Skip to main page content

• HOME
• Current Issue
• Archive
• Alerts
• About ASM
• Contact us
• Tech Support
• Journals.ASM.org

This Article Abstract Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Reprints and Permissions Copyright Information Books from ASM Press MicrobeWorld Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Qian, Q. Articles by Kirby, J. E. Search for Related Content PubMed PubMed Citation Articles by Qian, Q. Articles by Kirby, J. E.

 Previous Article  |  Next Article 

Journal of Clinical Microbiology, July 2007, p. 2267-2269, Vol. 45, No. 7
0095-1137/07/$08.00+0     doi:10.1128/JCM.00369-07
Copyright © 2007, American Society for Microbiology. All Rights Reserved.

Rapid Identification of Staphylococcus aureus in Blood Cultures by Use of the Direct Tube Coagulase Test

Qinfang Qian,^* Karen Eichelberger, and James E. Kirby

Division of Laboratory and Transfusion Medicine, Department of Pathology, Beth Israel Deaconess Medical Center and Harvard Medical School, Boston, Massachusetts 02215

Received 16 February 2007/ Returned for modification 5 April 2007/ Accepted 11 May 2007

Top ABSTRACT TEXT REFERENCES

 
Direct tube coagulase testing for identification of Staphylococcus aureus from BACTEC culture broth showed a sensitivity, a specificity, and positive and negative predicative values of 34%, 100%, 100%, and 80.2% with 2 h of incubation and 65%, 98.7, 99.7%, and 88.6% with 4 h of incubation. Anaerobic blood culture contributed significantly to the detection of S. aureus.

Top ABSTRACT TEXT REFERENCES

 
Staphylococcus aureus is one of the leading causes of bacteremia, with high levels of accompanying morbidity and mortality (7, 10, 11, 18). Complication rates rise steadily with the duration of untreated bacteremia (5). Therefore, methods for the rapid identification of S. aureus in blood culture broth have been developed, including peptide nucleic acid fluorescence in situ hybridization, PCR, and the enzymatic RAPIDEC test (8, 12, 15, 16). However, they are expensive and labor intensive and the RAPIDEC test (3, 16) shows suboptimal specificity. In contrast, the direct tube coagulase (DTC) test is rapid, simple, and inexpensive. Previously, the DTC test showed good sensitivity and specificity when applied to the BacT/Alert (17), ESP (3), and Bactec 660 (9) systems. However, only a small study was previously performed with the BACTEC 9240 system with a single 2-h incubation (16). We therefore performed an extensive evaluation of BACTEC 9240-based medium by incorporating it into routine clinical work.

From 2003 to 2005, blood culture broth from Standard/10 Aerobic/F and LYTIC/10 Anaerobic/F bottles was evaluated by DTC test when Gram staining suggested staphylococci (16). Clot formation was assessed after incubation of a mixture of 5 drops of culture broth and 0.5 ml of rabbit plasma at 35°C for 2 and 4 h. Among 1,780 positive blood cultures tested, there were 477 S. aureus isolates and 1,303 other bacteria (Table 1). At 2 h (Table 2), 125 S. aureus isolates showed obvious gelling and 35 additional isolates showed partial gelling, with reactivity independent of methicillin resistance status (data not shown). At 4 h, an additional 133 and 17 showed strong and weak positivity, respectively. When both complete gelling and partial gelling were considered positive, the sensitivity, specificity, positive predicative value, and negative predicative value for the 2- and 4-h time points were 34%, 100%, 100%, and 80.2% and 65%, 99.7%, 98.7%, and 88.6%, respectively.

View this table: [in this window] [in a new window]

TABLE 1. Identification of organisms other than S. aureus in blood culture broth tested by DTC test

View this table: [in this window] [in a new window]

TABLE 2. Characteristics of DTC test-positive samples

The potential for false-positive DTC test results has not been sufficiently studied in actual clinical practice. One previous study evaluated a limited variety of organisms in simulated blood culture and found no false positives after a 2-h incubation (9). Here, we evaluated a much larger number and variety of bacteria initially thought to have a Gram stain compatible with S. aureus (Table 1). Four false-positive results (at 4 h) were found, including three isolates identified as coagulase-negative staphylococci (CoNS) and one isolate identified as Enterococcus faecalis (Table 2). Unfortunately, the three CoNS isolates were not saved for further analysis but potentially may have been coagulase-producing species (1).

Additionally, we showed for the first time that the DTC test performed equally well with both aerobic broth and anaerobic broth. Among the 32 sets evaluated (both bottles were evaluated since they were flagged simultaneously), 29/32 aerobic and 25/32 anaerobic samples were positive at 2 h (P = 0.3; Fisher's exact test) and 31/32 aerobic and 30/32 anaerobic samples were positive at 4 h (P = 1.0).

