Antibiotic susceptibility of Burkholderia pseudomallei from tropical northern Australia and implications for therapy of melioidosis

From a prospective melioidosis study commencing in 1989 at Royal Darwin Hospital, 170 initial isolates of Burkholderia pseudomallei were available for susceptibility testing. Of these 163 (96%) were susceptible to meropenem/imipenem, ceftazidime, trimethoprim-sulphamethoxazole (SMX/TMP) and doxycycline. Seven (4%) showed primary resistance; three had low-level resistance to SMX/TMP, one to ceftriaxone and amoxycillin/clavulanate (AMOX/CA) and three to doxycycline. Of 167 patients who survived their initial presentation, seven (4%) had culture positive infections which persisted for greater than 3 months after start of therapy. All ultimately cleared carriage of B. pseudomallei though three required changing to SMX/TMP after development of doxycycline resistance. Nineteen (11%) of the initial survivors clinically relapsed and 17 of these had repeat isolates available for testing. Four of these had acquired resistance: one to doxycycline, one to AMOX/CA and ceftazidime, one to SMX/TMP and one to both SMX/TMP and doxycycline. Molecular typing using randomly amplified polymorphic DNA and pulsed-field gel electrophoresis showed all but one relapse isolate to be the same as the original strain. These data are similar to published data from Thailand. As melioidosis has a high mortality (21% in this series) these results emphasize the need for prolonged eradication therapy and regular clinical and microbiological monitoring so that the emergence of resistance can be detected early and appropriate treatment modifications made.