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Geisinger Medical Center, Danville, Pennsylvania
ABSTRACT
bioMerieux, Inc., has recently introduced plastic bottles to replace glass bottles for use in the BacT/ALERT blood culture system. We compared the performance of the plastic to the glass bottles in a large clinical evaluation. Two blood cultures were collected from each patient, one using glass FA (aerobic) and FN (anaerobic) bottles and one using plastic FA and FN bottles. Of the 4,040 sets of four bottles collected, 3,110 contained the recommended 8 to 12 ml of blood, yielding 524 microorganisms with 359 judged to be clinically significant. Of the 359 significant organisms, 255 were recovered in either one or two bottles from both pairs of bottles in a set while 56 organisms were recovered only from the glass bottles and 48 were recovered only from the plastic bottles (P, not significant [NS]). Of the 286 significant organisms recovered only in the FA bottles (glass and plastic), 180 were recovered in both bottles, 57 in the plastic bottles only, and 49 in the glass bottles only (P, NS). Of the 303 significant organisms recovered in the FN bottles only (glass and plastic), 212 were recovered in both bottles, 46 in the plastic bottles only, and 45 in the glass bottles only (P, NS). For individual organisms, the only significant difference in recovery was obtained for Escherichia coli, with more isolates recovered in the FN plastic than in the FN glass bottles (P = 0.02). These data suggest that recovery of microorganisms with plastic FA/FN bottles is at least equal to that with glass FA/FN bottles while offering greater safety for users.
INTRODUCTION
bioMerieux, Inc. (Durham, NC), recently introduced plastic blood culture bottles to replace the previously utilized glass blood culture bottles. This change was made to reduce or eliminate the possibility of breakage. The purpose of this study was to compare the performance of the glass and plastic aerobic (FA) and anaerobic (FN) bottles with a full 10-ml blood draw in each bottle.
MATERIALS AND METHODS
The standard of care for adult patients at Geisinger Medical Center is two pairs of blood cultures collected sequentially via separate venipunctures or separate line access. For this study, sets of four BacT/ALERT blood culture bottles were specially prepared in the laboratory. Sets included one each of a plastic FA (PFA), plastic FN (PFN), glass FA (GFA), and glass FN (GFN) blood culture bottle. Each pair of PFA-PFN or GFA-GFN bottles was labeled with the number one or two in order to facilitate collecting first into the PFA-PFN pair for approximately one-half of the patients while the remainder of the patient draws were collected first into the GFA-GFN pair. The standard Geisinger Medical Center protocol was followed for skin preparation prior to collection. Blood volumes were verified (8 to 12 ml) by the use of a visual standard.
For the sake of clarity, the following terminology is consistently utilized in this report: the term "set" refers to all four bottles collected during a patient episode, the term "pair" refers to two bottles collected by a single collection procedure, and the term "bottle" refers to a single bottle. Hence, there are two bottles in a pair and two pairs in a set. All bottles were incubated in BacT/ALERT blood culture cabinets at 35°C, using a 5-day protocol. Culture workup and identification were performed using the standard Geisinger Medical Center microbiology laboratory procedures. All cultures were worked up and reported by the standard protocols used by the microbiology laboratory at Geisinger Medical Center. A 5-day incubation period was used for all negative bottles.
If one or more bottles from a set gave a positive signal by the instrument and there was growth upon subculturing, any remaining bottles from the set that were instrument negative after 5 days of incubation were subcultured.
For the purposes of this study, isolates of coagulase-negative staphylococci, Bacillus spp., viridans group streptococci, Propionibacterium spp., and aerobic diphtheroids isolated from only one pair of bottles in a set were considered not to be clinically significant. Statistical analysis was performed as described by Ilstrup (1).
RESULTS
A total of 4,040 sets of four bottles were collected. Of these 4,040 sets, 3,110 contained the recommended 8 to 12 ml of blood in each of the four bottles. These 3,110 sets yielded 524 microorganisms, including 359 judged to be clinically significant and 165 judged to be probable contaminants. Of the 359 significant organisms, 255 were recovered in either one or two bottles from both pairs of bottles in a set while 56 were recovered only from the glass bottles and 48 were recovered only from the plastic bottles (P > 0.05; not significant [NS]) (Table 1). Separate analyses were performed to compare the performances of the two aerobic (PFA and GFA) and the two anaerobic (PFN and GFN) bottles. Of the 286 significant organisms recovered in the FA bottles (both glass and plastic), 180 were recovered in both bottles, 57 in the PFA bottles only, and 49 in the GFA bottles only (P, NS) (Table 2). Of the 303 significant organisms recovered in the FN bottles (both glass and plastic), 212 were recovered in both bottles, 46 in the plastic bottles only, and 45 in the glass bottles only (P, NS) (Table 3). For individual organisms, the only significant difference in recovery was obtained for Escherichia coli, with more isolates recovered in the plastic FN bottles (P = 0.02). There were no significant differences in the number of probable contaminants isolated between the glass and the plastic bottle sets overall or between the aerobic bottles. However, more contaminants were recovered from the plastic anaerobic bottles than were recovered from the glass anaerobic bottles (P = 0.03).
