Skip to main page content

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

This Article 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 Google Scholar Google Scholar Articles by Acuner, I. C. Articles by Appelbaum, P. C. Search for Related Content PubMed PubMed Citation Articles by Acuner, I. C. Articles by Appelbaum, P. C.

 Previous Article  |  Next Article 

Journal of Clinical Microbiology, June 2006, p. 2318-2319, Vol. 44, No. 6
0095-1137/06/$08.00+0     doi:10.1128/JCM.00453-06

LETTER TO THE EDITOR

Unacceptable Performance and the Lack of Reproducibility Results in the Report of Colorimetric Methods for Early Detection of Vancomycin and Oxacillin Resistance in Staphylococcus aureus

Top Letter References Letter

 
In a recent paper by Coban and colleagues (6), two colorimetric methods for early detection of vancomycin and oxacillin resistance in Staphylococcus aureus were reported. The authors state that the results were compared by calculating essential agreement, absolute agreement, and minor, major, and very major errors, as recommended by the FDA (10). However, in the cited version of the FDA document, these terms were replaced by categorical agreement and minor, major, and very major discrepancy (10). The authors noted that all tests were performed in the duplicate (6, 10, 14). However, the authors did not report the results of duplicate testing that is necessary for the reproducibility evaluation. In fact, the cited FDA document describes a separate reproducibility (i.e., 95%) evaluation step with a triplicate testing (10). The aim of the FDA document is premarket evaluation of new methods which may not guarantee the validity of performance, and even the literature that assays the validity of performance should be read critically (13). In parallel to this view, the Journal of Clinical Microbiology's editorial policy advocates Standards for Reporting of Diagnostic Accuracy (STARD) guidance in the description of diagnostic microbiology assays and comparison of assay performance (1a, 4, 15). However, to our knowledge, a study design in compliance with STARD criteria in the field of microbiology does not exist in the literature to date, possibly because this evidence-based initiative is both new and not easy to comply with. Additionally, the authors report lower-than-90% essential agreement for both methods, except in the nitrate reductase assay for oxacillin testing, and state that results were in concordance with the standard method (6). Contrarily, this is an unacceptable performance according to the criteria described in the cited FDA document (10).

In conclusion, the report lacks the reproducibility evaluation, and whether this affects the final performance metrics cannot be known. In addition, the report does not show an acceptable performance of essential agreement, except in the nitrate reductase assay for oxacillin testing. Therefore, this research note should be considered a report of colorimetric methods with preliminary results that need reproducibility testing before acceptable validation through a study design as recommended by the FDA scheme or STARD initiative. It should also be noted that there are founding and preceding milestone articles that either contributed to the development of or directly used the oxidation-reduction color indicators and nitrate reductase assays in susceptibility testing of microorganisms, none of which are cited by the authors (1, 2, 3, 5, 7, 12, 16-18). It should be underlined that the use of the rapid colorimetric method for MIC testing is not new and is already available as FDA-approved and patented technology in certain nonautomated and automated commercial susceptibility systems (9, 16). The authors stated that such an automated system is expensive, which may refer to only the original capital investment for the initial technology acquisition purchase, but the reagent rental option usually also exists (8). In fact, it has been shown that the use of approved and standardized automated systems in routine rapid susceptibility testing can be cost-effective, not to mention the added values of computerized expert systems for data analysis and interpretation (9).

Top Letter References Letter

 

