JAC Advance Access originally published online on June 9, 2005
Journal of Antimicrobial Chemotherapy 2005 56(2):432-433; doi:10.1093/jac/dki188
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Correspondence |
Endocarditis guidelines: authors' response
Department of Microbiology, Freeman Hospital, Newcastle-upon-Tyne, UK
* E-mail: jdp{at}blueyonder.co.uk
Keywords: antibiotic therapy , guidelines , endocarditis , BSAC
Sir,
Professor Shah1 has questioned the recommendation2 for an MIC determination to be performed on strains isolated from cases of infective endocarditis (IE). When considering the need for MIC determination, one has to consider the nature of the infecting microorganism, the antimicrobial under test and the reliability of any alternative methodology.
It has been stated that disc susceptibility testing is often adequate to determine susceptibility for bacteria causing IE,3,4 however the choice of disc susceptibility method is often not stated or discussed. For example, many laboratories in the UK now use the BSAC Standardized Disc Susceptibility Testing Method.5 However, guidelines for testing 
-haemolytic streptococci, which remain the leading cause of native valve IE, were not available at the end of 2004, which leads to questions as to how such tests might be interpreted. Moreover, the BSAC Working Party2 and other authorities,6,7 recommend therapeutic regimens for -haemolytic streptococci that vary according to the MIC for the causative strain.
Other examples exist where disc susceptibility methods may not be appropriate, for example, in assessing the penicillin susceptibility of enterococci.8 The determination of glycopeptide susceptibility in enterococci remains problematic as shown in recent surveys9,10 and the emergence of staphylococci with intermediate resistance to glycopeptides in cases of IE is likely to provide a further challenge to the diagnostic laboratory in future years.11
Professor Shah cites the report of Walton et al.4 who performed a case study to examine the contribution of the MIC to the decision to treat endocarditis surgically. The authors concluded that a moderately elevated MIC of flucloxacillin may be associated with failure of medical treatment, when flucloxacillin is used, even in combination. They also agreed that the MIC of penicillin for -haemolytic streptococci was useful in determining length of treatment. Such findings support MIC determination for strains causing IE and further studies that examine the relationship between MIC and treatment outcome are warranted.
In conclusion, we accept that for some organism/antimicrobial combinations, disc susceptibility testing may be adequate for guiding therapy, however, our consensus opinion is that our general recommendation to perform MIC testing is justified. IE remains an uncommon disease with high mortality in which the choice and duration of therapy are critical to a successful outcome. Also, if MIC testing is considered by some laboratories to be technically demanding, the availability of the Etest methodology provides an alternative option for MIC testing.
References
1. Shah PM. Comment on: Guidelines for the antibiotic treatment of endocarditis in adults: report of the Working Party of the British Society for Antimicrobial Chemotherapy. J Antimicrob Chemother 2005; 56: 432.
2.
Elliott TSJ, Foweraker J, Gould FK et al. Guidelines for the antibiotic treatment of endocarditis in adults: report of the Working Party of the British Society for Antimicrobial Chemotherapy. J Antimicrob Chemother 2004; 54: 971–81.
3.
Eykyn SJ. Infective endocarditis: some popular tenets debunked? Heart 1997; 77: 191–3.
4. Walton BI, Wallace SM, Kukreja N et al. Is the MIC useful in deciding to treat endocarditis surgically? Int J Antimicrob Agents 2004; 23: 394–7.[CrossRef][Web of Science][Medline]
5.
Andrews JM. BSAC standardized disc susceptibility testing method (version 3). J Antimicrob Chemother 2004; 53: 713–28.
6.
Horstkotte D, Follath F, Gutschik E et al. Guidelines on prevention, diagnosis and treatment of infective endocarditis executive summary; the task force on infective endocarditis of the European Society of Cardiology. Eur Heart J 2004; 25: 267–76.
7.
Wilson WR, Karchmer AW, Dajani AS et al. Antibiotic treatment of adults with infective endocarditis due to streptococci, enterococci, staphylococci, and HACEK microorganisms. JAMA 1995; 274: 1706–13.
8.
Snell JJ, Brown DF, Perry SF et al. Antimicrobial susceptibility testing of enterococci: results of a survey conducted by the United Kingdom National External Quality Assessment Scheme for Microbiology. J Antimicrob Chemother 1993; 32: 401–11.
9.
Potz NA, Mushtaq S, Johnson AP et al. Reliability of routine disc susceptibility testing by the British Society for Antimicrobial Chemotherapy (BSAC) method. J Antimicrob Chemother 2004; 53: 729–38.
10. Hageman JC, Fridkin SK, Mohammed JM et al. Antimicrobial proficiency testing of National Nosocomial Infections Surveillance System hospital laboratories. Infect Control Hosp Epidemiol 2003; 24: 356–61.[CrossRef][Web of Science][Medline]
11. Leung KT, Tong MK, Siu YP et al. Treatment of vancomycin-intermediate Staphylococcus aureus endocarditis with linezolid. Scand J Infect Dis 2004; 36: 483–5.[CrossRef][Web of Science][Medline]
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