Resistance to trimethoprim/sulfamethoxazole and Tropheryma whipplei

Abstract

Whipple's disease (WD) is a chronic infection caused by Tropheryma whipplei. A 1-year treatment of oral trimethoprim/sulfamethoxazole (SXT) is commonly used. Advances in the culture of T. whipplei have allowed for full genome sequencing and antibiotic susceptibility testing, which has demonstrated resistance of T. whipplei to trimethoprim. Several mutations in the folP gene that encodes dihydropteroate synthase, the target of sulphonamides, has been reported for one patient with clinically acquired resistance to SXT. Here we report three new patients who experienced clinically acquired resistance to SXT during treatment and one patient with biological failure. Sixty-two folP sequences from DNA samples of 59 WD patients were also obtained. Among the detected amino acid changes, two positions (N4S and S234F) significantly predicted secondary sulfamethoxazole failure (four of five). We suggest that these mutations should be detected at the time of WD diagnosis by sequencing folP in order to avoid sulfamethoxazole monotherapy.

Introduction

Whipple's disease (WD) is a chronic infection caused by the bacterium Tropheryma whipplei, which was fatal before the advent of antibiotics [1]. Since 1952 and the first successful use of chloramphenicol, treatment has been empirical until the possible determination of antibiotic susceptibilities [1]. In 1966, Ruffin et al. [2] proposed a therapy based on penicillin and streptomycin administered parenterally for 2 weeks, named induction therapy, followed by tetracycline orally for 3–12 months. Physicians then described patients who responded to numerous antibiotics, including tetracyclines, chloramphenicol, penicillin, streptomycin and trimethoprim/sulfamethoxazole (SXT). For many years, tetracycline was the drug of choice for maintenance therapy. In 1985, a study revealed a relapse rate as high as 35% among tetracycline-treated patients, with a high rate of central nervous system (CNS) relapse [3]. Induction treatment of parenteral streptomycin together with penicillin G for 2 weeks, followed by maintenance therapy of oral SXT [160 mg trimethoprim (TMP) and 800 mg (SMX) sulfamethoxazole] twice daily for 1 year was then proposed as a ‘reasonable compromise’ [4].

Currently, there is lack of an accurate definition of treatment failure because of misinterpretation of previous studies as well as a lack of follow-up to evaluate relapses. Primary failure after initiation of adequate WD therapy should be differentiated from relapse after antibiotic cessation (Fig. 1). Primary failure includes immediate failure observed <3 months after initiation of antibiotics and late failure observed >3 months after initiation of antibiotics. Immediate failure includes either a lack of amelioration, mainly described in patients with initial neurological involvement and treated with tetracyclines, and symptom exacerbation, which may be observed during leprosy, during lepromatous reactions or in immune reconstitution [5], [6]. Such immediate failures may not be due to antibiotic failure or resistance. Late failure corresponds with acquired resistance to the treatment and is mainly described for SXT [7], [8].

Owing to recent success in T. whipplei culture methods, susceptibility tests and full genome sequencing have been achieved. Many antibiotics, including doxycycline and SXT, are active in vitro [1]. Ceftriaxone and levofloxacin are active in axenic cultures, but cephalosporins (including ceftriaxone) and fluoroquinolones are not active in cell cultures. Genomic analysis indicates that T. whipplei lacks the coding sequence for dihydrofolate reductase, which is a target of TMP [5]. In vitro tests confirm that TMP is not active, whereas sulphonamide compounds, such as SMX and sulfadiazine, exhibit activity [5]. Current recommendations for WD treatment involve sulphonamide monotherapy. Recently, we reported mutations in the target gene of SMX, folP, that lead to in vitro resistance and secondary clinical failure [8]. Herein, we report three new patients with secondary clinical failure in response to SXT, one patient who developed biological failure as well as 62 complete sequences of folP from 59 patients.