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Revista de salud publica del Paraguay

versión impresa ISSN 2224-6193versión On-line ISSN 2307-3349


MELGAREJO TOUCHET, Nancy et al. Evaluation of colistin susceptibility testing methods among Enterobacterales strains isolated in Paraguay. Rev. salud publica Parag. [online]. 2021, vol.11, n.2, pp.17-23. ISSN 2307-3349.


The evolution of antimicrobial resistance has put at risk the value of broad-spectrum drugs available for the treatment of infectious diseases and has promoted the use of others such as colistin, especially in multi-resistant Enterobacterales infections, being necessary to know and define reliable methodologies that can predict its sensitivity.


With the aim of evaluating different colistin susceptibility test methods; the present study was carried out on isolated strains in different hospitals in Paraguay.


Retrospective, cross-sectional study, carried out with isolated strains in different hospitals in Paraguay, during the period between 2016-2019. Five colistin susceptibility testing methods were evaluated: disk diffusion (Kirby Bauer), gradient diffusion strips (Epsilometer test), colistin broth disk elution, automated Vitek®2 and mcr-1 gene by PCR, and compared with the reference method: broth macrodilution. MIC results were evaluated using interpretive criteria available from the EUCAST. In addition, the error rates (major and very major), and categorical agreement were calculated.


Categorical agreement between colistin broth disk elution and broth macrodilution was 100%. With the Vitek®2 automated and gradient diffusion strips methods, very severe errors were found: 42% and 56% respectively. Strains with a zona diameter 14 mm were 50% resistant. The carriage of mcr-1 was 10.5%, 1 of them being sensitive to colistin.


Our findings showed that the colistin broth disk elution method is reliable for the study of susceptibility in Enterobacterales. The other methods evaluated should not be used to predict sensitivity to colistin, as they could lead to inappropriate treatment. Furthermore, mcr-1 carrier strains with MIC≤2ug/mL were found .

Palabras clave : drug resistance, bacterial; colistin; microbial sensitivity tests; Enterobacteriaceae; Paraguay.

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