At the start of the COVID-19 pandemic, there was an increase in the use of antibiotics for the tr... more At the start of the COVID-19 pandemic, there was an increase in the use of antibiotics for the treatment of community-acquired respiratory tract infection (CA-ARI) in patients admitted for suspected or confirmed COVID-19, raising concerns for misuse. These antibiotics are not under the usual purview of the antimicrobial stewardship unit (ASU). Serum procalcitonin, a biomarker to distinguish viral from bacterial infections, can be used to guide antibiotic recommendations in suspected lower respiratory tract infection. We modified our stewardship approach, and used a procalcitonin-guided strategy to identify “high yield” interventions for audits in patients admitted with CA-ARI. With this approach, there was an increase in the proportion of patients with antibiotics discontinued within 4 days (16.5% vs. 34.9%, p < 0.001), and the overall duration of antibiotic therapy was significantly shorter [7 (6–8) vs. 6 (3–8) days, p < 0.001]. There was a significant decrease in patients wi...
Carbapenemase-producing Enterobacterales (CPE) infection control practices are based on the parad... more Carbapenemase-producing Enterobacterales (CPE) infection control practices are based on the paradigm that detected carriers in the hospital transmit to other patients who stay in the same ward. The role of plasmid-mediated transmission at population level remains largely unknown. In this retrospective cohort study over 4.7 years involving all multi-disciplinary public hospitals in Singapore, we analysed 779 patients who acquired CPE (1215 CPE isolates) detected by clinical or surveillance cultures. 42.0% met putative clonal transmission criteria, 44.8% met putative plasmid-mediated transmission criteria and 13.2% were unlinked. Only putative clonal transmissions associated with direct ward contact decreased in the second half of the study. Both putative clonal and plasmid-mediated transmission associated with indirect (no temporal overlap in patients’ admission period) ward and hospital contact did not decrease during the study period. Indirect ward and hospital contact were identif...
Background: Increasing prevalence of ertapenem-resistant, carbapenem-susceptible Enterobacteriace... more Background: Increasing prevalence of ertapenem-resistant, carbapenem-susceptible Enterobacteriaceae (ERE) in Singapore presents a major therapeutic problem. Our objective was to determine risk factors associated with the acquisition of ERE in hospitalized patients; to assess associated patient outcomes; and to describe the molecular characteristics of ERE. Methods: A retrospective case-case-control study was conducted in 2009 at a tertiary care hospital. Hospitalized patients with ERE and those with ertapenem-sensitive Enterobacteriaceae (ESE) were compared with a common control group consisting of patients with no prior gram-negative infections. Risk factors analyzed included demographics; co-morbidities; instrumentation and antibiotic exposures. Two parallel multivariate logistic regression models were performed to identify independent variables associated with ERE and ESE acquisition respectively. Clinical outcomes were compared between ERE and ESE patients. Results: Twenty-nine ...
Frontiers in Cellular and Infection Microbiology, 2022
ObjectivesThe increasing incidence of carbapenem-nonsusceptible Enterobacterales as major pathoge... more ObjectivesThe increasing incidence of carbapenem-nonsusceptible Enterobacterales as major pathogens in healthcare associated infections (HAIs) is of paramount concern. To implement effective prevention strategies against carbapenem-nonsusceptible Enterobacterales (CnSE) HAIs, it is crucial to identify modifiable factors associated with these infections. We identified risk factors for CnSE-HAIs, and compared clinical outcomes of CnSE-HAI and carbapenem-sensitive Enterobacterales (CSE)-HAI patients.MethodsWe conducted a multi-centre parallel matched case-control study in two 1700-bedded Singapore acute-care hospitals from 2014–2016. Patients with CnSE-HAIs and CSE-HAIs were compared to a common control group without HAIs (1:1:3 ratio), matched by time-at-risk and patient ward. Carbapenem nonsusceptible was defined as non-susceptibility to either meropenem or imipenem. Presence of healthcare associated infections were defined by the criteria provided by the European Centre for Disease ...