1
1. Ali-Vehmas, T., M. Louhi, and M. Sandholm. 1991. Automation of the resazurin reduction test using fluorometry of microtitration trays. Zentralbl. Veterinarmed. B 38:358-372.[Medline]
1
2. American Society for Microbiology. 2006 instructions to authors. J. Clin. Microbiol. 44:1-19.[Free Full Text]
2
3. Angeby, K. A., L. Klintz, and S. E. Hoffner. 2002. Rapid and inexpensive drug susceptibility testing of Mycobacterium tuberculosis with a nitrate reductase assay. J. Clin. Microbiol. 40:553-555.[Abstract/Free Full Text]
3
4. Baker C. N., and F. C. Tenover. 1996. Evaluation of Alamar colorimetric broth microdilution susceptibility testing method for staphylococci and enterococci. J. Clin. Microbiol. 34:2654-2659.[Abstract]
4
5. Bossuyt, P. M., J. B. Reitsma, D. E. Bruns, C. A. Gatsonis, P. P. Glasziou, L. M. Irwig, J. G. Lijmer, D. Moher, D. Rennie, and H. C. de Vet. 2003. Towards complete and accurate reporting of studies of diagnostic accuracy: the STARD initiative. Standards for reporting of diagnostic accuracy. Clin. Chem. 49:1-6.[Abstract/Free Full Text]
5
6. Carter, C. H., A. J. Gaspar, and J. M. Leise. 1956. Resazurin staining of bacterial colonies on membrane filters. J. Bacteriol. 71:623.[Free Full Text]
6
7. Coban, A. Y., B. Bozdogan, C. C. Cihan, E. Cetinkaya, K. Bilgin, O. Darka, A. Akgunes, B. Durupinar, and P. C. Appelbaum. 2006. Two new colorimetric methods for early detection of vancomycin and oxacillin resistance in Staphylococcus aureus. J. Clin. Microbiol. 44:580-582.[Abstract/Free Full Text]
7
8. De Felip G., S. Alberti, and von Lorch. 1959. Rapid titration of antibiotics by the use of resazurin. Rend. Ist. Sup. Sanit. 22:534-542. (In Italian.)
8
9. Eleanor M. T. 1997. Clinical laboratory management, p. 333-375. Williams and Wilkins, Baltimore, Md.
9
10. Ferraro, M. J., and J. H. Jorgensen. 2003. Susceptibility testing instrumentation and computerized expert systems for data analysis and interpretation, p. 208-217. In P. R. Murray, E. J. Baron, J. H. Jorgensen, M. A. Pfaller, and R. H. Yolken (ed.), Manual of clinical microbiology, 8th ed. ASM Press, Washington, D.C.
10
11. Food and Drug Administration. 2003. Class II special controls guidance document: antimicrobial susceptibility test (AST) systems; guidance for industry and FDA. [Online.] http://www.fda.gov/cdrh/ode/631.pdf.
11
12. Reference deleted.
12
13. Kanazawa Y., and T. Kuramata. 1966. Resazurin disc method for rapid determination of drug-sensitivities of microorganisms. J. Antibiot. (Tokyo) 19:229-233.[Medline]
13
14. National Committee for Clinical Laboratory Standards. 1994. Specifications for immunological testing for infectious diseases. Approved guideline I/LA-18-A. National Committee for Clinical Laboratory Standards, Villanova, Pa.
14
15. National Committee for Clinical Laboratory Standards. 2000. Methods for dilution antimicrobial susceptibility tests for bacteria that grow aerobically, 5th ed. Approved standard M7-A5. National Committee for Clinical Laboratory Standards, Wayne, Pa.
15
16. The STARD Group. 2003. The STARD initiative—towards complete and accurate reporting of studies on diagnostic accuracy. [Online.] http://www.consort-statement.org/stardstatement.htm. Accessed 23 February 2006.
16
17. Tenover F. C., J. M. Swenson, C. M. O'Hara, and S. A. Stocker. 1995. Ability of commercial and reference antimicrobial susceptibility testing methods to detect vancomycin resistance in enterococci. J. Clin. Microbiol. 33:1524-1527.[Abstract]
17
18. Tiballi, R. N., X. He, L. T. Zarins, S. G. Revankar, and C. A. Kauffman. 1995. Use of a colorimetric system for yeast susceptibility testing. J. Clin. Microbiol. 33:915-917.[Abstract]
18
19. Zabransky, R. J., A. R. Dinuzzo, and G. L. Woods. 1995. Detection of vancomycin resistance in enterococci by the Alamar MIC system. J. Clin. Microbiol. 33:791-793.[Abstract]

						Ibrahim C. Acuner* Department of Microbiology and Clinical Microbiology Kurupelit Campus, Kurupelit 55139 Samsun, Turkey ,1 Cafer Eroglu Department of Infectious Diseases and Clinical Microbiology Kurupelit Campus, Kurupelit 55139 Samsun, Turkey,2
						* Phone: (90) 362 3121919 Fax: (90) 362 4576041 E-mail: humanus{at}superonline.com

Authors' Reply

Top Letter References Letter

 
We thank I. C. Acuner and C. Eroglu for their interest in our article. We will try to answer their concerns.

We proposed these two colorimetric methods for early detection of methicillin-resistant Staphylococcus aureus and vancomycin-resistant Staphylococcus aureus strains. These methods determine the susceptibility and nonsusceptibility of strains with 100% accuracy. Only one vancomycin-resistant Staphylococcus aureus strain is defined as intermediate resistant instead of resistant. As is mentioned in the text, some FDA-approved systems are not able to discriminate these resistant strains either. We believe that our proposed methods perform well as "rapid tests." These tests, which give results in 5 to 6 h, were compared to broth microdilution, which gives results after 18 to 24 h, using FDA methodology, even though these are only "rapid-screening" tests. We did not perform all the tests required by the FDA for industry because we do not intend to develop these methods as "commercial systems." However, to answer Acuner and Eroglu's concern, we repeated all of the tests which agreed 100%, so these tests do not have reproducibility problems. Some references, including some of the references proposed by I. C. Acuner and C. Eroglu, had to be deleted when the manuscript was rewritten as a Note.

We hope that one day all laboratories in the world will be able to use "cost-effective commercial systems" and there will be no need to use easy and cheap in-house tests. But until then, we believe that these methods may be used by several laboratories, especially in the developing world.

						Ahmet Yilmaz Coban Department of Microbiology and Clinical Microbiology Medical School Ondokuz Mayis University 55139 Samsun, Turkey,2 Bülent Bozdogan Adnan Menderes Universitesi Hastanesi Mikrobiyoloji ve Klinik Mikrobiyoloji AD 09100 Aydin, Turkey,2 Belma Durupinar Department of Microbiology and Clinical Microbiology Medical School Ondokuz Mayis University 55139 Samsun, Turkey,2 Peter C. Appelbaum3* Department of Pathology Hershey Medical Center P.O. Box 850 Hershey, PA 17033,3
						* Phone: (717) 531-5113 Fax: (717) 531-7953 E-mail: pappelbaum{at}psu.edu

---

Journal of Clinical Microbiology, June 2006, p. 2318-2319, Vol. 44, No. 6
0095-1137/06/$08.00+0     doi:10.1128/JCM.00453-06

This Article 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 Google Scholar Google Scholar Articles by Acuner, I. C. Articles by Appelbaum, P. C. Search for Related Content PubMed PubMed Citation Articles by Acuner, I. C. Articles by Appelbaum, P. C.