Mary K. York

Evaluation of BACTEC MYCO/F Lytic Medium for Recovery of Mycobacteria, Fungi, and Bacteria from Blood

ABSTRACT MYCO/F Lytic medium (MFL), a liquid medium developed for use with the BACTEC 9240 blood culture system, was compared to the Isolator system (IS) for the recovery of fungi and to the BACTEC 13A medium for the recovery of mycobacteria. Recovery of bacteria was compared to routine BACTEC Plus Aerobic/F (AF) blood cultures. Microbial growth was detected in 203 (17%) of 1,166 blood cultures. Fifty-seven specimens were positive for fungi: 35 were positive with both IS and MFL; six were positive with IS only (three Candida albicans, oneHistoplasma capsulatum, one Candida glabrata, and one Fusarium species isolate); three were positive with AF only (two C. albicans and one Candida parapsilosis isolate); and 13 were positive with MFL only (fiveC. glabrata, three C. albicans, twoCandida krusei, two Candida tropicalis, and oneC. parapsilosis isolate; P > 0.05 versus IS). Eighteen of 19 blood cultures positive for H. capsulatum grew in both IS and MFL, although the time to detection for MFL was greater. The mean time to detection for all fungi was 8.15 days for IS and 12.07 days for MFL. Seven hundred forty specimens were also cultured for mycobacteria with MFL and 13A. Forty-four grew mycobacteria; 38 were positive with both 13A and MFL; and 16 were positive with MFL only. Mycobacterium avium was recovered from 41 specimens; 36 were positive for both systems and 5 were positive for MFL alone. MFL was also compared to the AF bottle for the same 740 specimens. MFL and AF both detected 34 of the 40 clinically significant bacteria, while IS detected only 15 of 40. In summary, MFL is an excellent medium for the recovery of fungi, mycobacteria, and bacteria; however, the time to detection of H. capsulatum is increased.

Reporting susceptibility test results—are we really communicating with physicians?

Abstract The laboratory report or lack of a report for susceptibility testing can influence the choice of drugs used to treat patients. In addition to knowing and accurately reporting results for drugs tested, the laboratory must be aware of both appropriate and inappropriate drug/organism reporting based on knowledge of treatment failures and successes. Because results for one drug that is tested can predict or not predict susceptibility to other drugs, laboratories should consider annotating their reports to explain confusing or misleading results. Communication with those prescribing antimicrobial therapy is imperative to understanding the implications and consequences of the reports generated by the laboratory.

Abbreviated, rapid identification of bacteria and yeasts

Summary As described above, many alternative ways to rapidly identify organisms commonly seen in clinical specimens are available. While most reagents can be purchased, large laboratories may find it cost-effective to make a few. Examples of these reagents are summarized in Table 3. Use of rapid spot-test methods is at the discretion of each laboratory, but clearly a large amount of time and resources can be saved and patient care will benefit from the rapid reporting of organism identifications.

Comparison of two Bactec anaerobic culture media for recovery of anaerobic bacteria

A selection of 22 anaerobic isolates, originally recovered from sterile body sites or wounds, was cultured in parallel in BACTEC anaerobic NR7A and lytic 37A bottles supplemented with volunteer human blood. The overall detection rate was 95% for the 37A medium and 75% for the NR7A medium (P = 0.003). The growth indices were consistently higher in the 37A bottles, and a positive result occurred sooner in the 37A medium in 11 of the 32 bottles positive in both media. In an analysis of patient specimens, the NR7A bottle had a 14% false-positive rate compared with 3% for the 37A bottle. The increase in recovery, coupled with the decrease in false-positive readings, make the lytic 37A bottle more efficacious than the NR7A bottle as an anaerobic culture medium.