Clinical laboratory comparison of lysis-centrifugation and BACTEC radiometric blood culture techniques

Abstract

The lysis-centrifugation technique (ISOLATOR; E. I. du Pont de Nemours & Co., Wilmington, Del.) and the radiometric blood culture technique (BACTEC; Johnston Laboratories, Inc., Cockeysville, Md.) were compared on 1,000 blood cultures. A total of 16 ml of blood was distributed: 8 ml into an ISOLATOR 7.5 microbial tube and 4 ml each into BACTEC 7C and 8B bottles. The concentrate from the ISOLATOR tubes was inoculated under a laminar-flow hood onto two sheep blood agar plates (one incubated in CO2 and one incubated anaerobically), one chocolate agar plate, and one brain heart infusion agar plate. Of 91 blood specimens obtained that yielded clinically significant organisms, 52 were positive by both systems, 27 were positive by the ISOLATOR system only, and 12 were positive by the BACTEC system only. From the positive blood specimens, 97 clinically significant organisms were isolated: 57 by both systems, 27 by the ISOLATOR system only, and 13 by the BACTEC system only. Of the 57 organisms detected by both systems, 28 were detected simultaneously, 13 were detected earlier by the ISOLATOR system, and 16 were detected earlier by the BACTEC system. Isolated colonies were obtained earlier by the ISOLATOR system in 40 cases and by the BACTEC system in 5 cases. Organisms determined to be contaminants by thorough chart review were isolated from 138 ISOLATOR tubes. In 98 instances, these were represented by one colony of Staphylococculs epidermidis, alpha-hemolytic streptococci, or diphtheroids. The ability to determine CFU per milliliter with the ISOLATOR system did not help differentiate clinically significant organisms from contaminants.

Quantitative aspects of septicemia.

“…The superiority of the lysis-centrifugation method for the recovery of mycobacteria (30,45), especially Mycobacterium avium-M. intracellulare complex (31,43,44,58,104), Cryptococcus neoformans (5,6), and Histoplasma capsulatum (5,100), from blood has been useful in diagnosis of these infections in immunocompromised patients. Enhanced isolation of staphylococci and members of the family Enterobacteriaceae was also found in several studies (6,33,34,38,39,46,63). However, the Isolator system may not be optimal for recovery of Streptococcus pneumoniae, Pseudomonas aeruginosa, and anaerobic bacteria (6,33,34,39,46,63).…”

“…Enhanced isolation of staphylococci and members of the family Enterobacteriaceae was also found in several studies (6,33,34,38,39,46,63). However, the Isolator system may not be optimal for recovery of Streptococcus pneumoniae, Pseudomonas aeruginosa, and anaerobic bacteria (6,33,34,39,46,63).…”

Contaminating coagulase‐negative staphylococci isolated in a lysis‐centrifugation (Isolator®) blood culture system

“…The results are shown in Tables 1 and 2. The 14 unidentified staphylococcal isolates are not shown in Tables 1 and 2, but they were also mutually compared with 3 plasmids (1) No plasmids (12) sensitive ( 13) T (1) 1 plasmid ( I ) 1 plasmid (10) 4-5 plasmids (1) No plasmids (3) sensitive (7) 2 plasmids", different from xx and xxx (1) 2 plasmids", different from x and xxx (1) S. haemolyticus (14) NT (14) 2 plasmidsxxx, different from x and xx (1)…”

“…Recently, a different approach, involving lysing of blood cells and followed by centrifugation, has been introduced. This system, Isolator@, generally has better detection power than several conven-tional blood culture systems (2,4,10,11,12,13), but often has a disturbingly high rate, 10-15%, of supposed contaminants, mainly coagulase-negative staphylococci (2, 10, 1 1, 13). In a recent comparative investigation in our laboratory, 1 1% of the cultures in the Isolator@ system grew coagulase-negative staphylococci of doubtful clinical importance, as compared with 1% in our routine 12-tube system (2).…”

Distribution of bacteria and yeasts within the 10-ml Isolator during the processing of seeded blood samples

“…While most studies on the Isolator (E. I. du Pont de Nemours & Co., Inc., Wilmington, Del.) report that it enables the recovery of significantly more bacteria and fungi from the blood than do conventional bottle systems, the lysis-centrifugation device nevertheless failed to detect from 9 to 29% of the pathogens in these studies (1, 2, 4-6, [8][9][10][11][12]. One of the assets of the Isolator is the frequency with which it detects very small numbers of pathogens which may be missed by bottle systems.…”