A host-directed macrocyclic peptide therapeutic for MDR gram negative bacterial infections.

The emergence of infections by carbapenem resistant Enterobacteriaceae (CRE) pathogens has created an urgent public health threat, as carbapenems are among the drugs of last resort for infections caused by a growing fraction of multi-drug resistant (MDR) bacteria. There is global consensus that new preventive and therapeutic strategies are urgently needed to combat the growing problem of MDR bacterial infections. Here, we report on the efficacy of a novel macrocyclic peptide, minimized theta-defensin (MTD)-12813 in CRE sepsis. MTD12813 is a theta-defensin inspired cyclic peptide that is highly effective against CRE pathogens K. pneumoniae and E. coli in vivo. In mouse septicemia models, single dose administration of MTD12813 significantly enhanced survival by promoting rapid host-mediated bacterial clearance and by modulating pathologic cytokine responses, restoring immune homeostasis, and preventing lethal septic shock. The peptide lacks direct antibacterial activity in the presence of mouse serum or in peritoneal fluid, further evidence for its indirect antibacterial mode of action. MTD12813 is highly stable in biological matrices, resistant to bacterial proteases, and nontoxic to mice at dose levels 100 times the therapeutic dose level, properties which support further development of the peptide as a first in class anti-infective therapeutic.

Epidemiology, risk factors, and prediction score of carbapenem resistance among inpatients colonized or infected with 3rd generation cephalosporin resistant Enterobacterales.

In this study, we determined the incidence and risk factors of Carbapenem-resistant Enterobacterales (CRE) acquisition in inpatients with 3rd generation cephalosporin-resistant (3GCR) Enterobacterales at a tertiary-care hospital in Lebanon, and suggested a risk prediction score for it. This is a retrospective matched case-control study of inpatients with 3GCR Enterobacterales that are carbapenem resistant (cases) versus those with carbapenem-sensitive isolates (controls). Data analysis was performed on IBM SPSS program, version 23.0 (Armonk, NY, USA: IBM Corp.). Categorical variables were compared between cases and controls through bivariate analysis and those with statistical significance (P < 0.05) were included in the forward stepwise multiple logistic regression analysis. To develop the CRE acquisition risk score, variables that maintained statistical significance in the multivariate model were assigned a point value corresponding to the odds ratio (OR) divided by the smallest OR identified in the regression model, and the resulting quotient was multiplied by two and rounded to the nearest whole number. Summation of the points generated by the calculated risk factors resulted in a quantitative score that was assigned to each patient in the database. Predictive performance was determined by assessing discrimination and calibration. The sensitivity, specificity, positive predictive value, negative predictive value, and accuracy were calculated for different cutoffs of the score. The incidence of CRE acquisition significantly increased with time from 0.21 cases/1000 patient-days (PD) in 2015 to 1.89 cases/1000PD in 2019 (r2 = 0.789, P = 0.041). Multivariate analysis of matched data revealed that the history of cerebrovascular disease (OR 1.96; 95% CI 1.04-3.70; P = 0.039), hematopoietic cells transplantation (OR 7.75; 95% CI 1.52-39.36; P = 0.014), presence of a chronic wound (OR 3.38; 95% CI 1.73-6.50; P < 0.001), endoscopy done during the 3 months preceding the index hospitalization (OR 2.96; 95% CI 1.51-4.73; P = 0.01), nosocomial site of acquisition of the organism in question (OR 2.68; 95% CI 1.51-4.73; P = 0.001), and the prior use of meropenem within 3 months of CRE acquisition (OR 5.70; 95% CI 2.61-12.43; P < 0.001) were independent risk factors for CRE acquisition. A risk score ranging from 0 to 25 was developed based on these independent variables. At a cut-off of ≥ 5 points, the model exhibited a sensitivity, specificity, positive predictive value, negative predictive value, and accuracy of 64.5%, 85.8%, 82%, 70.7% and 75%, respectively. We also showed that only meropenem consumption intensity and CRE acquisition incidence density showed a strong positive correlation(r = 0.798, P = 0.106), unlike imipenem (r = - 0.868, P = 0.056) and ertapenem (r = 0.385, P = 0.522). Patients with a score of ≥ 5 points in our model were likely to acquire CRE. Only meropenem was associated with CRE carriage. Our proposed risk prediction score would help target surveillance screening for CRE amongst inpatients at the time of hospital admission and properly guide clinicians on using anti-CRE therapy.

