In vitro evaluation of the antimicrobial activity of meropenem in combination with polymyxin B and gatifloxacin against Pseudomonas aeruginosa and Acinetobacter baumannii

The antimicrobial activity of meropenem combined with either polymyxin B or gatifloxacin was evaluated by the checkerboard method against Pseudomonas aeruginosa (10 strains) and Acinetobacter baumannii (10 strains). In addition, the triple combination of polymyxin B, gatifloxacin, and meropenem was also studied as well as the polymyxin B and gatifloxacin combination. A partial synergism interaction between meropenem and polymyxin B was observed for 80% of the A. baumannii strains. In contrast, this combination showed an indifferent effect for 80% of the P. aeruginosa strains tested. The combination of meropenem and gatifloxacin showed synergism only for two strains of A. baumannii, and partial synergism and additive effect for seven strains and indifference for four strains of both species. For the strains of P. aeruginosa, the double combination of polymyxin B and gatifloxacin and the triple combination of meropenem, polymyxin B and gatifloxacin were indifferent for the majority of the strains tested, that is, 90 and 80% respectively.     

In vitro activity studies of doripenem and two other carbapenems tested against Pseudomonas aeruginosa and other non-fermentative bacilli

Over the past decade, an increasing prevalence of infections caused by non-fermenting Gram-negative bacteria has been reported in many countries. Among these bacteria, Pseudomonas aeruginosa and Acinetobacter baumannii have been associated with high mortality and treatment failures. Treatment options for multidrug-resistant P. aeruginosa and A. baumannii infections are limited to carbapenems in most cases. The mechanisms of carbapenem resistance have been identified in P. aeruginosa and other Gram-negative non-fermenters, including enzyme production, overexpression of efflux pumps, porin deficiencies, and target- site alterations. This article reviews the in vitro activity of doripenem and compares it with that of imipenem and meropenem against a large collection of non-fermenting Gram-negative bacilli, obtained in worldwide surveillance studies between 2000 and 2010. A detailed examination of the available data demonstrate that doripenem has more potent in vitro antibacterial activity against P. aeruginosa and Acinetobacter species compared to other carbapenems. Furthermore, doripenem has a limited ability to select for carbapenem-resistant mutants in vitro.     

In vitro interactions of aminoglycosides with imipenem or ciprofloxacin against aminoglycoside resistant Acinetobacter baumannii.

The in vitro interactions between gentamicin, tobramycin, netilmicin and amikacin with imipenem and ciprofloxacin were evaluated by the killing curve technique against 20 clinical isolates of Acinetobacter baumannii highly resistant to aminoglycosides which were susceptible or moderately susceptible to imipenem and resistant or moderately susceptible to ciprofloxacin. Imipenem enhanced killing by gentamicin, tobramycin, netilmicin and amikacin in tests with 9, 12, 10 and 15 strains (45-75%) while ciprofloxacin with 3, 7, 5 and 6 strains (15-35%) respectively. Interaction results were influenced by the height of aminoglycoside minimum bactericidal concentrations (MBCs) but were independent of imipenem or ciprofloxacin MBCs and the presence of aminoglycoside modifying enzymes. It is concluded that enhanced killing after aminoglycoside interaction with imipenem or ciprofloxacin versus A. baumannii cannot be predicted but it should be carefully tested in vitro. The in vivo significance of the reported findings mandates clinical studies in humans.     

In vitro effects of sulbactam combinations with different antibiotic groups against clinical Acinetobacter baumannii isolates