Frontiers in Cellular and Infection Microbiology, 2022
ObjectivesThe increasing incidence of carbapenem-nonsusceptible Enterobacterales as major pathoge... more ObjectivesThe increasing incidence of carbapenem-nonsusceptible Enterobacterales as major pathogens in healthcare associated infections (HAIs) is of paramount concern. To implement effective prevention strategies against carbapenem-nonsusceptible Enterobacterales (CnSE) HAIs, it is crucial to identify modifiable factors associated with these infections. We identified risk factors for CnSE-HAIs, and compared clinical outcomes of CnSE-HAI and carbapenem-sensitive Enterobacterales (CSE)-HAI patients.MethodsWe conducted a multi-centre parallel matched case-control study in two 1700-bedded Singapore acute-care hospitals from 2014–2016. Patients with CnSE-HAIs and CSE-HAIs were compared to a common control group without HAIs (1:1:3 ratio), matched by time-at-risk and patient ward. Carbapenem nonsusceptible was defined as non-susceptibility to either meropenem or imipenem. Presence of healthcare associated infections were defined by the criteria provided by the European Centre for Disease ...
Advances in Experimental Medicine and Biology, 2019
In the last decade, considerable advancements have been made to identify the pharmacokinetic/phar... more In the last decade, considerable advancements have been made to identify the pharmacokinetic/pharmacodynamic (PK/PD) index that defines the antimicrobial activity of polymyxins. Dose-fractionation studies performed in hollow-fiber models found that altering the dosing schedule had little impact on the killing or suppression of resistance emergence, alluding to AUC/MIC as the pharmacodynamic index that best describes polymyxin's activity. For in vivo efficacy, the PK/PD index that was the most predictive of the antibacterial effect of colistin against P. aeruginosa and A. baumannii was ƒAUC/MIC.
Polymyxin B is the last line of defense in treating multidrug-resistant gram-negative bacterial i... more Polymyxin B is the last line of defense in treating multidrug-resistant gram-negative bacterial infections. Dosing of polymyxin B is currently based on total body weight, and a substantial intersubject variability has been reported. We evaluated the performance of different population pharmacokinetic models to predict polymyxin B exposures observed in individual patients. In a prospective observational study, standard dosing (mean 2.5 mg/kg daily) was administered in 13 adult patients. Serial blood samples were obtained at steady state, and plasma polymyxin B concentrations were determined by a validated liquid chromatography tandem mass spectrometry (LC-MS/MS) method. The best-fit estimates of clearance and daily doses were used to derive the observed area under the curve (AUC) in concentration–time profiles. For comparison, 5 different population pharmacokinetic models of polymyxin B were conditioned using patient-specific dosing and demographic (if applicable) variables to predic...
European Journal of Clinical Microbiology & Infectious Diseases, 2021
Antimicrobial therapy in terminally ill patients remains controversial as goals of care tend to b... more Antimicrobial therapy in terminally ill patients remains controversial as goals of care tend to be focused on optimizing comfort. International guidelines recommend for antibiotic stewardship program (ASP) involvement in antibiotic decisions in palliative patients. The primary objective was to evaluate the clinical impact of ASP interventions made to stop broad-spectrum intravenous antibiotics in terminally ill patients. This was a retrospective chart review of 459 terminally ill patients in Singapore General Hospital audited by ASP between December 2010 and December 2018. Antibiotic duration, time-to-terminal discharge for end-of-life care, time-to-mortality, and mortality rates of patients with antibiotics ceased or continued upon ASP recommendations were compared. A total of 283 and 176 antibiotic courses were ceased and continued post-intervention, respectively. The intervention acceptance rate was 61.7%. The 7-day mortality rate (47.3% vs 61.9%, p = 0.003) was lower in the ceased group, while 30-day mortality rate (76.0% vs 81.2%, p = 0.203) and time-to-mortality post-intervention (3 [0-24] vs 2 [0-27] days, p = 0.066) did not differ between the ceased and continued groups. After excluding the 57 patients who had antibiotics continued until death within 48 h of intervention, only time-to-mortality post-intervention was statistically significantly shorter in the ceased group (3 [0-24] vs 4 [0-27], p < 0.001). Of the 131 terminally discharged patients, antibiotic duration (4 [0-17] vs 6.5 [1-14] days, p = 0.001) and time-to-terminal discharge post-intervention (6 [0-74] vs 10.5 [3-63] days, p = 0.001) were shorter in the ceased group. Antibiotic cessation in terminally ill patients was safe, and was associated with a significantly shorter time-to-terminal discharge.