Carbapenem-resistant Enterobacter cloacae complex in a tertiary Hospital in Northeast China, 2010-2019.

BACKGROUND: Carbapenem-resistant Enterobacter cloacae complex (CREC) is a new emerging threat to global public health. The objective of the study was to investigate the clinical characteristics and molecular epidemiology of CREC infections in the medical center of northeast China. METHODS: Twenty-nine patients were infected/colonized with CREC during a ten-year period (2010-2019) by WHONET analysis. Antibiotic susceptibilities were tested with VITEK 2 and micro broth dilution method (for polymyxin B and tigecycline). Carbapenemase encoding genes, ß-lactamase genes, and seven housekeeping genes for MLST were amplified and sequenced for 18 cryopreserved CREC isolates. Maximum likelihood phylogenetic tree was built with the concentrated sequences to show the relatedness between the 18 isolates. RESULTS: There was a rapid increase in CREC detection rate during the ten-year period, reaching 8.11% in 2018 and 6.48% in 2019. The resistance rate of CREC isolates to imipenem and meropenem were 100.0 and 77.8%, however, they showed high sensitivity to tigecycline, polymyxin B and amikacin. The 30-day crude mortality of CREC infection was 17.4%, indicating that it may be a low-virulence bacterium. Furthermore, molecular epidemiology revealed that ST93 was the predominant sequence type followed by ST171 and ST145, with NDM-1 and NDM-5 as the main carbapenemase-encoding genes. Moreover, E. hormaechei subsp. steigerwaltii and E. hormaechei subsp. oharae were the main species, which showed different resistance patterns. CONCLUSION: Rising detection rate of CREC was observed in a tertiary hospital, which showed heterogeneity in drug resistance patterns, resistance genes, and MLST types. Effective infection prevention and control measures should be taken to reduce the spread of CREC.

Amikacin for the treatment of carbapenem-resistant Klebsiella pneumoniae infections: clinical efficacy and toxicity.

Infections by carbapenem-resistant Klebsiella pneumoniae (CRKp) are an increasing global threat with limited therapeutic options. Our objective was to evaluate clinical and microbiological outcomes of patients treated with amikacin for CRKp infections. We did a retrospective cohort of patients > 18 years old, with CRKp infections treated with amikacin in two tertiary care hospitals in Porto Alegre, Brazil. The impact of clinical factors, antibiotic treatment, and amikacin minimum inhibitory concentration (MIC) on patients' 30-day mortality was assessed. Microbiological clearance and nephrotoxicity (assessed by RIFLE score) were evaluated as secondary outcomes. A Cox regression analysis was done for mortality. We included 84 patients for analysis. Twenty-nine (34.5%) patients died in 30 days. Amikacin MIC values ranged from 0.125 to 8 µg/mL and did not influence on mortality, regardless of the prescribed dose of this antibiotic (P = 0.24). Bacterial clearance occurred in 17 (58.6%) of 29 patients who collected subsequent cultures. Two (16.6%) of the 12 persistently positive cultures changed the amikacin susceptibility profile from susceptible to intermediate. Twenty-nine (37.2%) patients developed acute kidney injury (AKI): risk 13, injury 11, and failure 5. Risk factors for AKI were higher baseline eGFR (P < 0.01) and combination therapy with colistin (P = 0.02). Comparing patients who received combination with colistin vs polymyxin B, AKI occurred in 60.0% vs 20.6%, respectively, P < 0.01. Fifteen of the 16 (16.6%) patients who developed renal injury or failure were receiving colistin. In conclusion, amikacin was an effective treatment for CRKp infections. Within susceptible range, amikacin MIC values did not influence on clinical outcomes. Combination therapy of amikacin and colistin was highly nephrotoxic and should be used with caution.

Biosynthesis of Zinc Oxide Nanoparticles from Acacia nilotica (L.) Extract to Overcome Carbapenem-Resistant Klebsiella Pneumoniae.

