Comparative evaluation of Vitek 2 identification and susceptibility testing of urinary tract pathogens directly and isolated from chromogenic media

Abstract

We evaluated the use of urine specimens for direct identification and antibiotic testing of urinary tract pathogens using the Vitek system. A total of 343 urine specimens from patients with suspected UTI were selected by pyuria and screened by Gram staining to detect bacteriuria. Of those, 132 were analysed after Gram staining, showing a high number of micro-organisms of a single morphological type. Direct susceptibility testing and identification were performed by using the Vitek system. Results were compared using the standard inoculation method based on the incubation of solid media. After sub-culture, 107 specimens grew a significant count of a single species and were used for the comparative analysis. The direct method correctly identified 88 isolates (82.3 %). When compared according to antibiotic susceptibility testing, the error rate was 2.4 % overall with 0.2 % very major, 0.4 % major and 1.8 % minor errors. 84.7 % of the Gram-negative bacilli had a complete susceptibility report in ≤ 8 h. This method offers the advantage of prompt processing and earlier reporting of complete results for positive urine specimens.