- Email: [email protected]
Usefulness of the Etest for studying tigecycline susceptibility of non-pigmented rapidly growing mycobacteria
366
Letters to the Editor / International Journal of Antimicrobial Agents 32 (2008) 363–371
effective antifungal prophylaxis in high-risk groups and should be diligently evaluated throughout transplantation. Future studies using earlier and improved diagnostics combined with current and future antifungal agents will better determine optimal prophylaxis in high-risk populations such as haematopoietic stem cell transplant patients. Funding: No funding sources. Competing interests: None declared. Ethical approval: Not required.
References [1] Ullmann AJ, Lipton JH, Vesole DH, Chandrasekar P, Langston A, Tarantolo SR, et al. Posaconazole or fluconazole for prophylaxis in severe graft-versus-host disease. N Engl J Med 2007;356:335–47. [2] Wexler D, Courtney R, Richards W, Banfield C, Lim J, Laughlin M. Effect of posaconazole on cytochrome P450 enzymes: a randomized, open-label, two-way crossover study. Eur J Pharm Sci 2004;21:645– 53. [3] Ustun C, Farrow S, DeRemer D, Fain H, Jilella A. Early fatal Rhizopus infection on voriconazole prophylaxis following allogeneic stem cell transplantation. Bone Marrow Transplant 2007;39:807–8. [4] Courtney R, Wexler D, Radwanski E, Lim J, Laughlin M. Effect of food on the relative bioavailability of two oral formulations of posaconazole in healthy adults. Br J Clin Pharmacol 2004;57:218–22. [5] Cornely OA, Ullmann AJ, Hardalo C. Authors’ reply to: posaconazole prophylaxis in hematological cancer. N Engl J Med 2007;356:2214–8. [6] Pfeiffer CD, Fine JP, Safdar N. Diagnosis of invasive aspergillosis using a galactomannan assay: a meta-analysis. Clin Infect Dis 2006;42:1417–27. [7] Cornely OA, Maertens J, Winston DJ, Perfect J, Ullmann AJ, Walsh TJ, et al. Posaconazole vs. fluconazole or itraconazole prophylaxis in patients with neutropenia. N Engl J Med 2007;356:348–59.
Celalettin Ustun ∗ Medical College of Georgia, Department of Medicine, Section of Hematology/Oncology, Augusta, GA 30912, USA David L. DeRemer University of Georgia College of Pharmacy, Augusta, GA, USA John C.H. Steele Jr Medical College of Georgia, Department of Pathology, Augusta, GA, USA Caralee Forseen Medical College of Georgia, Department of Medicine, Section of Pulmonary Medicine, Augusta, GA, USA John F. Fisher Medical College of Georgia, Department of Medicine, Section of Infectious Disease, Augusta, GA, USA Anand P. Jillella Medical College of Georgia, Department of Medicine, Section of Hematology/Oncology, Augusta, GA 30912, USA ∗ Corresponding
author. Tel.: +1 706 721 2505; fax: +1 706 721 8302. E-mail address: [email protected] (C. Ustun)
doi:10.1016/j.ijantimicag.2008.04.014
Usefulness of the Etest for studying tigecycline susceptibility of non-pigmented rapidly growing mycobacteria Sir, Non-pigmented rapidly growing mycobacteria (NPRGM) are amongst the most commonly isolated mycobacteria in clinical mycobacteriology laboratories. However, although many isolates are considered as contaminants or colonisers, many cases are true infections that require proper therapy, especially in the case of non-respiratory isolates where most isolates can be clinically significant. Therapy for these organisms needs to be individualised as there are differences between strains in antimicrobial susceptibility and some of them are resistant to many antimicrobials [1]. Tigecycline is a new antibiotic that has shown good activity against these organisms [2] and appears to be a potentially useful drug to treat these infections. However, susceptibility testing by the microdilution reference method is not easily available for clinical laboratories, therefore other techniques are required for testing this and other antimicrobials. Here we report a study to evaluate the usefulness of the Etest technique to determine susceptibility to tigecycline of clinical isolates of NPRGM. We studied the susceptibility of clinical isolates of NPRGM to tigecycline using the previously described microdilution method [3]. To determine the minimum inhibitory concentration (MIC) using the Etest (AB BIODISK, Solna, Sweden), a M¨uller–Hinton agar plate supplemented with 5% sheep blood was inoculated with a 1 McFarland suspension of NPRGM. Plates were incubated under normal atmosphere at 30 ◦ C for 3 days. The MIC was read as the intersection of bacterial growth with the Etest strip. To evaluate the correlation between