Sitafloxacin Expresses Potent Anti-Mycobacterium abscessus Activity

Therapeutic options for treating Mycobacterium abscessus infections are extremely limited; quinolones are important. The in vitro anti-M. abscessus activities of nine quinolones, emphasizing sitafloxacin, were investigated. Antimicrobial susceptibility testing was performed on 10 non-tuberculous mycobacterium reference strains and 194 clinical, M. abscessus isolates. The activity of sitafloxacin against intracellular M. abscessus residing within macrophages was also evaluated. A checkerboard assay was conducted to determine synergy between sitafloxacin and 10 clinically important antibiotics. Among the nine quinolones tested, sitafloxacin exhibited the greatest anti-M. abscessus activity with MIC50 and MIC90 of 1 and 2 mg/L, respectively. Sitafloxacin exerted a bacteriostatic effect on M. abscessus and inhibited the intracellular growth of M. abscessus at concentrations equivalent to clarithromycin. No antagonism between sitafloxacin and 10 clinically important anti-M. abscessus antibiotics was evident. In summary, sitafloxacin exhibited a significant advantage relative to other quinolones in inhibiting the growth of M. abscessus in vitro, suggesting the potential inclusion of sitafloxacin in new strategies to treat M. abscessus infections.

A Novel Tigecycline Adjuvant ML-7 Reverses the Susceptibility of Tigecycline-Resistant Klebsiella pneumoniae

The increasing incidence of tigecycline resistance undoubtedly constitutes a serious threat to global public health. The combination therapies had become the indispensable strategy against this threat. Herein, 11 clinical tigecycline-resistant Klebsiella pneumoniae which mainly has mutations in ramR, acrR, or macB were collected for tigecycline adjuvant screening. Interestingly, ML-7 hydrochloride (ML-7) dramatically potentiated tigecycline activity. We further picked up five analogs of ML-7 and evaluated their synergistic activities with tigecycline by using checkerboard assay. The results revealed that ML-7 showed certain synergy with tigecycline, while other analogs exerted attenuated synergistic effects among tigecycline-resistant isolates. Thus, ML-7 was selected for further investigation. The results from growth curves showed that ML-7 combined with tigecycline could completely inhibit the growth of bacteria, and the time-kill analysis revealed that the combination exhibited synergistic bactericidal activities for tigecycline-resistant isolates during 24 h. The ethidium bromide (EtBr) efflux assay demonstrated that ML-7 could inhibit the functions of efflux pump. Besides, ML-7 disrupted the proton motive force (PMF) via increasing ΔpH, which in turn lead to the inhibition of the functions of efflux pump, reduction of intracellular ATP levels, as well as accumulation of ROS. All of which promoted the death of bacteria. And further transcriptomic analysis revealed that genes related to the mechanism of ML-7 mainly enriched in ABC transporters. Taken together, these results revealed the potential of ML-7 as a novel tigecycline adjuvant to circumvent tigecycline-resistant Klebsiella pneumoniae.

Synergistic Antibacterial Effects of Meropenem in Combination with Aminoglycosides against Carbapenem-Resistant Escherichia coli Harboring blaNDM-1 and blaNDM-5

Infections due to carbapenem-resistant Escherichia coli (CREC) are problematic due to limitation in treatment options. Combination therapies of existing antimicrobial agents have become a reliable strategy to control these infections. In this study, the synergistic effects of meropenem in combination with aminoglycosides were assessed by checkerboard and time-kill assays. Of the 35 isolates, 19 isolates (54.3%) were resistant to carbapenems (imipenem and meropenem) with the MIC ranges from 16 to 128 µg/mL. These isolates were resistant to almost all antibiotic classes. Molecular characteristics revealed co-harboring of carbapenemase (blaNDM-1, blaNDM-5 and blaOXA-48) and extended-spectrum β-lactamases (ESBL) genes (blaCTX-M, blaSHV and blaTEM). The checkerboard assay displayed synergistic effects of meropenem and several aminoglycosides against most CREC isolates. Time-kill assays further demonstrated strong synergistic effects of meropenem in combination with either amikacin, gentamicin, kanamycin, streptomycin, and tobramycin. The results suggested that meropenem in combination with aminoglycoside therapy might be an efficient optional treatment for infections cause by CREC.

