In vitro synergistic activity of fosfomycin in combination with meropenem, amikacin and colistin against OXA-48 and/or NDM-producing Klebsiella pneumoniae

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.

Synergistic antibacterial activity of ceftazidime-avibactam in combination with colistin, gentamicin, amikacin, and fosfomycin against carbapenem-resistant Klebsiella pneumoniae

Carbapenem-resistant Klebsiella pneumoniae (CPKP) infections seriously threaten global public health. The main objective of this study was to assess the in-vitro synergistic activity of ceftazidime-avibactam (CZA) in combination with colistin (COL), amikacin (AK), gentamicin (GEN), and fosfomycin (FOS) against CPKP isolates. The secondary goal was to determine the antibiotic susceptibility performance of BD Phoenix. OXA-48 (49.1%) was the predominant carbapenemase, followed by KPC (29.1%). We used the broth microdilution (BMD) method to determine the minimum inhibitory concentrations (MICs) of CZA, COL, AK, and GEN. Meanwhile, the MICs of FOS were determined by the agar dilution (AD) method. To examine the antibacterial activity of CZA, we conducted a checkerboard assay (CBA) with COL, AK, GEN, and FOS against CRKP isolates. We randomly selected three strains and performed synergy testing via time-kill assay (TKA). CRKP isolates were 89.1% susceptible to CZA, 16.4% to COL, 21.8% to GEN, and 29.1% to AK using BMD, 47.3% to FOS by AD. The most synergistic effects were observed in the combination of CZA-COL (78.2%) and CZA-FOS (63.6%). Given the limited therapeutic options for treating severe CRKP infections, combining CZA with COL and FOS may enhance in-vitro activity against clinical CRKP isolates.

A comparative study of ceftazidime/avibactam-based and fosfomycin plus meropenem-based regimens for managing infections caused by carbapenem-resistant Klebsiella pneumoniae in critically ill patients

The main aim of this study was to compare and analyze the effectiveness of treatment regimens using ceftazidime/avibactam (CAZ/AVI) versus fosfomycin plus meropenem (FOS/MER) for managing bloodstream infections (BSI) or ventilator-associated pneumonia (VAP) caused by carbapenem-resistant Klebsiella pneumoniae (CRKP) in critically ill patients. Between 4 January 2019, and 16 July 2023, adult patients (≥18 years old) diagnosed with BSI or VAP due to culture confirmed CRKP in ICU of a tertiary care hospital were investigated retrospectively. A total of 71 patients were categorized into two groups: 30 patients in CAZ/AVI-based, and 41 patients in FOS/MER-based group. No substantial disparities were found in the total duration of ICU hospitalization, as well as the 14- and 30-day mortality rates, between patients treated with CAZ/AVI-based and FOS/MER-based therapeutic regimens. We consider that our study provides for the first time a comprehensive understanding of treatment outcomes and associated risk factors among patients with CRKP-related infections.

Intravenous fosfomycin in combination regimens as a treatment option for difficult-to-treat infections due to multi-drug-resistant Gram-negative organisms: A real-life experience

AIM

To investigate the efficacy of intravenous (IV) fosfomycin as combination therapy for treatment of difficult-to-treat (DTT) acute and subacute infections with multi-drug-resistant (MDR) Gram-negative bacteria (GNB), and risk factors associated with 90-day mortality.

METHODS

A retrospective, observational, monocentric study enrolled patients treated with IV fosfomycin in combination regimens (≥72 h) for proven DTT-MDR-GNB infection. Multi-variate regression analysis identified independent risk factors for 90-day mortality. A propensity score for receiving fosfomycin was performed to control for confounding factors.

RESULTS

In total, 70 patients were included in this study: 54.3% had carbapenem-resistant isolates, 31.4% had ceftazidime/avibactam-resistant isolates and 28.6% had ceftolozane/tazobactam-resistant isolates. The main pathogens were Pseudomonas aeruginosa (57.1%) and Klebsiella pneumoniae (22.9%). The most prevalent infections were nosocomial pneumonia (42.9%), osteomyelitis (17.1%) and intra-abdominal infections. All-cause 30- and 90-day mortality were 15.7% and 31.4%, respectively (18.9% and 50% considering acute DTT-MDR-GNB infections alone). Relapse at 30 days occurred in 22.9% of cases (29% with emergence of fosfomycin resistance). Mortality at 90 days was independently associated with septic shock and ceftolozane/tazobactam resistance. The relationship between resistance to ceftolozane/tazobactam and 90-day mortality was confirmed to be significant after adjustment by propensity score analysis (hazard ratio 5.84, 95% confidence interval 1.65-20.68; P=0.006).

