Determination of synergy between sulbactam, meropenem and colistin in carbapenem-resistant Klebsiella pneumoniae and Acinetobacter baumannii isolates and correlation with the molecular mechanism of resistance

Efficacy of Cefoperazone Sulbactam in Patients with Acinetobacter Infections: A Systematic Review of the Literature

Introduction: Acinetobacter baumannii (AB) is a multidrug-resistant pathogen commonly associated with nosocomial infections. The resistance profile and ability to produce biofilm make it a complicated organism to treat effectively. Cefoperazone sulbactam (CS) is commonly used to treat AB, but the associated data are scarce. Methods: We conducted a systematic review of articles downloaded from Cochrane, Embase, PubMed, Scopus, and Web of Science (through June 2022) to study the efficacy of CS in treating AB infections. Our review evaluated patients treated with CS alone and CS in combination with other antibiotics separately. The following outcomes were studied: clinical cure, microbiological cure, and mortality from any cause. Results: We included 16 studies where CS was used for the treatment of AB infections. This included 11 studies where CS was used alone and 10 studies where CS was used in combination. The outcomes were similar in both groups. We found that the pooled clinical cure, microbiological cure, and mortality with CS alone for AB were 70%, 44%, and 20%, respectively. The pooled clinical cure, microbiological cure, and mortality when CS was used in combination with other antibiotics were 72%, 43%, and 21%, respectively. Conclusions: CS alone or in combination needs to be further explored for the treatment of AB infections. There is a need for randomized controlled trials with comparator drugs to evaluate the drug’s effectiveness.

Growth kinetics of multiple Acinetobacter baumannii resistotype after meropenem-based antibiotic combination exposure

Background: Carbapenems are the treatment of choice for multidrug-resistant (MDR) and extensively drug-resistant (XDR)  Acinetobacter baumannii infections, but the emergence of carbapenem-resistant  A. baumannii (CRAB) has rendered it ineffective in the vast majority of cases. Combination therapy has grown in popularity over the last decade; this study aims to analyze  A.baumannii growth kinetics after exposure to meropenem and ampicillin-sulbactam compared with meropenem and amikacin antibiotic combinations in clinically relevant concentrations.  Methods: This experimental laboratory study was conducted on the  A. baumannii ATCC 19606 isolate and three clinical isolates that were intermediate or resistant to tested antibiotics. Meropenem and ampicillin-sulbactam, as well as meropenem and amikacin, were tested at four different concentrations against isolates. Turbidity measurements were taken at predetermined time points of 0, 1, 2, 4, 6, 8, and 24 hours following exposure; bacterial concentration was enumerated using the agar plate method, with the results plotted in a time-kill curve.   Results: A bactericidal effect was achieved in isolates that were intermediate to ampicillin-sulbactam and resistant to meropenem after the administration of meropenem and ampicillin-sulbactam combination with a concentration of 4 µg/ml and 16/8 µg/ml, respectively. The combination of meropenem and ampicillin-sulbactam demonstrated bacteriostatic activity against isolates that were resistant to both antibiotics. Isolates treated with resistant antibiotics showed an increased growth rate compared to the growth control.  Conclusion: The combination of meropenem and ampicillin-sulbactam could be a promising combination therapy in treating CRAB infections. The mechanism and degree of antibiotic resistance in the isolates affect the efficacy of antibiotic combinations; further research is needed to corroborate the findings of this study.

Isothermal microcalorimetry versus checkerboard assay to evaluate in vitro synergism of meropenem-amikacin and meropenem-colistin combinations against multidrug-resistant Gram-negative pathogens

OBJECTIVES

To evaluate the activity of meropenem-amikacin and meropenem-colistin combinations with checkerboard broth microdilution (CKBM) compared to isothermal microcalorimetry (ITMC) assays against a multicentric collection of multidrug-resistant Gram-negative (MDR-GN) clinical isolates, to compare the Fractional inhibitory concentration index (FICI) and time to results of CKBM and ITMC assays.

METHODS

A collection of 333 MDR-GNs showing reduced susceptibility to meropenem (121 Klebsiella pneumoniae, 14 Escherichia coli, 130 Pseudomonas aeruginosa and 68 Acinetobacter baumannii) isolated from different centres (Florence, Madrid, Rotterdam, and Stockholm) was included in the study. The antimicrobial activity of selected combinations was evaluated with CKBM and ITMC. FICI results were interpreted as synergistic/additive and indifferent for values ≤0.5/0.5<x≤1 and >1, respectively. WGS data in a subset of strains was used to evaluate their clonality.