Preliminary study on the synergistic interaction of Garcinia kola and Vernonia amygdalina against Candida albicans

Introduction: Due to the emergence and spread of infections caused by Candida albicans especially among immunocompromised patients and increase in resistance by this group of fungi to commonly used antifungal agents, this study was undertaken to investigate the possible synergy between Garcinia kola seed and Vernonia amygdalina leaves extracts against organism. Methods: Ethanol extraction of Vernonia amygdalina leaves and Garcinia kola seeds were carried out and extract evaluated for anti-candida activities. The combined anti-candida activities of the extracts were also assessed using Checkerboard assay. Results: Extract of G. kola seed showed minimal anti-candida activity against the C. albicans with an inhibition zone of 5 mm and minimum inhibitory concentration of 50 mg/mL. The combined effect of both extract was demonstrated to be synergistic at most combination ratios tested. Furthermore, the combined effect was observed to have outweighed their individual effect, inhibiting the test isolates at concentration far less than the MICs of each of the extracts. The fractional inhibitory concentration index of the combined extracts at their various combination ratios against C. albicans ranged between 0.14 – 0.45 mg/ml indicating a synergistic effect by the various combinations against the organism. Conclusion: The combined activities by the two extracts showed marked improvement in anti-candida activities compared with their individual activities. The results support harnessing the individual bioactive constituents of the extracts and combining them for the development of potential antifungal agents.

Antibacterial activity of human defensins against Staphylococcus aureus and Escherichia coli

Background The global problem of antibiotic resistance requires the search for and development of new methods of treatment. One of the promising strategies is the use of low doses of antimicrobial peptides, in particular, human defensins HNP-1, hBD-1, and hBD-3, in combination with antibacterial drugs already used in clinical practice. This approach may be used to increase the effectiveness of conventional antibiotics. However, this requires thorough study of the effectiveness of defensins in combination with antibiotics against a large number of bacterial strains with known phenotypes of antibiotic resistance. The aim of this work was to study the antibacterial effect of HNP-1, hBD-1 and hBD-3 in combination with rifampicin or amikacin against clinical isolates of Staphylococcus aureus (n = 27) and Escherichia coli (n = 24) collected from hospitalized patients. Methods The standard checkerboard assay was used to determine minimum inhibitory concentrations (MICs) of antimicrobials. The combined microbicidal effects of two substances (defensin + conventional antibiotic) were assessed by the fractional inhibitory concentration index (FICI). Results The highest anti-staphylococcal activity (including methicillin-resistant strains) among defensins was demonstrated by hBD-3 that had MIC of 1 (0.5–4) mg/L (hereinafter, MIC values are presented as median and interquartile range). The MIC of HNP-1 against S. aureus was 4 (2–8) mg/L; the MIC of hBD-1 was 8 (4–8) mg/L. Against E. coli, the most effective was also found to be hBD-3 that had MIC of 4 (4–8) mg/L; the MIC of HNP-1 was 12 (4–32) mg/L. The combinations of HNP-1 + rifampicin and hBD-3 + rifampicin demonstrated synergistic effects against S. aureus. Against E. coli, combinations of HNP-1 + amikacin and hBD-3 + amikacin also showed synergy of action.

Unravelling the Antifungal Effect of Red Thyme Oil (Thymus vulgaris L.) Compounds in Vapor Phase

The aim of this work was to evaluate the antifungal activity in vapor phase of thymol, p-cymene, and γ-terpinene, the red thyme essential oil compounds (RTOCs). The Minimum Inhibitory Concentration (MIC) of RTOCs was determined against postharvest spoilage fungi of the genera Botrytis, Penicillium, Alternaria, and Monilinia, by measuring the reduction of the fungal biomass after exposure for 72 h at 25 °C. Thymol showed the lowest MIC (7.0 µg/L), followed by γ-terpinene (28.4 µg/L) and p-cymene (40.0 µg/L). In the case of P. digitatum ITEM 9569, resistant to commercial RTO, a better evaluation of interactions among RTOCs was performed using the checkerboard assay and the calculation of the Fractional Inhibitory Concentration Index (FICI). During incubation, changes in the RTOCs concentration were measured by GC-MS analysis. A synergistic effect between thymol (0.013 ± 0.003 L/L) and γ-terpinene (0.990 ± 0.030 L/L) (FICI = 0.50) in binary combinations, and between p-cymene (0.700 ± 0.010 L/L) and γ-terpinene (0.290 ± 0.010 L/L) in presence of thymol (0.008 ± 0.001 L/L) (FICI = 0.19), in ternary combinations was found. The synergistic effect against the strain P. digitatum ITEM 9569 suggests that different combinations among RTOCs could be defined to control fungal strains causing different food spoilage phenomena.

