Fractional Inhibitory Concentration Index Range Research Articles

In Vitro Comparison of Aztreonam/Amoxicillin-Clavulanate Versus Aztreonam/Ceftazidime-Avibactam on Ceftazidime-Avibactam Resistant Stenotrophomonas maltophilia.

We investigated the in vitro susceptibility of ceftazidime-avibactam (CZA) resistant Stenotrophomonas maltophilia to the associations aztreonam/amoxicillin-clavulanate (ATM-AMC) and ATM-CZA. Forty clinical isolates of S. maltophilia recovered from sputum samples of 40 cystic fibrosis people were selected from the collection of the Nantes University Hospital, based on their resistance to CZA. Minimum inhibitory concentrations (MICs) of ATM-CZA and ATM-AMC were determined for each isolate by an Etest strip superposition method, and by Etest for each individual antibiotic. MICs of CZA, ATM, and AMC ranged from 12 to ≥256, ≥256, and 16 to ≥256 mg/L, respectively. Synergistic effects were observed with the ATM-CZA combination for all isolates (fractional inhibitory concentration index range of 0.01 to 0.27), with combination MICs ranging from 0.75 to 16 mg/L (MIC50/90 = 3/12 mg/L), corresponding to a decrease of at least 16-folds in the MIC of ATM. In 23 (57.5%) S. maltophilia isolates, the association of AMC to ATM was also synergistic and combination MICs were ≤16 mg/L (EUCAST breakpoint for ATM resistance in Pseudomonas aeruginosa). Our results show that ATM-CZA or ATM-AMC could be alternative therapeutic options against some highly resistant S. maltophilia. This encourages further experimental studies, in particular time-kill analyses, and clinical trials to delineate conditions required for use of these combinations in practice.

1597. Ceftolozane-Tazobactam and Meropenem Synergy Testing Against Multi-Drug and Extensively-Drug Resistant Pseudomonas aeruginosa

BackgroundMultidrug-resistant (MDR) and extensively drug-resistant (XDR) Pseudomonas aeruginosa (PA) have limited therapeutic options for treatment. Ceftolozane/tazobactam is a newer anti-pseudomonal drug effective against resistant PA infections, however resistance against this drug has now also developed and is increasing. In this study, we explored the combination of ceftolozane/tazobactam (CT) and meropenem (MP) as a possible effective regimen against MDR and XDR PA.MethodsWe obtained 33 non-duplicate isolates of MDR and XDR PA grown from blood, urine and respiratory samples collected from patients admitted between 2015 and 2019 at our two affiliate teaching hospitals. MDR PA was defined as resistance to 3 or more classes of anti-pseudomonal antibiotics, and XDR PA as resistance to all but two or less classes of anti-pseudomonal antibiotics. Antimicrobial preparations of both MP and CT were made according to manufacturer instructions. Susceptibility testing was performed using the checkerboard method in accordance to CLSI guidelines (CLSI M100, 2017). The ATCC 27853 strain of PA used as control. Synergy, additive effect, indifference and antagonism were defined as FIC (fractional inhibitory concentration) indices of ≤0.5, >0.5 to <1, >1 to <4, and >4, respectively.ResultsThirteen (39%) of 33 PA isolates were classified as XDR, while 20 (61%) PA isolates were MDR. All isolates were resistant to MP (MIC50 >32 ug/mL), while only 2 (6%) isolates were susceptible to CT (MIC50 64 ug/mL). A synergistic effect was seen in 9 (27.3%) of PA isolates (FIC index range 0.28 to 0.5)— 2 of which were XDR PA, and 7 were MDR PA. An additive effect was seen in 12 (36.4%), with indifference seen in 12 (36.4%) of isolates. In this study, no antagonism was seen when CT and MP were combined.ConclusionWhen used in combination, CT and MP can exert a synergistic effect against MDR and XDR PA. Additive effect and indifference can also be seen when both antibiotics were used. Moreover, there was no antagonism seen when both antibiotics were combined. This study shows that the use of CT and MP in combination may be an option against XDR and MDR PA infections.Disclosures All Authors: No reported disclosures

Sclerotiorin: a Novel Azaphilone with Demonstrated Membrane Targeting and DNA Binding Activity against Methicillin-Resistant Staphylococcus aureus