both techniques, we considered that the results were matched if the difference was only ±1 dilution. In total, 169 clinical strains of NPRGM were tested, comprising Mycobacterium abscessus (10), Mycobacterium chelonae (32), Mycobacterium fortuitum (91), Mycobacterium mageritense (6), Mycobacterium mucogenicum (7) and Mycobacterium peregrinum (23). MICs were identical in 61 strains (12 M. chelonae, 34 M. fortuitum, 2 M. mageritense, 2 M. mucogenicum and 11 M. peregrinum), whilst minor errors (MIC higher by Etest than microdilution) were detected in 77 cases (4 M. abscessus, 13 M. chelonae, 45 M. fortuitum, 3 M. mageritense, 2 M. mucogenicum and 10 M. peregrinum) and major errors (MIC lower by Etest than microdilution) were detected in 31 cases (6 M. abscessus, 7 M. chelonae, 12 M. fortuitum, 1 M. mageritense, 3 M. mucogenicum and 2 M. peregrinum). If we consider the above mentioned criteria for correlation of values (±1 dilution), major errors were detected only in 13 cases and minor errors in 50 cases. No resistant strains were detected in the study, either by microdilution or by Etest. Evaluation of antimicrobial susceptibility of NPRGM in many clinical laboratories is still a problem. The
Letters to the Editor / International Journal of Antimicrobial Agents 32 (2008) 363–371
microdilution technique, although considered as the reference in such studies, is difficult to perform in many medium to small laboratories as it requires experience and a lot of homemade work. The disk diffusion assay has been evaluated, but it appears problematic in many cases [4] and it is not recommended for this purpose. The Etest has been studied for antimicrobial susceptibility testing of NPRGM [5] and, although it has shown reproducibility problems [6], it may be a useful alternative for many clinical laboratories until results obtained by the reference technique (often performed by reference laboratories only) are available. The Etest has been used to study tigecycline susceptibility of other bacteria with good results [7], therefore we believe that it could be useful for MIC determination amongst NPRGM. However, our results showed that MIC determination by the Etest had many differences from the microdilution technique (only 36% of the strains gave identical results), even if we considered a ±1 dilution discrepancy as acceptable (only 62.7% of the strains matched both results). Although there were no resistant strains in our study, we believe that owing to these data susceptibility results for tigecycline obtained by the Etest must be considered with caution and should be confirmed by the reference technique performed by an experienced laboratory. Funding: This work was financed by a grant from Wyeth. Nieves Z. Mart´ın-de-Hijas was funded by a grant from the Fundaci´on Conchita R´abago de Jim´enez D´ıaz, Madrid, Spain. Competing interests: None declared. Ethical approval: Not required.
References [1] De Groote MA, Huitt G. Infections due to rapidly growing mycobacteria. Clin Infect Dis 2006;42:1756–63. [2] Wallace Jr RJ, Brown-Elliott BA, Crist CJ, Mann L, Wilson RW. Comparison of the in vitro activity of the glycylcycline tigecycline (formerly GAR-936) with those of tetracycline, minocycline, and doxycycline against isolates of nontuberculous mycobacteria. Antimicrob Agents Chemother 2002;46:3164–7. [3] Woods GL, Bergmann JS, Witebsky FG, Fahle GA, Wanger A, Boulet B, et al. Multisite reproducibility of results obtained by the broth microdilution method for susceptibility testing of Mycobacterium abscessus, Mycobacterium chelonae, and Mycobacterium fortuitum. J Clin Microbiol 1999;37:1676–82. [4] Esteban J, Gadea I, Torres MV, Cabria F, Rollan E, Santos-O’Connor FG, et al. A comparison between disk diffusion and microdilution for susceptibility testing of Mycobacterium fortuitum complex. J Chemother 2002;14:547–53. [5] Biehle JR, Cavalieri SJ, Saubolle MA, Getsinger LJ. Evaluation of Etest for susceptibility testing of rapidly growing mycobacteria. J Clin Microbiol 1995;33:1760–4. [6] Woods GL, Bergmann JS, Witebsky FG, Boulet B, Plaunt M, Brown BA, et al. Multisite reproducibility of Etest for susceptibility testing of Mycobacterium abscessus, Mycobacterium chelonae, and Mycobacterium fortuitum. J Clin Microbiol 2000;38:656–61. [7] Bolmstr¨om A, Karlsson A, Engelhardt A, Ho P, Petersen PJ, Bradford PA, et al. Validation and reproducibility assessment of tige-
367
cycline MIC determinations by Etest. J Clin Microbiol 2007;45: 2474–9.
