Chequerboard titrations: the influence of the composition of serial dilutions of antibiotics on the fractional inhibitory concentration index and fractional bactericidal concentration index

Horrevorts, A. M.; Ridder, Corrina M. de; Poot, Martin; Jonge, Maja J.A. de; Degener, John E.; Dzoljic-Danilovic, G.; Michel, M. F.; Kerrebijn, K. F.

doi:10.1093/jac/19.1.119

Cited by 21 publications

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“…This may be due to the methodology itself. FIC indices are highly dependent on the applied dilution series (42), and synergy is usually considered significant only if the FIC is lower than 0.5, which means a 4-fold reduction in the MIC measured for the combination versus each drug alone (43). Yet, more minor synergies (with FICs between 0.5 and 1, such as those observed in the present study) could be of clinical importance as well (44).…”

Section: Discussionmentioning

confidence: 59%

Activities of Antibiotic Combinations against Resistant Strains of Pseudomonas aeruginosa in a Model of Infected THP-1 Monocytes

Buyck

Tulkens

Bambeke

2015

Antimicrob Agents Chemother

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Antibiotic combinations are often used for treating Pseudomonas aeruginosa infections but their efficacy toward intracellular bacteria has not been investigated so far. We have studied combinations of representatives of the main antipseudomonal classes (ciprofloxacin, meropenem, tobramycin, and colistin) against intracellular P. aeruginosa in a model of THP-1 monocytes in comparison with bacteria growing in broth, using the reference strain PAO1 and two clinical isolates (resistant to ciprofloxacin and meropenem, respectively). Interaction between drugs was assessed by checkerboard titration (extracellular model only), by kill curves, and by using the fractional maximal effect (FME) method, which allows studying the effects of combinations when dose-effect relationships are not linear. For drugs used alone, simple sigmoidal functions could be fitted to all concentrationeffect relationships (extracellular and intracellular bacteria), with static concentrations close to (ciprofloxacin, colistin, and meropenem) or slightly higher than (tobramycin) the MIC and with maximal efficacy reaching the limit of detection in broth but only a 1 to 1.5 (colistin, meropenem, and tobramycin) to 2 to 3 (ciprofloxacin) log 10 CFU decrease intracellularly. Extracellularly, all combinations proved additive by checkerboard titration but synergistic using the FME method and more bactericidal in kill curve assays. Intracellularly, all combinations proved additive only based on both FME and kill curve assays. Thus, although combinations appeared to modestly improve antibiotic activity against intracellular P. aeruginosa, they do not allow eradication of these persistent forms of infections. Combinations including ciprofloxacin were the most active (even against the ciprofloxacin-resistant strain), which is probably related to the fact this drug was the most effective alone intracellularly.A ntibiotic combination is widely recognized as a useful strategy not only for increasing the chances to effectively cover the offending organism(s) upon initiation of an empirical therapy but also to accelerate the reduction of the inoculum at the early stage of infection and to avoid the selection of resistance (1-4). This may be particularly critical when dealing with infections caused by organisms like Pseudomonas aeruginosa, which is often multiresistant and causes severe diseases. Accordingly, antibiotic combinations have been widely studied in vitro using both static (5-10) and dynamic (11-14) models. Most of these studies concluded that there was synergy but to an extent that proved to be highly strain dependent. While the exact mechanism of this synergy often remains uncertain, a number of pharmacological reasons have been proposed, such as the enhancement of the uptake of the companion antibiotics by colistin through its destabilizing effects on the outer membrane (15) or the increased diffusion of entry of aminoglycosides through the peptidoglycan when altered by ␤-lactams (16).There is, however, increasing evidence that specific lifestyles,...

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Section: Discussionmentioning

confidence: 59%

Activities of Antibiotic Combinations against Resistant Strains of Pseudomonas aeruginosa in a Model of Infected THP-1 Monocytes

Buyck

Tulkens

Bambeke

2015

Antimicrob Agents Chemother

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“…This technique has proven to be a useful tool for the examination of the degree of interaction between antibiotics (2,12 FBCIs. Because most A. actinomycetemcomitans strains are relatively nonsusceptible to metronidazole, the use of metronidazole alone may not be effective enough.…”

Section: Discussionmentioning

confidence: 99%

“…To specify the degree of interaction between the antibiotics, we calculated fractional inhibitory concentrations (FICs), fractional bactericidal concentrations (FBCs), fractional inhibitory concentration indices (FICIs), and fractional bactericidal concentration indices (FBCIs) from wells in which no visible growth could be detected and from wells with less than 0.1% survival of the original inoculum. The criteria on the basis of which one decides whether a combination of antibiotics acts synergistically, additively, or antagonistically are based on the accuracy of the MIC and MBC determinations (12 The MICs and MBCs of the hydroxymetabolite of metronidazole' for each bacterial strain were two to four times lower than the MICs and MBCs of metronidazole. The results of the checkerboard titrations are listed in Table 2.…”