Recently, concerns have been raised globally about antimicrobial resistance, the prevalence of which has increased significantly. Carbapenem-resistant Klebsiella pneumoniae (KPC) is considered one of the most common resistant bacteria, which has spread to ICUs in Saudi Arabia. This study was established to investigate the antibacterial activity of biosynthesized zinc oxide nanoparticles (ZnO-NPs) against KPC in vitro and in vivo. In this study, we used the aqueous extract of Acacia nilotica (L.) fruits to mediate the synthesis of ZnO-NPs. The nanoparticles produced were characterized by UV-vis spectroscopy, zetasizer and zeta potential analyses, X-ray diffraction (XRD) spectroscopy, Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), and transmission electron microscopy (TEM). The antimicrobial activity of ZnO-NPs against KPC was determined via the well diffusion method, and determining minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC), the results showed low MIC and MBC when compared with the MIC and MBC of Imipenem and Meropenem antibiotics. The results of in vitro analysis were supported by the results upon applying ZnO-NP ointment to promote wound closure of rats, which showed better wound healing than the results with imipenem ointment. The biosynthesized ZnO-NPs showed good potential for use against bacteria due to their small size, applicability, and low toxicity to human cells.

Optimal empiric treatment for KPC-2-producing Klebsiella pneumoniae infections in critically ill patients with normal or decreased renal function using Monte Carlo simulation.

BACKGROUND: Limited clinical studies describe the pharmacodynamics of fosfomycin (FOS), tigecycline (TGC) and colistin methanesulfonate (CMS) in combination against KPC-producing Klebsiella pneumoniae (KPC-Kp). Population pharmacokinetic models were used in our study. Monte Carlo simulation was conducted to calculate probability of target attainment (PTA) and cumulative fraction of response (CFR) of each agent alone and in combination against KPC-Kp in patients with normal or decreased renal function. RESULTS: The simulated regimen of FOS 6 g q8h reached ≥90% PTA against a MIC of 64 mg/L in patients with normal renal function. For patients with renal impairment, FOS 4 g q8h could provide sufficient antimicrobial coverage against a MIC of 128 mg/L. And increasing the daily dose could result to the cut-off value to 256 mg/L in decreased renal function. For TGC, conventional dosing regimens failed to reach 90% PTA against a MIC of 2 mg/L. Higher loading and daily doses (TGC 200/400 mg loading doses followed by 100 mg q12h/200 mg q24h) were needed. For CMS, none achieved 90% PTA against a MIC of 2 mg/L in normal renal function. Against KPC-Kp, the regimens of 200/400 mg loading dose followed by 100 q12h /200 mg q24h achieved > 80% CFRs regardless of renal function, followed by CMS 9 million IU loading dose followed by 4.5/3 million IU q12h in combination with FOS 8 g q8h (CFR 75-91%). CONCLUSIONS: The use of a loading dose and high daily dose of TGC and CMS in combination with FOS can provide sufficient antimicrobial coverage against critically ill patients infected with KPC-Kp.

Clinical impact of cefepime breakpoint in patients with carbapenem-resistant Klebsiella pneumoniae bacteraemia.

The application of cefepime breakpoint for carbapenem-resistant Klebsiella pneumoniae (CRKP) bacteraemia has not been explored. Adult cases of monomicrobial bloodstream infection (BSI) caused by cefepime-susceptible [minimum inhibitory concentration (MIC) ≤8 mg/L] K. pneumoniae isolates with carbapenem resistance between 2010 and 2015 were reviewed. Patients treated with cefepime were compared with those treated by other active agents using a propensity score-matched analysis to assess therapeutic effectiveness. The primary endpoint was 30-day crude mortality. A total of 114 patients experienced cefepime-susceptible CRKP bacteraemia and 40 (35.1%) died during hospitalisation. A total of 33 patients (28.9%) received cefepime therapy. Fifteen patients (13.2%) had BSI due to carbapenemase-producing isolates, and 86.7% (13/15) of carbapenemase-producing isolates were classified as cefepime susceptible dose-dependent (SDD). In the multivariate logistic regression analysis, 30-day mortality was independently associated with the presence of a critical illness [adjusted odds ratio (aOR) = 12.89, 95% confidence interval (CI) 3.88-42.83; P < 0.001], pneumonia (aOR = 5.97, 95% CI 1.65-21.76; P = 0.007) and rapidly fatal underlying disease (aOR = 6.43, 95% CI 1.30-31.09; P = 0.02). In contrast, cefepime-based therapy (aOR = 0.03, 95% CI 0.003-0.38; P = 0.006) and combination therapy (aOR = 0.09, 95% CI 0.02-0.36; P = 0.001) were protective against a fatal outcome. Based on current breakpoints for Enterobacterales, cefepime therapy was not associated with an unfavourable outcome for CRKP BSI with MIC-based dosing strategies. However, the susceptibility result of SDD to cefepime should alert clinicians for possible therapeutic failure.