N.Z. Mart´ın-de-Hijas R. Fern´andez-Roblas A.I. Fernandez-Mart´ınez I. Gadea J. Esteban ∗ Department of Clinical Microbiology, Fundaci´on Jim´enez D´ıaz, Av. Reyes Cat´olicos 2, 28040 Madrid, Spain ∗ Corresponding
author. Tel.: +34 915 504 900; fax: +34 915 442 636. E-mail address: [email protected] (J. Esteban)
doi:10.1016/j.ijantimicag.2008.04.016
Prevalence of sulphonamide resistance and class 1 integron genes in Escherichia coli isolates obtained from broilers, broiler meat, healthy humans and urinary infections in Denmark夽 Sir, Most urinary tract infections (UTIs) are caused by extraintestinal Escherichia coli. In Denmark, sulphamethizole is one of the first treatments of choice for uncomplicated UTI in humans. A recent study has shown a high similarity between E. coli of animal origin and isolates from UTI [1]. In light of this, we investigated the presence of sulphonamide resistance (sulR ) genes (sul1, sul2 and sul3) and their association with class 1 integrons among resistant E. coli from broilers, broiler meat, healthy humans and UTIs in Denmark to assess possible connections between the E. coli populations. Isolates were obtained in 2004 from faecal samples of healthy persons (n = 111), Danish broiler meat (n = 216), imported broiler meat (n = 93) and broiler faeces (n = 142) in Denmark as a part of the Danish Integrated Antimicrobial Resistance Monitoring and Research Programme (DANMAP) [2]. Furthermore, 136 E. coli isolates were collected from UTIs (complicated and uncomplicated) in primary health care in Køge (Denmark) between December 2005 and March 2006. The sulR genes and the intI1 integron-associated gene were detected by polymerase chain reaction according to the methods used by Hammerum et al. [3]. It was found that 18% of the E. coli isolates from broiler faeces, 15% from Danish broiler meat, 45% from imported broiler meat, 22% from healthy humans and 37% from UTI were sulphonamide resistant. The detected prevalence among broiler isolates was lower than previously reported in Danish pigs and pork (26%) [3], which probably reflects the lower use of sulphonamides in broiler production. 夽 Part of this study was presented at the 2nd Symposium on Antimicrobial Resistance in Animals and the Environment (ARAE), 17–19 December 2007, Tours, France.
Letters to the Editor / International Journal of Antimicrobial Agents 32 (2008) 363–371
effective antifungal prophylaxis in high-risk groups and should be diligently evaluated throughout transplantation. Future studies using earlier and improved diagnostics combined with current and future antifungal agents will better determine optimal prophylaxis in high-risk populations such as haematopoietic stem cell transplant patients. Funding: No funding sources. Competing interests: None declared. Ethical approval: Not required.
References [1] Ullmann AJ, Lipton JH, Vesole DH, Chandrasekar P, Langston A, Tarantolo SR, et al. Posaconazole or fluconazole for prophylaxis in severe graft-versus-host disease. N Engl J Med 2007;356:335–47. [2] Wexler D, Courtney R, Richards W, Banfield C, Lim J, Laughlin M. Effect of posaconazole on cytochrome P450 enzymes: a randomized, open-label, two-way crossover study. Eur J Pharm Sci 2004;21:645– 53. [3] Ustun C, Farrow S, DeRemer D, Fain H, Jilella A. Early fatal Rhizopus infection on voriconazole prophylaxis following allogeneic stem cell transplantation. Bone Marrow Transplant 2007;39:807–8. [4] Courtney R, Wexler D, Radwanski E, Lim J, Laughlin M. Effect of food on the relative bioavailability of two oral formulations of posaconazole in healthy adults. Br J Clin Pharmacol 2004;57:218–22. [5] Cornely OA, Ullmann AJ, Hardalo C. Authors’ reply to: posaconazole prophylaxis in hematological cancer. N Engl J Med 2007;356:2214–8. [6] Pfeiffer CD, Fine JP, Safdar N. Diagnosis of invasive aspergillosis using a galactomannan assay: a meta-analysis. Clin Infect Dis 2006;42:1417–27. [7] Cornely OA, Maertens J, Winston DJ, Perfect J, Ullmann AJ, Walsh TJ, et al. Posaconazole vs. fluconazole or itraconazole prophylaxis in patients with neutropenia. N Engl J Med 2007;356:348–59.