RESULTS

A total of 254 and 286 strains were tested with meropenem-colistin and meropenem-amikacin combinations with ITMC and CKBM, respectively. Synergism/additive effects were observed with 46 strains (20 K. pneumoniae, 4 E. coli, 22 P. aeruginosa) and 20 strains (3 K. pneumoniae, 11 P. aeruginosa and 6 A. baumannii) with meropenem-amikacin and meropenem-colistin combination, respectively, with CKBM. ITMC showed a good concordance with CKBM with 89.5% and 92.2% of cases interpreted within the same FICI category for meropenem-amikacin and meropenem-colistin combinations, respectively. Most of the synergism/additivity effects were detected within 6 hours by ITMC.

CONCLUSIONS

ITMC showed a very good concordance with CKBM against a large collection of MDR-GN and could be implemented for the rapid evaluation of in vitro activity of antimicrobial combinations.

Demonstration of the efficacy of curcumin on carbapenem-resistant Pseudomonas aeruginosa with Galleria mellonella larvae model

Due to increasing antimicrobial resistance, studies where new treatment options are investigated along with the synergistic effects of natural products with antibiotics have arisen. Pseudomonas aeruginosa (P. aeruginosa) is an opportunistic pathogen and infection with multi-drug resistant (MDR) P. aeruginosa poses a critical problem during treatment. Curcumin (CUR) is listed in the literature as one of the promising natural ingredients with its strong antimicrobial activity. In our study, our aim was to investigate the in vitro synergistic effect of CUR with imipenem (IMP) and Colistin (CST) in MDR P. aeruginosa isolates and in vivo activity on Galleria mellonella (G. mellonella) larvae. Three clinical isolates of MDR P. aeruginosa, which were determined to be phenotypically resistant to carbapenems, were used, and KPC and OXA48 resistance genes were determined by PCR method. The synergistic effect of CUR with antibiotics were investigated by the checkerboard method. Larval survival and bacterial load were compared with the in vivo study. In this study, IMP MIC values were significantly reduced (two to eight-fold decrease) in the presence of CUR, and partial synergy was observed. For CST, this value decreased two-fold. Bacterial load was evaluated to investigate the effect of antimicrobials during infection. While the CFUs increased over time in non-treated larvae as compared to the initial inoculum, bacterial load was significantly decreased for the groups treated with CUR, IMP and CST compared to the untreated group (p < 0.05). It was concluded CUR-antibiotic combinations can provide an alternative approach in the treatment of infections with MDR bacteria.

In vitro activities of antibiotic combinations against mature biofilms of ventilator-associated pneumonia isolates

Background: The authors aimed to determine the efficacy of frequently used antibiotics, alone or in combination, against biofilms of ventilator-associated pneumonia isolates. Materials & methods: The authors determined the MICs, minimum biofilm inhibitory concentrations and minimum biofilm eradication concentrations of meropenem, ciprofloxacin and colistin as well as their combinations against planktonic forms and biofilms of Pseudomonas aeruginosa, Klebsiella pneumoniae and Acinetobacter baumannii clinical isolates. Results: Generally, the minimum biofilm inhibitory concentrations and minimum biofilm eradication concentrations of the antibiotics were 1000-fold higher than their MICs, and synergy was provided by different concentrations of meropenem-colistin and meropenem-ciprofloxacin combinations with checkerboard and time-kill curve methods. Conclusion: The combination of meropenem and ciprofloxacin seems to be a good candidate for the treatment of biofilm-associated infections; none of the concentrations obtained as a result of the synergy test were clinically significant.

Infections Due to Acinetobacter baumannii-calcoaceticus Complex: Escalation of Antimicrobial Resistance and Evolving Treatment Options

Bacteria within the genus Acinetobacter (principally A. baumannii-calcoaceticus complex [ABC]) are gram-negative coccobacilli that most often cause infections in nosocomial settings. Community-acquired infections are rare, but may occur in patients with comorbidities, advanced age, diabetes mellitus, chronic lung or renal disease, malignancy, or impaired immunity. Most common sites of infections include blood stream, skin/soft-tissue/surgical wounds, ventilator-associated pneumonia, orthopaedic or neurosurgical procedures, and urinary tract. Acinetobacter species are intrinsically resistant to multiple antimicrobials, and have a remarkable ability to acquire new resistance determinants via plasmids, transposons, integrons, and resistance islands. Since the 1990s, antimicrobial resistance (AMR) has escalated dramatically among ABC. Global spread of multidrug-resistant (MDR)-ABC strains reflects dissemination of a few clones between hospitals, geographic regions, and continents; excessive antibiotic use amplifies this spread. Many isolates are resistant to all antimicrobials except colistimethate sodium and tetracyclines (minocycline or tigecycline); some infections are untreatable with existing antimicrobial agents. AMR poses a serious threat to effectively treat or prevent ABC infections. Strategies to curtail environmental colonization with MDR-ABC require aggressive infection-control efforts and cohorting of infected patients. Thoughtful antibiotic strategies are essential to limit the spread of MDR-ABC. Optimal therapy will likely require combination antimicrobial therapy with existing antibiotics as well as development of novel antibiotic classes.

