Synergistic activities of meropenem double and triple combinations against carbapenemase-producing Enterobacteriaceae

In Vitro Synergistic Effect of Colistin with Fosfomycin Against Carbapenem-Resistant Klebsiella pneumoniae

BACKGROUND

The dwindling antibiotic reserve owing to augmented drug-resistant bacteria is a major handicap for treating physicians. Klebsiella pneumoniae, a gram-negative encapsulated member of the Enterobacteriaceae family, is one such pathogenic bacteria. Carbapenemase-producing Klebsiella pneumoniae is globally recognized as one of the most critical bacterial threats to public health due to its extremely limited treatment options. Carbapenem-resistant Klebsiella pneumoniae (CRKP) infections pose therapeutic challenges due to simultaneous resistance to various other groups of antibiotics. In this study, we have evaluated the synergistic effect of fosfomycinagainst CRKP isolates when used in combination with colistin by applying the Checkerboard method.

METHODS

A laboratory-based prospective study was conducted in the Department of Microbiology, JSS Hospital, Mysuru, for a period of one year after obtaining ethical clearance. Klebsiella pneumoniae isolates obtained from clinical samples were screened for carbapenem resistance by the VITEK-2 compact system (bioMérieux, Marcy-l'Étoile, France). The minimum inhibitory concentration (MIC) of colistin and fosfomycin was individually ascertained by broth microdilution (BMD). Finally, the synergistic activity of the fosfomycin-colistin combination was determined by the BMD-based Checkerboard method.

RESULTS

Among the 50 CRKP isolates, 36 (72%) isolates showed synergism, eight (16%) isolates showed indifference and six (12%) isolates showed partial synergism, while none of them showed additivity and antagonism by the Checkerboard method. These results are found to be statistically significant (chi-square value of 116.204 and p-value of < 0.00001).

CONCLUSION

This study showed a promising in-vitro synergy between the drugs fosfomycin and colistin by Checkerboard BMD testing protocol. Colistin being a reserve antibiotic, monotherapy comes with the limitations of higher chances of resistance as well as toxicity, which can be overcome by combination therapy, thereby decreasing CRKP-associated mortality rates and delivering holistic patient benefit.

Evaluation of In Vitro Activity of Double-Carbapenem Combinations against KPC-2-, OXA-48- and NDM-Producing Escherichia coli and Klebsiella pneumoniae

Double-carbapenem combinations have shown synergistic potential against carbapenemase-producing Enterobacterales, but data remain inconclusive. This study evaluated the activity of double-carbapenem combinations against 51 clinical KPC-2-, OXA-48-, NDM-1, and NDM-5-producing Escherichia coli and Klebsiella pneumoniae and against constructed E. coli strains harboring genes encoding KPC-2, OXA-48, or NDM-1 in an otherwise isogenic background. Two-drug combinations of ertapenem, meropenem, and doripenem were evaluated in 24 h time-lapse microscopy experiments with a subsequent spot assay and in static time-kill experiments. An enhanced effect in time-lapse microscopy experiments at 24 h and synergy in the spot assay was detected with one or more combinations against 4/14 KPC-2-, 17/17 OXA-48-, 2/17 NDM-, and 1/3 NDM-1+OXA-48-producing clinical isolates. Synergy rates were higher against meropenem- and doripenem-susceptible isolates and against OXA-48 producers. NDM production was associated with significantly lower synergy rates in E. coli. In time-kill experiments with constructed KPC-2-, OXA-48- and NDM-1-producing E. coli, 24 h synergy was not observed; however, synergy at earlier time points was found against the KPC-2- and OXA-48-producing constructs. Our findings indicate that the benefit of double-carbapenem combinations against carbapenemase-producing E. coli and K. pneumoniae is limited, especially against isolates that are resistant to the constituent antibiotics and produce NDM.

