Mean Fractional Inhibitory Concentration Index Research Articles

In vitro efficacy of combinations of antibiotics used in clinical practice on clinical isolates of Helicobacter pylori.

The main antibiotics used against Helicobacter pylori have been chosen empirically over time, with few preclinical studies to provide support. The rise in resistance to some of these antibiotics is prompting a reassessment of their use. This work aimed to evaluate the invitro efficacy of 2 × 2 combinations of the most widely used antibiotics against H. pylori. J99 reference strains and 19 clinical isolates of H. pylori with various antibiotic resistance phenotypes were used. Minimum inhibitory concentrations were carried out using the microdilution method in 96-well plates. The activity of 15 possible combinations of two antibiotics including amoxicillin, clarithromycin (CLA), levofloxacin, rifampicin, tetracycline, and metronidazole was determined for all strains by the checkerboard method. A mean fractional inhibitory concentration index (FICmean) was calculated for each combination and strain and the type of pharmacodynamic interaction was considered as synergic if FICmean ≤ 0.5, additive if 0.5 < FICmean ≤ 1, indifferent if 1 < FICmean < 4 or antagonistic if FICmean ≥ 4. Most of the 285 pharmacodynamic interactions tested with clinical strains were close to additivity (average FICmean = 0.89 [0.38-1.28]). No interaction was found to be antagonistic. When two antibiotics to which a strain was resistant were combined, the concentrations required to inhibit bacterial growth were higher than their respective breakpoints. The present results have shown that invitro, the different antibiotics used in therapeutics have additive effects. The addition of the effects of two antibiotics to which a strain was resistant was not sufficient to inhibit bacterial growth. In probabilistic treatment, the choice of antibiotics to combine should therefore be based on the local epidemiology of resistance, and on susceptibility testing in the case of CLA therapy, so that at least one antibiotic to which the strain is susceptible is used.

Efficacy of a Novel Antibiotic Drug Combination Toward Multidrug-Resistant Ocular Pathogens.

Antimicrobial resistance is a global health threat, compounded by the reduction in the discovery of new antibiotics. A repurposed drugs-based approach could provide a viable alternative for the treatment of multidrug-resistant (MDR) bacterial infections. In this study, we sought to evaluate the in vitro efficacy of a novel drug combination, polymyxin B/trimethoprim (PT) + rifampin on MDR isolates from patients with bacterial keratitis in India. Forty-three isolates, which included 20 Staphylococcus aureus , 19 Pseudomonas aeruginosa , 3 Pseudomonas stutzeri , and 1 Acinetobacter baumannii , were evaluated for their antibiotic resistance by minimum inhibitory concentration (MIC). Fractional Inhibitory Concentration Index (FICI) testing was performed to measure the antimicrobial impact of PT + rifampin in combination. Among S. aureus isolates, 100% were resistant to at least 1 antibiotic class, 12 (60%) were MDR, and 14 (70%) were classified as methicillin-resistant. Among the gram-negative isolates, >90% were classified as MDR. Fractional Inhibitory Concentration (FIC) testing revealed that PT + rifampin was effective in completely inhibiting growth of all isolates while also displaying additive or synergistic activity in approximately 70% of the strains. Mean FICI values were 0.753 ± 0.311 and 0.791 ± 0.369 for S. aureus and gram-negative isolates, respectively, and a >2-fold reduction in MIC was measured for both PT and rifampin when tested in combination versus alone. Our data demonstrate the ability of PT + rifampin to eliminate all isolates tested, even those conferring MDR, highlighting the promise of this drug combination for the treatment of bacterial keratitis.

