Effect of Antibiotics Combination and Comparison of Methods for Detection of Synergism in Multiresistant Gram-Negative Bacteria
|Gleice Cristina Leite1,2, Lauro Vieira Perdigão Neto1,2, Juliana Januário Gaudereto1,2, Cláudia Maria Dantas de Maio Carrilho3, Flavia Rossi5, Anna Sara Levin1,4 and Silvia Costa1*,2,6|
|1Department of Infectious Diseases, University of São Paulo, Brazil|
|2Laboratory of Medical Investigation 54 (LIM-54), Hospital Das Clínicas of FMUSP, São Paulo, Brazil|
|3Hospital Universitário, Londrina State University, Londrina, Brazil|
|4Department of Infection Control, Hospital das Clínicas, University of São Paulo, Brazil|
|5Laboratory of Microbiology, Hospital Das Clínicas, University of São Paulo, Brazil|
|6Institute of Tropical Medicine, University of São Paulo, Brazil|
|Corresponding Author :||Silvia Figueiredo Costa
Laboratory of Medical Investigation 54 (LIM-54)
Hospital Das Clínicas of FMUSP, São Paulo, Brazil
E-mail: [email protected]
|Received December 17, 2014; Accepted March 18, 2015; Published March 25, 2015|
|Citation: Leite GC, Neto LVP, Gaudereto JJ, Carrilho CMDdM, Rossi F, et al. (2015) Effect of Antibiotics Combination and Comparison of Methods for Detection of Synergism in Multiresistant Gram-Negative Bacteria. J Infect Dis Ther 3:207. doi:10.4172/2332-0877.1000207|
|Copyright: © 2015 Leite GC, et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.|
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Background: Because of the rapid spread of antimicrobial resistance and the slow development of novel antimicrobials, Gram-negative infections treatments are challenging clinicians and the Public Health. We aimed to evaluate the activities of antimicrobial combination against MDR Gram-negative bacteria.
Methods: Twenty-eight P. aeruginosa, 20 A. baumannii and 17 K. pneumoniae carbapenem-resistant clinical isolates had MIC determined by broth microdilution. Synergistic effect was investigated using checkerboard method and time-kill assay, the gold standard method. PCR for carbapenemase genes and PFGE clonality assessment were done.
Results: All P. aeruginosa isolates were resistant to meropenem, but susceptible to colistin; the genes blaSPM and blaKPC were found in 82% and 25% of them, respectively; synergistic effect was seen only in combinations of colistin with meropenem (43%), meropenem with amikacin (36%) and colistin with amikacin (7%), by time-kill. Twenty-five P. aeruginosa isolates belonged to the same clonal profile. All 20 isolates of A. baumannii were resistant to meropenem, rifampicin, fosfomycin and harbored blaOXA-51-like; the genes blaOXA-23-like, blaOXA-143-like and blaIMP were found in 50%, 35% and 15% of them, respectively. Eleven in thirteen colistin-susceptible A. baumannii isolates showed distinct profiles and six in seven colistin-resistant isolates belonged to the same clone; synergistic effect was observed in almost all combinations by time-kill. Resistance to polymyxin B and resistance to imipenem were found in 100% and 91% of K. pneumoniae isolates. The blaKPC gene was found in 82% of them; five clusters were identified (each one with two isolates) and other seven different isolates; synergistic effect occurred in most of threedrug combinations.
Conclusion: We demonstrated that time kill assay must be considered the gold standard method to detect synergism in vitro, as it allows greater dynamic assessment and higher sensitivity, when compared to the other methods. We detected that colistin combinations are frequently synergic against A. baumannii and K. pneumoniae. For P. aeruginosa, the results were not that optimistic.