Fosfomycin-based combination therapy has emerged as an attractive option in our armamentarium due... more Fosfomycin-based combination therapy has emerged as an attractive option in our armamentarium due to its synergistic activity against carbapenem-resistant Gram-negative bacteria (CRGNB). The ability to simultaneously measure fosfomycin and other antibiotic drug levels will support in vitro and clinical investigations to develop rational antibiotic combination dosing regimens against CRGNB infections. We developed an analytical assay to measure fosfomycin with nine important antibiotics in human plasma and cation-adjusted Mueller–Hinton II broth (CAMHB). We employed a liquid-chromatography tandem mass spectrometry method and validated the method based on accuracy, precision, matrix effect, limit-of-detection, limit-of-quantification, specificity, carryover, and short-term and long-term stability on U.S. Food & Drug Administration (FDA) guidelines. Assay feasibility was assessed in a pilot clinical study in four patients on antibiotic combination therapy. Simultaneous quantification o...
Annals of the Academy of Medicine, Singapore, 2019
Dear Editor, Optimal antibiotic regimen is unknown for severe community-acquired pneumonia (SCAP)... more Dear Editor, Optimal antibiotic regimen is unknown for severe community-acquired pneumonia (SCAP) which has mortality rates of up to 67% locally.1 Recommended empiric regimens from the West cannot be extrapolated to our region where melioidosis is endemic2 and Streptococcus pneumoniae penicillin resistance is common.3 Unfortunately, studies that compare optimal antibiotic regimens for SCAP in Southeast Asia are lacking. Considering local epidemiology, our hospital’s guidelines recommended ceftazidime as empiric therapy for SCAP due to its activity against Burkholderia pseudomallei. To complement its poorer activity against S. pneumoniae,4 levofloxacin or moxifloxacin was added for pneumococcal and atypical coverage. However, physicians could deviate from the guidelines and use meropenem with a macrolide instead. Anecdotally, we observed higher mortality rates in patients on empiric ceftazidime-based regimen. Hence, this retrospective study was conducted with a primary objective of c...
Antimicrobial stewardship programmes (ASPs) in hospitals are predominantly led by specific ASP ph... more Antimicrobial stewardship programmes (ASPs) in hospitals are predominantly led by specific ASP physicians and pharmacists. Limited studies have been conducted to appreciate non-ASP-trained hospital pharmacists’ perspectives on their roles in antimicrobial stewardship. Focus group discussions (FGDs) were conducted with 74 pharmacists, purposively sampled from the 3 largest acute-care public hospitals in Singapore, to explore facilitators and barriers faced by them in antimicrobial stewardship. Applied thematic analysis was conducted and codes were categorised using the social–ecological model (SEM). At the intrapersonal level, pharmacists identified themselves as reviewers for drug safety before dispensing, confining to a restricted advisory role due to lack of clinical knowledge, experience, and empowerment to contribute actively to physicians’ prescribing decisions. At the interpersonal level, pharmacists expressed difficulties conveying their opinions and recommendations on antibi...
Pseudomonas aeruginosa infection is one of the most difficult health care-associated infections t... more Pseudomonas aeruginosa infection is one of the most difficult health care-associated infections to treat due to the ability of the organism to acquire a multitude of resistance mechanisms and express the multidrug resistance phenotype. Ceftolozane/tazobactam (C/T), a novel β -lactam/ β -lactamase inhibitor combination, addresses an unmet medical need in patients with these multidrug-resistant P. aeruginosa infections.