Importantly, during this analysis, we found that anaerobic blood culture contributed significantly to S. aureus detection (P < 0.001). Among 447 S. aureus culture sets analyzed, 299 (62.7%) were positive in both aerobic and anaerobic bottles, 42 (8.8%) were positive in aerobic bottles alone, and 136 (28.5%) were isolated in anaerobic bottles alone. Methicillin resistance was not associated with growth preference (data not shown). Clinical chart review revealed that for 82 (17.2%) patients, S. aureus was detected solely on the basis of anaerobic culture (Table 3). Among these, a mean of 3.4 ± 1.3 blood culture sets per patient were drawn within 3 days of the first positive culture and 30% had multiple positive anaerobic cultures. Conversely, aerobic culture was necessary for diagnosis in only 15 (3.1%) patients. Here, a mean of 2.1 ± 0.8 blood culture sets were drawn within 3 days of the first positive culture. Two of these patients had multiple positive aerobic cultures. Our data suggest that some strains grow preferentially in either anaerobic or aerobic bottles, although the lytic component rather than anaerobic conditions might account for preferential growth in the former. Similar results were obtained with the BacT/ALERT system (13). Interestingly, a previous study found the BACTEC PLUS aerobic/F bottle superior to the LYTIC anaerobic/F bottle used here; nevertheless, 13% of the S. aureus isolates were still missed in the absence of anaerobic culture (14). Therefore, both bottles need to be used for optimal detection of S. aureus, providing an additional rationale for the routine use of anaerobic culture (4, 6, 14).

View this table: [in this window] [in a new window]

TABLE 3. Detection of S. aureus bacteremic episodes by aerobic versus anaerobic bottles alone

Previously, a number of variables have been examined for optimizing the sensitivity of the DTC test. In our study, we found that increasing the incubation period from 2 to 4 h greatly enhanced sensitivity, although this contrasts with a BACTEC 660 study (9) in which no difference was found. The sensitivity (65%) of the DTC test in our study was lower than the sensitivities found in studies performed with the BACTEC 660 (79.5%) (9) and ESP (84.1%) (3) systems and a small study performed with the BACTEC 9240 system (92%) (16). Of note, in our study, the DTC test was performed by a large number of rotating laboratory personnel as a part of the routine workup. When the DTC test was performed by one of us (100 S. aureus and 179 CoNS isolates), the sensitivity increased to 68% at 2 h and 90% at 4 h and the specificity was 100%. The higher sensitivity potentially relates to better appreciation of weak positive reactions, as suggested previously (9). A potentially expected decrease in specificity was not observed here because of the smaller number of CoNS isolates examined and/or the high specificity of even weak DTC reactions.

Even with a sensitivity of 65% and the potential for higher sensitivity with further training, we believe the assay is clinically valuable. The DTC test rapidly identifies the majority of S. aureus isolates. In cases where clinical suspicion is low, this early identification prevents therapy being withheld for a day pending the identification of a presumed contaminant (i.e., CoNS) to the species level, as documented elsewhere (2). Because of its low cost and simplicity, we believe it will continue to serve an important role in laboratories that can neither afford nor implement around-the-clock testing by more-sensitive methods such as PCR.

 
We thank all of the technologists in our laboratory for help with this evaluation, especially Joanna Dakos and Jaleh Shafa.

 
* Corresponding author. Mailing address: Department of Pathology, Beth Israel Deaconess Medical Center, Yamins 309, 330 Brookline Avenue, Boston, MA 02215. Phone: (617) 667-4911. Fax: (617) 667-4533. E-mail: qqian{at}bidmc.harvard.edu

Published ahead of print on 23 May 2007.

Top ABSTRACT TEXT REFERENCES

 