CONCLUSIONS

Fosfomycin seems to be a promising salvage, combination treatment in DTT-MDR-GNB infections. Resistance to ceftolozane/tazobactam seems to be independently associated with treatment failure. Randomized clinical trials focusing on pathogen and infection sites are needed urgently to demonstrate the superiority of fosfomycin in combination with other agents for the resolution of DTT-MDR-GNB infections.

Evaluation of the combination treatments with intravenous fosfomycin for carbapenem-resistant Klebsiella pneumoniae

OBJECTIVE

The aim of this study was to evaluate the combination treatments with intravenous fosfomycin for carbapenem-resistant Klebsiella pneumoniae infections in a tertiary-care center.

METHODS

Between December 24, 2018 and November 21, 2022, adult patients diagnosed with bloodstream infection or ventilator-associated pneumonia due to culture-confirmed carbapenem-resistant Klebsiella pneumoniae in the anesthesiology and reanimation intensive care units were investigated retrospectively.

RESULTS

There were a total of 62 patients fulfilling the study inclusion criteria. No significant difference was recorded in 14- and 30-day mortality among different types of combination regimens such as fosfomycin plus one or two antibiotic combinations. Hypokalemia (OR:5.651, 95%CI 1.019-31.330, p=0.048) was found to be a significant risk factor for 14-day mortality, whereas SOFA score at the time of diagnosis (OR:1.497, 95%CI 1.103-2.032, p=0.010) and CVVHF treatment (OR:6.409, 95%CI 1.395-29.433, p=0.017) were associated with 30-day mortality in multivariate analysis.

CONCLUSION

In our study, high mortality rates were found in patients with bloodstream infection or ventilator-associated pneumonia due to carbapenem-resistant Klebsiella pneumoniae, and no significant difference was recorded in 14- and 30-day mortality among different types of combination regimens such as fosfomycin plus one or two antibiotic combinations.

Assessment of In-Vitro Synergy of Fosfomycin with Meropenem, Amikacin and Tigecycline in Whole Genome Sequenced Extended and Pan Drug Resistant Klebsiella Pneumoniae: Exploring A Colistin Sparing Protocol

Fosfomycin has emerged as a very useful antimicrobial in management of extremely drug resistant (XDR) and pan drug resistant (PDR) Klebsiella pneumoniae. In this study, we assessed in-vitro synergy of colistin sparing combinations of fosfomycin (FOS) with meropenem (MEM), tigecycline (TGC) and amikacin (AK) against XDR and PDR Klebsiella pneumoniae. Method: Non-replicate fully characterised 18 clinical isolates of K. pneumoniae (15 XDR and 3 PDR strains) were subjected to in-vitro synergy testing by checkerboard and time kill assay. Combinations tested were FOS-MEM, FOS-TGC and FOS-AK with glucose-6-phosphate being incorporated in all runs.WGS was carried out on the Illumina next-generation sequencing platform. Results: FOS-MEM and FOS-AK both demonstrated excellent synergy against all PDRs and all but one XDR. Synergy led to lowering of MICs to susceptible breakpoints. FOS-TGC demonstrated antagonism. MLST-231 K. pneumoniae predominated (14), followed by ST-395 (3) and ST147 (1). Majority harboured OXA-232 (n = 15), while n = 2 carried NDM-1 type and n = 1 co-carried NDM-5 + OXA-232. Mortality was high in both ST-231 (57.1%) and ST-395 (66.6%). Synergy was observed despite widespread presence of resistance markers against aminoglycosides [aph(3′)-Ic, aacA4, and rmtf], beta-lactams [blaSHV-11, blaTEM-1b, blaCTX-M-15, and blaOXA-232], fosfomycin [fosA6 and fosA5] and presence of porin proteins OmpK37, OmpA and K. pneumoniae antibiotic efflux pumps Kpn F, H, G, and E. Conclusion: FOS + MEM and FOS + AK are excellent colistin sparing combinations against ST 231, ST-395 and ST-147 XDR and PDR K. pneumoniae. FOS with fewer side effects than colistin, excellent tissue distribution and minimal side effects may be recommended in combination with meropenem.

