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Published on: July 9, 2012
Rapid antibiotic susceptibility testing (RAST) of blood cultures in enterobacteria with inducible chromosomal
Blanca Carrasco1, Gloria Zaragoza1, David M Arana1
1Servicio de Microbiología, Hospital Universitario de Getafe, Getafe, Madrid, Spain.
Introduction:
Early and adequate treatment of bloodstream infections decreases patient morbidity and mortality. The objective is to develop a preliminary method for rapid antibiotic susceptibility testing (RAST) in enterobacteria with inducible chromosomal AmpC.
Methods:
RAST was performed directly on spiked blood cultures of 49 enterobacteria with inducible chromosomal AmpC. Results were read at 4, 6 and 8h of incubation. Commercial broth microdilution was considered the reference method. Disks of 10 antibiotics were evaluated.
Results:
The proportion of readable tests at 4h was 85%. All RAST could be read at 6 and 8h. For most antibiotics, the S or R result at 4, 6 and 8h was greater than 80% after tentative breakpoints were established and Area of Technical Uncertainty was defined.
Conclusions:
This preliminary method seems to be of practical use, although it should be extended to adjust the breakpoints and differentiate them by species.
