JAC Advance Access originally published online on August 9, 2008
Journal of Antimicrobial Chemotherapy 2008 62(5):1166-1167; doi:10.1093/jac/dkn328
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Letters to the Editor |
Comment on: Effect of different Mueller–Hinton agars on tigecycline disc diffusion susceptibility for Acinetobacter spp.
Sanatorio San José, Infectología Institucional SRL, Argentina
* Corresponding author. Tel: +54-11-4567-4426; Fax: +54-11-4822-2748; E-mail: djcurcio{at}gmail.com
Keywords: MHA , media , Argentina
Thamlikitkul and Tiengrim1 have recently published in the Journal of Antimicrobial Chemotherapy that the susceptibility of Acinetobacter spp. to tigecycline by disc diffusion method was 86.2% using Mueller–Hinton agar (MHA) Becton–Dickinson (BD), whereas that using MHA Oxoid was only 28.5%. The high content of manganese in the Oxoid medium could be the cause of this discrepancy.1
We consider that the problem with the brand media detailed by Thamlikitkul and Tiengrim is particularly important in Argentina (and probably in other countries of Latin America) for different reasons: (i) over 90% of the Argentinean clinical microbiology laboratories perform the antibiotic susceptibility test only through the disc diffusion method (D. Curcio and F. Fernández, unpublished results); (ii) the hospitals (especially in the public system) do not have the possibility of choosing which brand media to buy (i.e. BD instead of Oxoid); (iii) the commercial microdilution tests (i.e. TREK Diagnostics, Cleveland, OH, USA) are very expensive for most laboratories and, in addition, only the reference laboratories are able to perform another susceptibility ‘gold-standard’ method (manual broth or agar dilution) to confirm the disc diffusion results; (iv) the prevalence of carbapenem-resistant Acinetobacter spp. in Argentina is high (over 50%);2 and (v) most of the prescriptions of tigecycline in Argentina are for multidrug-resistant Acinetobacter spp., especially ventilator-associated pneumonia.3
Considering these limitations of the ‘real world’ in our settings, we believe that microbiologists and attending physicians would have to consider the published evidence in order to improve patient outcomes.
The TEST programme (Tigecycline Evaluation and Surveillance Trial) found, by microdilution test, that the prevalence of Acinetobacter spp. with MICs >2 mg/L was 2.4% around the world and 2.6% in Argentina4 (Table 1); therefore, independent of the brand media used and of the breakpoint considered for the disc diffusion test (
16/
12 mm according to Jones et al.5 or 19/14 mm according to the US Food and Drug Administration,6 to define susceptibility/resistance, respectively), all of the isolates of Acinetobacter spp. resistant to tigecycline should be re-tested by the microdilution test in a reference laboratory as there are high probabilities of there being a false result.
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As mentioned earlier, tigecycline is used mainly in critically ill patients with severe infections; therefore, until the definite result of the susceptibility test is obtained, physicians should evaluate the benefits/risks of using this antibiotic based on the pharmacological and microbiological profile of the drug (i.e. concentration of the drug in the source of infection and the probable MIC for Acinetobacter spp. according to the surveillance system evidence).
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D. C. is a speaker for Wyeth SA (Argentina) for TygacilTM. F. F.: none to declare.
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1 Thamlikitkul V, Tiengrim S. Effect of different Mueller–Hinton agars on tigecycline disc diffusion susceptibility for Acinetobacter spp. J Antimicrob Chemother (2008) 62:847–8.
2
Pasterán F, Rapoport M, Petroni A, et al. Emergence of PER-2 and VEB-1a in Acinetobacter baumannii strains in the Americas. Antimicrob Agents Chemother (2006) 50:3222–4.
3 Curcio D, Fernández F, Duret F. Initial use of tigecycline in Argentina. Rev Chilena Infectol (2007) 24:497–9.[Web of Science][Medline]
4 Tigecycline Evaluation and Surveillance Trial (TEST). http://www.testsurveillance.com/home.php (1 July 2008, date last accessed).
5
Jones RN, Ferraro MJ, Reller LB, et al. Multicenter studies of tigecycline disk diffusion susceptibility results for Acinetobacter spp. J Clin Microbiol (2007) 45:227–30.
6 Tygacil package insert [June 2005]. Philadelphia, PA: Wyeth Pharmaceuticals Inc.
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