Letters to the Editor / International Journal of Antimicrobial Agents 28 (2006) 477–483 481 zolid was initiated after obtaining the informed consent of the patient. Evolution was satisfactory and the patient was discharged soon afterwards on oral linezolid for 4 weeks. No adverse events were detected. A control CT scan demon- strated resolution of the spleen infarcts. The patient remained well after 7 months. Our report emphasises three important aspects. First, it is possible to speculate that the origin of listeriosis in this patient is related to the colonoscopic procedure performed 2 weeks previously. In fact, listerial meningitis and bacteraemia have been described shortly after colonoscopy or sigmoi- doscopy [3] and Listeria endocarditis may be an indicator of underlying gastrointestinal tract abnormality, including can- cer. Second, it shows the impact of new molecular techniques applied systematically to the heart valve tissue of patients with suspicion of infective endocarditis. Finally, we report the first patient with Listeria endocardi- tis treated with linezolid. Our reasons for choosing linezolid were that (i) after 2 weeks of therapy with vancomycin our patient’s condition had not improved and (ii) linezolid has demonstrated in vitro and in vivo efficacy against Listeria [4]. Its good penetration in biofilms and central nervous system tissues and its very advantageous pharmacokinetic proper- ties makes linezolid a very attractive option for sequential oral therapy in patients with listeriosis requiring prolonged therapy [5]. To our knowledge, only one other patient with rhombencephalitis caused by L. monocytogenes has been treated with linezolid [6]. However, linezolid is not yet recognised as a standard ther- apy for this indication owing to concerns regarding its bac- teriostatic activity and long-term toxicity. We have recently reported another nine patients with endocarditis treated with linezolid in our institution and reviewed 33 from the medical literature. Linezolid was administered for a mean of 37 days and outcome was successful in 79% of cases [7]. Reversible adverse effects were described in 10 cases and mean follow- up was 8.5 months. Our case points out the importance of molecular tech- niques for the diagnosis of culture-negative infectious endo- carditis and also shows the potential use of linezolid as an alternative drug for the treatment of infective endocarditis, at least during the post-operative period. Acknowledgment This study was supported in part by a grant from the Spanish Social Security Health Investigation Fund (Red Espa˜ nola de Investigaci´ on en Patolog´ ıa Infecciosa (REIPI)) (FIS C03/14). References [1] Spyrou N, Anderson M, Foale R. Listeria endocarditis: current management and patient outcome—world literature review. Heart 1997;77:380–3. [2] Fernandez Guerrero ML, Rivas P, Rabago R, Nunez A, de Gorgolas M, Martinell J. Prosthetic valve endocarditis due to Listeria monocytogenes. Report of two cases and reviews. Int J Infect Dis 2004;8:97–102. [3] Witlox MA, Klinkenberg-Knol EC, Meuwissen SG. Listeria sepsis as a complication of endoscopy. Gastrointest Endosc 2000;51:235–6. [4] Hansen JM, Gerner-Smidt P, Bruun B. Antibiotic susceptibility of Lis- teria monocytogenes in Denmark 1958–2001. APMIS 2005;113:31–6. [5] Villani P, Regazzi MB, Marubbi F, et al. Cerebrospinal fluid linezolid concentrations in postneurosurgical central nervous system infections. Antimicrob Agents Chemother 2002;46:936–7. [6] Morosi S, Francisci D, Baldelli F. A case of rhombencephalitis caused by Listeria monocytogenes successfully treated with linezolid. J Infect 2006;52:e73–5. [7] Mu˜ noz P, Rodr´ ıguez-Creix´ ems M, Moreno M, et al. Linezolid therapy for infective endocarditis: report of nine cases and review of the literature. Clin Microbiol Infect, 2006, in press. Patricia Mu˜ noz ∗ Luc´ ıa Ferreira Mercedes Mar´ ın Marta Rodr´ ıguez-Cr´ eixems Emilio Bouza Departments of Clinical Microbiology and Infectious Diseases, Hospital General Universitario ‘Gregorio Mara˜ n´ on’, University of Madrid, Spain Miguel Angel Garc´ ıa-Fernandez Department of Cardiology, Hospital General Universitario ‘Gregorio Mara˜ n´ on’, University of Madrid, Spain The GAME Study Group 1 ∗ Corresponding author. Present address: Hospital General Universitario ‘Gregorio Mara˜ n´ on’, Doctor Esquerdo 46, 28007 Madrid, Spain. Tel.: +34 915 868 453; fax: +34 915 044 906. E-mail address: pmunoz@micro.hggm.es (P. Mu˜ noz) 1 The GAME Study Group participants were: E. Bouza, M. Desco, F. D´ ıaz, M.A. Garc´ ıa-Fern´ andez, M. Mar´ ın, M. Mart´ ınez-Selles, M. Moreno, P. Mu˜ noz, B. Pinilla, A. Pinto, V. Ramallo, M. Rodr´ ıguez-Creix´ ems, I. Tamallo and J.L. Vallejo. doi: 10.1016/j.ijantimicag.2006.08.010 Genetic stability of class 1 integron-borne bla GES -type genes under short-term in vitro antibiotic stress Sir, In reports describing novel point mutations in GES-type genes, selective antibiotic pressure is thought to be a factor facilitating selection and possible dissemination in the noso- comial environment [1]. Major changes in class 1 integrons, such as novel cassette integration events in the variable region, preferentially take place at the attI1 recombination site [2]. This study examined two well characterised bacterial isolates with class 1 integron-located bla GES -type genes for