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Park, Shim, Yoon, and Kim: Clinical Relevance of Time-to-positivity in BACTEC9240 Blood Culture System
Original Article

Korean J Leg Med 2010;30(3):276-283.

Published online: 14 January 2010

DOI: https://doi.org/10.3343/kjlm.2010.30.3.276

Clinical Relevance of Time-to-positivity in BACTEC9240 Blood Culture System

Sang Hyuk Park, M.D., Hyoeun Shim, M.D., Nam Seop Yoon, M.T., Mi-Na Kim, M.D.

Department of Laboratory Medicine, University of Ulsan College of Medicine and Asan Medical Center, Seoul, Korea

Corresponding author: Mi-Na Kim, M.D. Department of Laboratory Medicine, Asan Medical Center, 86 Asanbyeongwon-gil, Songpa-gu, Seoul 138-736, Korea Tel: +82-2-3010-4511, Fax: +82-2-478-0884 E-mail: mnkim@amc.seoul.kr

      Revised 2 February 201019 March 2010       Accepted 12 May 2010

Copyright © 2010 Korean Society for Legal Medicine

This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/3.0/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

Background:

Continuous monitoring systems have allowed determination of the time-to-positivity (TTP). We evaluated the clinical relevance of TTP in the BACTEC9240 system (Becton-Dickinson, USA).

Methods:

A total of 2,354 vials of positive blood cultures were evaluated over 2 months. TTP was monitored from each of BACTEC Plus Aerobic/F (BD) or Pediatric Plus/F and Lytic Anaerobic/F bottles, and the differential time-to-positivity (DTP) for blood samples drawn simultaneously via catheter and a peripheral site was determined.

Results:

The average TTP of the positive vials was 17.4 hr, and 79.9% and 95.2% of the vials showed positivity within 24 and 48 hr, respectively. While the average TTP values for Aeromonas hydrophila, Bacillus cereus, Acinetobacter baumannii, and Streptococcus pneumoniae were less than 10 hr, those for Candida spp., anaerobes, Propionibacterium acnes, Corynebacterium spp, Bacillus spp. other than cereus, and coagulase-negative staphylococci were 35.3, 27.0, 56.8, 45.8, 23.0, and 26.3 hr, respectively. The negative predictive values of TTP over 24 hr to predict Staphylococcus aureus among staphylococci and S. pneumoniae among α-hemolytic streptococci were 76.7% and 100%, respectively. Enterobacteriaceae and Enterococcus faecalis showed shorter TTP in anaerobic vials than in aerobic vials. DTP of more than 2 hr was observed for 27.8%, 72.2%, and 45.5% of S. aureus, S. epidermidis, and Candida spp.

Conclusions:

TTP can be used to discriminate pathogens and contaminants. The shorter TTP in anaerobic vials of certain Enterobacteriaceae and Enterococcus spp. would facilitate further identification. DTP is useful for diagnosing catheter-related bloodstream infection by S. aureus, S. epidermidis, and Candida spp.

Keywords: Blood culture, Time-to-positivity, Differential time-to-positivity

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Fig. 1.
Cumulative percentages of positive blood culture vials at different time-to-positivity values.
kjlm-30-276f1.tif
Table 1.
Time-to-positivity and number of positive vials of frequently isolated organisms
Organisms N of vials TTP (hr) mean±SD N of vials
Total Aerobic Anaerobic TTP >24 hr TTP >48 hr  
Acinetobacter baumannii 51 51 0 8.8±2.9 0 0
Aeromonas hydrophila 17 10 7 7.2±2.6 0 0
Bacillus cereus 13 6 7 7.2±3.9 0 0
Bacillus spp. other than cereus 18 10 8 23.0±13.2 11 3
Bacteroides spp. 3 0 3 27.1±16.8 2 0
Candida albicans 34 33 1 37.5±11.8 28 0
Candida glabrata 17 8 9 50.8±19.6 16 11
Candida parapsilosis 5 5 0 35.3±11.3 4 0
Candida tropicalis 32 32 0 22.4±10.3 12 0
Clostridium spp. 2 0 2 26.9±29.9 1 0
Corynebacterium spp. 3 2 1 45.8±3.0 3 2
Enterobacter aerogenes 16 6 10 16.5±7.6 2 0
Enterobacter cloacae 37 16 21 11.5±7.6 1 0
Enterococcus faecalis 56 26 30 13.6±13.2 7 2
Enterococcus faecium 76 34 42 15.8±9.3 6 1
Escherichia coli 496 235 261 10.5±7.9 16 6
Klebsiella pneumoniae 218 107 111 12.3±15.1 16 3
Propionibacterium acnes 5 0 5 56.8±19.5 5 4
Pseudomonas aeruginosa 66 64 2 18.3±16.8 8 3
Staphylococcus aureus 378 204 174 18.8±10.7 55 11
Staphylococcus epidermidis 291 155 136 25.6±13.3 143 21
CNS other than S. epidermidis 69 47 22 29.3±15.2 38 9
Stenotrophomonas maltophilia 11 11 0 20.4±9.6 3 0
Streptococcus agalactiae 20 9 11 13.4±18.2 2 1
Viridans streptococci 62 25 37 20.8±13.8 16 3
Streptococcus pneumoniae 20 11 9 9.8±2.4 0 0

