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

Axel Hamprecht,Matthias Willmann,Sara Riedel-Christ,Aitor Gonzaga,Stephan Göttig,Felix F Krause,Christina Brender,Florian Wild,Ulrich Nübel,Julian Sommer,Can Imirzalioglu,Yvonne Stelzer,Tsvetan Tsvetkov,Julia Kutschenreuter

doi:10.3389/fmicb.2019.02509

Abstract

OXA-48 is the most common carbapenemase in Enterobacterales in Germany and one of the most frequent carbapenemases worldwide. Several reports have associated blaOXA–48 with a virulent host phenotype. To challenge this hypothesis, 35 OXA-48-producing clinical isolates of Escherichia coli (n = 15) and Klebsiella pneumoniae (n = 20) were studied in vitro, in vivo employing the Galleria mellonella infection model and by whole-genome sequencing. Clinical isolates belonged to 7 different sequence types (STs) in E. coli and 12 different STs in K. pneumoniae. In 26/35 isolates blaOXA–48 was located on a 63 kb IncL plasmid. Horizontal gene transfer (HGT) to E. coli 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 in vivo. 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 in silico analysis of OXA-48 plasmids. The 63 kb plasmid was highly stable and did not impair growth or fitness in E. coli 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.

Highlights

Escherichia coli and Klebsiella pneumoniae are the most common species causing Gram-negative sepsis (Goto et al, 2016)
In contrast to other successful β-lactamase producing clonal lineages (e.g., K. pneumoniae KPC-2 ST258 or E. coli CTX-M-15 ST131), OXA-48 isolates belong to different sequence types (STs) but frequently harbor similar plasmids (Beyrouthy et al, 2013; Potron et al, 2013)
35 OXA-48 producing E. coli and K. pneumoniae clinical isolates were molecularly characterized and factors involved in dissemination and virulence were investigated in silico, in vitro, and in vivo

Summary

Introduction

Escherichia coli and Klebsiella pneumoniae are the most common species causing Gram-negative sepsis (Goto et al, 2016). The increasing incidence of multidrug-resistant (MDR) E. coli and K. pneumoniae strains has complicated the treatment of Gramnegative sepsis and other invasive infections. Among MDR bacteria, carbapenemase-producing Enterobacterales (CPE) are a major threat to our health system, because of resistance to most or all β-lactam antibiotics and a lack of therapeutic options. OXA-48 has been successful and is the most common carbapenemase in Germany. It has rapidly disseminated from Europe and the Middle East to every continent (Canton et al, 2012). The reasons for the successful dissemination of OXA-48 are currently not fully understood

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Conclusion