Burkholderia pseudomallei acquired ceftazidime resistance due to gene duplication and amplification.

Ceftazidime is the antibiotic of choice for treatment of Burkholderia pseudomallei infections (melioidosis). The chromosomally encoded PenA β-lactamase possesses weak cephalosporinase activity. The wild-type penA gene confers clinically significant ceftazidime resistance only when overexpressed due to a promoter mutation, transcriptional anti-termination or by gene duplication and amplification (GDA). Here we characterize a reversible 33-kb GDA event involving wild-type penA in a ceftazidime resistant clinical isolate from Thailand. We show that duplication arises from exchanges between short (<10 base pairs, bp) chromosomal sequences, which in this example consist of 4 bp repeats flanked by 3 bp inverted repeats. GDA involving β-lactamase may be a common ceftazidime resistance mechanism in B. pseudomallei.