Contamination of cultures processed with the isolator lysis-centrifugation blood culture tube

Abstract

Overall contamination (on-plus off-streak) of the Isolator (Du Pont Co.) blood culture tube (23%) was greater than that of a conventional broth blood culture bottle (0.6%) or that of a biphasic blood culture bottle (1.3%). To determine the source of this contamination, Isolator cultures of blood from 59 healthy volunteers and of sterile broth from 60 vials were made. A total of 37% of the blood cultures and 22% of the broth cultures were contaminated (P = 0.06). Staphylococcus epidermidis-contaminated cultures represented 31 and 10% of the blood and broth cultures, respectively (P = 0.06). Contamination of plates processed on a bench top, in front of horizontal laminar flow, and in a biological safety cabinet with vertical laminar flow were compared. Processing plates in a biological safety cabinet resulted in a significant reduction in the number of contaminated plates (P < 0.05). The contamination rate for 7,874 Isolator blood cultures processed in the biological safety cabinet was significantly decreased to 6.7% on-streak (9.3% on-plus offstreak). Contamination of Isolator-processed blood cultures originated from the laboratory and the patient. The former can be reduced by inoculating plates in a vertical laminar flow biological safety cabinet and by maintaining adequate quality control of media. The latter may be unavoidable.

E Test versus Agar Dilution for Antimicrobial Susceptibility Testing of Viridans Group Streptococci

“…The proportion of VGS isolates categorized as significant, indeterminate, or not significant in our study is in keeping with the proportions generated by other studies of unselected VGS populations (25,30,31). That the use of a lysis-centrifugation culture method is associated with a higher rate of clinically insignificant isolates has been demonstrated previously (17,27).…”

Quantitative aspects of septicemia.

“…It appears that use of a laminar flow cabinet is a critical factor for reducing contamination rates to an acceptable level. In one study, the contamination rate dropped from 9.5 to 6.2% (87) and in another study it dropped from 9.6 to 2.5% (94) when lysis-centrifugation blood cultures were processed in a laminar flow cabinet.…”

Comparison of lysis-centrifugation with lysis-filtration and a conventional unvented bottle for blood cultures

“…Moreover, the increased isolation of one or two colonies of staphylococci is a decided diagnostic dilemma in many cases, and we are not confident that the distinction of contaminant versus significant can be made with any degree of reliability. It is possible that transient low-level bacteremia with these organisms may occur with greater frequency than previously suspected (9,13). Although erring on the side of caution by reporting all onstreak colonies to the physician may seem reasonable from the point of view of a laboratory, added patient care costs for treatment, additional blood cultures, and extra tests are certainly undesirable.…”