The emergence of multi-drug resistant, pathogenic methicillin-resistant Staphylococcus aureus (MRSA) is a threat to global health and has created a need for novel functional therapeutic agents. In this study, we evaluated the underlying mechanisms of the anti-MRSA effect of an azaphilone pigment, sclerotiorin (SCL) from Penicillium sclerotiorum. The antimicrobial activity of SCL was evaluated using agar disc diffusion, broth microdilution, time-kill assays and biophysical studies. SCL exhibits selective activity against Gram positive bacteria including MRSA (range, MIC = 128-1028 μg/ml) and exhibited rapid bactericidal action against MRSA with a > 4 log reduction in colony forming units within three hours of administration. Biophysical studies, using fluorescent probes and laser or electron microscopy, demonstrated a SCL dose-dependent alternation in membrane potential (62.6 ± 5.0.4% inhibition) and integrity (> 95 ± 2.3%), and the release of UV260 absorbing materials within 60 min (up to 3.2 fold increase, p < 0.01) of exposure. Further, SCL localized to the cytoplasm and hydrolyzed plasmid DNA. While in vitro checkerboard studies revealed that SCL potentiated the antimicrobial activity of topical antimicrobials such as polymixin, neomycin, and bacitracin (Fractional Inhibitory Concentration Index range, 0.26-0.37). Taken together these results suggest that SCL targets the membrane and DNA of MRSA to facilitate its anti- MRSA antimicrobial effect.

In Vitro Interaction of Geldanamycin with Triazoles and Echinocandins Against Common and Emerging Candida Species.

The aim of this study was to determine the in vitro interactions of geldanamycin (Hsp90-inhibitor) with triazoles and echinocandins against common and emerging Candida species. Twenty clinically important Candida strains comprising C. auris, C. albicans, C. parapsilosis, and C. glabrata (each five strains) were included. In vitro interactions of geldanamycin with fluconazole, itraconazole, caspofungin and anidulafungin were determined using a checkerboard method. The results were interpreted as synergistic, indifferent and antagonistic based on the fractional inhibitory concentration index (FICI). In vitro combination of fluconazole with geldanamycin resulted in synergistic effect against C. albicans (100%), C. glabrata (80%) and C. parapsilosis (80%) (FICI range 0.009-0.5), while indifferent interactions were obtained against C. auris (FICI range 1.5-2). The overall minimum inhibitory concentration (MIC) range of fluconazole against C. albicans, C. glabrata and C. parapsilosis reduced from 16-256 to 0.25-64mg/L when combined with geldanamycin. Regarding the synergistic effect of geldanamycin with itraconazole against all strains of C. albicans, C. glabrata and C. parapsilosis (FICI range 0.009-0.375), the MIC range of this antifungal was reduced from 0.125-32mg/L when tested alone, to 0.03-1mg/L. Combinations of geldanamycin with fluconazole and itraconazole against C. auris, as well as combination of geldanamycin with caspofungin and anidulafungin against all studied Candida species, resulted in indifferent effects. No antagonism was observed. Simultaneous targeting of Hsp90 and lanosterol 14-α demethylase seems an effective approach against C. albicans, C. glabrata and C. parapsilosis. However, this combination is ineffective against the emerging pathogen C. auris.

In vitro interactions of crocin with fluconazole against Candida isolates.

Background and Purpose:The incidence of invasive fungal infections has been increased in recent years. The growing use of azole drugs for prophylactic and therapeutic purposes has resulted in the gradual emergence of azole-resistant species. Accordingly, the introduction of a new strategy to improve the management of Candida infections is an urgent need. Regarding this, the present study was performed to evaluate the antifungal activities of crocin (Cro) alone and in combination with fluconazole.Materials and Methods: This study was conducted on 50 clinical isolates of four different Candida species. The identity of the isolates was confirmed using the internal transcribed spacer identification system. The interactions of Cro with fluconazole were investigated using a microdilution checkerboard method based on the Clinical and Laboratory Standards Institute reference technique with 96-well microtiter plates. Furthermore, the assessment of the interaction of drug combinations was accomplished using the fractional inhibitory concentration index (FICI) based on the Loewe additivity theory. Results:According to the results, Cro alone showed a relatively high MIC50 value (1 g/ml) against Candida species. Our results demonstrated indifferent interactions between Cro and fluconazole with a FICI range of 0.5-4 against Candida strains.Conclusion:The high MIC value for Cro against Candida species indicated its failure to show appropriate antifungal activity against this species. The MIC of this agent was not significantly reduced even by the addition of fluconazole. Therefore, other mechanisms which are not related to the mechanism of azole drugs are involved at high concentration of Cro.

Effect of 2-Phenylethanol as Antifungal Agent and Common Antifungals (Amphotericin B, Fluconazole, and Itraconazole) on Candida Species Isolated from Chronic and Recurrent Cases of Candidal Vulvovaginitis.