Subculture of bottles that were reported as negative by the instrument but had a companion positive bottle from the set detected by the instrument yielded 17 organisms. There were 10 Pseudomonas aeruginosa isolates (5 from PFN and 5 from GFN bottles) and 1 Alcaligenes sp. isolate (PFN) detected by subculture from an anaerobic bottle of a pair that had a positive aerobic bottle. One isolate of Eubacterium lentum was detected in a PFN bottle but not in the GFN bottle, while one isolate of Pseudomonas aeruginosa was instrument positive in a PFA bottle but detected only by subculture from the GFA bottle. One Alcaligenes sp. isolate was detected by subculture of the PFN bottle, while the GFA bottle from the set was instrument positive for an isolate of Klebsiella pneumoniae and the GFN bottle from the same set was instrument positive for an isolate of Serratia marcescens. Two Propionibacterium sp. isolates and one Corynebacterium sp. isolate were detected by subculture of bottles while each of the paired bottles was instrument positive for isolates of a Staphylococcus sp. other than Staphylococcus aureus.
DISCUSSION
Since the introduction of the original BacT/ALERT blood culture system, several "generations" of new bottles have been introduced. Initially, only bottles with the designations "standard aerobic" and "standard anaerobic" were available; at a later time, additional bottles with the designations "FAN aerobic" and "FAN anaerobic" were introduced. The FAN bottles were designed to enhance the recovery of fastidious bacteria, bacteria from patients receiving antimicrobial therapy, and yeasts in comparison to recovery with the standard BacT/ALERT blood culture bottles (4, 5). Subsequently, nonvented BacT/ALERT bottles, designated FA and FN, replaced the FAN aerobic and FAN anaerobic blood culture bottles. The FA and FN bottles have a different medium formulation and a different type of sensor than the FAN bottles (2). The FA bottles contain a different concentration of charcoal, a smaller volume of medium, and more headspace gas than the FAN aerobic bottles. Lastly, the FA bottles are unvented, while the FAN aerobic bottles required transient venting.
In addition to the obvious change from glass to plastic in the bottles, the plastic bottle necessitated a change in the liquid sensor used in the bottles (Steven Rothenberg, personal communication). No changes were made in media or atmosphere in the bottles. Consequently, it is not unexpected that there would be little if any difference in recovery between the glass and plastic bottles. Petti et al. reported no difference in recovery between plastic and glass PF bottles (3).
The plastic bottles weigh approximately 4 pounds less per 100 bottles than glass bottles. In our laboratory, which performs around 25,000 blood cultures per year, use of plastic bottles results in approximately 2,000 pounds less of biohazard waste per year than use of glass bottles. The potential cost savings for biohazard waste disposal would be determined by disposal costs for each laboratory.
When we routinely used glass bottles in our laboratory, we periodically received a bottle that was cracked during transit to the laboratory. Because the glass bottles had a plastic wrapper to curtail shattering if dropped, cracks that developed as a result of dropping were not always visually apparent. On several occasions, we did not detect cracked bottles until after they were loaded into the instruments. Subsequent leaks required decontamination of individual cells and, on one occasion, decontamination of an entire block. This potential problem should be eliminated with plastic bottles.
In conclusion, in our evaluation, which included 3,110 blood culture sets, we found no significant difference in recovery of clinically significant microorganisms between the glass and plastic FA and FN bottles, although the plastic bottles did recover more organisms. Moreover, plastic bottles offer greater safety and, potentially, lower disposal costs than glass bottles.
REFERENCES
Ilstrup, D. M. 1978. Statistical methods employed in the study of blood culture media, p. 31-39. In J. A. Washington (ed.), The detection of septicemia. CRC Press, West Palm Beach, Fla.
Mirrett, S., R. J. Everts, and L. B. Reller. 2001. Controlled comparison of original vented aerobic FAN medium with new nonvented BacT/ALERT FA medium for culturing blood. J. Clin. Microbiol. 39:2098-2101.
Petti, C. A., S. Mirrett, C. W. Woods, and L. B. Reller. 2005. Controlled clinical comparison of plastic versus glass bottles of BacT/ALERT PF medium for culturing blood from children. J. Clin. Microbiol. 43:445-447.
Weinstein, M., S. Mirrett, L. Reimer, M. Wilson, S. Smith-Elekes, C. Chuard, K. Joho, and L. Reller. 1995. Controlled evaluation of BacT/Alert standard aerobic and FAN aerobic blood culture bottles for detection of bacteremia and fungemia. J. Clin. Microbiol. 33:978-981.
Wilson, M., M. Weinstein, S. Mirrett, L. Reimer, R. Feldman, C. Chuard, and L. Reller. 1995. Controlled evaluation of BacT/Alert standard anaerobic and FAN anaerobic blood culture bottles for the detection of bacteremia and fungemia. J. Clin. Microbiol. 33:2265-2270.