Bloodstream Infections due to Carbapenem-Resistant Klebsiella pneumoniae: A Single-Center Retrospective Study on Risk Factors and Therapy Options.

We aimed to compare efficacy of different patterns of antibiotics and explore the risk factors related to mortality in patients with bloodstream infections (BSIs) due to carbapenem-resistant Klebsiella pneumoniae (CRKP). This study retrospectively included 89 patients with BSIs due to CRKP with complete data during the year of 2018 in the First Affiliated Hospital of Zhejiang University School of Medicine. Overall, the 28-day mortality was 47.2% (42/89). Multivariate analysis of Cox regression revealed that hematological malignancy (hazard ratio [HR] 5.698; 95% confidence interval [CI], 2.405-13.504; p < 0.001) and Pitt bacteremia score (HR per unit increase, 1.303; 95% CI, 1.109-1.532; p = 0.001) were identified as independent predictors for 28-day mortality. Among 70 patients with appropriate therapy, 35 received tigecycline (TGC)-based therapy, 20 received polymyxin B (PMB)-based therapy, 9 received ceftazidime/avibactam-based therapy, and 6 patients had other kinds of antibiotics, including ciprofloxacin, amikacin, and cotrimoxazole. By adjusting variables selected by crude analysis, it showed that receiving PMB-based therapy provided a survival benefit comparing with TGC-based therapy (HR, 0.068; 95% CI, 0.018-0.260; p < 0.001). Hematological malignancy and Pitt bacteremia score were independent risk factors of death in patients with BSIs due to CRKP and PMB-based therapy improved survival rate compared with TGC-based therapy.

Efficacy of generic meropenem products in combination with colistin in carbapenemase-producing Klebsiella pneumoniae experimental osteomyelitis.

Guidelines for the management of carbapenemase-producing Enterobacterales (CPE) infections recommend a combination of two active agents, including meropenem if the minimum inhibitory concentration (MIC) is ≤8 mg/L. The therapeutic equivalence of meropenem generics has been challenged. We compared the bactericidal activity of meropenem innovator (AstraZeneca) and four generic products (Actavis, Kabi, Mylan and Panpharma), both in vitro and in vivo, in association with colistin. In vitro time-kill studies were performed at 4 × MIC. An experimental model of KPC-producing Klebsiella pneumoniae osteomyelitis was induced in rabbits by tibial injection of a sclerosing agent followed by 2 × 108 CFU of K. pneumoniae KPC-99YC (meropenem MIC = 4 mg/L; colistin MIC = 1 mg/L). At 14 days after inoculation, treatment for 7 days started in seven groups of ≥10 rabbits, including a control group, a colistin group, and one group for each meropenem product (i.e. the innovator and four generics), in combination with colistin. In vitro, meropenem + colistin was bactericidal with no viable bacteria after 6 h, and this effect was similar with all meropenem products. In the osteomyelitis model, there was no significant difference between meropenem generics and the innovator when combined with colistin. Colistin-resistant strains were detected after treatment with colistin + meropenem innovator (n = 3) and generics (n = 3). The efficacy of four meropenem generics did not differ from the innovator in vitro and in an experimental rabbit model of KPC-producing K. pneumoniae osteomyelitis in terms of bactericidal activity and the emergence of resistance.

Successful treatment of invasive carbapenemase-producing Enterobacteriaceae infections in children using carbapenem-aminoglycoside combination therapy: A case series.

Multidrug-resistant infections present a treatment challenge for pediatric clinicians and these infections have been associated with increased morbidity and mortality. There are very limited published data to support safe and effective treatment regimens for carbapenemase-producing Enterobacteriaceae (CPE) infections, particularly in children. We report the successful treatment of three children with invasive CPE infections using a combination of extended-infusion meropenem and amikacin.

Factors associated with mortality in Infections caused by Carbapenem-resistant Enterobacteriaceae.

