Tolerância induzida por drogas : efeito da associação in vitro de antimicrobianos em Stenotrophomonas maltophilia
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Data
2019-02-22
Autores
Ferreira, Mariana Abou Mourad
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Universidade Federal do Espírito Santo
Resumo
Introduction: Bacterial tolerance is characterized by the ability of a microbial population to survive the high concentrations of a bactericidal drug without alteration in the Minimum Inhibitory Concentration. At the end of the antimicrobial treatment, the tolerant strains multiply again, which may cause recalcitrant infections and facilitate resistance. Many studies relate antimicrobial exposure to tolerance induction. Although observed in several species, tolerance has not yet been investigated for the opportunistic bacillus Stenotrophomonas maltophilia, commonly exposed in the clinical scenario to antibiotics that have no action on this pathogen. Thus, our objective was to investigate whether the prior use of certain non-targeted antimicrobials induces cross-tolerance in S. maltophilia. Materials and methods: Qualitative and quantitative screening tests were performed to evaluate possible tolerance-inducing antimicrobials. In these assays, we exposed the S. maltophilia ATCC® 13637™ to daptomycin (DAP), vancomycin (VAN) and gentamicin (GEN) and evaluated the occurrence of cross-tolerance to the following drugs targeting S. maltophilia: sulfamethoxazole/trimethoprim (SXT), ceftazidime (CAZ) and levofloxacin (LVX). After the screening, strains with tolerance-induced characteristics were tested for genetic similarity by ERIC-PCR. To exclude the contamination hypothesis and confirm the genus and species of the strains, the MALDI-TOF MS was performed. To evaluate tolerance, the following tests were carried out: determination of the Minimum Bactericidal Concentration (MBC) / Minimum Inhibitory Concentration (MIC) ratio for LVX; adapted disk-diffusion test for SXT, CAZ, LVX, ticarcillin-clavulanate (TCC), chloramphenicol (CLO), minocycline (MIN) and polymyxin B (PXB) and time-kill curve for LVX, CAZ and ciprofloxacin (CIP). Results: After induction of the parental strain ATCC® 13637™ to DAP and VAN, three potentially tolerant strains (D25, V15.6 and V3.9) were isolated, whose genetic similarity to parental was confirmed by ERIC-PCR (100% similarity). The induced strains maintained the same MIC value of LVX as the parental strain (0.125 μg/mL), with the MBC/MIC ratio ranging from 2.64 to 3.04 among the induced strains. In the adapted disc-diffusion test, strain D25 showed high tolerance for LVX, CAZ and TCC. In the stationary phase time-kill curves against 50 times the MIC of LVX, strain D25 presented a minimum duration for killing 99,99% of all population (MDK99.99) higher than the parental. The survival rate was also higher for the D25 strain in the presence of CAZ (50xMIC). In general, strain D25 had a higher survival rate in all time-kill curves, except for CIP. Conclusions: Previous exposure of S. maltophilia to daptomycin induces cross-tolerance to levofloxacin, ceftazidime and ticarcillinclavulanate. Thus, erroneous empirical therapy with daptomycin could lead to the failure of these antimicrobials to eradicate S. maltophilia, culminating in chronic infections or death by a subpopulation of tolerant microorganisms.
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Tolerance , Persistence , Daptomycin , Stenotrophomonas maltophilia , Tolerância , Persistência , Daptomicina , Testes de sensibilidade bacteriana , Bactérias gram-negativas