Carbapenem-Only Combination Therapy against Multi-Drug Resistant Pseudomonas aeruginosa: Assessment of In Vitro and In Vivo Efficacy and Mode of Action

The aim of the study was to determine the efficacy of carbapenem-only combination treatments derived from four approved drugs (meropenem, doripenem, ertapenem and imipenem) against a MDR strain of P. aeruginosa in a Galleria mellonella larvae infection model. G. mellonella larvae were infected with P. aeruginosa NCTC 13437 (carrying the VIM 10 carbapenamase) and the efficacy of the six possible dual, four triple, and one quadruple carbapenem combination(s) were compared to their constituent monotherapies. Four of these combinations showed significantly enhanced survival compared to monotherapies and reduced the bacterial burden inside infected larvae but without complete elimination. Bacteria that survived combination therapy were slower growing, less virulent but with unchanged carbapenem MICs-observations that are consistent with a persister phenotype. In vitro time-kill assays confirmed that the combinations were bactericidal and confirmed that a low number of bacteria survived exposure. Mass spectrometry was used to quantify changes in the concentration of carbapenems in the presence of carbapenemase-carrying P. aeruginosa. The rate of degradation of individual carbapenems was altered, and often significantly reduced, when the drugs were in combinations compared with the drugs alone. These differences may account for the enhanced inhibitory effects of the combinations against carbapenem-resistant P. aeruginosa and are consistent with a 'shielding' hypothesis. In conclusion, carbapenem combinations show promise in combating MDR P. aeruginosa and are worthy of additional study and development.

Carbapenem Combinations for Infections Caused by Carbapenemase-Producing Pseudomonas aeruginosa: Experimental In Vitro and In Vivo Analysis

In the context of difficult-to-treat carbapenem-resistant Pseudomonas aeruginosa infections, we evaluated imipenem, meropenem, and doripenem combinations against eleven carbapenemase-producing P. aeruginosa isolates. According to the widespread global distribution of high-risk clones and carbapenemases, four representative isolates were selected: ST175 (OXA-2/VIM-20), ST175 (VIM-2), ST235 (GES-5), and ST111 (IMP-33), for efficacy studies using a sepsis murine model. Minimum inhibitory concentration (mg/L) ranges were 64–256 for imipenem and 16–128 for meropenem and doripenem. In vitro, imipenem plus meropenem was synergistic against 72% of isolates and doripenem plus meropenem or imipenem against 55% and 45%, respectively. All combinations were synergistic against the ST175, ST235, and ST155 clones. In vivo, meropenem diminished the spleen and blood bacterial concentrations of four and three isolates, respectively, with better efficacy than imipenem or doripenem. The combinations did not show efficacy compared with the more active monotherapies, except for imipenem plus meropenem, which reduced the ST235 bacterial spleen concentration. Mortality decreased with imipenem plus meropenem or doripenem for the ST175 isolate. Results suggest that carbapenem combinations are not an alternative for severe infections by carbapenemase-producing P. aeruginosa. Meropenem monotherapy showed in vivo efficacy despite its high MIC, probably because its dosage allowed a sufficient antimicrobial exposure at the infection sites.

Control of extensively drug-resistant Pseudomonas aeruginosa co-harboring metallo-β-lactamase enzymes with oprD gene downregulation

PURPOSE

to study control and treatment of infection with extensive drug-resistant carbapenem-resistant Pseudomonas aeruginosa (XDR-CRPA).

METHODS

Eleven Pseudomonas aeruginosa (XDR-CRPA) strains used in this study were isolated from a clinical sample, identified, and antibiotics susceptibility recorded in a previous study. Real-time PCR (RT-PCR) was performed to determine the expression level of the OprD gene. Besides, a checkerboard technique was performed to assess the effect of polymyxin-B (POX), colistin (COL), rifampicin (RIF), imipenem (IPM), and meropenem (MEM) during 2 and 3- dimensional antibiotic combinations. Further, the time-kill study was determined for the most potent combination against four representative strains, log₁₀ changes of viable cell counts were expressed as their mean value (±SD) values.

RESULTS

Molecular analysis by Real-time PCR revealed that the diminished expression level of OprD mRNA was overwhelming to various degrees. The checkerboard method demonstrated that the relevant synergism was achieved in 90.9% of strains for both carbapenem antibiotics during the triple combinations. While an additive effect was noted for all the dual regimen assays. Regarding time-kill experiments, a remarkable bactericidal effect with [99.9% killing rate] was observed toward only one strain whilst a bacteriostatic attitude was proven with ≥95% bacterial eradication against the three remaining strains.