Synergistic activity of colistin combined with PFK-158 against colistin-resistant and colistin-susceptible Gram-negative bacteria

Background: The emergence of colistin resistance among Gram-negative bacteria poses a serious public health threat and warrants immediate action. Therefore, it is necessary to enhance the antibacterial activity of colistin through the combination with other drugs. In this study, we demonstrate the synergistic activity of colistin combined with PFK-158 against colistin-susceptible but more importantly against colistin-resistant Gram-negative bacteria, including non-fermenting bacteria (P. aeruginosa, A. baumannii) and Enterobacteriaceae (E. coli and K. pneumoniae).Methods: 18 colistin-resistant and 12 colistin-susceptible Gram-negative bacteria were collected as the experimental strains, and the minimum inhibitory concentrations (MICs) of colistin and PFK-158 against all strains were determined by the broth microdilution method. The MICs of routine antimicrobial agents including aztreonam (ATM), ceftazidime (CAZ), cefepime (FEP), imipenem (IMP), ciprofloxacin (CIP), levofloxacin (LVX), gentamicin (GEN), tobramycin (TOB) for all 30 experimental strains were determined by bioMerieux VITEK-2 (BioMérieux, Marcy-l’Étoile, France). The synergistic activity of colistin combined with PFK-158 in vitro was assessed using the checkerboard assay and the time-kill assays.Results: The results of the checkerboard assay showed that when colistin was used in combination with PFK-158, synergistic activity was observed against the 18 colistin-resistant and the 8 colistin-susceptible Gram-negative bacteria, and the remaining 4 colistin-susceptible strains showed additive activity. No irrelevant activity and antagonistic activity was observed for all strains. The results of the time-killing assays presented that the killing activity against the colistin-resistant Gram-negative bacterium were evident for the combination of colistin and PFK-158, compared with the groups adding colistin or PFK-158 alone. Conclusions: In conclusion, our results strongly exhibited that the combination of colistin and PFK-158 displayed the significant synergistic activity against all tested colistin-resistant and most colistin-susceptible Gram-negative strains. PFK-158 was found to potentiate the antibacterial activity of colistin against a wide panel of colistin-resistant and colistin-susceptible Gram-negative strains no matter what species (including non-fermenting bacteria and Enterobacteriaceae). It may be a potential new choice for the treatment of infections caused by the clinical Gram-negative strains.

1626. Synergistic Effect of Cefiderocol with Other Antibiotics Against PER-Producing Acinetobacter baumannii Isolates from the Multinational SIDERO-WT Studies

Background Cefiderocol (CFDC), a novel siderophore cephalosporin, showed potent activity at minimum inhibitory concentrations (MICs) of ≤4 μg/mL against ≥99% of Gram-negative isolates in the multinational SIDERO-WT studies. PER-producing Acinetobacter baumannii, mainly from Russia, showed high CFDC MICs of 8– >64 μg/mL. This study evaluated the synergistic effects of CFDC combined with other antibiotics against PER-producing A. baumannii isolates with high CFDC MICs. Methods Two isolates of PER-producing A. baumannii with resistance to CFDC (MIC 16 μg/mL), meropenem (MEM; MIC 64 μg/mL), ceftazidime-avibactam (CZA; MIC 64/4 μg/mL), amikacin (AMK; MIC 32 or 64 μg/mL), and ciprofloxacin (CIP; MIC ≥64 μg/mL) were tested. Against ampicillin-sulbactam (SAM), one isolate was resistant (MIC 32/64 μg/mL) and another was susceptible (MIC 8/16 μg/mL). Effects of CFDC combined with other antibiotics were evaluated by checkerboard assay and chemostat model reproducing humanized antibiotic exposure. The checkerboard assay used a single agent (e.g. ceftazidime [CAZ], avibactam [AVI], ampicillin [AMP] or sulbactam [SUL]). Iron-depleted cation-adjusted Mueller‒Hinton broth was used as the standard medium for CFDC, as recommended by the Clinical Laboratory and Standards Institute. Results Against both isolates, synergy with CFDC was seen for two β-lactamase inhibitors, AVI and SUL, with a fractional inhibitory concentration (FIC) index of 0.026–0.033 and 0.26–0.27, respectively. A synergistic to additive effect was seen for MEM and AMK, with an FIC index of 0.53–0.75 and 0.25–0.52, respectively. In the chemostat model, regrowth during 24-h treatment was observed with single agents (CFDC 2 g, q8h, 3-h infusion; MEM 2 g, q8h, 1-h infusion; CZA 2 g, q8h, 2-h infusion; SAM 3 g, q8h, 3-h infusion; AMK 15 mg/kg, q8h, 3-h infusion) for both isolates, including the SAM-susceptible isolate. However, no regrowth was seen when CFDC was combined with CZA, MEM, SAM or AMK. Conclusion The most potent synergy was seen between CFDC and AVI against PER-producing A. baumannii with a decreased MIC to ≤1 µg/mL for all isolates, followed by SUL and MEM. Under humanized pharmacokinetic exposure, combination of CFDC and CZA, MEM, SAM or AMK is expected to be effective against PER-producing A. baumannii in spite of high CFDC MICs. Disclosures Yoshinori Yamano, PhD, Shionogi & Co., Ltd. (Employee) Miki Takemura, MSc, Shionogi & Co., Ltd. (Employee) Naomi Anan, MSc, Shionogi & Co., Ltd. (Employee) Rio Nakamura, BSc, Shionogi & Co., Ltd. (Employee) Roger Echols, MD, Shionogi Inc. (Consultant)