INTRODUCTION: There is little information about weigh of factors possibly associated with mortality, in infections caused by Carbapenem-resistant Enterobacteriaceae (CRE) in Latin America. METHODOLOGY: A case-controls study nested in a historical cohort was performed including all patients with CRE infections diagnosed between June 2013 and December 2018 at Hospital Universitario San Ignacio in Bogotá, Colombia. Univariate and multivariate analysis were performed to compare cases of mortality within the first month after the infection diagnosis with surviving patients. RESULTS: A total of 131 patients were included. The overall 30-day mortality rate was 38.17%. In the multivariate analysis, a direct association was found between mortality and septic shock (OR 26.7 CI6.6-107.3 p < 0.01), post-chemotherapy febrile neutropenia (OR 3.3 CI1.06-10.8 p = 0.04) and Charlson Index ≥ 3 (OR 5.5 CI 1.5-20.06 p < 0.01). An inverse association was found with interventions to control the infectious focus (OR 0.3 CI0.1-0.7 p < 0.01). The MIC of different antibiotics and the use of combined antibiotic therapy (triple therapy vs. double therapy or monotherapy) were not associated with mortality. CONCLUSIONS: In patients with CRE infections, septic shock, a Charlson comorbidity index ≥ 3, and post-chemotherapy febrile neutropenia are independently related to an increase in mortality. The control of the infectious focus is a protective factor. A rapid identification of these patients, and the implementation of measures to control infectious focus and to detect CRE colonization in patients who are going to be taken to myelosuppressive chemotherapy could impact positively the prognosis of these patients.

Evaluation of rapid polymyxin Nordmann Poirel test for detection of polymyxin resistance in clinical isolates of Enterobacteriaceae.

Polymyxins play a significant role against carbapenem-resistant Enterobacteriaceae (CRE). A total of 121 clinical samples yielded growth of CRE that were included in the study. Rapid Polymyxin NP test was performed on all the isolates as described by Nordmann P et al. and results were compared with broth microdilution method. Majority of the isolates were Klebsiella pneumoniae (70.2%) followed by Escherichia coli (17.4%). A total of 71 isolates were found resistant and 50 as susceptible by broth microdilution. Sensitivity and specificity of rapid polymyxin NP test were found to be 97.2% and 100%, respectively. Our study concluded that rapid polymyxin NP test is reliable and can be used as an alternative to broth microdilution in resource limited settings.

Identification of a newly isolated lytic bacteriophage against K24 capsular type, carbapenem resistant Klebsiella pneumoniae isolates.

The increasing incidence of carbapenemase-producing K. pneumoniae strains (CP-Kps) in the last decade has become a serious global healthcare problem. Therapeutic options for the treatment of emerging hospital clones have drastically narrowed and therefore novel approaches must be considered. Here we have isolated and characterized a lytic bacteriophage, named vB_KpnS_Kp13, that was effective against all Verona integron-encoded metallo-ß-lactamase (VIM) producing K. pneumoniae isolates originating from hospital samples (urine, blood, sputum and faeces), belonging to the ST15 clonal lineage and expressing the K24 capsule. Morphological characterization of vB_KpnS_Kp13 showed that the newly identified phage belonged to the Siphoviridae family, and phylogenetic analysis showed that it is part of a distinct clade of the Tunavirinae subfamily. Functional analysis revealed that vB_KpnS_Kp13 had relatively short latent period times (18 minutes) compared to other K. pneumoniae bacteriophages and could degrade biofilm by more than 50% and 70% in 24 and 48 hours respectively. Complete in vivo rescue potential of the new phage was revealed in an intraperitoneal mouse model where phages were administered intraperitoneally 10 minutes after bacterial challenge. Our findings could potentially be used to develop specific anti-CP-Kps bacteriophage-based therapeutic strategies against major clonal lineages and serotypes.

New strategies and structural considerations in development of therapeutics for carbapenem-resistant Enterobacteriaceae.