In vitro activity of carvacrol, cinnamaldehyde and thymol combined with antifungals against Malassezia pachydermatis

Malassezia pachydermatis is an important opportunistic agent of dermatitis and otitis in dogs. M. pachydermatis is generally treated with topical therapies using combinations of antifungal, antimicrobial and anti-inflammatory agents. We investigated the in vitro activities of carvacrol (CRV), cinnamaldehyde (CIN) and thymol (THY) alone and in combination with antifungal agents (fluconazole, itraconazole, ketoconazole, clotrimazole, miconazole, terbinafine and nystatin) against M. pachydermatis. The assays were performed according to the Clinical and Laboratory Standards Institute (CLSI), using Sabouraud dextrose broth and checkerboard microdilution. The mean fractional inhibitory concentration index (FICI) showed primary synergies for the combinations carvacrol+nystatin, thymol+nystatin, and carvacrol+miconazole (80%). In conclusion, the results obtained indicate that the phytochemicals tested showed relevant in vitro anti-M. pachydermatis activity. Future in vivo experiments are needed to elucidate the safety and therapeutic potential of these combinations.

ANTIMICROBIAL ACTIVITY OF THUJA ORIENTALIS IN COMBINATION WITH CIPROFLOXACIN AGAINST PSEUDOMONAS AERUGINOSA

OBJECTIVES: To compare the combined antimicrobial effect of Thuja orientalis and Ciprofloxacin against Pseudomonas aeruginosa in vitro samples. METHODS: In-vitro antibacterial activity of plant-extracts was evaluated alone and in combination with ciprofloxacin against Pseudomonas aeruginosa using disc-diffusion susceptibility assay (Kirby Bauer method) and minimum inhibitory concentration (96 well broth microdilution method) following CLSI guidelines. Pseudomonas aeruginosa clinical strains were collected from Rehman Medical Institute (RMI) and Northwest General Hospital Peshawar, Pakistan and ATCC strains (no.9721) of this bacterium were collected from Agriculture University Peshawar. The organism was tested six times with crude extract and fractionation with different solvents such as n-hexane, chloroform, ethyl acetate and butanol at concentrations of 1, 4, 8, 12, 16, 20, 24, 30 and 36 mg/ml. The mean MIC and FICI (fractional inhibitory concentration index) was obtained to report the synergism. The data were analysed using SPSS version-21. RESULTS: In combination, methanolic crude extract, chloroform and butanol fraction showed synergistic effect at all tested concentrations against Pseudomonas aeruginosa (ATCC 9721 and clinical) except with 1, 4, 16 mg/ml concentrations. Ethyl acetate and aqueous fractions shows indifference and synergistic effect against Pseudomonas aeruginosa (ATCC 9721 and clinical) at different concentrations. The fractional inhibitory concentration index (FICI) ranged from 1.24 to 3.24 against Pseudomonas aeruginosa alone and in combination with ciprofloxacin. CONCLUSION: By disc diffusion method, this study shows synergistic effect against Pseudomonas aeruginosa in combination with ciprofloxacin. However, through minimum inhibitory concentration method, it shows antagonism and indifference but no synergistic effect against different fractions of plant.

Evaluation of in vitro activity of iclaprim in combination with other antimicrobials against pulmonary pathogens: a pilot study.

In this pilot study, the in vitro antimicrobial activity of iclaprim, a diaminopyrimidine, tested in combination with other antimicrobials against recent and common Gram-positive and Gram-negative respiratory pathogens, was examined by the checkerboard method. The range of minimal inhibitory concentrations (MICs) for iclaprim against all bacteria tested in the study was 0.03 to >128 µg ml−1. Iclaprim exhibited synergy with sulfamethoxazole against 11 of the 16 bacterial strains tested, with mean fractional inhibitory concentration index (FICI) values of 0.2–0.5. Synergy with sulfamethoxazole was demonstrated against all Gram-positive bacteria and selected Gram-negative bacteria. Neither synergy nor antagonism was observed for combinations of iclaprim with ampicillin, meropenem, tetracycline, levofloxacin, aztreonam, piperacillin/tazobactam, colistin, cefepime or gentamicin against any of the bacterial strains tested. The significant reduction in the MIC values observed with the combination of iclaprim and sulfamethoxazole demonstrates that this regimen could be effective against common Gram-positive and selected Gram-negative respiratory bacteria.