Abstract

Treatment of multidrug resistant (MDR) Acinetobacter baumannii infections causes some problems as a result of possessing various antibacterial resistance mechanisms against available antibiotics. Combination of antibiotics, acting by different mechanisms, is used for the treatment of MDR bacterial infections. It is an important factor to determine synergy or antagonism between agents in the combination for the constitution of effective therapy. The study aimed to determine in vitro interactions interpreted according to calculated fractional inhibitory concentration (FIC) index between sulbactam and ceftazidime, ceftriaxone, cefepime, ciprofloxacin, gentamicin, meropenem, tigecycline, and colistin. Ten clinical isolates of A. baumannii were tested for determination of synergistic effects of sulbactam with different antimicrobial combinations. Minimal inhibitory concentration (MIC) values of both sulbactam and combined antibiotics decreased 2- to 128-fold. Synergy and partial synergy were determined in combination of sulbactam with ceftazidime and gentamicin (FIC index: ≤0·5 or >0·5 to <1) and MIC values of both ceftazidime and gentamicin for five isolates fell down below the susceptibility break point. Similarly, MIC value of ciprofloxacin for six ciprofloxacin resistant isolates was determined as below the susceptibility break point in combination. However, all isolates were susceptible to colistin and tigecycline, MIC values of both were decreased in combination with sulbactam. Although synergistic and partial synergistic effects were observed in the combination of sulbactam and ceftriaxone, all isolates remained resistant to ceftriaxone. The effect of cefepime–sulbactam combination was synergy in five, partial synergy in one and indifferent in four isolates. Meropenem and sulbactam showed a partial synergistic effect (FIC index: >0·5 to <1) in three, an additive effect (FIC index: 1) in one and an indifferent effect (FIC index: >1–2) in six isolates. Antagonism was not determined in any combination for clinical A. baumannii isolates in the study. In conclusion, sulbactam is a good candidate for combination treatment regimes for MDR A. baumannii infections.     

In vitro and in vivo synergy of levofloxacin or amikacin both in combination with ceftazidime against clinical isolates of Pseudomonas aeruginosa

The aim of the present study was to explore the antibacterial activity of the levofloxacin (LVX) and ceftazidime (CAZ) combination compared with the amikacin (AMK)/CAZ combination against Pseudomonas aeruginosa. Minimum inhibitory concentrations (MICs) were determined according to NCCLS. FIC indices (Fl) were calculated by the checkerboard technique. CAZ combined with LVX or AMK yielded Fls indicating synergism (Fl < or = 0.5) for 71/102 (69.6%) and 81/102 (79.4%) (p = 0.108), indifference (FI > 0.5-4) for 24/102 (23.5%) and 12/102 (11.7%) (p = 0.027), and antagonism (Fl > 4) for 7/102 (6.8%) and 9/102 (8.8%) (p = 0.602) strains, respectively. In vivo, CAZ/LVX was as bactericidal as CAZ/AMK combination. Our results support the potential role of LVX as an alternative to AMK in the combination therapy with CAZ in the treatment of P. aeruginosa severe infections. Anyway, further investigations and clinical trials are awaited until any definitive conclusions can be drawn.     

In-vitro activity of ciprofloxacin and other beta-lactam antibiotics against gentamicin- and carbenicillin-resistant isolates of Pseudomonas aeruginosa

The susceptibilities of gentamicin- and carbenicillin-resistant clinical isolates of Pseudomonas aeruginosa to newer beta-lactams, netilmicin and ciprofloxacin were studied by a broth microdilution technique. Imipenem, aztreonam and ceftazidime were active against most of the P. aeruginosa strains with minimum inhibitory concentration (MIC) for 90% of the isolates at clinically achievable levels. Piperacillin, azlocillin, cefotaxime, ceftriaxone, cefsulodin, cefoperazone and netilmicin showed poor activity against these organisms, ciprofloxacin exhibited poor activity, inhibiting only 30% of these strains.     

In Vitro Bactericidal Effect of a β-lactam + Aminoglycoside Combination Against Multiresistant Pseudomonas aeruginosa and Acinetobacter baumannii