Antimicrobial resistance poses a significant threat to our ability to treat infections. Especially concerning is the emergence of carbapenem-resistant Enterobacteriaceae (CRE). In the new 2019 United States Centers for Disease Control and Prevention Antibiotic Resistance Report, CRE remain in the most urgent antimicrobial resistance threat category. There is good reason for this concerning designation. In particular, the combination of several resistance elements in CRE can make these pathogens untreatable or effectively untreatable with our current armamentarium of anti-infective agents. This article reviews recently approved agents with activity against CRE and a range of modalities in the pipeline, from early academic investigation to those in clinical trials, with a focus on structural aspects of new antibiotics. Another article in this series addresses the need to incentive pharmaceutical companies to invest in CRE antimicrobial development and to encourage hospitals to make these agents available in their formularies. This article will also consider the need for change in requirements for antimicrobial susceptibility testing implementation in clinical laboratories to address practical roadblocks that impede our efforts to provide even existing CRE antibiotics to our patients.

Activity of Plazomicin Tested against Enterobacterales Isolates Collected from U.S. Hospitals in 2016-2017: Effect of Different Breakpoint Criteria on Susceptibility Rates among Aminoglycosides.

Plazomicin was active against 97.0% of 8,783 Enterobacterales isolates collected in the United States (2016 and 2017), and only 6 isolates carried 16S rRNA methyltransferases conferring resistance to virtually all aminoglycosides. Plazomicin (89.2% to 95.9% susceptible) displayed greater activity than amikacin (72.5% to 78.6%), gentamicin (30.4% to 45.9%), and tobramycin (7.8% to 22.4%) against carbapenem-resistant and extensively drug-resistant isolates. The discrepancies among the susceptibility rates for these agents was greater when applying breakpoints generated using the same stringent contemporary methods applied to determine plazomicin breakpoints.

Pharmacokinetics and Efficacy of Ceftazidime-Avibactam in the Treatment of Experimental Pneumonia Caused by Klebsiella pneumoniae Carbapenemase-Producing K. pneumoniae in Persistently Neutropenic Rabbits.

Klebsiella pneumoniae carbapenemase-producing Klebsiella pneumoniae (KPC-Kp) is an emerging global public health threat that causes life-threatening pneumonia and bacteremia. Ceftazidime-avibactam (CZA) represents a promising advance for the treatment of serious infections caused by KPC-Kp We investigated the pharmacokinetics and efficacy of ceftazidime-avibactam in the treatment of experimental KPC-Kp pneumonia in persistently neutropenic rabbits. For single-dose and multidose (administration every 8 h) pharmacokinetics, rabbits received ceftazidime-avibactam intravenous infusions at 60/15, 90/22.5, and 120/30 mg/kg of body weight. Ceftazidime mean area under the concentration-time curves (AUCs) ranged from 287 to 608 µg·h/ml for a single dose and from 300 to 781 µg·h/ml for multiple doses. Avibactam AUCs ranged from 21 to 48 µg·h/ml for a single dose and from 26 to 48 µg·h/ml for multiple doses. KPC-Kp pneumonia was established by direct endotracheal inoculation. Treatments consisted of ceftazidime-avibactam at 120/30 mg/kg every 6 h, a polymyxin B (PMB) loading dose of 2.5 mg/kg followed by 1.5 mg/kg every 12 h q12h, or no treatment (untreated controls [UC]). There were significant reductions in the residual bacterial burden, lung weights, and pulmonary hemorrhage scores in CZA- and PMB-treated rabbits for a 7-day or a 14-day (P ≤ 0.01) course in comparison with those in the UC. These results corresponded to significant decreases in the bacterial burden in bronchoalveolar lavage fluid after a 7-day or a 14-day treatment (P ≤ 0.01). The outcomes demonstrated an improved response at 14 days versus that at 7 days. There was significantly prolonged survival in rabbits treated with CZA for 14 days in comparison with that in the PMB-treated or UC rabbits (P ≤ 0.05). This study demonstrates that ceftazidime-avibactam displays linear dose-proportional exposures simulating those seen from human plasma pharmacokinetic profiles, is active for the treatment of experimental KPC-Kp pneumonia in persistently neutropenic rabbits, and provides an experimental foundation for the treatment of severely immunocompromised patients with this life-threatening infection.

In vitro effect of an antimicrobial combination therapy without colistin and tigecycline for CPE and non-CPE.