A bedaquiline/clofazimine combination regimen might add activity to the treatment of clinically relevant non-tuberculous mycobacteria.

Non-tuberculous mycobacteria (NTM) infections are hard to treat. New antimicrobial drugs and smarter combination regimens are needed. Our aim was to determine the in vitro activity of bedaquiline against NTM and assess its synergy with established antimycobacterials. We determined MICs of bedaquiline for clinically relevant NTM species and Mycobacterium tuberculosis by broth microdilution for 30 isolates. Synergy testing was performed using the chequerboard method for 22 reference strains and clinical isolates of Mycobacterium abscessus (MAB) and Mycobacterium avium complex (MAC). Time-kill kinetics (TK) assays with resistance monitoring of bedaquiline alone and combined with clofazimine were performed for MAB CIP 104536 and M. avium ATCC 700898; bedaquiline/clarithromycin combinations were evaluated against M. avium ATCC 700898. Interactions were assessed for TK experiments based on Bliss independence. Bedaquiline had modest activity against tested NTM, with MICs between <0.007 and 1 mg/L. Bedaquiline showed no interaction with tested drugs against MAB or MAC. Lowest mean fractional inhibitory concentration index (FICI) values were 0.79 with clofazimine for MAB and 0.97 with clofazimine and 0.82 with clarithromycin for MAC. In TK assays, bedaquiline showed a bacteriostatic effect. Clofazimine extended the bacteriostatic activity of bedaquiline against MAB and yielded a slight bactericidal effect against M. avium. The bedaquiline/clofazimine combination slowed emergence of bedaquiline resistance for M. avium but promoted it for MAB. Relative to Bliss independence, bedaquiline/clofazimine showed synergistic interaction over time for MAB and no interaction for M. avium and bedaquiline/clarithromycin showed antagonistic interaction for M. avium. Following these in vitro data, a bedaquiline/clofazimine combination might add activity to MAB and MAC treatment. The bedaquiline/clarithromycin combination might have lower activity compared with bedaquiline alone for MAC treatment.

In Vitro Synergy Testing of Gentamicin, an Old Drug Suggested as Future Treatment Option for Gonorrhoea, in Combination With Six Other Antimicrobials Against Multidrug-Resistant Neisseria gonorrhoeae Strains.

Emergence of multidrug-resistant (MDR) and extensively drug-resistant (XDR) Neisseria gonorrhoeae is a serious concern and combination therapy has been recommended to delay the onset of treatment failures. Gentamicin, an old and inexpensive antibiotic, is recommended in combination with azithromycin for treatment failures cases with the first-line regimen as per the latest Centers for Disease Control and Prevention sexually transmitted disease treatment guidelines. However, not much literature is available on in vitro and in vivo efficacy of this combination. Therefore, this study was carried out to evaluate the in vitro synergy of gentamicin in combination with azithromycin and 5 other antimicrobials. In vitro synergy of gentamicin in combination with cefixime, ceftriaxone, spectinomycin, azithromycin, moxifloxacin, and ertapenem was determined by Etest for 75 N. gonorrhoeae strains, of which 65 were MDR and one was XDR. Fractional inhibitory concentration index (FICI) of ≤0.5 and >4.0 denoted synergy and antagonism respectively. Maximum efficacy of gentamicin was observed in combination with ertapenem (geometric mean FICI, 0.56) followed by cefixime (FICI, 0.87). There was no antagonism for both these combinations. However, antagonism was demonstrated in 5.3%, 8%, 8%, and 10.7% strains when gentamicin was paired with spectinomycin (FICI, 1.34), ceftriaxone (FICI, 1.13), azithromycin (FICI, 1.49), and moxifloxacin (FICI, 1.30), respectively. The findings suggest that gentamicin significantly enhances the in vitro therapeutic potency of ertapenem and cefixime which will be potentially effective to control the spread of MDR and XDR N. gonorrhoeae. The study warrants more in vitro studies and clinical trials for gentamicin + azithromycin and other 3 combinations because of considerable antagonism.