Abstract

Pseudomonas aeruginosa and Acinetobacter baumannii are frequently isolated in hospital outbreaks of nosocomial infections. In our hospital, among 1018 strains isolated one year in an intensive care unit, 84 strains (8.3%) of P. aeruginosa and 155 strains (15.2%) of A. baumannii were considered responsible for infections. The major problem related to these bacteria is their multiresistant characteristic which confers great difficulty in treating infections. We carried out a 24 h time-kill study to assess the bactericidal effect of three β-lactams [imipenem (IPM), ticarcillin + clavulanic acid (TCC), piperacillin + tazobactam (PTB)] in combination with each other and with sulbactam (SUL) and amikacin (AKN) against 8 P. aeruginosa strains and 8 A. baumannii strains. The initial inoculum was 10⁶ cfu/ml. Antibiotics were tested at clinically achievable concentrations: TCC (112 mg/l), PTB (100 mg/l), IPM (25 mg/l) and AKN (15 mg/l). The results showed: IMP+TCC+AKN = PTB+SUL+AKN = PTB+TCC+ AKN >> IMP+SUL+AKN against P. aeruginosa; and PTB+SUL+AKN = PTB+TCC+AKN > IMP+SUL+AKN or IMP+TCC+AKN against A. baumannii. When infection due to these multiresistant strains was suspected, PTB+AKN combined with either TCC or SUL was bactericidal against both strains. These combinations appeared to be an alternative therapy in the treatment of undocumented nosocomial infections in intensive care units. These In Vitro results are being evaluated in patients and seem to give good results for the moment.     

In vitro activity of diphenyl diselenide and ebselen alone and in combination with antifungal agents against Trichosporon asahii

This study evaluated the in vitro susceptibility of Trichosporon asahii strains to diphenyl diselenide (DPDS) and ebselen (EBS) alone and in combination with amphotericin B (AMB), fluconazole (FCZ), itraconazole (ITZ) and caspofungin (CAS) using the microdilution method. EBS showed in vitro activity against T asahii strains with minimal inhibitory concentration (MIC) ranged from 0.25 to 8.0 μg/mL. For DPDS, the MIC ranged from 8.0 to 64 μg/mL. The combinations demonstrating the greatest synergism rate against fluconazole‐resistant T asahii strains were the following: CAS + DPDS (96.67%), AMB + DPDS (93.33%), FCZ + DPDS (86.67%) and ITZ + DPDS (83.33%). The combinations AMB + DPDS and AMB + EBS exhibited the highest synergism rate against the fluconazole‐susceptible (FS) T asahii strains (90%). Antagonism was observed in the following combinations: FCZ + EBS (80%) and FCZ + DPDS (13.33%) against the FS strains, and ITZ + EBS (20%) against the FR strains. Our findings suggest that the antimicrobial activity of DPDS and EBS against T. asahii and its use as an adjuvant therapy with antifungal agents warrant in vivo experimental investigation.     

In Vitro Evaluation of the Antimicrobial Activity of Meropenem in Combination with Polymyxin B and Gatifloxacin Against Pseudomonas aeruginosa and Acinetobacter baumannii

Abstract

The antimicrobial activity of meropenem combined with either polymyxin B or gatifloxacin was evaluated by the checkerboard method against Pseudomonas aeruginosa (10 strains) and Acinetobacter baumannii (10 strains). In addition, the triple combination of polymyxin B, gatifloxacin, and meropenem was also studied as well as the polymyxin B and gatifloxacin combination. A partial synergism interaction between meropenem and polymyxin B was observed for 80% of the A. baumannii strains. In contrast, this combination showed an indifferent effect for 80% of the P. aeruginosa strains tested. The combination of meropenem and gatifloxacin showed synergism only for two strains of A. baumannii, and partial synergism and additive effect for seven strains and indifference for four strains of both species. For the strains of P. aeruginosa, the double combination of polymyxin B and gatifloxacin and the triple combination of meropenem, polymyxin B and gatifloxacin were indifferent for the majority of the strains tested, that is, 90 and 80% respectively.     

In vitro activity of clarithromycin alone or in combination with other antimicrobial agents against Mycobacterium avium-intracellulare. Complex strains isolated from AIDS patients.