INTRODUCTION: This study aimed to investigate the in vitro effects of a combination of antimicrobials other than colistin (CL) and tigecycline (TGC) on carbapenem-resistant Enterobacteriaceae (CRE). METHODS: We used 72 CRE strains including 65 carbapenemase-producing Enterobacteriaceae (CPE) that produce IMP-1, IMP-6, NDM, KPC, and OXA-48-like carbapenemases; and 7 carbapenemase-nonproducing Enterobacteriaceae (non-CPE) strains. These strains were assessed using antimicrobial susceptibility testing, breakpoint checkerboard (BC) plate method, and kill curve experiment to determine the effect of the combination therapy. RESULTS: NDM, KPC, and OXA-48-like carbapenemase-producers showed higher MICs of carbapenem and aminoglycosides, and lower MICs of minocycline, compared to non-CPE and IMP-1/-6-producers. The results of the BC plate method suggested that the suitability of combinations of antimicrobials differ depending on the type of carbapenemases. Killing curve experiments demonstrated bactericidal or bacteriostatic action of the combination of antimicrobials even in sub-MIC concentrations of drugs. Our results suggest that the most effective antimicrobial combinations for each carbapenemase-producers are as follows; IMP-1 (tobramycin + tazobactam/piperacillin), IMP-6 (gentamicin + meropenem), NDM (minocycline + biapenem), KPC (arbekacin + doripenem) and OXA-48-like (minocycline + imipenem). CONCLUSION: These results suggest that the combination of antimicrobials other than CL and TGC may be another candidate for the treatments of CPE infections, even though we have to choose effective antimicrobial combinations depending on the type of carbapenemase.

The new perspective of old antibiotic: In vitro antibacterial activity of TMP-SMZ against Klebsiella pneumoniae.

BACKGROUND/PURPOSE: Trimethoprim-sulfamethoxazole (TMP-SMZ) is broadly administered to treat multiple infections, and the paucity of effective treatment alternatives for infections caused by Klebsiella pneumoniae has led to a renewed interest in TMP-SMZ. The aim of this study is to evaluate the antibacterial efficacy of TMP-SMZ against K. pneumoniae. METHODS: The resistance genes of K. pneumoniae clinical isolates were investigated by PCR, followed by conjugation experiments and multilocus sequence typing. RESULTS: The resistance rate of K. pneumoniae to TMP-SMZ decreased over the collection period from 26.7% (88/330) to 16.9% (56/332). The high carrying rates (173/175, 98.9%) of resistance determinants (sul genes or dfr genes) were the main mechanisms of TMP-SMZ resistance isolates, with sul1 (142/175, 81.1%) and dfrA1 (119/175, 68.0%). Only class 1 integron was detected, the prevalence of which in TMP-SMZ resistant K. pneumoniae was 63.4% (111/175). CONCLUSION: These results provided insights into the antimicrobial efficacy of TMP-SMZ against K. pneumoniae, also illustrating the wide distribution of SMZ and TMP resistance genes among resistant K. pneumoniae. Simultaneously, the present study highlights the significance of reasonable administration and effective continued monitoring.

Quercetin inhibits carbapenemase and efflux pump activities among carbapenem-resistant Gram-negative bacteria.

Rapid dissemination of carbapenem-resistant Gram-negative bacteria (CRGNB) is a global threat. Quercetin is known for its antimicrobial activity. In this study, carbapenemase and efflux pump inhibitory activities of quercetin were demonstrated against carbapenem-resistant Escherichia coli, Klebsiella pneumoniae, Pseudomonas aeruginosa and Acinetobacter baumannii. Further, molecular docking was performed to elucidate molecular mechanisms of such inhibition. CRGNB, expressing one of the carbapenemases, demonstrated significant inhibition of carbapenemase activity when pre-incubated with 64 µg/ml quercetin. Moreover, acrB overexpressing enterobacterial isolates exhibited significant inhibition of efflux activity upon quercetin treatment. Molecular docking studies revealed stability of quercetin-carbapenemase complexes. (i) Virtual superimposition of quercetin onto meropenem, (ii) proximity of quercetin to attacking nucleophile and (iii) involvement of same amino acids that stabilize both meropenem and quercetin - indicated competition between quercetin and meropenem for ligand binding. Although quercetin and PAßN, a standard efflux pump inhibitor, docked at both central cavity and periplasmic drug binding sites of AcrB, they did not virtually superimpose on each other. However, sufficient release of Gibb's free energy and involvement of same set of amino acids in PAßN and quercetin stability predicted quercetin's efflux pump inhibitory potential. Hence, quercetin could be potential adjuvant therapeutics for CRGNB-mediated infections.