Polymyxin B-based combinations are increasingly prescribed as a last-line option against extensiv... more Polymyxin B-based combinations are increasingly prescribed as a last-line option against extensively-drug resistant Acinetobacter baumannii (XDRAB). It is unknown if such combinations can result in the development of non-dividing persister cells in XDRAB. We investigated persister development upon exposure of XDRAB to polymyxin B-based antibiotic combinations using flow cytometry. Time-kill studies (TKS) were conducted in three non-clonal XDRAB strains with 5log10 CFU/ml bacteria against polymyxin B alone and in polymyxin-B based two-drug combinations over 24h. At different time-points, samples were obtained and enumerated by viable plating and flow cytometry. Propidium iodide and carboxyfluorescein succinimidyl ester dyes were used to differentiate between live/dead cells and dividing/non-dividing cells respectively at the single-cell level, and non-dividing live cells were resuscitated and characterized phenotypically. Our results in viable plating showed that polymyxin B + merope...
Polymyxin B-based combinations have emerged as a mainstay treatment against carbapenem-resistant ... more Polymyxin B-based combinations have emerged as a mainstay treatment against carbapenem-resistant Escherichia coli (CREC). We investigated the activity of polymyxin B-based two-antibiotic combinations against CREC using time-kill studies (TKS) and validated the findings in a hollow-fiber infection model (HFIM). TKS were conducted using 5 clinical CREC strains at 5 log 10 CFU/ml against 10 polymyxin B-based two-antibiotic combinations at maximum clinically achievable concentrations. HFIMs simulating dosing regimens with polymyxin B (30,000U/kg/day) and tigecycline (100 mg every 12 h) alone and in combination were conducted against two CREC strains at 5 log 10 CFU/ml over 120 h. Emergence of resistance was quantified using antibiotic-containing media. Phenotypic characterization (growth rate and stability of resistant phenotypes) of the resistant isolates was performed. All five CREC strains harbored carbapenemases. Polymyxin B and tigecycline MICs ranged from 0.5 mg/liter to 2 mg/lite...
At the start of the COVID-19 pandemic, there was an increase in the use of antibiotics for the tr... more At the start of the COVID-19 pandemic, there was an increase in the use of antibiotics for the treatment of community-acquired respiratory tract infection (CA-ARI) in patients admitted for suspected or confirmed COVID-19, raising concerns for misuse. These antibiotics are not under the usual purview of the antimicrobial stewardship unit (ASU). Serum procalcitonin, a biomarker to distinguish viral from bacterial infections, can be used to guide antibiotic recommendations in suspected lower respiratory tract infection. We modified our stewardship approach, and used a procalcitonin-guided strategy to identify “high yield” interventions for audits in patients admitted with CA-ARI. With this approach, there was an increase in the proportion of patients with antibiotics discontinued within 4 days (16.5% vs. 34.9%, p < 0.001), and the overall duration of antibiotic therapy was significantly shorter [7 (6–8) vs. 6 (3–8) days, p < 0.001]. There was a significant decrease in patients wi...
Carbapenemase-producing Enterobacterales (CPE) infection control practices are based on the parad... more Carbapenemase-producing Enterobacterales (CPE) infection control practices are based on the paradigm that detected carriers in the hospital transmit to other patients who stay in the same ward. The role of plasmid-mediated transmission at population level remains largely unknown. In this retrospective cohort study over 4.7 years involving all multi-disciplinary public hospitals in Singapore, we analysed 779 patients who acquired CPE (1215 CPE isolates) detected by clinical or surveillance cultures. 42.0% met putative clonal transmission criteria, 44.8% met putative plasmid-mediated transmission criteria and 13.2% were unlinked. Only putative clonal transmissions associated with direct ward contact decreased in the second half of the study. Both putative clonal and plasmid-mediated transmission associated with indirect (no temporal overlap in patients’ admission period) ward and hospital contact did not decrease during the study period. Indirect ward and hospital contact were identif...