7,10-Epoxyoctadeca-7,9-dienoic Acid: A Small Molecule Adjuvant That Potentiates β-Lactam Antibiotics Against Multidrug-Resistant Staphylococcus aureus.

The emergence of methicillin-resistant Staphylococcus aureus (MRSA) infections with multi-drug resistance needs effective and alternative control strategies. In this study we investigated the adjuvant effect of a novel furan fatty acid, 7,10-epoxyoctadeca-7,9-dienoic acid (7,10-EODA) against multidrug-resistant S. aureus (MDRSA) strain 01ST001 by disc diffusion, checker board and time kill assays. Further the membrane targeting action of 7,10-EODA was investigated by spectroscopic and confocal microscopic studies. 7,10-EODA exerted synergistic activity along with β-lactam antibiotics against all clinical MRSA strains, with a mean fractional inhibitory concentration index below 0.5. In time-kill kinetic study, combination of 7,10-EODA with oxacillin, ampicillin, and penicillin resulted in 3.8-4.2 log10 reduction in the viable counts of MDRSA 01ST001. Further, 7,10-EODA dose dependently altered the membrane integrity (p<0.001) and increased the binding of fluorescent analog of penicillin, Bocillin-FL to the MDRSA cells. The membrane action of 7,10-EODA further facilitated the uptake of several other antibiotics in MDRSA. The results of the present study suggested that 7,10-EODA could be a novel antibiotic adjuvant, especially useful in repurposing β-lactam antibiotics against multidrug-resistant MRSA.

Evaluating synergy between marbofloxacin and gentamicin in Pseudomonas aeruginosa strains isolated from dogs with otitis externa.

The aim of this study was to determine antimicrobial susceptibility of Pseudomonas aeruginosa strains to marbofloxacin and gentamicin, and investigate the possible synergistic, additive, indifferent or antagonistic effects between the two agents. P. aeruginosa strains can develop resistance quickly against certain antibiotics if used alone, thus the need emerges to find synergistic combinations. A total of 68 P. aeruginosa strains isolated from dogs were examined. In order to describe interactions between marbofloxacin and gentamicin the checkerboard microdilution method was utilized. The MICs (minimum inhibitory concentrations) for marbofloxacin and gentamicin were in the range 0.25-64 mg/L and 0.25-32 mg/L, respectively. The combination of marbofloxacin and gentamicin was more effective with a MIC range of 0.031-8 mg/L and a MIC90 of 1 mg/L, compared to 16 mg/L for marbofloxacin alone and 8 mg/L for gentamicin alone. The FIC (fractional inhibitory concentration) indices ranged from 0.0945 (pronounced synergy) to 1.0625 (indifference). Synergy between marbofloxacin and gentamicin was found in 33 isolates. The mean FIC index is 0.546, which represents a partial synergistic/additive effect close to the full synergy threshold. In vitro results indicate that marbofloxacin and gentamicin as partially synergistic agents may prove clinically useful in combination therapy against P. aeruginosa infections. Although marbofloxacin is not used in the human practice, the interactions between fluoroquinolones and aminoglycosides may have importance outside the veterinary field.

