Correction: Discovery, biosynthesis and antifungal mechanism of the polyene-polyol meijiemycin.

Correction for 'Discovery, biosynthesis and antifungal mechanism of the polyene-polyol meijiemycin' by Zhen Jie Low et al., Chem. Commun., 2020, DOI: .

Discovery, biosynthesis and antifungal mechanism of the polyene-polyol meijiemycin.

Produced by a newly isolated Streptomycetes strain, meijiemycin is a gigantic linear polyene-polyol that exhibits structural features not seen in other members of the polyene-polyol family. We propose a biosynthetic mechanism and demonstrate that meijiemycin inhibits hyphal growth by inducing the aggregation of ergosterol and restructuring of the fungal plasma membrane.

Clinically Relevant Plasmid-Host Interactions Indicate that Transcriptional and Not Genomic Modifications Ameliorate Fitness Costs of Klebsiella pneumoniae Carbapenemase-Carrying Plasmids.

The rapid dissemination of antimicrobial resistance (AMR) around the globe is largely due to mobile genetic elements, such as plasmids. They confer resistance to critically important drugs, including extended-spectrum beta-lactams, carbapenems, and colistin. Large, complex resistance plasmids have evolved alongside their host bacteria. However, much of the research on plasmid-host evolution has focused on small, simple laboratory plasmids in laboratory-adapted bacterial hosts. These and other studies have documented mutations in both host and plasmid genes which occur after plasmid introduction to ameliorate fitness costs of plasmid carriage. We describe here the impact of two naturally occurring variants of a large AMR plasmid (pKpQIL) on a globally successful pathogen. In our study, after pKpQIL plasmid introduction, no changes in coding domain sequences were observed in their natural host, Klebsiella pneumoniae However, significant changes in chromosomal and plasmid gene expression may have allowed the bacterium to adapt to the acquisition of the AMR plasmid. We hypothesize that this was sufficient to ameliorate the associated fitness costs of plasmid carriage, as pKpQIL plasmids were maintained without selection pressure. The dogma that removal of selection pressure (e.g., antimicrobial exposure) results in plasmid loss due to bacterial fitness costs is not true for all plasmid/host combinations. We also show that pKpQIL impacted the ability of K. pneumoniae to form a biofilm, an important aspect of virulence. This study used highly relevant models to study the interaction between AMR plasmids and pathogens and revealed striking differences from results of studies done on laboratory-adapted plasmids and strains.IMPORTANCE Antimicrobial resistance is a serious problem facing society. Many of the genes that confer resistance can be shared between bacteria through mobile genetic elements, such as plasmids. Our work shows that when two clinically relevant AMR plasmids enter their natural host bacteria, there are changes in gene expression, rather than changes to gene coding sequences. These changes in gene expression ameliorate the potential fitness costs of carriage of these AMR plasmids. In line with this, the plasmids were stable within their natural host and were not lost in the absence of selective pressure. We also show that better understanding of the impact of resistance plasmids on fundamental pathogen biology, including biofilm formation, is crucial for fighting drug-resistant infections.

Inactivation or inhibition of AcrAB-TolC increases resistance of carbapenemase-producing Enterobacteriaceae to carbapenems.

OBJECTIVES: The objective of this study was to study the contribution of the multidrug resistance AcrAB-TolC efflux system to carbapenem resistance in carbapenemase-producing Enterobacteriaceae and the impact of the efflux inhibitor PABN on this resistance. METHODS: Klebsiella pneumoniae, Escherichia coli, Salmonella enterica serovar Typhimurium and their corresponding AcrAB-TolC mutants, each carrying carbapenemase-carrying plasmids (pKpQIL-UK with blaKPC and pNDM-HK with blaNDM), were tested for their susceptibility to six ß-lactam antibiotics according to the BSAC agar dilution method. MICs were also determined in the presence of efflux inhibitors. The susceptibility of ertapenem in the presence of 25 and 100 mg/L PABN was also determined for 86 non-replicate clinical isolates of carbapenemase-producing Enterobacteriaceae with OXA-48-like (n = 18), IMP (n = 12), VIM (n = 16), NDM (n = 20) or KPC (n = 20) enzymes. Outer membrane protein profiles were determined with SDS-PAGE. RESULTS: The carbapenemase-producing AcrAB mutants of K. pneumoniae and E. coli and the TolC mutant of Salmonella Typhimurium had elevated resistance to carbapenem antibiotics. In Salmonella Typhimurium, the increase in carbapenem MIC correlated with the loss of OmpF. Sixty-two (72%) of the clinical isolates tested were also more resistant to ertapenem in the presence of PABN. SDS-PAGE showed that the presence of PABN affected outer membrane porin production, which was associated with the increased MIC values of ertapenem. CONCLUSIONS: The decreased susceptibility to carbapenems of carbapenemase-producing Enterobacteriaceae in the absence of AcrAB or TolC and/or in the presence of an efflux inhibitor (e.g. PABN) is likely due to the changes in porin expression (e.g. OmpF). Efflux inhibitors may not potentiate carbapenem activity, but rather could increase levels of resistance in carbapenemase-producing organisms.

Functional genomics to identify the factors contributing to successful persistence and global spread of an antibiotic resistance plasmid.

BACKGROUND: The spread of bacterial plasmids is an increasing global problem contributing to the widespread dissemination of antibiotic resistance genes including ß-lactamases. Our understanding of the details of the biological mechanisms by which these natural plasmids are able to persist in bacterial populations and are able to establish themselves in new hosts via conjugative transfer is very poor. We recently identified and sequenced a globally successful plasmid, pCT, conferring ß-lactam resistance. RESULTS: Here, we investigated six plasmid encoded factors (tra and pil loci; rci shufflon recombinase, a putative sigma factor, a putative parB partitioning gene and a pndACB toxin-antitoxin system) hypothesised to contribute to the 'evolutionary success' of plasmid pCT. Using a functional genomics approach, the role of these loci was investigated by systematically inactivating each region and examining the impact on plasmid persistence, conjugation and bacterial host biology. While the tra locus was found to be essential for all pCT conjugative transfer, the second conjugation (pil) locus was found to increase conjugation frequencies in liquid media to particular bacterial host recipients (determined in part by the rci shufflon recombinase). Inactivation of the pCT pndACB system and parB did not reduce the stability of this plasmid. CONCLUSIONS: Our findings suggest the success of pCT may be due to a combination of factors including plasmid stability within a range of bacterial hosts, a lack of a fitness burden and efficient transfer rates to new bacterial hosts rather than the presence of a particular gene or phenotype transferred to the host. The methodology used in our study could be applied to other 'successful' globally distributed plasmids to discover the role of currently unknown plasmid backbone genes or to investigate other factors which allow these elements to persist and spread.