The activity of clarithromycin and five other antimicrobial agents, namely amikacin, rifampicin, rifabutin, clofazimine and ciprofloxacin, was assessed both by an agar dilution and a radiometric method in broth on 11 Mycobacterium avium-intracellulare complex (MAC) strains, recently isolated from AIDS patients. Minimum inhibitory concentrations (MICs) radiometrically determined were, in general, several times lower than MICs assessed in agar, probably because of a partial degradation of antimicrobials during the long incubation period needed for tests in solid medium. When tested in broth, rifabutin and clofazimine showed very low MICs 90 (0.24 and 0.78 microgram/ml, respectively). Ciprofloxacin and clarithromycin also had MICs90 in the range of peak serum levels (1.93 and 3.76 micrograms/ml, respectively). Moreover, all these antimicrobials are known to concentrate several times in macrophages. MICs90 were higher for amikacin (11 micrograms/ml) and for rifampicin (8 micrograms/ml). When clarithromycin was tested against three MAC strains in combination with another drug, it showed a synergistic effect only when combined with rifampicin. Some synergistic effect was observed also when combining clarithromycin with rifampicin and amikacin, whereas in combination with rifabutin and clofazimine there was only an additive effect.     

In Vitro Activity of β-Lactam Antimicrobial Agents in Combination with Aztreonam Tested Against Metallob-β-Lactamase-Producing Pseudomonas aeruginosa and Acinetobacter baumannii

Abstract

We evaluate the antimicrobial interactions between aztreonam and selected beta-lactams when tested against metallo-β-lactamase (MβL)-producing clinical strains. Ten Pseudomonsa aeruginosa strains, including nine MβL-producers (IMP- 1, -2, -13, -16, VIM-1, -2, -7, SPM-1 and GIM-1) and five Acinetobacter baumannii strains, including three MβL-producers (IMP-1 and -2) were tested using time kill/bactericidal activity methods. Aztreonam at 4, 8 and 16 mg/L was combined with four other β-lactam antimicrobials (cefepime, ceftazidime, meropenem and piperacillin/tazobactam or ampicillin/sulbactam), each tested at the recognized susceptible breakpoint concentration. Enhanced activity (synergism or additive effect) was observed with four P. aeruginosa strains (IMP-16, VIM-2, SPM-1 and GIM-1 containing strains) and four A. baumannii strains, while antagonism was observed with two P. aeruginosa (IMP-16 and SPM-1-producing strains) and one A. baumannii (non-MβL) strain. All other strains showed indifferent interaction (variation of ± 1 log₁₀ CFU/ml) with any combination evaluated.     

In vitro synergy of colistin combinations against extensively drug-resistant Acinetobacter baumannii producing OXA-23 carbapenemase

Fifty extensively drug-resistant Acinetobacter baumannii (XDRAB) were isolated from patients. The chequerboard microdilution method was used to determine the in vitro activities of five colistin (COL)-based combinations including COL+fosfomycin (FOS), COL+rifampicin (RIF), COL+imipenem (IMP), COL+sulbactam (SUP) and COL+levofloxacin (LVX). The synergistic activity was evaluated by the fractional inhibitory concentration index (FICI). According to our results, the combination of COL was synergistic with FOS, RIF, IMP, SUP and LVX with the ratios of 50, 72, 88, 92 and 64%, respectively. When combined with COL, the other five agents showed increased antimicrobial activities. In addition, two of the combinations, COL+RIF and COL+IMP, were more active than the combinations of COL+FOS, COL+SUP and COL+LVX. More importantly, these combination regimens could exert synergistic effects at the sub-minimum inhibitory concentration (MIC) levels against XDRAB strains.     

In vitro activity of the protegrin IB‐367 alone and in combination compared with conventional antifungal agents against dermatophytes

The occurrence of resistance or side effects in patients receiving antifungal agents leads to failure in the treatment of mycosis. The aim of this experimental study was to investigate the in vitro effects of IB‐367 alone and in combination with three standard antifungal drugs, fluconazole (FLU), itraconazole (ITRA) and terbinafine (TERB), against 20 clinical isolates of dermatophytes belonging to three species. Minimum inhibitory concentrations (MICs), minimal fungicidal concentrations (MFCs), synergy test, time‐kill curves, fungal biomass (FB) and hyphal damage using 2,3‐bis‐(2‐methoxy‐4‐nitro‐5‐sulfenylamino carbonil)‐2H‐tetrazolium hydroxide assay (XTT) were performed to study the efficacy of IB‐367. In this study, we observed that TERB and ITRA had MICs lower values for all the strains compared to IB‐367 and FLU. Synergy was found in 35%, 30% and 25% of IB‐367/FLU, IB‐367/ITRA and IB‐367/TERB interactions respectively. IB‐367 exerted a fungicidal activity against Trichophyton mentagrophytes, T. rubrum and Microsporum canis at concentrations starting from 1x MIC. At a concentration of 5x MIC, IB‐367 showed the highest rates of hyphae damage for M. canis 53% and T. mentagrophytes 50%; against the same isolates it caused a reduction of 1 log of the total viable count cell hyphae damage. We propose IB‐367 as a promising candidate for the future design of antifungal drugs.     

