Vol.63 No.1 January 2015
A study on the antimicrobial susceptibility testing of trimethoprim-sulfamethoxazole against Stenotrophomonas maltophilia isolated from bacteremia patients
1)Faculty of Medicine and Biosystemic Science, Graduate School of Medical Science, Kyushu University, 3-1-1 Maidashi, Higashi-ku, Fukuoka, Japan
2)Faculty of Clinical Chemistry and Laboratory Medicine, Kyushu University Hospital
3)Center for the Study of Global Infection, Kyushu University Hospital
Abstract
The virulence of Stenotrophomonas maltophilia is low, but once it causes bacteremia in immunocompromised patients, the course sometimes becomes fatal. Trimethoprim-sulfamethoxazole(ST) is the standard antimicrobial agents for the treatment of S. maltophilia. In our hospital, the resistance rate of S. maltophilia against ST had been reported at around 90%.
Our institution uses the broth microdilution method in antimicrobial susceptibility testing(AST) for S. maltophilia, but assessment of the result is not always easy. From April 2005 through March 2011, 22 clinical strains of S. maltophilia were isolated from bacteremia patients in Kyushu University Hospital in Japan. Using these strains, we compared the results of 4 different AST methods; the broth microdilution method(BMD) combined with visual judgment by a single medical technologist(BMD sgl) and BMD judged by two or more experienced medical technologists(BMD pl), an E test(ET) and the agar dilution method(AD).
The results demonstrated the following AST resistance: 90.9% with BMD sgl, 54.5% with BMD pl, 27.3% with ET, and 31.8% with AD. From these results, it has become apparent the difficulty of visual assessment in BMD. Compared to AD, which is regarded as a standard method, we detected major errors(ME) in 4.5% with ET, 49.0% with BMD sgl and 13.7% with BMD pl. The reason why we observed more ME cases in BMD was judged to be the influence of the gross visual assessment process. With regard to the adverse effects of ME cases in BMD sgl, we studied the clinical and laboratory information by extracting digital medical records. In 13 cases with ME, in BMD sgl, ST was administered in 3 cases, and the mortality rate was 33.3%, whereas the mortality rate of the cases without administration of ST was 30%.
Fortunately, there was no significant adverse difference between the groups with or without administration of ST. However, considering the difficulty in evaluating the AST results of ST against S. maltophilia with BMD, we should try ET for confirmation of the results.
Key word
Stenotrophomonas maltophilia, sulfamethoxazole-trimethoprim, broth microdilution method, E test, agar dilution method
Received
January 6, 2014
Accepted
October 1, 2014
Jpn. J. Chemother. 63 (1): 1-6, 2015