1
1. Bannerman, T. L. 2003. Staphylococcus, Micrococcus and other catalase-positive cocci that grow aerobically, p. 384-404. In P. R. Murray, E. J. Baron, J. H. Jorgensen, M. A. Pfaller, and R. H. Yolken (ed.), Manual of clinical microbiology, 7th ed. ASM Press, Washington, DC.
2
2. Bates, D. W., and T. H. Lee. 1992. Rapid classification of positive blood cultures. Prospective validation of a multivariate algorithm. JAMA 267:1962-1966.[Abstract/Free Full Text]
3
3. Chapin, K., and M. Musgnug. 2003. Evaluation of three rapid methods for the direct identification of Staphylococcus aureus from positive blood cultures. J. Clin. Microbiol. 41:4324-4327.[Abstract/Free Full Text]
4
4. Cornish, N., B. A. Kirkley, K. A. Easley, and J. A. Washington. 1999. Reassessment of the routine anaerobic culture and incubation time in the BacT/Alert FAN blood culture bottles. Diagn. Microbiol. Infect. Dis. 35:93-99.[CrossRef][Medline]
5
5. Khatib, R., L. B. Johnson, M. G. Fakih, K. Riederer, A. Khosrovaneh, M. Shamse Tabriz, M. Sharma, and S. Saeed. 2006. Persistence in Staphylococcus aureus bacteremia: incidence, characteristics of patients and outcome. Scand. J. Infect. Dis. 38:7-14.[CrossRef][Medline]
6
6. Lassmann, B., D. R. Gustafson, C. M. Wood, and J. E. Rosenblatt. 2007. Reemergence of anaerobic bacteremia. Clin. Infect. Dis. 44:895-900.[CrossRef][Medline]
7
7. Lodise, T. P., P. S. McKinnon, L. Swiderski, and M. J. Rybak. 2003. Outcome analysis of delayed antibiotic treatment for hospital-acquired Staphylococcus aureus bacteremia. Clin. Infect. Dis. 36:1418-1423.[CrossRef][Medline]
8
8. Marlowe, E. M., J. J. Hogan, J. F. Hindler, I. Andruszkiewicz, P. Gordon, and D. A. Bruckner. 2003. Application of an rRNA probe matrix for rapid identification of bacteria and fungi from routine blood cultures. J. Clin. Microbiol. 41:5127-5133.[Abstract/Free Full Text]
9
9. McDonald, C. L., and K. Chapin. 1995. Rapid identification of Staphylococcus aureus from blood culture bottles by a classic 2-hour tube coagulase test. J. Clin. Microbiol. 33:50-52.[Abstract]
10
10. Mitchell, D. H., and B. P. Howden. 2005. Diagnosis and management of Staphylococcus aureus bacteremia. Int. Med. J. 35:S17-S24.[CrossRef]
11
11. Morin, C. A., and J. L. Hadler. 2001. Population-based incidence and characteristics of community-onset Staphylococcus aureus infections with bacteremia in 4 metropolitan Connecticut areas. J. Infect. Dis. 184:1029-1034.[CrossRef][Medline]
12
12. Peters, R. P. H., P. H. M. Savelkoul, A. M. Simoons-Smit, S. A. Danner, C. M. J. E. Vandenbroucke-Grauls, and M. A. van Agtmeal. 2006. Faster identification of pathogens in positive blood cultures by fluorescence in situ hybridization in routine practice. J. Clin. Microbiol. 44:119-123.[Abstract/Free Full Text]
13
13. Riley, J. A., B. J. Heiter, and P. P. Bourbeau. 2003. Comparison of recovery of blood culture isolates from two BacT/ALERT FAN aerobic blood culture bottles with recovery from one FAN aerobic bottle and one FAN anaerobic bottle. J. Clin. Microbiol. 41:213-217.[Abstract/Free Full Text]
14
14. Rohner, P., B. Pepey, and R. Auckenthaler. 1997. Advantage of combining resin with lytic BACTEC blood culture media. J. Clin. Microbiol. 35:2634-2638.[Abstract]
15
15. Sakai, H., G. W. Procop, N. Kobayashi, D. Togawa, D. A. Wilson, L. Borden, V. Krebs, and T. W. Bauer. 2004. Simultaneous detection of Staphylococcus aureus and coagulase-negative staphylococci in positive blood cultures by real-time PCR with two fluorescence resonance energy transfer probe sets. J. Clin. Microbiol. 42:5739-5744.[Abstract/Free Full Text]
16
16. Speers, D. J., T. R. Olma, and G. L. Gilbert. 1998. Evaluation of four methods for rapid identification of Staphylococcus aureus from blood cultures. J. Clin. Microbiol. 36:1032-1034.[Abstract/Free Full Text]
17
17. Varettas, K., C. Mukerjee, and P. C. Taylor. 2005. Anticoagulant carryover may influence clot formation in direct tube coagulase tests from blood cultures. J. Clin. Microbiol. 43:4613-4615.[Abstract/Free Full Text]
18
18. Weinstein, M. P., M. L. Towns, S. M. Quartey, S. Mirrett, L. G. Reimer, G. Parmigiani, and L. B. Reller. 1997. The clinical significance of positive blood cultures in the 1990s: a prospective comprehensive evaluation of the microbiology, epidemiology, and outcome of bacteremia and fungemia in adults. Clin. Infect. Dis. 24:584-602.[Medline]

---

Journal of Clinical Microbiology, July 2007, p. 2267-2269, Vol. 45, No. 7
0095-1137/07/$08.00+0     doi:10.1128/JCM.00369-07
Copyright © 2007, American Society for Microbiology. All Rights Reserved.

This article has been cited by other articles:

• Kerremans, J. J., Goessens, W. H. F., Verbrugh, H. A., Vos, M. C. (2008). Rapid Identification of Staphyloccocus aureus in Positive-Testing Blood Cultures by Slidex Staph Plus Agglutination Test. J. Clin. Microbiol. 46: 395-395 [Full Text]  
• Lagace-Wiens, P. R. S., Alfa, M. J., Manickam, K., Karlowsky, J. A. (2007). Thermostable DNase Is Superior to Tube Coagulase for Direct Detection of Staphylococcus aureus in Positive Blood Cultures. J. Clin. Microbiol. 45: 3478-3479 [Full Text]  

This Article Abstract Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Reprints and Permissions Copyright Information Books from ASM Press MicrobeWorld Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Qian, Q. Articles by Kirby, J. E. Search for Related Content PubMed PubMed Citation Articles by Qian, Q. Articles by Kirby, J. E.