In Vitro Interactions of Aminoglycosides with Imipenem or Ciprofloxacin against Aminoglycoside Resistant Acinetobacter baumannii

Summary

The in vitro interactions between gentamicin, tobramycin, netilmicin and amikacin with imipenem and ciprofloxacin were evaluated by the killing curve technique against 20 clinical isolates of Acinetobacter baumannii highly resistant to aminoglycosides which were susceptible or moderately susceptible to imipenem and resistant or moderately susceptible to ciprofloxacin. Imipenem enhanced killing by gentamicin, tobramycin, netilmicin and amikacin in tests with 9, 12, 10 and 15 strains (45-75%) while ciprofloxacin with 3, 7, 5 and 6 strains (15-35%) respectively. Interaction results were influenced by the height of aminoglycoside minimum bactericidal concentrations (MBCs) but were independent of imipenem or ciprofloxacin MBCs and the presence of aminoglycoside modifying enzymes. It is concluded that enhanced killing after aminoglycoside interaction with imipenem or ciprofloxacin versus A. baumannii cannot be predicted but it should be carefully tested in vitro. The in vivo significance of the reported findings mandates clinical studies in humans.     

In vitro activity of daptomycin alone and in combination with various antimicrobials against Gram-positive cocci

The increasing prevalence of resistant Gram-positive cocci requires the need to search for more effective agents and synergistic combinations. Forty-two vancomycin-resistant Enterococcus faecium (VREF), 30 methicillin-resistant Staphylococcus aureus (MRSA) and 36 Staphylococcus epidermidis (MRSE) strains were studied. Minimum inhibitory concentrations (MICs) were determined and synergy testing was performed by using E test for daptomycin, ampicillin-sulbactam, piperacillin-tazobactam and ticarcillin-clavulanate against staphylococci; for daptomycin, ampicillin, rifampin, and gentamicin against enterococci. Daptomycin in combination with ampicillin, rifampin, and gentamicin was tested against enterococci; daptomycin in combination with ampicillin-sulbactam, piperacillin-tazobactam, and ticarcillin-clavulanate was tested against staphylococci. Interaction categories were defined by the fractional inhibitory concentration (FIC) index. All strains of staphylococci and enterococci were susceptible to daptomycin. All three combinations showed synergy against more than 70% of the MRSA strains. Daptomycin in combination with ampicillin, rifampin, and gentamicin against enterococci showed synergies of 64.2%, 57.1% and 21.4%, respectively. This study indicates that daptomycin alone and combined with beta-lactams seems to be effective against MRSA, but further in vitro and in vivo studies on the subject are required before clinical use can be recommended.     

In vitro and in vivo activity of antifungal agents in combination with fleroxacin, a new quinolone

The in vitro and in vivo interaction of fleroxacin with amphotericin B (Amph B), flucytosine (5-FC) and azoles against Candida albicans strains was tested. In vitro the interaction between fleroxacin and various antifungals was not dependent on the incubation time. Fleroxacin neither enhances nor antagonizes the in vitro activity of Amph B at high concentration (50-100 micrograms/ml). Fleroxacin has a synergistic effect with ketoconazole (KETO), but this is not observed with itraconazole (ITRA) or fluconazole (FLU). In no instance antagonism was observed. The activity of 5-FC was antagonized by fleroxacin being generally reduced by 2-4 dilution steps. In murine candidosis the efficacies of all antifungal drugs were not influenced by addition of 100 mg/kg fleroxacin. Therefore, the effects seen in in vitro tests are most probably not relevant for the clinical use of a combination of fleroxacin with antifungal drugs.     