Sulbactam and Colistin Susceptibility Pattern Among Multidrug-Resistant Acinetobacter Isolates From Respiratory Samples

Background

Acinetobacter species are known to be important hospital-acquired pathogens. Unfortunately, multidrug-resistant Acinetobacter spp. has very limited options for an effective treatment.

Aim

To identify the common pathogens causing lower respiratory tract infections (LRTI), their antimicrobial susceptibility pattern, and determine the minimum inhibitory concentration (MIC) of sulbactam and colistin for Acinetobacter spp.

Materials and methods

A prospective study was done for a period of six months in a tertiary care hospital in Eastern India. The organisms causing LRTI were identified by conventional biochemical techniques and VITEK 2 Compact System (bioMérieux Inc., France). Antimicrobial susceptibility testing was performed using the Kirby‑Bauer disc diffusion method. MIC was also measured for Acinetobacter spp. to confirm certain antimicrobial agents using E-strips and micro broth dilution techniques.

Results

A total of 542 sputum and endotracheal tube aspirate (ETA) samples were examined during the study period. Among these, 109 samples showed growth of significant colony count of one or two organisms, yielding a sum of 115 isolates. Among these, there were 51 (44.35%) isolates of Klebsiella pneumoniae, 32 (27.83%) isolates of Pseudomonas spp., 30 (26.09%) isolates of Acinetobacter spp., and two (1.74%) isolates of Stenotrophomonas maltophilia. Although they were susceptible to colistin, Acinetobacter spp. was highly resistant to sulbactam.

Conclusion

Although colistin susceptibility was noted, the common pathogens causing LRTI were highly resistant to most drugs. Therefore, the causative organisms of LRTI and their susceptibility pattern should be determined to manage these cases effectively.

In search for a synergistic combination against pandrug-resistant A. baumannii; methodological considerations

PURPOSE

Pending approval of new antimicrobials, synergistic combinations are the only treatment option against pandrug-resistant A. baumannii (PDRAB). Considering the lack of a standardized methodology, the aim of this manuscript is to systematically review the methodology and discuss unique considerations for assessing antimicrobial combinations against PDRAB.

METHODS

Post-hoc analysis of a systematic review (conducted in PubMed and Scopus from inception to April 2021) of studies evaluating antimicrobial combination against A. baumannii, based on antimicrobials that are inactive in vitro alone.

RESULTS

Eighty-four publications were reviewed, using a variety of synergy testing methods, including; gradient-based methods (n = 11), disk-based methods (n = 6), agar dilution (n = 2), checkerboard assay (n = 44), time-kill assay (n = 50), dynamic in vitro PK/PD models (n = 6), semi-mechanistic PK/PD models (n = 5), and in vivo animal models (n = 11). Several variations in definitions of synergy and interpretation of each method were observed and are discussed. Challenges related to testing combinations of antimicrobials that are inactive alone (with regards to concentrations at which the combinations are assessed), as well as other considerations (assessment of stasis vs killing, clinical relevance of re-growth in vitro after initial killing, role of in vitro vs in vivo conditions, challenges of clinical testing of antimicrobial combinations against PDRAB infections) are discussed.

CONCLUSION

This review demonstrates the need for consensus on a standardized methodology and clinically relevant definitions for synergy. Modifications in the methodology and definitions of synergy as well as a roadmap for further development of antimicrobial combinations against PDRAB are proposed.