Background: Increasing prevalence of ertapenem-resistant, carbapenem-susceptible Enterobacteriace... more Background: Increasing prevalence of ertapenem-resistant, carbapenem-susceptible Enterobacteriaceae (ERE) in Singapore presents a major therapeutic problem. Our objective was to determine risk factors associated with the acquisition of ERE in hospitalized patients; to assess associated patient outcomes; and to describe the molecular characteristics of ERE. Methods: A retrospective case-case-control study was conducted in 2009 at a tertiary care hospital. Hospitalized patients with ERE and those with ertapenem-sensitive Enterobacteriaceae (ESE) were compared with a common control group consisting of patients with no prior gram-negative infections. Risk factors analyzed included demographics; co-morbidities; instrumentation and antibiotic exposures. Two parallel multivariate logistic regression models were performed to identify independent variables associated with ERE and ESE acquisition respectively. Clinical outcomes were compared between ERE and ESE patients. Results: Twenty-nine ...
Frontiers in Cellular and Infection Microbiology, 2022
ObjectivesThe increasing incidence of carbapenem-nonsusceptible Enterobacterales as major pathoge... more ObjectivesThe increasing incidence of carbapenem-nonsusceptible Enterobacterales as major pathogens in healthcare associated infections (HAIs) is of paramount concern. To implement effective prevention strategies against carbapenem-nonsusceptible Enterobacterales (CnSE) HAIs, it is crucial to identify modifiable factors associated with these infections. We identified risk factors for CnSE-HAIs, and compared clinical outcomes of CnSE-HAI and carbapenem-sensitive Enterobacterales (CSE)-HAI patients.MethodsWe conducted a multi-centre parallel matched case-control study in two 1700-bedded Singapore acute-care hospitals from 2014–2016. Patients with CnSE-HAIs and CSE-HAIs were compared to a common control group without HAIs (1:1:3 ratio), matched by time-at-risk and patient ward. Carbapenem nonsusceptible was defined as non-susceptibility to either meropenem or imipenem. Presence of healthcare associated infections were defined by the criteria provided by the European Centre for Disease ...
Frontiers in Cellular and Infection Microbiology, 2022
ObjectivesThe increasing incidence of carbapenem-nonsusceptible Enterobacterales as major pathoge... more ObjectivesThe increasing incidence of carbapenem-nonsusceptible Enterobacterales as major pathogens in healthcare associated infections (HAIs) is of paramount concern. To implement effective prevention strategies against carbapenem-nonsusceptible Enterobacterales (CnSE) HAIs, it is crucial to identify modifiable factors associated with these infections. We identified risk factors for CnSE-HAIs, and compared clinical outcomes of CnSE-HAI and carbapenem-sensitive Enterobacterales (CSE)-HAI patients.MethodsWe conducted a multi-centre parallel matched case-control study in two 1700-bedded Singapore acute-care hospitals from 2014–2016. Patients with CnSE-HAIs and CSE-HAIs were compared to a common control group without HAIs (1:1:3 ratio), matched by time-at-risk and patient ward. Carbapenem nonsusceptible was defined as non-susceptibility to either meropenem or imipenem. Presence of healthcare associated infections were defined by the criteria provided by the European Centre for Disease ...
Advances in Experimental Medicine and Biology, 2019
In the last decade, considerable advancements have been made to identify the pharmacokinetic/phar... more In the last decade, considerable advancements have been made to identify the pharmacokinetic/pharmacodynamic (PK/PD) index that defines the antimicrobial activity of polymyxins. Dose-fractionation studies performed in hollow-fiber models found that altering the dosing schedule had little impact on the killing or suppression of resistance emergence, alluding to AUC/MIC as the pharmacodynamic index that best describes polymyxin's activity. For in vivo efficacy, the PK/PD index that was the most predictive of the antibacterial effect of colistin against P. aeruginosa and A. baumannii was ƒAUC/MIC.
