Comparative Evaluation of Antibiotic Susceptibility Testing on Vitek-2 Compact and Direct Sensitivity Test from Blood Cultures from a Tertiary Care Centre in South India

Bloodstream infections (BSIs), recognized to be a major cause of morbidity and mortality globally, are increasing in incidence. India currently tackles an estimated 7,50,000 cases of BSI every year which includes 2% of hospitalized patients and 70% of patients admitted in the Intensive Care Unit. The associated crude mortality rate is 14-57%. Blood culture samples were subjected simultaneously to susceptibility testing by Direct Sensitivity Test (DST) by disk diffusion method and Antibiotic Sensitivity Test (AST) by Vitek-2 Compact (BioMerieux) a reference method from positive blood cultures flagged by BacT/ALERT 3D System, with the culture bottles FA and PA was used for blood culture. All the blood cultures flagged positive by BacT ALERT 3D system were included in the study. A total of 102 positive blood cultures showing monomicrobial gram-positive cocci or gram-negative bacilli identified after doing a Gram’s stain, were taken for further testing. A total of 102 blood cultures yielding mono-microbial bacterial growth were evaluated in this study. Organisms belonging to the family Enterobacteriaceae accounted for 41.2% of the isolates (42/102) followed by Staphylococcus spp. giving 40.2% of the isolates (41/102). E. coli and Klebsiella spp. were the commonest Gram negative isolates. These data suggest that VITEK 2 cards inoculated with samples taken directly from positive Bact/ALERT blood culture bottles would provide acceptable antimicrobial susceptibility testing results for Gram-negative bacilli, but not for Gram-positive cocci. Compared to the reference method, the direct method would reduce turnaround time by at least 24 h.