A study on the antimicrobial susceptibility testing of trimethoprim-sulfamethoxazole against Stenotrophomonas maltophilia isolated from bacteremia patients

Noriko Iwasaki, Noriko Miyake, Kyoko Onozawa, Ruriko Nishida, Masako Kadowaki, Makiko Kiyosuke, Nobuyuki Shimono

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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 pi), 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 pi, 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 pi. 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.

Original languageEnglish
Pages (from-to)1-6
Number of pages6
JournalJapanese Journal of Chemotherapy
Issue number1
Publication statusPublished - Jan 1 2015


All Science Journal Classification (ASJC) codes

  • Pharmacology
  • Pharmacology (medical)

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