Determination of in vitro synergy for dual antimicrobial therapy against resistant Neisseria gonorrhoeae using Etest and agar dilution

In response to antimicrobial resistance of Neisseria gonorrhoeae to last-resort extended-spectrum cephalosporins, combination therapy of azithromycin+ceftriaxone is now recommended. Dual therapy can be effective to treat monoresistant strains as well as multidrug-resistant strains, preferably employing the effect of in vitro synergy. As reports on in vitro synergy of azithromycin+ceftriaxone in N. gonorrhoeae are conflicting, in this study an evaluation of this combination was performed using a cross-wise Etest method and agar dilution. Synergy was defined as a fractional inhibitory concentration index (FICI) of ≤0.5. To identify other dual treatment options for gonorrhoea, in vitro synergy was evaluated for 65 dual antimicrobial combinations using Etest. Azithromycin, cefixime, ceftriaxone, colistin, ertapenem, fosfomycin, gentamicin, minocycline, moxifloxacin, rifampicin, spectinomycin and tigecycline were screened for synergy in all possible combinations. No synergy or antagonism was found for any of the 65 combinations. The geometric mean FICI ranged from 0.82 to 2.00. The mean FICI of azithromycin+ceftriaxone was 1.18 (Etest) and 0.55 (agar dilution). The difference between both methods did not result in a difference in interpretation of synergy. Ceftriaxone-resistant strain F89 was tested in all combinations and no synergy was found for any of them. Most importantly, the ceftriaxone minimum inhibitory concentration of F89 was not decreased below the breakpoint with any concentration of azithromycin.

O21.4 In Vitro Synergy Determination For Dual Antibiotic Therapy Against Resistant Neisseria Gonorrhoeae Using Etest® and Agar Dilution

BackgroundAntimicrobial resistance (AMR) of Neisseria gonorrhoeae (Ng) is increasing. With recent resistance to last resort extended-spectrum cephalosporins, combination therapy of azithromycin (AZ) and ceftriaxone (TX) is now widely recommended. We...

In vitro activities of antimicrobial combinations against clinical isolates of Neisseria gonorrhoeae

The Centers for Disease Control and Prevention (CDC) now recommend combination therapy with ceftriaxone 250 mg plus azithromycin (AZM) 1 g as a first-line regimen for gonorrhea because the increase of Neisseria gonorrhoeae resistant to multiple antimicrobial agents. However, reports on the in vitro activity of antimicrobial combinations against clinical isolates of N. gonorrhoeae are very rare. In the present study, a checkerboard method was utilized to examine the in vitro activity of ceftriaxone (CTRX), cefodizime (CDZM), spectinomycin (SPCM), or gentamicin (GM) in combination with AZM against 25 clinical isolates of N. gonorrhoeae. The SPCM + AZM combination demonstrated the lowest mean fractional inhibitory concentration index (FICI) of 0.69, followed by the CDZM + AZM combination (mean FICI, 0.75), the CTRX + AZM combination (mean FICI, 0.81), and the GM + AZM combination (mean FICI, 0.83). Additivity/indifference effect was detected for the SPCM + AZM combination, the CDZM + AZM combination, the CTRX + AZM combination, and the GM + AZM combination, against 96%, 72%, 92%, and 100% of the isolates, respectively. There was no antagonism for any of the antimicrobial combinations against the 25 N. gonorrhoeae isolates. These results suggest that the antimicrobial combinations may be worthy of clinical evaluation as an alternative regimen for gonococcal infections caused by antimicrobial-resistant strains.

Combination therapy for gonorrhoea: in vitro synergy testing

Antimicrobial resistance in Neisseria gonorrhoeae is an increasing problem worldwide and combinations of antimicrobial agents have been recommended to delay the onset of treatment failures. The objective of this study was to obtain in vitro data on the activity of current (ceftriaxone or cefixime plus azithromycin) and alternative (gentamicin plus azithromycin) regimens. A panel of 64 gonococcal isolates displaying various cefixime MICs was selected for inclusion in the study. Determination of the activities of the antimicrobial combinations of ceftriaxone, cefixime or gentamicin with azithromycin was performed using the agar dilution method and subsequent calculation of the fractional inhibitory concentration index (FICI) values. No antagonism for any of the antimicrobial combinations was detected among the 64 gonococcal isolates. When cefixime or ceftriaxone was combined with azithromycin all isolates showed additivity/indifference with a mean FICI of 2.0. All gonococcal isolates also showed additivity/indifference with the antimicrobial combination of gentamicin with azithromycin, but with a lower mean FICI of 1.7. No significant difference in the mean FICI between isolates fully susceptible to cefixime and isolates with decreased susceptibility to cefixime was observed. The results obtained support the gonorrhoea treatment currently recommended in the UK national guidelines and suggest that gentamicin with azithromycin could be a future treatment option. The in vivo activity and efficacy of these combinations remain unknown and prospective clinical studies should be addressed.