Systematic Review of Antimicrobial Combination Options for Pandrug-Resistant Acinetobacter baumannii

Antimicrobial combinations are at the moment the only potential treatment option for pandrug-resistant A. baumannii. A systematic review was conducted in PubMed and Scopus for studies reporting the activity of antimicrobial combinations against A. baumannii resistant to all components of the combination. The clinical relevance of synergistic combinations was assessed based on concentrations achieving synergy and PK/PD models. Eighty-four studies were retrieved including 818 eligible isolates. A variety of combinations (n = 141 double, n = 9 triple) were tested, with a variety of methods. Polymyxin-based combinations were the most studied, either as double or triple combinations with cell-wall acting agents (including sulbactam, carbapenems, glycopeptides), rifamycins and fosfomycin. Non-polymyxin combinations were predominantly based on rifampicin, fosfomycin, sulbactam and avibactam. Several combinations were synergistic at clinically relevant concentrations, while triple combinations appeared more active than the double ones. However, no combination was consistently synergistic against all strains tested. Notably, several studies reported synergy but at concentrations unlikely to be clinically relevant, or the concentration that synergy was observed was unclear. Selecting the most appropriate combinations is likely strain-specific and should be guided by in vitro synergy evaluation. Furthermore, there is an urgent need for clinical studies on the efficacy and safety of such combinations.

Curcumin-meropenem synergy in carbapenem resistant Klebsiella pneumoniae curcumin-meropenem synergy

Background and Objectives:

The frequency of multiple resistant bacterial infections, including carbapenems, is increasing worldwide. As the decrease in treatment options causes difficulties in treatment, interest in new antimicrobials is increasing. One of the promising natural ingredients is curcumin. It is known to be effective in bacteria such as Pseudomonas aeruginosa, Escherichia coli, Burkholderia pseudomallei through efflux pump inhibition, toxin inhibition and enzymes. However, because its bioavailability is poor, it seffectiveness occurs in combination with antibiotics. In the study, the interaction of meropenem and curcumin in carbapenemase producing strains of Klebsiella pneumoniae was tested.

Materials and Methods:

Thirty-nine Klebsiella pneumoniae isolates, resistant to meropenem, were used in this study. From those 15 MBL, 6 KPC, 17 OXA-48 and 1 AmpC resistance pattern were detected by combination disk method. Meropenem and Curcumin MIC values were determined by liquid microdilution. Checkerboard liquid microdilution was used to determine the synergy between meropenem and curcumin.

Results:

Synergistic effects were observed in 4 isolates producing MBL, 3 isolates producing KPC, 4 isolates producing OXA-48, and 1 isolates producing AmpC (totally 12 isolates) according to the calculated FICI. No antagonistic effects were observed in any isolates.

Conclusion:

Curcumin was thought to be an alternative antimicrobial in combination therapies that would positively contribute to the treatment of bacterial infection. The effectiveness of this combination should be confirmed by other in vitro and clinical studies.

Losing the Battle but Winning the War: Can Defeated Antibacterials Form Alliances to Combat Drug-Resistant Pathogens?

Despite the recent development of antibacterials that are active against multidrug-resistant pathogens, drug combinations are often necessary to optimize the killing of difficult-to-treat organisms. Antimicrobial combinations typically are composed of multiple agents that are active against the target organism; however, many studies have investigated the potential utility of combinations that consist of one or more antibacterials that individually are incapable of killing the relevant pathogen. The current review summarizes in vitro, in vivo, and clinical studies that evaluate combinations that include at least one drug that is not active individually against Pseudomonas aeruginosa, Klebsiella pneumoniae, Acinetobacter baumannii, or Staphylococcus aureus. Polymyxins were often included in combinations against all three of the Gram-negative pathogens, and carbapenems were commonly incorporated into combinations against K. pneumoniae and A. baumannii. Minocycline, sulbactam, and rifampin were also frequently investigated in combinations against A. baumannii, whereas the addition of ceftaroline or another β-lactam to vancomycin or daptomycin showed promise against S. aureus with reduced susceptibility to vancomycin or daptomycin. Although additional clinical studies are needed to define the optimal combination against specific drug-resistant pathogens, the large amount of in vitro and in vivo studies available in the literature may provide some guidance on the rational design of antibacterial combinations.