The antifungal effects of 2-phenylethanol are clearly visible through its intervention in Candida morphogenesis. Chronic and recurrent vulvovaginitis, however, does not respond to this standard experimental therapy; therefore, the study presented in this article investigated the effect of common antifungal drugs (amphotericin B [AMB], fluconazole [FLU], and itraconazole [ITC]), in combination with 2-phenylethanol, on the Candida species isolated from cases of chronic and recurrent vulvovaginitis, thereby allowing the recommendation of a more appropriate treatment option. Forty isolates from patients with chronic and recurrent vaginal candidiasis were investigated in this experimental study. The specimens were examined by direct microscopy, culturing, and PCR to identify the species. The antifungal effects of 2-phenylethanol and conventional drugs, both alone and in combination, were determined in duplicate. Finally, the findings were analyzed. In this study, 40 strains of Candida species were identified, whose agents were Candida albicans (95%) and Candida africana (5%). After 48 h, the minimum inhibitory concentration (MIC) range of the 2-phenylethanol was 800-3,200 μg/mL. Also, in the final study on the MIC levels of common antifungal drugs, AMB (0.42 μg/mL) had the lowest MIC, FLU (40.51 μg/mL) had the highest MIC, and the combination of ITC and 2-phenylethanol had the lowest fractional inhibitory concentration index (FICI) of any of the combinations (FICI range, 0.26-1.03). Combining FLU and ITC with 2-phenylethanol can effectively increase their antifungal effect.

In vitro efficacy of 21 dual antimicrobial combinations comprising novel and currently recommended combinations for treatment of drug resistant gonorrhoea in future era.

BackgroundRecent WHO guidelines recommend dual therapy with ceftriaxone or cefixime plus azithromycin for gonorrhea. Azithromycin in combination with gentamicin or spectinomycin has been recommended in treatment failure cases. Due to emergence of multi-drug resistant (MDR) and extensively-drug resistant (XDR) Neisseria gonorrhoeae strains, it is important to look for efficacy of these combinations and also of others that might be used in future. Therefore, we aimed to evaluate in vitro synergy of 21 dual combinations including current and alternative WHO recommended treatment regimens and other dual combinations.Methods and findingsThe potential utility of in-vitro interactions of 21 combinations was investigated against 95 N. gonorrhoeae strains including 79 MDR and one XDR strain collected during March 2013 to July 2017 and fractional inhibitory concentration index (FICI) was calculated. These 21 combinations comprised of two WHO currently recommended (cefixime+azithromycin, ceftriaxone+azithromycin); two WHO recommended in treatment failure cases (azithromycin+gentamicin, spectinomycin+azithromycin) and other 17 combinations.ResultsFICI of the four WHO recommended antimicrobial combinations were higher (>1.0) than the five novel combinationbreeds (FICI range 0.603–0.951) in the study i.e. gentamicin+ertapenem, moxifloxacin+ertapenem, spectinomycin+ertapenem, azithromycin+ moxifloxacin, cefixime+gentamicin. No antagonistic effect of the above four WHO recommended combinations except spectinomycin+azithromycin (FICI = 4.25) was observed for the XDR strain. Out of above five novel combinations, four combinations produced high synergistic effects in overall 95 strains and also for the XDR strain with FICI of 0.13 to 0.38. Antagonistic effects varying from 3.2 to 12.6% were observed for 10 out of 21 tested combinations (azithromycin in combination with gentamicin and spectinomycin; ceftriaxone with moxifloxacin, gentamicin, spectinomycin and ertapenem; spectinomycin with moxifloxacin and gentamicin; cefixime and gentamicin combination with moxifloxacin).ConclusionWHO recommended cefixime+azithromycin, ceftriaxone+azithromycin combinations having no antagonism indicates their continuing clinical utility. Highest antagonism without any synergistic effect for the WHO recommended spectinomycin+azithromycin in treatment failure cases suggests that this combination should be evaluated further both in vitro and in vivo. Highest synergistic or additive effect without any antagonistic effect of the above five novel combinations suggests that these may be recommended for treatment in future.