CONCLUSIONS

These findings underscore the promising implications of these combinations for treatment against XDR-Pseudomonas aeruginosa even they are resistant to carbapenems due to multiple mechanisms of action.

OXA-48 Carbapenemase-Producing Enterobacterales in Spanish Hospitals: An Updated Comprehensive Review on a Rising Antimicrobial Resistance

Carbapenemase-producing Enterobacterales (CPE) are significant contributors to the global public health threat of antimicrobial resistance. OXA-48-like enzymes and their variants are unique carbapenemases with low or null hydrolytic activity toward carbapenems but no intrinsic activity against expanded-spectrum cephalosporins. CPEs have been classified by the WHO as high-priority pathogens given their association with morbidity and mortality and the scarce number of effective antibiotic treatments. In Spain, the frequency of OXA-48 CPE outbreaks is higher than in other European countries, representing the major resistance mechanism of CPEs. Horizontal transfer of plasmids and poor effective antibiotic treatment are additional threats to the correct prevention and control of these hospital outbreaks. One of the most important risk factors is antibiotic pressure, specifically carbapenem overuse. We explored the use of these antibiotics in Spain and analyzed the frequency, characteristics and prevention of CPE outbreaks. Future antibiotic stewardship programs along with specific preventive measures in hospitalized patients must be reinforced and updated in Spain.

Double-carbapenem therapy in the treatment of multidrug resistant Gram-negative bacterial infections: a systematic review and meta-analysis

BACKGROUND

To compare the efficacy and safety of double-carbapenem therapy (DCT) with other antibiotics for the treatment of multidrug resistant (MDR) Gram-negative bacterial infections.

METHODS

Cochrane Library, PubMed, Embase and Web of Science as well as Chinese databases were searched from database establishment to February 2019. All types of studies were included if they had evaluated efficacy and safety of DCT regimens in patients with MDR Gram-negative bacterial infections. Clinical response, microbiological response, adverse events and mortality were the main outcomes. The protocol was registered with PROSPERO No. CRD42019129979.

RESULTS

Three cohort or case-control studies consisting of 235 patients and 18 case series or case reports consisting of 90 patients were included. The clinical and microbiological responses were similar between DCT and other regimens in patients with carbapenem-resistant Enterobacteriaceae (CRE) infection. DCT achieved a lower mortality than comparators in patients with CRE infection (OR = 0.44, 95% CI = 0.24-0.82, P = 0.009). Ertapenem was the most reported antibiotic in DCT regimens in case series or case reports. Moreover, clinical and microbiological improvements were found in 59 (65.6%) and 63 (70%) in total 90 cases, respectively.

CONCLUSIONS

DCT was as effective as other antibiotics in treating MDR Gram-negative bacterial infections, with similar efficacy response and lower mortality. DCT could be an alternative therapeutic option in the treatment of MDR Gram-negative bacterial infections. High-quality randomized controlled trials were required to confirm the beneficial effects of DCT.

How to manage KPC infections

Carbapenemase-producing Enterobacteriaceae represent an increasing global threat worldwide and Klebsiella pneumoniae carbapenemase (KPC)-producing K. pneumoniae (KPC-KP) has become one of the most important contemporary pathogens, especially in endemic areas. Risk stratification and rapid diagnostics laboratory workflows are of paramount importance and indication for therapy of KPC-KP infection must be individualized according to the baseline characteristics of the patient and severity of infection. The optimal treatment of infection because of KPC-KP organisms is uncertain and antibiotic options are limited. The knowledge of the patient's pathophysiology, infection site, and application of the pharmacokinetic/pharmacodynamic principles on the basis of minimum inhibitory concentration (MIC) has progressively gained major relevance. Combination therapies including high-dose meropenem, colistin, fosfomycin, tigecycline, and aminoglycosides are widely used, with suboptimal results. In the past few years, new antimicrobials targeting KPC-KP have been developed and are now at various stages of clinical research. However, their optimal use should be guaranteed in the long term for delaying, as much as possible, the emergence of resistance. Strict infection control measures remain necessary. The aim of this review is to discuss the challenges in the management and treatment of patients with infections because KPC-KP and provide an expert opinion.

