A single nucleotide in the promoter region modulates the expression of the -lactamase OXA-61 in Campylobacter jejuni

Abstract

Despite prevalent β-lactam resistance in Campylobacter jejuni, an important zoonotic enteric pathogen, the molecular basis of β-lactamase-mediated β-lactam resistance is still largely unknown. In particular, some C. jejuni strains that carry β-lactamase gene blaOXA-61 (Cj0299) are still susceptible to β-lactams with undetected β-lactamase activity, suggesting blaOXA-61 is subjected to regulation. The objective of this study was to determine the regulatory mechanism of β-lactamase in C. jejuni. An ampicillin-resistant derivative of C. jejuni NCTC 11168 was subjected to whole genome sequencing and comparative genomics analysis. Complementary molecular experiments were further performed to examine the identified regulatory mechanism of blaOXA-61, which included complementation, promoter fusion assay, real-time RT-PCR, natural transformation using a defined PCR fragment, survey of clinical isolates and transcription start site mapping. A single nucleotide mutation (G → T transversion) upstream of blaOXA-61 was identified in the ampicillin-resistant derivative of NCTC 11168. The role of the G → T point mutation in acquired β-lactam resistance through up-regulating the expression of blaOXA-61 was confirmed by multiple molecular approaches. The G → T transversion in the blaOXA-61 promoter was linked to high-level β-lactam resistance in C. jejuni isolates. Transcription start site mapping indicated that the G → T transversion restored the TATA box in the -10 region of blaOXA-61. We demonstrated a novel genetic mechanism of β-lactamase regulation in C. jejuni in this study, which will provide insights into the regulation and evolution of β-lactam resistance in Campylobacter.