New Teixobactin Analogues with a Total Lactam Ring

Teixobactin is a new antibiotic peptide with strong efficacy against several Gram-positive resistant bacteria, the structure of which is extremely difficult to obtain in the laboratory via multistep conventional synthesis. To face the increasing antibiotic resistant bacteria, it is fundamental to introduce new types of antibiotics with innovative mechanisms of action without resistance; thus, many scientists are studying and developing new methods to synthesize teixobactin analogues. In this work, seven Arg10-teixobactin analogues with a total lactam ring have been prepared via solid phase peptide synthesis. In order to obtain the total lactam ring, d-Thr8 was replaced by (2R,3S)-diamino-propionic acid. To verify their antimicrobial activity and efficacy, each analogue was tested with MIC against different resistant pathogens, showing an interesting activity for Nle11 containing compounds.

Development of teixobactin analogues containing hydrophobic, non-proteogenic amino acids that are highly potent against multidrug-resistant bacteria and biofilms

Teixobactin is a cyclic undecadepsipeptide that has shown excellent potency against multidrug-resistant pathogens, such as methicillin-resistant Staphylococcus aureus (MRSA) and vancomycin-resistant Enterococci (VRE). In this article, we present the design, synthesis, and antibacterial evaluations of 16 different teixobactin analogues. These simplified analogues contain commercially available hydrophobic, non-proteogenic amino acid residues instead of synthetically challenging expensive L-allo-enduracididine amino acid residue at position 10 together with different combinations of arginines at positions 3, 4 and 9. The new teixobactin analogues showed potent antibacterial activity against a broad panel of Gram-positive bacteria, including MRSA and VRE strains. Our work also presents the first demonstration of the potent antibiofilm activity of teixobactin analogoues against Staphylococcus species associated with serious chronic infections. Our results suggest that the use of hydrophobic, non-proteogenic amino acids at position 10 in combination with arginine at positions 3, 4 and 9 holds the key to synthesising a new generation of highly potent teixobactin analogues to tackle resistant bacterial infections and biofilms.

Mobile colistin resistance gene mcr-1 detected on an IncI1 plasmid in Escherichia coli from meat

OBJECTIVES

Mobile colistin resistance (mcr) genes encoded on conjugative plasmids, although described only relatively recently, have been reported globally both in humans and livestock. The genes are often associated with the insertion sequence ISApl1 that can transpose the genes to novel genetic locations. Since its first report, multiple variants of mcr have been discovered in a variety of genetic locations in Escherichia coli, in plasmids and integrated into the chromosome.

METHODS

Using hybrid assembly of short-read and long-read whole-genome sequencing data, the presence ofmcr-1 was confirmed on an IncI1 plasmid in E. coli. In vitro conjugation assays were performed to determine the potential to transfer between strains. Genetic comparison with previously reported IncI1 plasmids was performed.

RESULTS

The genomic sequence identified thatmcr-1 is present on a complete IncI1 plasmid. Comparison with previously reported extended-spectrum β-lactamase (ESBL)-encoding plasmids from E. coli in the Netherlands from the same time period indicated a distinct lineage for this plasmid.

CONCLUSIONS

The observation ofmcr-1 on an IncI1 plasmid confirms that the genetic region of this gene is actively transposed between genetic locations. This active transposition has consequences for the study of the epidemiology of mcr in populations.

Identification of a Type IV-A CRISPR-Cas System Located Exclusively on IncHI1B/IncFIB Plasmids in Enterobacteriaceae

Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR) are diverse immune systems found in many prokaryotic genomes that target invading foreign DNA such as bacteriophages and plasmids. There are multiple types of CRISPR with arguably the most enigmatic being Type IV. During an investigation of CRISPR carriage in clinical, multi-drug resistant, Klebsiella pneumoniae, a Type IV-A3 CRISPR-Cas system was detected on plasmids from two K. pneumoniae isolates from Egypt (isolated in 2002-2003) and a single K. pneumoniae isolate from the United Kingdom (isolated in 2017). Sequence analysis of all other genomes available in GenBank revealed that this CRISPR-Cas system was present on 28 other plasmids from various Enterobacteriaceae hosts and was never found on a bacterial chromosome. This system is exclusively located on IncHI1B/IncFIB plasmids and is associated with multiple putative transposable elements. Expression of the cas loci was confirmed in the available clinical isolates by RT-PCR. In all cases, the CRISPR-Cas system has a single CRISPR array (CRISPR1) upstream of the cas loci which has several, conserved, spacers which, amongst things, match regions within conjugal transfer genes of IncFIIK/IncFIB(K) plasmids. Our results reveal a Type IV-A3 CRISPR-Cas system exclusively located on IncHI1B/IncFIB plasmids in Enterobacteriaceae that is likely to be able to target IncFIIK/IncFIB(K) plasmids presumably facilitating intracellular, inter-plasmid competition.

Isolation of an antimicrobial-resistant, biofilm-forming, Klebsiella grimontii isolate from a reusable water bottle

A reusable water bottle was swabbed as part of the citizen science project "Swab and Send," and a Klebsiella grimontii isolate was recovered on chromogenic agar and designated SS141. Whole-genome sequencing of SS141 showed it has the potential to be a human pathogen as it contains the biosynthetic gene cluster for the potent cytotoxin, kleboxymycin, and genes for other virulence factors. The genome also contains the antibiotic-resistant genes, bla_OXY-6-4 , and a variant of fosA, which is likely to explain the observed resistance to ampicillin, amoxicillin, and fosfomycin. We have also shown that SS141 forms biofilms on both polystyrene and polypropylene surfaces, providing a reasonable explanation for its ability to colonize a reusable water bottle. With the increasing use of reusable water bottles as an alternative to disposables and a strong forecast for growth in this industry over the next decade, this study highlights the need for cleanliness comparable to other reusable culinary items.