Precision medicine for the diagnosis and treatment of carbapenem-resistant Enterobacterales: time to think from a different perspective

INTRODUCTION

Carbapenem-resistant Enterobacterales (CRE) represent a global public health problem. Precision medicine (PM) is a multicomponent medical approach that should be used to individualize the management of patients infected with CRE.

AREAS COVERED

Here, we differentiate carbapenem-producing CRE (CP-CRE) from non-CP-CRE and the importance of this distinction in clinical practice. The current phenotypic CRE-case definition and its implications are also discussed. Additionally, we summarize data regarding phenotypic and molecular diagnostic tools and available antibiotics. In order to review the most relevant data, a comprehensive literature search of peer-reviewed articles in PubMed and abstracts presented at high-impact conferences was performed.

EXPERT OPINION

PM in CRE infections entails a multi-step process that includes applying the current phenotypic definition, utilization of the right phenotypic or molecular testing methods, and thorough evaluation of risk factors, source of infection, and comorbidities. A powerful armamentarium is available to treat CRE infections, including recently approved agents. Randomized controlled trials targeting specific pathogens instead of site of infections may be appropriate to fill in the current gaps. In light of the diverse enzymology behind CP-CRE, PM should be employed to provide the best therapy based on the underlying resistance mechanism.

When Combined with Colistin, an Otherwise Ineffective Rifampicin-Linezolid Combination Becomes Active in Escherichia coli, Pseudomonas aeruginosa, and Acinetobacter baumannii

The synergistic action of colistin, with two antibiotics active in Gram-positive bacteria but unable to kill gram negatives (linezolid and rifampicin), was investigated, since triple combinations are emerging as a tool to overtake multidrug resistance. Checkerboard determinations demonstrated that, when combined with colistin, the combination of linezolid and rifampicin turns active in multidrug-resistant Escherichia coli, Pseudomonas aeruginosa, and Acinetobacter baumannii. Thus, the presence of sublethal concentrations of colistin resulted in a strongly synergistic interaction between these two drugs. Moreover, the minimum inhibitory concentrations of linezolid–rifampicin combinations in the presence of colistin were lower than the maximal concentrations of these antimicrobials ain blood. These findings suggest the use of this triple combination as an effective treatment of multidrug-resistant (MDR) bacterial infections.

Clinical relevance of in vitro synergistic activity of antibiotics for multidrug-resistant Gram-negative infections: A systematic review

OBJECTIVES

The aim of this review was to investigate the outcomes of patients infected with multidrug-resistant (MDR) or extensively drug-resistant (XDR) Gram-negative bacteria following synergy-guided antibiotic combination therapy (SGACT).

METHODS

A systematic review of PubMed and Scopus databases was performed. Published studies of any design reporting outcomes of patients with MDR Gram-negative bacteria treated with SGACT were included. Two reviewers independently assessed the relevancy and quality of the retrieved articles and extracted the available data.

RESULTS

Nineteen reports (530 patients) were included. Eleven case reports/series described 26 cases of systemic infection due to MDR Gram-negative bacteria treated with SGACT. Five deaths were reported, two of which were attributed to the infection. Six studies (including one randomised controlled trial) provided comparative data for patients treated with SGACT and those treated with unguided combination therapy (UCT) or active monotherapy. In the pooled analysis of unadjusted data from these studies (504 patients), there was no difference between SGACT and UCT or monotherapy (OR=0.47, 95% CI 0.21-1.04; I2=52%). Analysis of adjusted data showed that SGACT was significantly associated with survival (OR=0.44, 95% CI 0.20-0.98; I2=54%).

CONCLUSION

These limited but promising findings warrant further investigation of SGACT in the outcome of patients with MDR Gram-negative infections in well-designed trials.

