The Difficulty in Administering Appropriate Antimicrobial Therapy for Stenotrophomonas maltophilia Bacteremia

To the Editor We read with interest the recent study about the clinical characteristics of Stenotrophomonas maltophilia bacteremia by Ebara et al. in volume 56, issue 2 of Internal Medicine (1). The authors showed that the prognosis of patients who received appropriate antimicrobial therapy such as trimethoprim-sulfamethoxazole, minocycline or fluoroquinolones was poorer-though not to a significant degree-in comparison to patients who received nonspecific therapy. However, we are concerned about the timing of starting appropriate antimicrobial therapy. The treatment of S. maltophilia is generally challenging because of the bacterium’s inherent resistance to multiple classes of antibiotics, including beta-lactams, carbapenems and aminoglycosides (2). In Japan, beta-lactams and carbapenems are preferred as empiric therapy, and a delay in administering appropriate therapy can lead to a poor prognosis. Uehara et al. reported that Gram staining of blood cultures could help in selecting appropriate antimicrobials for patients with positive blood cultures (3). However, the presence of S. maltophilia is seldom suspected; most cases are thought to be Pseudomonas aeruginosa or a non-fermenting bacterium. We evaluated the Gram staining results of 27 cases of S. maltophilia bacteremia and found that only one case was reported to be “suspected S. maltophilia”, while “P. aeruginosa or other non-fermenting bacteria” was reported in six cases (4). In the remaining 20 cases, other Gram-negative bacteria, such as Enterobacteriaceae were reported and inappropriate therapy was continued based on the Gram staining results. Furthermore, appropriate antimicrobial therapy was not initiated in most cases of S. maltophilia bacteremia before making the final identification or obtaining the susceptibility testing results. This delay may also be a risk factor for a poor prognosis (5). Thus, we recommend that the authors include the timing for initiating appropriate antimicrobial therapy after blood culturing in their retrospective analysis.