Prediction of Prognosis in Adult Patients With Carbapenem-Resistant Klebsiella pneumoniae Infection

OBJECTIVE

Carbapenem-resistant Klebsiella pneumoniae (CRKP) infections are associated with poor patient outcomes. We aimed to analyze the clinical information of adult patients with CRKP infection in order to establish a nomogram for mortality risk as well as to determine the treatment effectiveness of different antimicrobial regimens.

METHODS

Adult patients diagnosed with CRKP infection in a tertiary hospital in Shanghai between September 2019 and March 2021 were included. The clinical characteristics and clinical outcomes of these patients were analyzed.

RESULTS

A total of 199 cases of CRKP infection were examined. Five factors, namely age ≥65 years, respiratory failure, Sequential Organ Failure Assessment score, serum procalcitonin ≥5 ng/mL, and appropriate treatments in 3 days, were found to be associated with 30-day mortality. Upon incorporating these factors, the nomogram achieved good concordance indexes of 0.85 (95% confidence interval [CI]: 0.80-0.90) and well-fitted calibration curves. Receiver-operating characteristic curves for 7-, 15-, and 30-day survival had areas under the curve of 0.90, 0.87, and 0.88, respectively. Three-drug combination therapy was observed to be associated with lower mortality in the high-risk group (adjusted hazard ratio = 0.24, 95% CI: 0.06-0.99) but not in the low-risk group. Ceftazidime-avibactam, fosfomycin, and amikacin were effective against infections caused by CRKP. Tigecycline improved the treatment efficiency in 7 days, but a trend toward increased mortality was seen (HR, 1.69; 95% CI: 0.98-2.94; P = 0.061).

CONCLUSION

The antimicrobial regimen efficacy data and the predictive nomogram established in this study can help clinicians in identifying high-risk adult patients with CRKP infection, improving the therapeutic effect, and reducing mortality.

An Evidence-Based Multidisciplinary Approach Focused at Creating Algorithms for Targeted Therapy of BSIs, cUTIs, and cIAIs Caused by Enterobacterales in Critically Ill Adult Patients

Prompt implementation of appropriate targeted antibiotic therapy represents a valuable approach in improving clinical and ecological outcome in critically septic patients. This multidisciplinary opinion article focused at developing evidence-based algorithms for targeted antibiotic therapy of bloodstream (BSIs), complicated urinary tract (cUTIs), and complicated intrabdominal infections (cIAIs) caused by Enterobacterales. The aim was to provide a guidance for intensive care physicians either in appropriately placing novel antibiotics or in considering strategies for sparing the broadest-spectrum antibiotics. A multidisciplinary team of experts (one intensive care physician, one infectious disease consultant, one clinical microbiologist and one MD clinical pharmacologist), performed several rounds of assessment to reach agreement in developing six different algorithms according to the susceptibility pattern (one each for multi-susceptible, extended-spectrum beta-lactamase-producing, AmpC beta-lactamase-producing, Klebsiella pneumoniae carbapenemase (KPC)-producing, OXA-48-producing, and Metallo-beta-lactamase (MBL)-producing Enterobacterales). Whenever multiple therapeutic options were feasible, a hierarchical scale was established. Recommendations on antibiotic dosing optimization were also provided. In order to retrieve evidence-based support for the therapeutic choices proposed in the algorithms, a comprehensive literature search was performed by a researcher on PubMed-MEDLINE from inception until March 2021. Quality and strength of evidence was established according to a hierarchical scale of the study design. Only articles published in English were included. It is expected that these algorithms, by allowing prompt revision of antibiotic regimens whenever feasible, appropriate place in therapy of novel beta-lactams, implementation of strategies for sparing the broadest-spectrum antibiotics, and pharmacokinetic/pharmacodynamic optimization of antibiotic dosing regimens, may be helpful either in improving clinical outcome or in containing the spread of antimicrobial resistance.

