LACK OF REQUIREMENT FOR BLIND SUBCULTURES OF BACTEC BLOOD CULTURE MEDIA

To determine the need for blind subculturing of BACTEC blood culture media, results of radiometric readings, visual inspection and blind subculturing were compared for nearly 7500 blood specimens. Visual inspection and radiometric testing were performed on days 1-7; blind subcultures were made on day 3. In the 1st phase of the study, 402 of 3896 aerobic bottles were positive by radiometric testing (growth index > 25), visual inspection or subculturing. Only 6 bottles were radiometrically negative but subculture positive on day 3. The 2nd phase of the study was designed to determine if aerobic bottles eventually became radiometrically positive in those cases in which they were radiometrically negative but subculture positive on day 3. Two bottles were subculture positive but never gave a growth index of .gtoreq. 25 by day 7. One yielded Staphylococcus epidermidis and 1 yielded viridans Streptococcus sp. A total of 35 anaerobic bacteria were isolated from 3896 blood specimens. All of these anaerobes were detected by both radiometric testing and subculturing. A total of 14,972 blood culture bottles were examined. Twenty-nine bottles considered negative by visual inspection or radiometric readings were found to be positive by subculturing. Fifteen of these were shown, by chart review, to contain contaminants. Organisms in the other negative bottles would not have gone undetected because companion bottles from the same patients were radiometrically or visually positive. It is evidently not necessary to perform blind subcultures of BACTEC 7B and 8B blood culture bottles.