Polymyxin B is the last line of defense in treating multidrug-resistant gram-negative bacterial i... more Polymyxin B is the last line of defense in treating multidrug-resistant gram-negative bacterial infections. Dosing of polymyxin B is currently based on total body weight, and a substantial intersubject variability has been reported. We evaluated the performance of different population pharmacokinetic models to predict polymyxin B exposures observed in individual patients. In a prospective observational study, standard dosing (mean 2.5 mg/kg daily) was administered in 13 adult patients. Serial blood samples were obtained at steady state, and plasma polymyxin B concentrations were determined by a validated liquid chromatography tandem mass spectrometry (LC-MS/MS) method. The best-fit estimates of clearance and daily doses were used to derive the observed area under the curve (AUC) in concentration–time profiles. For comparison, 5 different population pharmacokinetic models of polymyxin B were conditioned using patient-specific dosing and demographic (if applicable) variables to predic...
European Journal of Clinical Microbiology & Infectious Diseases, 2021
Antimicrobial therapy in terminally ill patients remains controversial as goals of care tend to b... more Antimicrobial therapy in terminally ill patients remains controversial as goals of care tend to be focused on optimizing comfort. International guidelines recommend for antibiotic stewardship program (ASP) involvement in antibiotic decisions in palliative patients. The primary objective was to evaluate the clinical impact of ASP interventions made to stop broad-spectrum intravenous antibiotics in terminally ill patients. This was a retrospective chart review of 459 terminally ill patients in Singapore General Hospital audited by ASP between December 2010 and December 2018. Antibiotic duration, time-to-terminal discharge for end-of-life care, time-to-mortality, and mortality rates of patients with antibiotics ceased or continued upon ASP recommendations were compared. A total of 283 and 176 antibiotic courses were ceased and continued post-intervention, respectively. The intervention acceptance rate was 61.7%. The 7-day mortality rate (47.3% vs 61.9%, p = 0.003) was lower in the ceased group, while 30-day mortality rate (76.0% vs 81.2%, p = 0.203) and time-to-mortality post-intervention (3 [0-24] vs 2 [0-27] days, p = 0.066) did not differ between the ceased and continued groups. After excluding the 57 patients who had antibiotics continued until death within 48 h of intervention, only time-to-mortality post-intervention was statistically significantly shorter in the ceased group (3 [0-24] vs 4 [0-27], p < 0.001). Of the 131 terminally discharged patients, antibiotic duration (4 [0-17] vs 6.5 [1-14] days, p = 0.001) and time-to-terminal discharge post-intervention (6 [0-74] vs 10.5 [3-63] days, p = 0.001) were shorter in the ceased group. Antibiotic cessation in terminally ill patients was safe, and was associated with a significantly shorter time-to-terminal discharge.
Fosfomycin-based combination therapy has emerged as an attractive option in our armamentarium due... more Fosfomycin-based combination therapy has emerged as an attractive option in our armamentarium due to its synergistic activity against carbapenem-resistant Gram-negative bacteria (CRGNB). The ability to simultaneously measure fosfomycin and other antibiotic drug levels will support in vitro and clinical investigations to develop rational antibiotic combination dosing regimens against CRGNB infections. We developed an analytical assay to measure fosfomycin with nine important antibiotics in human plasma and cation-adjusted Mueller–Hinton II broth (CAMHB). We employed a liquid-chromatography tandem mass spectrometry method and validated the method based on accuracy, precision, matrix effect, limit-of-detection, limit-of-quantification, specificity, carryover, and short-term and long-term stability on U.S. Food & Drug Administration (FDA) guidelines. Assay feasibility was assessed in a pilot clinical study in four patients on antibiotic combination therapy. Simultaneous quantification o...