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.

Evaluation of the Synergistic Antibacterial Effects of Fosfomycin in Combination with Selected Antibiotics against Carbapenem-Resistant Acinetobacter baumannii

The spread of multi-drug resistant (MDR) pathogens and the lagging pace in the development of novel chemotherapeutic agents warrant the use of combination therapy as a reliable, cost-effective interim option. In this study, the synergistic effects of fosfomycin in combination with other antibiotics were assessed. Of the 193 isolates, 90.6% were non-susceptible to fosfomycin, with minimum inhibitory concentrations (MICs) of ≥128 µg/mL. Antibacterial evaluation of fosfomycin-resistant isolates indicated multi-drug resistance to various antibiotic classes. Combinations of fosfomycin with 12 commonly used antibiotics synergistically inhibited most fosfomycin-resistant isolates. The fractional inhibitory concentration index indicated that combining fosfomycin with either aminoglycosides, glycylcyclines, fluoroquinolones, or colistin resulted in 2- to 16-fold reduction in the MIC of fosfomycin. Time-kill kinetics further confirmed the synergistic bactericidal effects of fosfomycin in combination with either amikacin, gentamicin, tobramycin, minocycline, tigecycline, or colistin, with more than 99.9% reduction in bacterial cells. Fosfomycin-based combination therapy might serve as an alternative option for the treatment of MDR A. baumannii. Further steps including in vivo efficacy and toxicity in experimental models of infection are required prior to clinical applications.

Synergistic antibacterial effects of colistin in combination with aminoglycoside, carbapenems, cephalosporins, fluoroquinolones, tetracyclines, fosfomycin, and piperacillin on multidrug resistant Klebsiella pneumoniae isolates

Multidrug resistant Enterobacterales have become a serious global health problem, with extended hospital stay and increased mortality. Antibiotic monotherapy has been reported ineffective against most drug resistant bacteria including Klebsiella pneumoniae, thus encouraging the use of multidrug therapies as an alternative antibacterial strategy. The present works assessed the antibacterial activity of colistin against K. pneumoniae isolates. Resistant isolates were tested against 16 conventional antibiotics alone and in combination with colistin. The results revealed that all colistin resistant isolates demonstrated multidrug resistance against the tested antibiotics except amikacin. At sub-inhibitory concentrations, combinations of colistin with amikacin, or fosfomycin showed synergism against 72.72% (8 of 11 isolates). Colistin with either of gentamicin, meropenem, cefoperazone, cefotaxime, ceftazidime, moxifloxacin, minocycline, or piperacillin exhibited synergism against 81.82% (9 of 11 isolates). Combinations of colistin with either of tobramycin or ciprofloxacin showed synergism against 45.45% (5 in 11 isolates), while combinations of colistin with imipenem or ceftolozane and tazobactam displayed 36.36% (4 of 11 isolates) and 63.64% (7 of 11 isolates) synergism. In addition, combinations of colistin with levofloxacin was synergistic against 90.91% (10 of 11 isolates). The results revealed that combinations of colistin with other antibiotics could effectively inhibit colistin resistant isolates of K. pneumoniae, and thus could be further explore for the treatment of multidrug resistant pathogens.

Treatment options for K. pneumoniae, P. aeruginosa and A. baumannii co-resistant to carbapenems, aminoglycosides, polymyxins and tigecycline: an approach based on the mechanisms of resistance to carbapenems