Celalettin Ustun ∗ Medical College of Georgia, Department of Medicine, Section of Hematology/Oncology, Augusta, GA 30912, USA David L. DeRemer University of Georgia College of Pharmacy, Augusta, GA, USA John C.H. Steele Jr Medical College of Georgia, Department of Pathology, Augusta, GA, USA Caralee Forseen Medical College of Georgia, Department of Medicine, Section of Pulmonary Medicine, Augusta, GA, USA John F. Fisher Medical College of Georgia, Department of Medicine, Section of Infectious Disease, Augusta, GA, USA Anand P. Jillella Medical College of Georgia, Department of Medicine, Section of Hematology/Oncology, Augusta, GA 30912, USA ∗ Corresponding
author. Tel.: +1 706 721 2505; fax: +1 706 721 8302. E-mail address: [email protected] (C. Ustun)
doi:10.1016/j.ijantimicag.2008.04.014
Usefulness of the Etest for studying tigecycline susceptibility of non-pigmented rapidly growing mycobacteria Sir, Non-pigmented rapidly growing mycobacteria (NPRGM) are amongst the most commonly isolated mycobacteria in clinical mycobacteriology laboratories. However, although many isolates are considered as contaminants or colonisers, many cases are true infections that require proper therapy, especially in the case of non-respiratory isolates where most isolates can be clinically significant. Therapy for these organisms needs to be individualised as there are differences between strains in antimicrobial susceptibility and some of them are resistant to many antimicrobials [1]. Tigecycline is a new antibiotic that has shown good activity against these organisms [2] and appears to be a potentially useful drug to treat these infections. However, susceptibility testing by the microdilution reference method is not easily available for clinical laboratories, therefore other techniques are required for testing this and other antimicrobials. Here we report a study to evaluate the usefulness of the Etest technique to determine susceptibility to tigecycline of clinical isolates of NPRGM. We studied the susceptibility of clinical isolates of NPRGM to tigecycline using the previously described microdilution method [3]. To determine the minimum inhibitory concentration (MIC) using the Etest (AB BIODISK, Solna, Sweden), a M¨uller–Hinton agar plate supplemented with 5% sheep blood was inoculated with a 1 McFarland suspension of NPRGM. Plates were incubated under normal atmosphere at 30 ◦ C for 3 days. The MIC was read as the intersection of bacterial growth with the Etest strip. To evaluate the correlation between both techniques, we considered that the results were matched if the difference was only ±1 dilution. In total, 169 clinical strains of NPRGM were tested, comprising Mycobacterium abscessus (10), Mycobacterium chelonae (32), Mycobacterium fortuitum (91), Mycobacterium mageritense (6), Mycobacterium mucogenicum (7) and Mycobacterium peregrinum (23). MICs were identical in 61 strains (12 M. chelonae, 34 M. fortuitum, 2 M. mageritense, 2 M. mucogenicum and 11 M. peregrinum), whilst minor errors (MIC higher by Etest than microdilution) were detected in 77 cases (4 M. abscessus, 13 M. chelonae, 45 M. fortuitum, 3 M. mageritense, 2 M. mucogenicum and 10 M. peregrinum) and major errors (MIC lower by Etest than microdilution) were detected in 31 cases (6 M. abscessus, 7 M. chelonae, 12 M. fortuitum, 1 M. mageritense, 3 M. mucogenicum and 2 M. peregrinum). If we consider the above mentioned criteria for correlation of values (±1 dilution), major errors were detected only in 13 cases and minor errors in 50 cases. No resistant strains were detected in the study, either by microdilution or by Etest. Evaluation of antimicrobial susceptibility of NPRGM in many clinical laboratories is still a problem. The
Letters to the Editor / International Journal of Antimicrobial Agents 32 (2008) 363–371
microdilution technique, although considered as the reference in such studies, is difficult to perform in many medium to small laboratories as it requires experience and a lot of homemade work. The disk diffusion assay has been evaluated, but it appears problematic in many cases [4] and it is not recommended for this purpose. The Etest has been studied for antimicrobial susceptibility testing of NPRGM [5] and, although it has shown reproducibility problems [6], it may be a useful alternative for many clinical laboratories until results obtained by the reference technique (often performed by reference laboratories only) are available. The Etest has been used to study tigecycline susceptibility of other bacteria with good results [7], therefore we believe that it could be useful for MIC determination amongst NPRGM. However, our results showed that MIC determination by the Etest had many differences from the microdilution technique (only 36% of the strains gave identical results), even if we considered a ±1 dilution discrepancy as acceptable (only 62.7% of the strains matched both results). Although there were no resistant strains in our study, we believe that owing to these data susceptibility results for tigecycline obtained by the Etest must be considered with caution and should be confirmed by the reference technique performed by an experienced laboratory. Funding: This work was financed by a grant from Wyeth. Nieves Z. Mart´ın-de-Hijas was funded by a grant from the Fundaci´on Conchita R´abago de Jim´enez D´ıaz, Madrid, Spain. Competing interests: None declared. Ethical approval: Not required.