Systematic review and meta-analysis of in vitro efficacy of antibiotic combination therapy against carbapenem-resistant Gram-negative bacilli

The superiority of combination therapy for carbapenem-resistant Gram-negative bacilli (CR-GNB) infections remains controversial. In vitro models may predict the efficacy of antibiotic regimens against CR-GNB. A systematic review and meta-analysis was performed including pharmacokinetic/pharmacodynamic (PK/PD) and time-kill (TK) studies examining the in vitro efficacy of antibiotic combinations against CR-GNB [PROSPERO registration no. CRD42019128104]. The primary outcome was in vitro synergy based on the effect size (ES): high, ES ≥ 0.75, moderate, 0.35 < ES < 0.75; low, ES ≤ 0.35; and absent, ES = 0). A network meta-analysis assessed the bactericidal effect and re-growth rate (secondary outcomes). An adapted version of the ToxRTool was used for risk-of-bias assessment. Over 180 combination regimens from 136 studies were included. The most frequently analysed classes were polymyxins and carbapenems. Limited data were available for ceftazidime/avibactam, ceftolozane/tazobactam and imipenem/relebactam. High or moderate synergism was shown for polymyxin/rifampicin against Acinetobacter baumannii [ES = 0.91, 95% confidence interval (CI) 0.44-1.00], polymyxin/fosfomycin against Klebsiella pneumoniae (ES = 1.00, 95% CI 0.66-1.00) and imipenem/amikacin against Pseudomonas aeruginosa (ES = 1.00, 95% CI 0.21-1.00). Compared with monotherapy, increased bactericidal activity and lower re-growth rates were reported for colistin/fosfomycin and polymyxin/rifampicin in K. pneumoniae and for imipenem/amikacin or imipenem/tobramycin against P. aeruginosa. High quality was documented for 65% and 53% of PK/PD and TK studies, respectively. Well-designed in vitro studies should be encouraged to guide the selection of combination therapies in clinical trials and to improve the armamentarium against carbapenem-resistant bacteria.

Synergy of polymyxin B, tigecycline and meropenem against carbapenem-resistant Enterobacter cloacae complex isolates

Here, we evaluated the combinations of antibiotics polymyxin B (PMB), tigecycline (TGC) and meropenem (MEM) by time-kill curves (TKC) against carbapenem-resistant Enterobacter cloacae isolates. Combination of PMB/TGC and PMB/MEM showed promising results in sub-inhibitory concentration of PMB indicating the possibility of reducing the dose of PMB used in the treatment.

Meropenem/colistin versus meropenem/ampicillin-sulbactam in the treatment of carbapenem-resistant pneumonia

AIM

Efficacy of colistin and ampicillin-sulbactam have not been compared in treatment of ventilator-associated pneumonia due to A. baumannii. Efficacy of colistin and ampicillin-sulbactam in combination with meropenem were compared in treatment of ventilator-associated pneumonia due to carbapenem-resistant A. baumannii.

METHOD

47 patients with ventilator-associated pneumonia due to carbapenem-resistant A. baumannii were randomized to receive meropenem/colistin or meropenem/ampicillin-sulbactam for 14 days. Clinical and microbiological responses and 28-day mortality were considered as outcomes.

RESULTS

Clinical response (75 vs 69.6%; p = 0.75) and microbial eradication (87.50 vs 91.3%; p = 0.59) were comparable between meropenem/colistin and meropenem/ampicillin-sulbactam groups, respectively.

CONCLUSION

In this study, clinical and microbiological response were comparable between the meropenem/colistin and meropenem/ampicillin-sulbactam groups.

An update on technical, interpretative and clinical relevance of antimicrobial synergy testing methodologies

Testing for antimicrobial interactions has gained popularity in the last decade due to the increasing prevalence of drug-resistant organisms and limited options for the treatment of these infections. In vitro combination testing provides information, on which two or more antimicrobials can be combined for a good clinical outcome. Amongst the various in vitro methods of drug interactions, time-kill assay (TKA), checkerboard (CB) assay and E-test-based methods are most commonly used. Comparative performance of these methods reveals the TKA as the most promising method to detect synergistic combinations followed by CB assay and E-test. Various combinations of antimicrobials have been tested to demonstrate synergistic activity. Promising results were obtained for the combinations of meropenem plus colistin and rifampicin plus colistin against Acinetobacter baumannii, colistin plus carbapenem and carbapenem plus fluoroquinolones against Pseudomonas aeruginosa and colistin/polymyxin B plus rifampicin/meropenem against Klebsiella pneumoniae. Antagonism was detected in only few instances. The presence of synergy or antagonism with a combination seems to correlate with minimum inhibitory concentration of the agent and molecular mechanism involved in the resistance. Further studies need to be conducted to assess the utility of in vitro testing to predict clinical outcome and direct therapy for drug-resistant organisms.

Synergy effect of meropenem-based combinations against Acinetobacter baumannii: a systematic review and meta-analysis

PURPOSE

The main objective of our meta-analysis was to examine the in vitro synergistic effect of meropenem-based combination therapies against Acinetobacter baumannii through a systematic review of the existing literature.

