Comparison of methods for the detection of in vitro synergy in multidrug-resistant gram-negative bacteria

Abstract

Background: The use of combined antibiotic therapy has become an option for infections caused by multidrugresistant (MDR) bacteria. The time-kill (TK) assay is considered the gold standard method for the evaluation of in vitro synergy, but it is a time-consuming and expensive method. The purpose of this study was to evaluate two methods for testing in vitro antimicrobial combinations: the disk diffusion method through disk approximation (DA) and the agar gradient diffusion method via the MIC:MIC ratio. The TK assay was included as the gold standard. MDR Gram-negative clinical isolates (n = 62; 28 Pseudomonas aeruginosa, 20 Acinetobacter baumannii, and 14 Serratia marcescens) were submitted to TK, DA, and MIC:MIC ratio synergy methods. Results: Overall, the agreement between the DA and TK assays ranged from 20 to 93%. The isolates of A. baumannii showed variable results of synergism according to TK, and the calculated agreement was statistically significant in this species against fosfomycin with meropenem including colistin-resistant isolates. The MIC:MIC ratiometric agreed from 35 to 71% with TK assays. The kappa test showed good agreement for the combination of colistin with amikacin (K = 0.58; P = 0.04) among the colistin-resistant A. baumannii isolates. Conclusions: The DA and MIC:MIC ratiometric methods are easier to perform and might be a more viable tool for clinical microbiology laboratories.

Antibacterial activity and carbapenem re‐sensitizing ability of 1,10‐phenanthroline‐5,6‐dione and its metal complexes against KPC‐producingKlebsiella pneumoniaeclinical strains

“…No previous studies have been conducted on evaluating the synergistic potential of phendione-based complexes against bacterial species. The current findings provide strong evidence of the beneficial effects rendered by drug combinations, since a time-kill assay is considered to be the gold standard for such evaluations as it is known to produce consistent results across different studies (Gaudereto et al 2020).…”

Antimicrobial Synergy Testing: Comparing the Tobramycin and Ceftazidime Gradient Diffusion Methodology Used in Assessing Synergy in Cystic Fibrosis-Derived Multidrug-Resistant Pseudomonas aeruginosa

“…Several methods have been described and evaluated, for agreement with checkerboard or time-kill assays, as reference standards using numerous bacteria/antimicrobial combinations [ 13 ]. The time-kill method has been shown to yield high concordance in various studies, but because it produces dynamic and longitudinal information that cannot be obtained by other methods, its use as the gold standard for synergy testing is debatable [ 17 ]. In contrast, the broth microdilution assay and the gradient synergy method measure the inhibitory activities of antibiotics [ 12 ].…”

Synergistic Antimicrobial Activity of Eugenol in Combination with Fosfomycin to Combat Escherichia coli and Potential Effect on Plasmid‐Mediated Fosfomycin Resistance Genes

“…The time-kill assay was performed as previously described. [50] Timekill assays were used to assess the antibacterial activities of Fosfomycin and Eugenol against Fosfomycin-resistant UPEC isolates. The reduction in CFU/mL count was measured after 18 hrs of incubation.…”