Infections Caused by Carbapenem-Resistant Enterobacteriaceae: An Update on Therapeutic Options

Carbapenems are considered as last-resort antibiotics for the treatment of infections caused by multidrug-resistant Gram-negative bacteria. With the increasing use of carbapenems in clinical practice, the emergence of carbapenem-resistant pathogens now poses a great threat to human health. Currently, antibiotic options for the treatment of carbapenem-resistant Enterobacteriaceae (CRE) are very limited, with polymyxins, tigecycline, fosfomycin, and aminoglycosides as the mainstays of therapy. The need for new and effective anti-CRE therapies is urgent. Here, we describe the current understanding of issues related to CRE and review combination therapeutic strategies for CRE infections, including high-dose tigecycline, high-dose prolonged-infusion of carbapenem, and double carbapenem therapy. We also review the newly available antibiotics which have potential in the future treatment of CRE infections: ceftazidime/avibactam, which is active against KPC and OXA-48 producers; meropenem/vaborbactam, which is active against KPC producers; plazomicin, which is a next-generation aminoglycoside with in vitro activity against CRE; and eravacycline, which is a tetracycline class antibacterial with in vitro activity against CRE. Although direct evidence for CRE treatment is still lacking and the development of resistance is a concern, these new antibiotics provide additional therapeutic options for CRE infections. Finally, we review other potential anti-CRE antibiotics in development: imipenem/relebactam and cefiderocol. Currently, high-dose and combination strategies that may include the new β-lactam/β-lactamase inhibitors should be considered in severe CRE infections to maximize treatment success. In the future, when more treatment options are available, therapy for CRE infections should be individualized and based on molecular phenotypes of resistance, susceptibility profiles, disease severity, and patient characteristics. More high-quality studies are needed to guide effective treatment for infections caused by CRE.

Entérobactéries productrices de carbapénémases en médecine intensive : thérapeutique

Les infections à entérobactéries productrices de carbapénémases peuvent représenter une pathologie redoutable, notamment dans les situations cliniques graves, en raison des possibilités thérapeutiques limitées. En France, les mécanismes OXA-48 et OXA-48-like (78 %) sont les plus fréquemment retrouvés. Les stratégies thérapeutiques actuelles limitées ont mis en exergue l’intérêt de certaines vieilles molécules et des associations d’antibiotiques avec une optimisation de leurs modalités d’administration. Dans l’attente de l’apport des futures options thérapeutiques, les essais contrôlés randomisés sont plus que nécessaires. Nous devons nous inspirer de l’expérience de ceux qui prennent en charge ces infections. La maîtrise du bon usage des antibiotiques reste toujours d’actualité afin de préserver l’efficacité des molécules existantes.

Treatment of Infections Caused by Extended-Spectrum-Beta-Lactamase-, AmpC-, and Carbapenemase-Producing Enterobacteriaceae

Therapy of invasive infections due to multidrug-resistant Enterobacteriaceae (MDR-E) is challenging, and some of the few active drugs are not available in many countries. For extended-spectrum β-lactamase and AmpC producers, carbapenems are the drugs of choice, but alternatives are needed because the rate of carbapenem resistance is rising. Potential active drugs include classic and newer β-lactam-β-lactamase inhibitor combinations, cephamycins, temocillin, aminoglycosides, tigecycline, fosfomycin, and, rarely, fluoroquinolones or trimethoprim-sulfamethoxazole. These drugs might be considered in some specific situations. AmpC producers are resistant to cephamycins, but cefepime is an option. In the case of carbapenemase-producing Enterobacteriaceae (CPE), only some "second-line" drugs, such as polymyxins, tigecycline, aminoglycosides, and fosfomycin, may be active; double carbapenems can also be considered in specific situations. Combination therapy is associated with better outcomes for high-risk patients, such as those in septic shock or with pneumonia. Ceftazidime-avibactam was recently approved and is active against KPC and OXA-48 producers; the available experience is scarce but promising, although development of resistance is a concern. New drugs active against some CPE isolates are in different stages of development, including meropenem-vaborbactam, imipenem-relebactam, plazomicin, cefiderocol, eravacycline, and aztreonam-avibactam. Overall, therapy of MDR-E infection must be individualized according to the susceptibility profile, type, and severity of infection and the features of the patient.