&amp;lt;i&amp;gt;In Vitro&amp;lt;/i&amp;gt; Activity of Colistin and Vancomycin or Azithromycin Combinations on Extensively Drug Resistant &amp;lt;i&amp;gt;Acinetobacter baumannii&amp;lt;/i&amp;gt; Clinical Isolates

Background: Extensively drug resistant Acinetobacter baumannii (XDR-AB) presents an increasing challenge to health care in Egypt as they are among the most common bacteria isolated in hospital setting. Treatment of such infections usually involves the use of antimicrobial agents in combination. Various combinations have been proposed, with colistin serving as the backbone in many of them even for colistin resistant isolates. Aim: The study was conducted in order to test the in vitro combined effects of colistin and vancomycin or azithromycin against (XDR-AB) causing infections at Alexandria Main University Hospital in Egypt, in an attempt to detect the possibility of a beneficial combination therapy. Material/Methods: Thirty XDR-AB clinical isolates were included in the study. Antibiotic susceptibility testing was performed using automated Vitek 2 compact system and disc diffusion method. Colistin antibiotic disc diffusion test was compared with broth microdilution method. Organisms were also tested against colistin and vancomycin or azithromycin in combination using checkerboard synergy test and FICI (Fractional Inhibitory Concentration Index) was calculated. Synergy was defined as a FICI of ≤0.5. Results: On comparing the two methods used to detect susceptibility to colistin to broth microdilution for MIC (minimum inhibitory concentration) determination, as a reference method, the Vitek showed 100% categorical agreement (CA), on the other hand, the disc diffusion showed CA of 93% with very major errors. Synergy was detected for all isolates (100%) when combining colistin with vancomycin (FICI mean = 0.08). As for azithromycin, 21 strains had FICI range from 0.7 to 1.001, denoting indifference; the remaining 9 strains showed synergy with FICI range from 0.06 to 0.241. The mean colistin/azithromycin FICI was 0.71 for the 30 isolates. Conclusion: These findings suggest that regimens containing vancomycin may confer therapeutic benefit for infection due to XDR-AB; however, other methods (time-kill assay) should be used to confirm such synergy. Furthermore, the optimal combination treatment for serious XDR-AB infection should be addressed in a prospective clinical trial.

Rifaximin combined with polymyxins: A potential regimen for selective decontamination of multidrug-resistant bacteria in the digestive tract?

Selective decontamination of the digestive tract (SDD) using combinations of oral non-absorbable antibiotics has been proposed as a means of preventing multidrug-resistant (MDR) infections. The minimum inhibitory concentrations (MICs) of rifaximin (RIFAX) were determined against 262 Gram-negative and Gram-positive bacterial isolates by broth microtitre assay. Rifampicin (RIF) was used as a comparator in the analysis. Synergistic interactions between RIFAX and polymyxin B (PMB) were assessed by using the chequerboard method and calculating the fractional inhibitory concentration index (FICI). The antimicrobial activities of both RIFAX and RIF were similar with little variation in the overall MIC distributions for Gram-negative non-fermenters and Gram-positive bacteria. However, against Enterobacteriaceae higher MICs (>16mg/L) were observed for RIFAX than for RIF (50% vs 27%). Amongst the 262 isolates tested, 100 could be considered resistant to RIFAX. Overall, the combination of RIFAX and PMB was more active against all of the isolates tested compared with either drug alone, with reductions of 2-11 doubling dilutions in individual MICs. Potent synergy was observed with the RIFAX+PMB combination using FICI criteria (FICI range 0.02-0.5). The data presented here suggest that combination therapy may be significantly more effective against isolates with RIFAX and/or PMB resistance and could be considered as part of a SDD regimen aimed at reducing enteric carriage of MDR pathogens in colonised and infected patients.

In Vitro Synergism Testing of Three Antimicrobial Agents against Multidrug- Resistant and Extensively Drug-Resistant Mycobacterium tuberculosis by Checkerboard Method

Objective: In view of the national key project for infectious diseases “the retreatment research of tuberculosis”, we determined the in vitro anti-mycobacterial activity of four drugs in the treatment, pasiniazid (Pa), moxifloxacin (Mfx), Rifabutin (Rfb) and rifapentini (Rft) in combination to multidrug-resistant and extensively drug-resistant Mycobacterium tuberculosis. Method: Three-dimensional checkerboard in Middlebrook 7H9 broth microdilutions was used to detect the fractional inhibitory concentration index (FICI) of anti-tuberculosis drug combination (MfxPa, MfxPaRfb and MfxPaRft) to twenty clinical isolates of Mycobacterium tuberculosis, including ten multidrug-resistant isolates and ten extensively drug-resistant isolates. The test results were interpreted by calculating the FICI to judge the in vitro synergy, with FICI <0. 5 and FICI <0.75 as the basis of two drugs and three drugs have synergy. Results: The FICI range of MfxPa combination for multidrug-resistant isolates and ten extensively drug-resistant isolates was 0.28-1, only three isolates <0.5, showed synergistic effect. The FICI range of MfxPaRfb combination for ten isolates of multidrug-resistant isolates was from 0.31 to 1.25, two isolates <0.75, showed synergistic effect and for ten isolates of extensively drug-resistant isolates was from 0.53 to 1.25, five isolates <0.75, showed synergistic effect. The FICI range of MfxPaRft combination for ten isolates of multidrug-resistant isolates was from 0.16 to 0.655, all showed synergistic effect and for ten isolates of extensively drug-resistant isolates was from 0.34 to 1.68, five isolates <0.75, showed synergistic effect. Conclusion: The synergism of MfxPa combination was poor. When a third agent (Rfb or Rft) was added to the combination, the synergistic effect was better. The MfxPaRft combination showed better synergism than MfxPaRfb combination.

