Pathogenicity of Clinical OXA-48 Isolates and Impact of the OXA-48 IncL Plasmid on Virulence and Bacterial Fitness

Abstract

OXA-48 is the most common carbapenemase in Enterobacterales in Germany and one of the most frequent carbapenemases worldwide. Several reports have associated <i>bla</i> _OXA _- ₄₈ with a virulent host phenotype. To challenge this hypothesis, 35 OXA-48-producing clinical isolates of <i>Escherichia coli</i> (<i>n</i> = 15) and <i>Klebsiella pneumoniae</i> (<i>n</i> = 20) were studied <i>in vitro</i>, <i>in vivo</i> employing the <i>Galleria mellonella</i> infection model and by whole-genome sequencing. Clinical isolates belonged to 7 different sequence types (STs) in <i>E. coli</i> and 12 different STs in <i>K. pneumoniae</i>. In 26/35 isolates <i>bla</i> _OXA- ₄₈ was located on a 63 kb IncL plasmid. Horizontal gene transfer (HGT) to <i>E. coli</i> J53 was high in isolates with the 63 kb IncL plasmid (transconjugation frequency: ∼10³/donor) but low in isolates with non-IncL plasmids (<10^-6/donor). Several clinical isolates were both highly cytotoxic against human cells and virulent <i>in vivo</i>. However, 63 kb IncL transconjugants generated from these highly virulent isolates were not more cytotoxic or virulent when compared to the recipient strain. Additionally, no genes associated with virulence were detected by <i>in silico</i> analysis of OXA-48 plasmids. The 63 kb plasmid was highly stable and did not impair growth or fitness in <i>E. coli</i> J53. In conclusion, OXA-48 clinical isolates in Germany are diverse but typically harbor the same 63 kb IncL plasmid which has been reported worldwide. We demonstrate that this 63 kb IncL plasmid has a low fitness burden, high plasmid stability and can be transferred by highly efficient HGT which is likely the cause of the rapid dissemination of OXA-48 rather than the expansion of a single clone or gain of virulence.