pulsed-field gel electrophoresis (PFGE) patterns exhibited genomic heterogeneity within and between both groups of isolates. However, in spite of this heterogeneity there were still substantial phenotypic similarities which suggested that food might be a potential vehicle for distribution of resistant bacteria among humans. In vitro conjugation experiments demonstrated transfer of the tetracycline resistant determinant, tet(M), from Enterococcus faecium S27 isolated from fermented sausage to clinical isolates of both E. faecium and Enterococcus faecalis. The streptomycin resistance of E. faecium S27 was also transferred to a clinical strain, E. faecalis 82916, which was confirmed by the presence of the streptomycin resistance gene, aadA, in the donor and transconjugant strains. Since the aadA gene is associated with a class 1 integron, results also suggested that resistance transfer might have occurred via an integron. It appears this is the first identification of a class 1 integron in E. faecium isolated from food. The importance of food enterococci as a reservoir of antibiotic resistance genes and the potential for their genetic transfer to human strains following consumption of uncooked or undercooked contaminated meat is underlined by this work. Copyright © 2015 Elsevier B.V. All rights reserved.
    International Journal of Food Microbiology 01/2015; 199C:78-85. DOI:10.1016/j.ijfoodmicro.2015.01.013 · 3.08 Impact Factor
  • J.A. Karlowsky · A.J. Walkty · M. R. Baxter · H. J. Adam · G. G. Zhanel ·
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    ABSTRACT: Gram-positive pathogens isolated in 15 Canadian hospital laboratories between 2011 and 2013 were tested for susceptibility to oritavancin and comparative antimicrobial agents using the CLSI broth microdilution method. Oritavancin demonstrated in vitro activity equivalent to, or more potent than, vancomycin, daptomycin, linezolid, and tigecycline against the isolates of methicillin-susceptible Staphylococcus aureus (n = 1460; oritavancin MIC90, 0.06 μg/ml; 99.7% oritavancin-susceptible), methicillin-resistant S. aureus (n = 427; oritavancin MIC90, 0.06 μg/ml; 99.5% oritavancin-susceptible), Streptococcus pyogenes (n = 132; oritavancin MIC90, 0.25 μg/ml; 99.2% oritavancin-susceptible), Streptococcus agalactiae (n = 156; oritavancin MIC90, 0.12 μg/ml; 100% oritavancin-susceptible), and Enterococcus faecalis (n = 304; oritavancin MIC90, 0.06 μg/ml; 98.7% oritavancin-susceptible) tested.
    Diagnostic Microbiology and Infectious Disease 09/2014; 80(4). DOI:10.1016/j.diagmicrobio.2014.09.003 · 2.46 Impact Factor
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    Dinesh M Fernando · Wayne Xu · Peter C Loewen · George G Zhanel · Ayush Kumar ·
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    ABSTRACT: In order to determine if triclosan can select for mutants of Acinetobacter baumannii ATCC 17978 that display reduced susceptibilities to antibiotics, we isolated a triclosan-resistant mutant, A. baumannii AB042, by serial passaging of A. baumannii ATCC 17978 in growth medium supplemented with triclosan. The antimicrobial susceptibility of AB042 was analyzed by the 2-fold serial dilution method. Expression of five different resistance-nodulation-division (RND) pump-encoding genes (adeB, adeG, adeJ, A1S_2818, and A1S_3217), two outer membrane porin-encoding genes (carO and oprD), and the MATE family pump-encoding gene abeM was analyzed using quantitative reverse transcriptase (qRT) PCR. A. baumannii AB042 exhibited elevated resistance to multiple antibiotics, including piperacillin-tazobactam, doxycycline, moxifloxacin, ceftriaxone, cefepime, meropenem, doripenem, ertapenem, ciprofloxacin, aztreonam, tigecycline, and trimethoprim-sulfamethoxazole, in addition to triclosan. Genome sequencing of A. baumannii AB042 revealed a 116G→V mutation in fabI, the gene encoding the target enzyme for triclosan. Expression analysis of efflux pumps showed overexpression of the AdeIJK pump, and sequencing of adeN, the gene that encodes the repressor of the adeIJK operon, revealed a 73-bp deletion which would cause a premature termination of translation, resulting in an inactive truncated AdeN protein. This work shows that triclosan can select for mutants of A. baumannii that display reduced susceptibilities to multiple antibiotics from chemically distinct classes in addition to triclosan resistance. This multidrug resistance can be explained by the overexpression of the AdeIJK efflux pump.
    Antimicrobial Agents and Chemotherapy 08/2014; 58(11). DOI:10.1128/AAC.03074-14 · 4.48 Impact Factor

Publication Stats

8k Citations
1,391.44 Total Impact Points


  • 1990-2015
    • University of Manitoba
      • • Faculty of Medicine
      • • Department of Chemistry
      • • Department of Medical Microbiology and Infectious Diseases
      • • Faculty of Pharmacy
      Winnipeg, Manitoba, Canada
  • 1991-2012
    • Health Sciences Centre Winnipeg
      Winnipeg, Manitoba, Canada
  • 2011
    • Diagnostic Services of Manitoba, Inc.
      Winnipeg, Manitoba, Canada
  • 2009
    • University of California, Los Angeles
      Los Angeles, California, United States
    • Infectious Diseases Society Of America
      Arlington, Virginia, United States
  • 2008
    • McMaster University
      • Division of Infectious Diseases
      Hamilton, Ontario, Canada
  • 2006
    • Emory University
      • Department of Microbiology and Immunology
      Atlanta, Georgia, United States
  • 2002
    • Mount Sinai Hospital, Toronto
      • Department of Microbiology
      Toronto, Ontario, Canada
  • 1994-2002
    • University of Toronto
      Toronto, Ontario, Canada
  • 1992
    • The University of Winnipeg
      Winnipeg, Manitoba, Canada
  • 1986
    • Hennepin County Medical Center
      Minneapolis, Minnesota, United States