In vitro activity of telithromycin, quinupristin/dalfopristin, linezolid and comparator antimicrobial agents against Staphylococcus aureus clinical isolates

We have studied the prevalence of the different macrolide, lincosamide, streptograminB (MLS(B)) phenotypes among clinical Staphylococcus aureus isolates erythromycin- and/or oxacillin-resistant; and also the activity of other antimicrobial agents including telithromycin, quinupristin/dalfopristin, linezolid, aminoglycosides, chloramphenicol and vancomycin. We found that 64.86% of S. aureus were oxacillin-resistant. While the most prevalent MLS(B) phenotype among methicillin-resistant S. aureus (MRSA) was constitutive MLS(B) (cMLS) (83%), among methicillin-susceptible S. aureus (MSSA) it was inducible MLS(B) (iMLS(B)) (90%). Kanamycin resistance was more frequent than resistance to other aminoglycosides, being 100% for MRSA. Telithromycin was only active against iMLS(B), MS and erythromycin-susceptible isolates, although resistance rates were found among iMLS(B) MSSA (2.78%). Quinupristin/dalfopristin showed greater activity, with resistance rates of 2.5% for MRSA and 1.53% for MSSA. Both vancomycin and linezolid were fully active against all the isolates tested, with the highest MIC value being 2 microg/ml and 4 microg/ml, respectively. Among MRSA strains, 81.67% displayed resistance to five or more antimicrobials. This multiresistance was more frequently found among cMLS(B) strains (96.38% MRSA resistant to 6-9 agents).     

Enhanced in-vitro activity of liposome-trapped penicillin-G against Pseudomonas aeruginosa

The growth inhibition of four Pseudomonas aeruginosa strains by liposome-trapped penicillin-G was investigated. There were indications of an association of the efficacy of liposomal penicillin-G with the nature of the 0-antigenic polymeric side chain. Namely, P28-800 and PCF-95 strains, characterized by a rough polysaccharide chain, were the most susceptible, whereas strain P28-0, possessing an intact lipopolysaccharide, resisted the activity of the entrapped drug. Among the rough strains, P642, a beta-lactamase producer, was not affected by the encapsulated drug. The composition of liposomes seems to have a significant impact in arresting the growth of the P. aeruginosa strain.     

In Vitro Activity of Meropenem against Ciprofloxacin-Resistant Enterobacteriaceae and Pseudomonas aeruginosa

Abstract

The in-vitro susceptibilities of a total of 174 ciprofloxacin-resistant Enterobacteriaceae and Pseudomonas aeruginosa were determined. According to the BSAC and NCCLS breakpoints, meropenem, aztreonam, ceftibuten, ceftazidime, imipenem and cefotaxime were the most active (>90%) antimicrobial agents tested against Enterobacteriaceae. Susceptibility of these strains to piperacillin/tazobactam, cefpodoxime and cefixime (84.96%) was higher than that to tobramycin, gentamicin and fosfomycin (50-75%). More than 90% of P. aeruginosa were susceptible to meropenem when both interpretative susceptibility breakpoint criteria were used. Piperacillin, piperacillin/tazobactam and ceftazidime were active against 50-75% of the same strains. Meropenem was the most active antimicrobial tested against all ciprofloxacin-resistant clinical isolates assayed.     

In vitro antimicrobial activity of olive leaves

We investigated the antimicrobial effect of olive leaves against bacteria and fungi. The microorganisms tested were inoculated in various concentrations of olive leaf water extract. Olive leaf 0.6% (w/v) water extract killed almost all bacteria tested, within 3 h. Dermatophytes were inhibited by 1.25% (w/v) plant extract following a 3-day exposure whereas Candida albicans was killed following a 24 h incubation in the presence of 15% (w/v) plant extract. Olive leaf extract fractions, obtained by dialysis, that showed antimicrobial activity consisted of particles smaller than 1000 molecular rate cutoffs. Scanning electron microscopic observations of C. albicans, exposed to 40% (w/v) olive leaf extract, showed invaginated and amorphous cells. Escherichia coli cells, subjected to a similar treatment but exposed to only 0.6% (w/v) olive leaf extract showed complete destruction. These findings suggest an antimicrobial potential for olive leaves.