Abbreviations: TTP, time-to-positivity; CNS, coagulase-negative staphylococci.

Table 2.
Comparison of time-to-positivity in 4 pairs of organisms
Organisms N (%) of vials TTP
Total TTP <24 hr TTP ≥24 hr P value Mean P value
Streptococcus pneumoniae 20 20 (100.0) 0 (0.0) 0.011 9.8 <0.001
Viridans streptococci 62 46 (74.2) 16 (25.8)   20.8  
Bacillus cereus 13 13 (100.0) 0 (0.0) 0.011 7.2 <0.001
Bacillus spp. other than cereus 18 7 (38.9) 11 (61.1)   23.0  
Staphylococcus aureus 378 323 (85.5) 55 (14.5) <0.001 18.8 <0.001
CNS 360 179 (49.7) 181 (50.3)   26.3  
Staphylococcus epidermidis 291 148 (50.9) 143 (49.1) 0.342 25.6 0.043
CNS other than S. epidermidis 69 31 (44.9) 38 (55.1)   29.3  

Abbreviations: TTP, time-to-positivity; CNS, coagulase-negative staphylococci.

Table 3.
Time-to-positivity distributions of Staphylococcus aureus and CNS
Time-to-positivity (hr) N (%) of organisms
S. aureus CNS Total
<8 30 (90.9) 3 (9.1) 33 (100.0)
≥8 <16 178 (79.4) 46 (20.6) 224 (100.0)
≥16 <24 115 (46.9) 130 (53.1) 245 (100.0)
≥24 <32 38 (35.5) 69 (64.5) 107 (100.0)
≥32 17 (13.2) 112 (86.8) 129 (100.0)

Abbreviations: CNS, coagulase-negative staphylococci.

Table 4.
Time-to-positivity of Enterobacteriaceae, Enterococcus spp., and Candida glabrata in aerobic and anaerobic vials
Organisms N of vials Average TTP (hr) P value
Aerobic Anaerobic
Escherichia coli 496 12.1 9.0 <0.001
Klebsiella pneumoniae 218 14.6 10.1 0.028
Enterobacter cloacae 37 15.2 8.6 0.008
Enterobacter aerogenes 16 19.1 14.9 0.306
Enterococcus faecalis 56 14.0 13.3 0.851
Enterococcus faecium 76 15.6 16.1 0.831
Candida glabrata 17 56.8 45.6 0.026

Abbreviations: TTP, time-to-positivity.

Table 5.
Differential time-to-positivity among frequent isolates of simultaneous peripheral and catheter culture
Organisms Ratio (%) of sets with DTP >2 hr DTP (mean±SD)
Acinetobacter baumannii 2/8 (25.0) -0.1±3.2
Bacillus cereus 1/3 (33.3) 3.3±5.4
Candida albicans 2/6 (33.3) 5.6±10.3
Candida glabrata 2/4 (50.0) 3.3±22.9
Candida parapsilosis 1/1 (100.0) 15.0
Candida tropicalis 0/7 (0.0) -7.0±12.8
Enterobacter cloacae 0/2 (0.0) -2.1±3.3
Enterococcus faecalis 1/7 (14.3) 0.8±0.9
Enterococcus faecium 0/7 (0.0) -4.5±8.8
Escherichia coli 1/16 (6.3) 0.3±0.9
Klebsiella pneumoniae 2/25 (8.0) 0.4±1.0
Pseudomonas aeruginosa 1/6 (16.7) 0.0±11.6
Serratia marcescens 1/3 (33.3) 5.7±2.9
Staphylococcus aureus 10/36 (27.8) -1.5±14.1
Staphylococcus capitis 1/1 (100.0) 8.2
Staphylococcus epidermidis 26/36 (72.2) 6.1±11.7
Stenotrophomonas maltophilia 1/1 (100.0) 3.0
Streptococcus mitis 2/3 (66.7) 3.8±2.8

Abbreviations: DTP, differential time-to-positivity.

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