Colistin In Isolates Research Articles

Resistência à Colistina em isolados de hemoculturas de recém-nascidos admitidos em um hospital escola

O objetivo deste estudo foi avaliar a resistência frente à colistina em isolados de hemoculturas de recém-nascidos (RN) admitidos em um Hospital Escola no período de 4 anos. Os testes de identificação e os perfis de sensibilidade frente aos antimicrobianos foram realizados através de sistemas automatizados. No período deste estudo, 923 hemoculturas foram positivas, 92,09% (850/923) causadas por microrganismos Gram-positivos e 7,91% (73/923) por Gram-negativos. Destas, dois isolados foram resistentes à colistina: Acinetobacter baumannii e Sphingomonas paucimobilis; e um isolado de Pseudomonas aeruginosa mostrou perfil intermediário a este antimicrobiano, apresentando também significativa resistência aos carbapenêmicos. Este perfil é preocupante uma vez que estes antimicrobianos constituem a última alternativa para o tratamento de infecções causadas por bacilos Gram-negativos multirresistentes. Os resultados deste estudo sinalizam para o seguimento do monitoramento desta resistência.

Resistance to tobramycin and colistin in isolates of Pseudomonas aeruginosa from chronically colonized patients with cystic fibrosis under antimicrobial treatment

Tobramycin and colistin represent 2 standard antimicrobial agents in the treatment of cystic fibrosis (CF) patients who are chronically colonized with Pseudomonas aeruginosa. In this study, we determined the rate of resistance to tobramycin and colistin in 1844 isolates of P. aeruginosa obtained from 22 CF patients under alternate therapy with inhaled tobramycin and colistin. Resistance to tobramycin was observed in 27.5% of isolates. In contrast, all isolates were susceptible to colistin. Molecular typing of selected isolates suggested that only 1 clone occurred over time in each patient. To conclude, resistance to tobramycin in P. aeruginosa isolates from CF patients under antimicrobial therapy may occur while colistin resistance remains uncommon.

Comparative Evaluation of the VITEK 2, Disk Diffusion, Etest, Broth Microdilution, and Agar Dilution Susceptibility Testing Methods for Colistin in Clinical Isolates, Including Heteroresistant Enterobacter cloacae and Acinetobacter baumannii Strains

Increasing antibiotic resistance in gram-negative bacteria has recently renewed interest in colistin as a therapeutic option. The increasing use of colistin necessitates the availability of rapid and reliable methods for colistin susceptibility testing. We compared seven methods of colistin susceptibility testing (disk diffusion, agar dilution on Mueller-Hinton [MH] and Isosensitest agar, Etest on MH and Isosensitest agar, broth microdilution, and VITEK 2) on 102 clinical isolates collected from patient materials during a selective digestive decontamination or selective oral decontamination trial in an intensive-care unit. Disk diffusion is an unreliable method to measure susceptibility to colistin. High error rates and low levels of reproducibility were observed in the disk diffusion test. The colistin Etest, agar dilution, and the VITEK 2 showed a high level of agreement with the broth microdilution reference method. Heteroresistance for colistin was observed in six Enterobacter cloacae isolates and in one Acinetobacter baumannii isolate. This is the first report of heteroresistance to colistin in E. cloacae isolates. Resistance to colistin in these isolates seemed to be induced upon exposure to colistin rather than being caused by stable mutations. Heteroresistant isolates could be detected in the broth microdilution, agar dilution, Etest, or disk diffusion test. The VITEK 2 displayed low sensitivity in the detection of heteroresistant subpopulations of E. cloacae. The VITEK 2 colistin susceptibility test can therefore be considered to be a reliable tool to determine susceptibility to colistin in isolates of genera that are known not to exhibit resistant subpopulations. In isolates of genera known to (occasionally) exhibit heteroresistance, an alternative susceptibility testing method capable of detecting heteroresistance should be used.