Annals of the Academy of Medicine, Singapore, 2019
Dear Editor, Optimal antibiotic regimen is unknown for severe community-acquired pneumonia (SCAP)... more Dear Editor, Optimal antibiotic regimen is unknown for severe community-acquired pneumonia (SCAP) which has mortality rates of up to 67% locally.1 Recommended empiric regimens from the West cannot be extrapolated to our region where melioidosis is endemic2 and Streptococcus pneumoniae penicillin resistance is common.3 Unfortunately, studies that compare optimal antibiotic regimens for SCAP in Southeast Asia are lacking. Considering local epidemiology, our hospital’s guidelines recommended ceftazidime as empiric therapy for SCAP due to its activity against Burkholderia pseudomallei. To complement its poorer activity against S. pneumoniae,4 levofloxacin or moxifloxacin was added for pneumococcal and atypical coverage. However, physicians could deviate from the guidelines and use meropenem with a macrolide instead. Anecdotally, we observed higher mortality rates in patients on empiric ceftazidime-based regimen. Hence, this retrospective study was conducted with a primary objective of c...
Antimicrobial stewardship programmes (ASPs) in hospitals are predominantly led by specific ASP ph... more Antimicrobial stewardship programmes (ASPs) in hospitals are predominantly led by specific ASP physicians and pharmacists. Limited studies have been conducted to appreciate non-ASP-trained hospital pharmacists’ perspectives on their roles in antimicrobial stewardship. Focus group discussions (FGDs) were conducted with 74 pharmacists, purposively sampled from the 3 largest acute-care public hospitals in Singapore, to explore facilitators and barriers faced by them in antimicrobial stewardship. Applied thematic analysis was conducted and codes were categorised using the social–ecological model (SEM). At the intrapersonal level, pharmacists identified themselves as reviewers for drug safety before dispensing, confining to a restricted advisory role due to lack of clinical knowledge, experience, and empowerment to contribute actively to physicians’ prescribing decisions. At the interpersonal level, pharmacists expressed difficulties conveying their opinions and recommendations on antibi...
Pseudomonas aeruginosa infection is one of the most difficult health care-associated infections t... more Pseudomonas aeruginosa infection is one of the most difficult health care-associated infections to treat due to the ability of the organism to acquire a multitude of resistance mechanisms and express the multidrug resistance phenotype. Ceftolozane/tazobactam (C/T), a novel β -lactam/ β -lactamase inhibitor combination, addresses an unmet medical need in patients with these multidrug-resistant P. aeruginosa infections.
Polymyxin B-based combinations are increasingly prescribed as a last-line option against extensiv... more Polymyxin B-based combinations are increasingly prescribed as a last-line option against extensively-drug resistant Acinetobacter baumannii (XDRAB). It is unknown if such combinations can result in the development of non-dividing persister cells in XDRAB. We investigated persister development upon exposure of XDRAB to polymyxin B-based antibiotic combinations using flow cytometry. Time-kill studies (TKS) were conducted in three non-clonal XDRAB strains with 5log10 CFU/ml bacteria against polymyxin B alone and in polymyxin-B based two-drug combinations over 24h. At different time-points, samples were obtained and enumerated by viable plating and flow cytometry. Propidium iodide and carboxyfluorescein succinimidyl ester dyes were used to differentiate between live/dead cells and dividing/non-dividing cells respectively at the single-cell level, and non-dividing live cells were resuscitated and characterized phenotypically. Our results in viable plating showed that polymyxin B + merope...
Polymyxin B-based combinations have emerged as a mainstay treatment against carbapenem-resistant ... more Polymyxin B-based combinations have emerged as a mainstay treatment against carbapenem-resistant Escherichia coli (CREC). We investigated the activity of polymyxin B-based two-antibiotic combinations against CREC using time-kill studies (TKS) and validated the findings in a hollow-fiber infection model (HFIM). TKS were conducted using 5 clinical CREC strains at 5 log 10 CFU/ml against 10 polymyxin B-based two-antibiotic combinations at maximum clinically achievable concentrations. HFIMs simulating dosing regimens with polymyxin B (30,000U/kg/day) and tigecycline (100 mg every 12 h) alone and in combination were conducted against two CREC strains at 5 log 10 CFU/ml over 120 h. Emergence of resistance was quantified using antibiotic-containing media. Phenotypic characterization (growth rate and stability of resistant phenotypes) of the resistant isolates was performed. All five CREC strains harbored carbapenemases. Polymyxin B and tigecycline MICs ranged from 0.5 mg/liter to 2 mg/lite...
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