Plasmid-mediated transfer of the bla(NDM-1) gene in Gram-negative rods

Relaxosome function and conjugation regulation in F-like plasmids - a structural biology perspective

The tra operon of the prototypical F plasmid and its relatives enables transfer of a copy of the plasmid to other bacterial cells via the process of conjugation. Tra proteins assemble to form the transferosome, the transmembrane pore through which the DNA is transferred, and the relaxosome, a complex of DNA-binding proteins at the origin of DNA transfer. F-like plasmid conjugation is characterized by a high degree of plasmid specificity in the interactions of tra components, and is tightly regulated at the transcriptional, translational and post-translational levels. Over the past decade, X-ray crystallography of conjugative components has yielded insights into both specificity and regulatory mechanisms. Conjugation is repressed by FinO, an RNA chaperone which increases the lifetime of the small RNA, FinP. Recent work has resulted in a detailed model of FinO/FinP interactions and the discovery of a family of FinO-like RNA chaperones. Relaxosome components include TraI, a relaxase/helicase, and TraM, which mediates signalling between the transferosome and relaxosome for transfer initiation. The structures of TraI and TraM bound to oriT DNA reveal the basis of specific recognition of DNA for their cognate plasmid. Specificity also exists in TraI and TraM interactions with the transferosome protein TraD.

Nosocomial clustering of NDM-1-producing Klebsiella pneumoniae sequence type 340 strains in four patients at a South Korean tertiary care hospital

In November 2010, NDM-1-producing Klebsiella pneumoniae (NDMKP) was identified for the first time in South Korea from four patients with no history of traveling abroad who stayed for 21 to 205 days in a tertiary care hospital. All were sequence type (ST) 340 and had nearly identical XbaI pulsed-field gel electrophoresis (PFGE) patterns. The bla(NDM-1)-carrying plasmids were in the IncN group, with sizes ranging from 50 to 200 kb. These findings suggest that NDMKP had already been introduced into South Korea before this clustering was found.

Introduction to antibiotic resistance

The inexorable rise in multidrug-resistant Gram-negative bacteria has been widely reported. Multiple modes of resistance often present in a single strain of bacteria, and this may also be combined with an increase in virulence, both of which are leading to a significant increase in morbidity and mortality in patients. Against this background, the absolute number of new antibiotics licensed has declined especially for Gram-negative multidrug-resistant pathogens. The reasons for this failure are presented here: market issues, big pharma changes, regulatory constraints, difficulties in finding drugable targets and, lastly, suitable compounds worthy of full development.

Antibiotics in phase II and III clinical trials

There are 19 compounds in late-stage clinical trials, of which ten may be suitable for Gram-positive infections. However, there are only five compounds in development for Gram-negative infections, in addition to four broad-spectrum ones. There are two new classes in late-stage clinical development. This chapter discusses in some detail each of the antibiotics in Phase II and Phase III clinical trials. Only those that appear in the literature are covered. The shortage of compounds in development for Gram-negatives and the small number of new classes in the pipeline is of serious concern; this matter needs to be addressed by governments, the regulatory authorities, the pharmaceutical industry and academia urgently.

Complete sequence of broad-host-range plasmid pRIO-5 harboring the extended-spectrum-β-lactamase gene blaBES₋₁

Broad-host-range plasmid pRIO-5, harboring the extended-spectrum β-lactamase bla(BES-1) gene in Serratia marcescens, was fully sequenced. Analysis of the 12,957-bp sequence of this IncP6-type plasmid revealed that the bla(BES-1) gene was associated with two copies of the insertion sequence IS26. The promoter responsible for the bla(BES-1) expression was hybrid, made of a -35 box located inside the inverted repeat of IS26 and a -10 box inside a remnant of an insertion sequence.

Genetic features of the widespread plasmid coding for the carbapenemase OXA-48

Complete sequencing of plasmid pOXA-48a carrying the bla(OXA-48) gene from a Klebsiella pneumoniae isolate was performed. Its backbone corresponded to that of an IncL/M-type plasmid, in which the bla(OXA-48) gene had been integrated through the acquisition of the Tn1999 composite transposon without any other antibiotic resistance gene. Molecular epidemiology using a collection of international OXA-48 producers revealed the wide diffusion of pOXA-48a or closely related plasmids.