Rapid, Direct Antibiotic Susceptibility Testing of Blood Culture Isolates Using the Abbott Avantage® System

The Abbott Avantage® (AV) is an updated version of the MS-2® system that provides antibiotic-susceptibility results in four to six hours. Although the system compared favorably with reference methods in several laboratory evaluations, little information exists regarding its performance with inocula obtained directly from blood cultures. The authors compared AV and a modified disk-diffusion test using standardized inocula obtained directly from the blood culture bottles for 58 isolates (46 patients). All isolates were also tested by the National Committee for Clinical Laboratory Standards standard disk-diffusion method, using inocula obtained from subcultures of the positive bottles. AV results for 553 antibiotic tests agreed with the direct disk results in 92.6% of the tests, and the agreement with the standard disk results was 88.2%. The concordance between direct and standard disk results was 93.5%. There were 2.2% very major, 1.8% major, and 7.8% minor discrepancies between results obtained with direct AV and standard disk methods. False sensitivity of Klebsiella pneumoniae to ampicillin and carbenicillin and induced clindamycin resistance in staphylococci were noted with AV. When one considers only the clinically meaningful antibiotic–organism combinations, direct AV is an acceptable, rapid alternative to direct disk susceptibility testing.