The management of carbapenem-resistant infections is often based on polymyxins, tigecycline, aminoglycosides and their combinations. However, in a recent systematic review, we found that Gram-negative bacteria (GNB) co-resistant to carbapanems, aminoglycosides, polymyxins and tigecycline (CAPT-resistant) are increasingly being reported worldwide. Clinical data to guide the treatment of CAPT-resistant GNB are scarce and based exclusively on few case reports and small case series, but seem to indicate that appropriate (in vitro active) antimicrobial regimens, including newer antibiotics and synergistic combinations, may be associated with lower mortality. In this review, we consolidate the available literature to inform clinicians dealing with CAPT-resistant GNB about treatment options by considering the mechanisms of resistance to carbapenems. In combination with rapid diagnostic methods that allow fast detection of carbapenemase production, the approach proposed in this review may guide a timely and targeted treatment of patients with infections by CAPT-resistant GNB. Specifically, we focus on the three most problematic species, namely Klebsiella pneumoniae, Pseudomonas aeruginosa and Acinetobacter baumannii. Several treatment options are currently available for CAPT-resistant K. pneumonia. Newer β-lactam-β-lactamase combinations, including the combination of ceftazidime/avibactam with aztreonam against metallo-β-lactamase-producing isolates, appear to be more effective compared to combinations of older agents. Options for P. aeruginosa (especially metallo-β-lactamase-producing strains) and A. baumannii remain limited. Synergistic combination of older agents (e.g., polymyxin- or fosfomycin-based synergistic combinations) may represent a last resort option, but their use against CAPT-resistant GNB requires further study.

fosA3 overexpression with transporter mutations mediates high-level of fosfomycin resistance and silence of fosA3 in fosfomycin-susceptible Klebsiella pneumoniae producing carbapenemase clinical isolates

The effective treatment of carbapenemase-producing Klebsiella pneumoniae infection has been limited and required novel potential agents. Due to the novel drug development crisis, using old antimicrobial agents and combination therapy have been highlighted. This study focused on fosfomycin which inhibits cell wall synthesis and has potential activity on Enterobacteriaceae. We evaluated fosfomycin activity against carbapenemase-producing K. pneumoniae and characterized fosfomycin resistance mechanisms. Fosfomycin revealed effective activity against only 31.8% of carbapenemase-producing K. pneumoniae isolates. The major resistance mechanism was FosA3 production. The co-occurrence of FosA3 overexpression with the mutation of glpT (or loss of glpT) and/or uhpT was mediated high-level resistance (MIC>256 mg/L) to fosfomycin. Moreover, fosA3 silenced in sixteen fosfomycin-susceptible isolates and the plasmid carrying fosA3 of these isolates increased 32- to 64-fold of fosfomycin MICs in Escherichia coli DH5α transformants. The in vitro activity of fosfomycin combination with amikacin by checkerboard assay showed synergism and no interaction in six (16.2%) and sixteen isolates (43.3%), respectively. No antagonism of fosfomycin and amikacin was observed. Notably, the silence of aac (6)’-Ib and aphA6 was observed in amikacin-susceptible isolates. Our study suggests that the combination of fosfomycin and amikacin may be insufficient for the treatment of carbapenemase-producing K. pneumoniae isolates.

Fosfomycin as Partner Drug for Systemic Infection Management. A Systematic Review of Its Synergistic Properties from In Vitro and In Vivo Studies

Fosfomycin is being increasingly prescribed for multidrug-resistant bacterial infections. In patients with systemic involvement, intravenous fosfomycin is usually administered as a partner drug, as part of an antibiotic regimen. Hence, the knowledge of fosfomycin pharmacodynamic interactions (synergistic, additive, indifferent and antagonistic effect) is fundamental for a proper clinical management of severe bacterial infections. We performed a systematic review to point out fosfomycin’s synergistic properties, when administered with other antibiotics, in order to help clinicians to maximize drug efficacy optimizing its use in clinical practice. Interactions were more frequently additive or indifferent (65.4%). Synergism accounted for 33.7% of total interactions, while antagonism occurred sporadically (0.9%). Clinically significant synergistic interactions were mostly distributed in combination with penicillins (51%), carbapenems (43%), chloramphenicol (39%) and cephalosporins (33%) in Enterobactaerales; with linezolid (74%), tetracyclines (72%) and daptomycin (56%) in Staphylococcus aureus; with chloramphenicol (53%), aminoglycosides (43%) and cephalosporins (36%) against Pseudomonas aeruginosa; with daptomycin (97%) in Enterococcus spp. and with sulbactam (75%) and penicillins (60%) and in Acinetobacter spp. fosfomycin-based antibiotic associations benefit from increase in the bactericidal effect and prevention of antimicrobial resistances. Taken together, the presence of synergistic interactions and the nearly total absence of antagonisms, make fosfomycin a good partner drug in clinical practice.