METHODS

An extensive search was performed with no restrictions on date of publication, language, and publication type. Our study evaluated the main conclusions drawn from various studies describing the synergistic activity of combination therapies in vitro.

RESULTS

In this review, 56 published studies were included. Our report included data on 20 types of antibiotics combined with meropenem in 1,228 Acinetobacter baumannii isolates. In time-kill studies, meropenem combined with polymyxin B and rifampicin showed synergy rates of 98.3% (95% CI, 83.7%-100.0%) and 89.4% (95% CI, 57.2%-100.0%), respectively, for Acinetobacter baumannii, modest synergy rates were found for meropenem combined with several antibiotics such as colistin and sulbactam, and no synergy effect was displayed in the combination of meropenem and ciprofloxacin, whereas in checkerboard method, the synergy rates of polymyxin B and rifampicin were 37.0% (95% CI, 0.00%-100.0%) and 56.3% (95% CI, 8.7%-97.8%), respectively.

CONCLUSION

We found that time-kill studies generally identified the greatest synergy, while checkerboard and Etest methods yielded relatively poor synergy rates. Further well-designed in vivo studies should be carried out to confirm these findings.

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.

The role of doxycycline in the therapy of multidrug-resistant E. coli - an in vitro study

This study assessed the in vitro antibacterial activity of combinations of amikacin and doxycycline or tigecycline against multidrug-resistant E. coli isolates. Twenty-four different pulsotypes, including 10 extended-spectrum β-lactamase (ESBL)-, 10 carbapenem-resistant, 2 New Delhi Metallo-beta-lactamase (NDM)- and 2 Klebsiella pneumoniae carbapenemase (KPC)-E. coli isolates were collected. All 24 isolates were susceptible to amikacin and tigecycline. Only 30% of ESBL and 50% of carbapenem-resistant E. coli were susceptible to doxycycline. Both of the NDM-E. coli had a MIC of 64 μg/ml. The checkerboard method showed that for the ESBL- and carbapenem-resistant E. coli, the synergistic effects of amikacin/doxycycline were 80% and 90%, respectively. For the two KPC- and two NDM-E. coli, the FIC index of amikacin/doxycycline were 0.5/0.375 and 0.5/0.281, respectively. For the ESBL- and carbapenem-resistant E. coli isolates, the combinations of amikacin and doxycycline exhibited synergistic activities against 80%, and 80% and 10% vs 60%, and 80% and 10% of the isolates at concentrations of 1x, 1/2x and 1/4xMIC, respectively. The synergistic effect seems to be similar for doxycycline and tigecycline based combinations with amikacin. In conclusion, the antibacterial activity of doxycycline can be enhanced by the addition of amikacin and is observed against most multidrug-resistant E. coli isolates.

Global Dissemination of Carbapenemase-Producing Klebsiella pneumoniae: Epidemiology, Genetic Context, Treatment Options, and Detection Methods

The emergence of carbapenem-resistant Gram-negative pathogens poses a serious threat to public health worldwide. In particular, the increasing prevalence of carbapenem-resistant Klebsiella pneumoniae is a major source of concern. K. pneumoniae carbapenemases (KPCs) and carbapenemases of the oxacillinase-48 (OXA-48) type have been reported worldwide. New Delhi metallo-β-lactamase (NDM) carbapenemases were originally identified in Sweden in 2008 and have spread worldwide rapidly. In this review, we summarize the epidemiology of K. pneumoniae producing three carbapenemases (KPCs, NDMs, and OXA-48-like). Although the prevalence of each resistant strain varies geographically, K. pneumoniae producing KPCs, NDMs, and OXA-48-like carbapenemases have become rapidly disseminated. In addition, we used recently published molecular and genetic studies to analyze the mechanisms by which these three carbapenemases, and major K. pneumoniae clones, such as ST258 and ST11, have become globally prevalent. Because carbapenemase-producing K. pneumoniae are often resistant to most β-lactam antibiotics and many other non-β-lactam molecules, the therapeutic options available to treat infection with these strains are limited to colistin, polymyxin B, fosfomycin, tigecycline, and selected aminoglycosides. Although, combination therapy has been recommended for the treatment of severe carbapenemase-producing K. pneumoniae infections, the clinical evidence for this strategy is currently limited, and more accurate randomized controlled trials will be required to establish the most effective treatment regimen. Moreover, because rapid and accurate identification of the carbapenemase type found in K. pneumoniae may be difficult to achieve through phenotypic antibiotic susceptibility tests, novel molecular detection techniques are currently being developed.