Direct identification and susceptibility testing of Gram-negative bacilli from turbid urine samples using VITEK2

Urinary tract infections (UTIs) are the most common infectious diseases occurring in either the community or healthcare setting. Turnaround time for urine culture is about 24 h, and antimicrobial susceptibility testing (AST) requires another 24 h. Consequently, initial antibiotic therapy is mostly empirical.

This study was conducted at Nizam's Institute of Medical Sciences, Hyderabad. Turbid urine samples which showed pus cells and Gram-negative (GN) bacilli of single morphotype were included. The turbidity of the urine was adjusted to 0.5 McFarland and uploaded directly in the VITEK 2 identification (ID) GN and N-280 panel for AST. The specimen was also inoculated on CHROMagar, and the ID and AST of the isolates from the agar plate were repeated on VITEK 2, and the results were compared.

Out of 844 turbid urines screened, 62 met the inclusion criteria. Escherichia coli was the most common isolate (71.9%). Complete agreement for ID was 80.7%, misidentified were 12.2%, and unidentified were 7%. Complete agreement with AST was 94.3%, very major errors 0.5%, major errors 2.2%, and minor errors 3%.

With a 94.3% agreement for AST and a reduced turnaround time by 24 h, the direct inoculation had a potential clinical benefit for initiating timely and appropriate antibiotic therapy for UTI.