Emergence of ceftazidime resistance in Burkholderia pseudomallei during therapy: Clinical, phenotypic and genotypic insights from paired isolates

Abstract

Objectives: This study aimed to characterize the clinical, phenotypic, and genomic attributes of Burkholderia pseudomallei isolates before and after the development of decreased susceptibility to β-lactam antibiotics during therapy. Methods: Paired B. pseudomallei isolates collected before (SCBP001) and 23 days after intravenous ceftazidime (CAZ) therapy (SCBP007) were evaluated. Minimal inhibitory concentrations (MICs) for CAZ and meropenem (MEM) were initially determined using Etest and subsequently confirmed by broth microdilution (BMD). Whole-genome sequencing (WGS) was performed to identify genetic mutations associated with resistance. Results: A 12-year-old boy presented with acute pyelonephritis and kidney injury. MICs showed decreased susceptibility to CAZ and MEM, although the value remained within the susceptible range according to Clinical and Laboratory Standards Institute (CLSI) breakpoint criteria. MICs increased from 1 µg/mL for both CAZ and MEM in SCBP001 to 8 µg/mL for CAZ and 3 µg/mL for MEM in SCBP007. BMD confirmed a further increase in CAZ MIC to 32 µg/mL in SCBP007. WGS revealed no known CAZ-resistance mutations in penA coding sequences but identified a G(-78)A mutation upstream of penA, associated with increased promoter activity and β-lactam resistance. Multi-locus sequence typing (MLST) confirmed both isolates as sequence type 99, originating from the same clone. Phenotypic evaluation on Ashdown's agar showed consistent morphotype I characteristics for both isolates. Conclusion: This case highlights the potential for B. pseudomallei to develop resistance during therapy. Early detection of decreased susceptibility, even within the susceptible range, using rapid molecular diagnostics is critical for timely antibiotic adjustments and improved patient outcomes.