Azole-synergistic anti-candidal activity of altenusin, a biphenyl metabolite of the endophytic fungus Alternaria alternata isolated from Terminalia chebula Retz.

In this study, a tropical endophytic fungus, Alternaria alternata Tche-153 was isolated from a Thai medicinal plant Terminalia chebula Rezt. The ethyl acetate extract prepared from the fermentation broth exhibited significant ketoconazole-synergistic activity against Candida albicans. Bioassay-directed fractionation of the ethyl acetate extract led to the isolation of altenusin (1), isoochracinic acid (2), and altenuic acid (3) together with 2,5-dimethyl-7-hydroxychromone (4). Using the disc diffusion method and the microdilution chequerboard technique, only altenusin (1) in combination with each of three azole drugs, ketoconazole, fluconazole or itraconazole at their low sub-inhibitory concentrations exhibited potent synergistic activity against C. albicans with the fractional inhibitory concentration index range of 0.078 to 0.188. This first discovery of altenusin (1) as a new azole-synergistic prototype possessing a biphenyl structure is of significance for further development of new azole-synergists to treat invasive candidiasis.

In vitro activity of miltefosine as a single agent and in combination with voriconazole or posaconazole against uncommon filamentous fungal pathogens

Antifungal treatment of uncommon filamentous fungal infections is problematic. This study determined the in vitro susceptibility of miltefosine, as a single agent and in combination with posaconazole or voriconazole, against these pathogens. Susceptibility to miltefosine of 34 uncommon filamentous fungi was tested using CLSI broth microdilution M38-A2 methodology. Twenty isolates were studied for potential synergy using miltefosine/posaconazole and miltefosine/voriconazole combinations and the chequerboard microdilution assay. MICs of miltefosine were high (in general, >8 mg/L) for most isolates compared with amphotericin B, echinocandins and the azoles. Miltefosine had greatest activity against Scedosporium spp., Lichtheimia corymbifera and Rhizomucor sp. (MICs ≤ 4 mg/L). Miltefosine in combination either with posaconazole or voriconazole demonstrated synergy [fractional inhibitory concentration index (FICI) ≤ 0.5] in 12 instances (11 isolates): miltefosine/posaconazole combinations were synergistic against 3 of 4 Fusarium oxysporum strains (FICI range 0.37-0.5) and 5 of 10 mucormycete strains (FICI range 0.06-0.5). The combination of voriconazole with miltefosine showed synergy against one Scedosporium prolificans isolate and three mucormycetes-a single strain each of L. corymbifera, Rhizopus oryzae and Rhizomucor sp. No antagonism was observed. Miltefosine demonstrated synergy in 8/20 (40%) and 4/20 (20%) instances when combined with posaconazole and voriconazole, respectively. Synergy was most often observed against F. oxysporum and the mucormycetes. Study of miltefosine/azole combinations as a novel antifungal approach is indicated.

In vitro Activity of Azithromycin in Combination with Amikacin, Ceftazidime, Ciprofloxacin or Imipenem against Clinical Isolates of Acinetobacter baumannii

The in vitro activity of the two-drug combinations of azithromycin with amikacin, ceftazidime, ciprofloxacin or imipenem against five clonally unrelated strains of Acinetobacter baumannii were evaluated. Synergy studies were performed by the checkerboard microtiter method. The fractional inhibitory concentration (FIC) index was calculated for each drug combination. None of the four combinations tested was antagonistic. The combination of azithromycin and ceftazidime was synergistic (FIC index ≤0.5) for one strain and partially synergistic (FIC index 0.75) for another strain. An additive effect (FIC index = 1) was observed for the combinations of azithromycin with imipenem (two strains) or ceftazidime (one strain). The activities of the other combinations were indifferent (FIC index range from 1.5 to 2.5). It is concluded that azithromycin combined with ceftazidime has moderate synergistic activity against some multiresistant A. baumannii.