Section: Methodsmentioning

confidence: 99%

Synergistic effects between amoxicillin, metronidazole, and the hydroxymetabolite of metronidazole against Actinobacillus actinomycetemcomitans

Pavičić

Winkelhoff

Graaff

1991

Antimicrob Agents Chemother

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Interactions between metronidazole and amoxicillin, metronidazole and its hydroxymetabolite, and amoxicillin and the hydroxymetabolite of metronidazole were investigated with checkerboard titrations in combination with accurately determined MICs and MBCs. Actinobacillus actinomycetemcomitans was used as the test organism. Synergism was found for all three combinations. Fractional inhibitory concentration indices and fractional bactericidal concentration indices varied from 0.3 to 0.7. These synergistic interactions between these antibiotics may explain the efficacy of the combination of metronidazole and amoxicillin in various bacterial infections, including periodontal disease.The efficacy of the combination of metronidazole and amoxicillin has been proven in a variety of mixed bacterial infections in humans (7,8). Helicobacter pylori infections have been treated with the combination of metronidazole, amoxicillin, and bismuth salts, and eradication of this microorganism was observed in over 90% of the cases (1, 4a). Recently, the combination of metronidazole and amoxicillin was evaluated in patients with oral infections, e.g., periodontal disease (6,9,29). In some forms of periodontal disease, Actinobacillus actinomycetemcomitans, a capnophilic, gram-negative rod, seems to be of major etiological importance (18-20, 23, 25). In A. actinomycetemcomitansassociated periodontal disease, adjunct antibiotics are often necessary to achieve a satisfactory clinical treatment response. Tetracyclines have been used often in conjunction with subgingival mechanical debridement (21,27). However, tetracyclines are not always successful in the elimination of A. actinomycetemcomitans (15,21,26,27,29). Unexpected clinical success was observed with the combination of metronidazole and amoxicillin in terms of the elimination of A. actinomycetemcomitans from periodontal lesions (6,29). It is known that the hydroxymetabolite of metronidazole, which is produced in the human liver, is even more active against A. actinomycetemcomitans in vitro, and it has been suggested that the combination of metronidazole and its hydroxymetabolite acts synergistically against A. actinomycetemcomitans (13). It is therefore possible that the hydroxymetabolite of metronidazole plays an important role in the effectiveness of the combination of metronidazole and amoxicillin. It has also been suggested that metronidazole combined with penicillin has a potentiating effect against Clostridium perfringens (3). The aim of this study was to investigate the in vitro interactions between metronidazole, the hydroxymetabolite of metronidazole, and amoxicillin and the activities of combinations of these three compounds against A. actinomycetemcomitans. * Corresponding author. MATERIALS AND METHODSBacterial strains. A total of 10 A. actinomycetemcomitans strains were included in the study; 6 strains had a rough appearance on the isolation medium (HG 1175, HG 1176, HG 1178, HG 1237, HG 1238, and HG 1239), and 4 strains had a smooth appearance on the isolation medium (H...

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“…Most commonly, the test is designed to assess inhibitory effects only, in which case it can be carried out with either broth or agar media. Serial twofold dilutions of antibiotics have been generally used; however, some authors have recommended smaller concentration intervals to permit greater precision (77,87).…”

Section: Checkerboard Titrationsmentioning

confidence: 99%

Antibiotic combinations: should they be tested?

1988

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When antibiotic combinations are used to provide a broader spectrum of antimicrobial activity or in an attempt to prevent the emergence of resistant organisms, it is rarely necessary or practical to perform tests of drug interactions in vitro. In vitro testing of combinations may be useful when combinations are used in an attempt to attain synergistic interactions. In some cases, screening methods can be used as substitutes for formal synergy testing. This paper examines the mechanisms of antibiotic interaction leading to synergism or antagonism, surveys attempts to correlate in vitro observations with efficacy in animal models, and reviews clinical data providing evidence for or against a useful role of synergistic antibiotic interactions in the treatment of human infections.

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Chequerboard titrations: the influence of the composition of serial dilutions of antibiotics on the fractional inhibitory concentration index and fractional bactericidal concentration index

Cited by 21 publications

References 0 publications

Activities of Antibiotic Combinations against Resistant Strains of Pseudomonas aeruginosa in a Model of Infected THP-1 Monocytes

Activities of Antibiotic Combinations against Resistant Strains of Pseudomonas aeruginosa in a Model of Infected THP-1 Monocytes

Synergistic effects between amoxicillin, metronidazole, and the hydroxymetabolite of metronidazole against Actinobacillus actinomycetemcomitans

Antibiotic combinations: should they be tested?

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