Clinical comparison of the resin-containing BACTEC 26 Plus and the Isolator 10 blood culturing systems.

The new resin-containing BACTEC 26 Plus blood culturing system (Becton Dickinson Diagnostic Instrument Systems, Towson, Md.) was compared with the Isolator 10 system (Wampole Laboratories, Cranbury, N.J.). Blood samples were drawn by syringe, and equal 10-ml volumes were evaluated in each blood culture system by the recommended methods. Both systems were incubated aerobically with 5% CO2. Of 11,506 acceptable study specimens, 1,788 aerobic isolates were recovered. Overall, recoveries was similar for the two systems, with 626 bacteria or fungi recovered in the BACTEC 26 Plus system only, 499 recovered in the Isolator system only, and 663 recovered in both systems. Of 345 gram-negative rods, 62 grew in the BACTEC system only and 109 grew in the Isolator system only (P less than 0.001). Thirty-three of these Isolator-only gram-negative organisms were Acinetobacter spp. Of 209 yeasts, 38 grew in BACTEC only and 81 grew in Isolator only (P less than 0.001). Of 200 streptococci and enterococci, 98 were recovered in BACTEC only and 26 grew in Isolator only (P less than 0.001). Two hundred twenty-eight independent episodes of gram-negative rod bacteremia occurred. Isolator was the first system positive in 59 of 197 episodes, compared with 45 of 197 for BACTEC when Acinetobacter episodes were excluded. Times to detection were similar for the two systems. High colony counts correlated with repeat positive blood cultures. Isolator and BACTEC had similar overall recoveries, with individual merits and deficiencies for both systems. The additional quantitative information derived from Isolator had utility in our institution.

Enzyme release of antigen from Streptococcus faecalis and Listeria monocytogenes cross-reactive with Lancefield group G typing reagents.

Enzyme extraction methods are commonly used to release antigen for Lancefield serogrouping of streptococci. Recently, up to 47% of enterococci have been found to possess antigens cross-reactive with both the group D and the group G grouping reagents. We investigated whether the organisms had recently emerged or whether changes in extraction methods (enzyme extraction) have resulted in our awareness of their existence. We found that approximately 20% of our enterococcal isolates released material cross-reactive with the group G reagents. These organisms have been present for at least 6 years, and probably for many more. In addition, we found that most strains of Listeria monocytogenes also released antigen cross-reactive with the group G reagent. The clinical significance of these findings is also discussed.

Routine use of BACTEC 16B bottles to remove antibacterial and antitumor agents from blood cultures of cancer patients.

A total of 1,764 paired sets of BACTEC 6B and 16B blood culture bottles were collected from patients for analysis. The majority of the patients were receiving antibiotic therapy at the time the blood specimens were collected. A total of 126 isolates were considered clinically significant. Of these, 58 grew in both 6B and 16B bottles, 25 grew only in 6B bottles, and 43 grew only in 16B bottles. In both bottles, the same amount of time was required to detect a positive culture. In 18 patients, septicemias were detected in the 16B bottles that were not detected in the 6B bottles. In seven patients, microorganisms were detected in the 6B bottles that were not detected in the 16B bottles. Interestingly, the antibiotic therapy was changed for only 4 of the 18 patients whose septicemias were detected only in the 16B bottles. Finally, an in vitro study showed that certain chemotherapeutic agents can cause the inhibition of growth of several microorganisms when tested in 6B bottles. These inhibitory effects were reduced or eliminated when the same organism-drug combinations were tested in 16B bottles.

Valuable of terminal subcultures from negative BACTEC blood culture bottles.

Terminal subcultures from 5,354 negative BACTEC blood culture bottles did not significantly improve the detection of positive cultures. Only 15 of the 545 total isolates were recovered from the terminal subcultures. All 15 of these isolates were either considered contaminants or had been previously detected.

Radiometric detection of yeasts in blood cultures of cancer patients.

During a 12-month period, 19,457 blood cultures were collected. Yeasts were isolated from 193 cultures derived from 76 cancer patients. Candida albicans or Candida tropicalis accounted for 79% of isolates. Of the three methods compared, the radiometric method required 2.9 days to become positive, "blind" subculture required 2.6 days, and Gram stains required 1 day. However, the radiometric method was clearly superior in detecting positive cultures, since 73% of all cultures were first detected radiometrically, 22% were detected by subculture, and only 5% were detected by Gram stain. Although 93% of the isolates were detected by aerobic culture, five (7%) isolates were obtained only from anaerobic cultures. Seven days of incubation appear to be sufficient for the radiometric detection of yeasts.