References [1] De Groote MA, Huitt G. Infections due to rapidly growing mycobacteria. Clin Infect Dis 2006;42:1756–63. [2] Wallace Jr RJ, Brown-Elliott BA, Crist CJ, Mann L, Wilson RW. Comparison of the in vitro activity of the glycylcycline tigecycline (formerly GAR-936) with those of tetracycline, minocycline, and doxycycline against isolates of nontuberculous mycobacteria. Antimicrob Agents Chemother 2002;46:3164–7. [3] Woods GL, Bergmann JS, Witebsky FG, Fahle GA, Wanger A, Boulet B, et al. Multisite reproducibility of results obtained by the broth microdilution method for susceptibility testing of Mycobacterium abscessus, Mycobacterium chelonae, and Mycobacterium fortuitum. J Clin Microbiol 1999;37:1676–82. [4] Esteban J, Gadea I, Torres MV, Cabria F, Rollan E, Santos-O’Connor FG, et al. A comparison between disk diffusion and microdilution for susceptibility testing of Mycobacterium fortuitum complex. J Chemother 2002;14:547–53. [5] Biehle JR, Cavalieri SJ, Saubolle MA, Getsinger LJ. Evaluation of Etest for susceptibility testing of rapidly growing mycobacteria. J Clin Microbiol 1995;33:1760–4. [6] Woods GL, Bergmann JS, Witebsky FG, Boulet B, Plaunt M, Brown BA, et al. Multisite reproducibility of Etest for susceptibility testing of Mycobacterium abscessus, Mycobacterium chelonae, and Mycobacterium fortuitum. J Clin Microbiol 2000;38:656–61. [7] Bolmstr¨om A, Karlsson A, Engelhardt A, Ho P, Petersen PJ, Bradford PA, et al. Validation and reproducibility assessment of tige-
367
cycline MIC determinations by Etest. J Clin Microbiol 2007;45: 2474–9.
N.Z. Mart´ın-de-Hijas R. Fern´andez-Roblas A.I. Fernandez-Mart´ınez I. Gadea J. Esteban ∗ Department of Clinical Microbiology, Fundaci´on Jim´enez D´ıaz, Av. Reyes Cat´olicos 2, 28040 Madrid, Spain ∗ Corresponding
author. Tel.: +34 915 504 900; fax: +34 915 442 636. E-mail address: [email protected] (J. Esteban)
doi:10.1016/j.ijantimicag.2008.04.016
Prevalence of sulphonamide resistance and class 1 integron genes in Escherichia coli isolates obtained from broilers, broiler meat, healthy humans and urinary infections in Denmark夽 Sir, Most urinary tract infections (UTIs) are caused by extraintestinal Escherichia coli. In Denmark, sulphamethizole is one of the first treatments of choice for uncomplicated UTI in humans. A recent study has shown a high similarity between E. coli of animal origin and isolates from UTI [1]. In light of this, we investigated the presence of sulphonamide resistance (sulR ) genes (sul1, sul2 and sul3) and their association with class 1 integrons among resistant E. coli from broilers, broiler meat, healthy humans and UTIs in Denmark to assess possible connections between the E. coli populations. Isolates were obtained in 2004 from faecal samples of healthy persons (n = 111), Danish broiler meat (n = 216), imported broiler meat (n = 93) and broiler faeces (n = 142) in Denmark as a part of the Danish Integrated Antimicrobial Resistance Monitoring and Research Programme (DANMAP) [2]. Furthermore, 136 E. coli isolates were collected from UTIs (complicated and uncomplicated) in primary health care in Køge (Denmark) between December 2005 and March 2006. The sulR genes and the intI1 integron-associated gene were detected by polymerase chain reaction according to the methods used by Hammerum et al. [3]. It was found that 18% of the E. coli isolates from broiler faeces, 15% from Danish broiler meat, 45% from imported broiler meat, 22% from healthy humans and 37% from UTI were sulphonamide resistant. The detected prevalence among broiler isolates was lower than previously reported in Danish pigs and pork (26%) [3], which probably reflects the lower use of sulphonamides in broiler production. 夽 Part of this study was presented at the 2nd Symposium on Antimicrobial Resistance in Animals and the Environment (ARAE), 17–19 December 2007, Tours, France.