In Vitro Activity of Antiretroviral Drugs against Plasmodium falciparum

Malaria and HIV infection are both very common in many developing countries. With the increasing availability of therapy for HIV infection, it was of interest to determine whether antiretroviral drugs exert antimalarial effects. We therefore tested the in vitro activity of 19 antiretroviral drugs against the W2 and 3D7 strains of Plasmodium falciparum at concentrations up to 50 μM. None of 5 tested nucleoside reverse transcriptase inhibitors demonstrated activity. Two nonnucleoside reverse transcriptase inhibitors, efavirenz (mean 50% inhibitory concentration [IC(50)] of 22 to 30 μM against the two strains) and etravirine (3.1 to 3.4 μM), were active; nevirapine was not active. Also active were the fusion inhibitor enfuvirtide (6.2 to 7.9 μM) and the entry inhibitor maraviroc (15 to 21 μM). Raltegravir was not active. However, for all active drugs mentioned above, the IC(50)s were considerably greater than the concentrations achieved with standard dosing. The effects most likely to be clinically relevant were with HIV protease inhibitors. Of the tested compounds, activity was seen with lopinavir (2.7 to 2.9 μM), atazanavir (3.3 to 13.0 μM), saquinavir (5.0 to 12.1 μM), nelfinavir (6.5 to 12.1 μM), ritonavir (9.5 to 10.9 μM), tipranavir (15.5 to 22.3 μM), and amprenavir (28.1 to 40.8) but not darunavir. Lopinavir was active at levels well below those achieved with standard dosing of coformulated lopinavir-ritonavir. Lopinavir also demonstrated modest synergy with the antimalarial lumefantrine (mean fractional inhibitory concentration index of 0.66 for W2 and 0.53 for 3D7). Prior data showed that lopinavir-ritonavir also extends the pharmacokinetic exposure of lumefantrine. Thus, when used to treat HIV infection, lopinavir-ritonavir may have clinically relevant antimalarial activity and also enhance the activity of antimalarials.

In vitro activity of sulphamethoxazole/trimethoprim and sulfadoxine/pyrimethamine againstChlamydia trachomatis SA2f in McCoy cell culture

Chequerboard titrations of sulphamethoxazole/trimethoprim and sulfadoxine/pyrimethamine were performed against Chlamydia trachomatis (strain SA2f) using McCoy cell monolayers in vials. The experiments were continued for ten passages each. The mean fractional inhibitory concentration index for each combination was calculated. Results demonstrated synergistic activity between sulphamethoxazole and trimethoprim, and between sulfadoxine and pyrimethamine.

Synergistic interaction in vitro with use of three antibiotics simultaneously against Pseudomonas maltophilia.

An abbreviated three-dimensional checkerboard titration method was devised to determine whether synergistic interaction of three antimicrobial agents could be found against multidrug-resistant bacteria. Pseudomonas maltophilia was used as the test organism because of its resistance to most commercially available antimicrobial agents, including those active against Pseudomonas aeruginosa. Three-dimensional isobolograms with concave surfaces were formed when synergy occurred. Triple combinations of gentamicin-carbenicillin-rifampin (mean fractional inhibitory concentration index, 0.32) and trimethoprim/sulfamethoxazole-carbenicillin-rifampin (mean fractional inhibitory concentration index, 0.18) were consistently synergistic against 14 clinical isolates of P. maltophilia.