Plasmid

Event Date: 
Wednesday, August 27, 2014 - 19:00 - 20:00
Institution: 
Macquarie University
Title: 

"Xenbiotics and Xenogenetics: Human Influence over Microbial Evolution"

Abstract: 

The extent of human effects on planetary and biological processes means that we are now the world’s greatest evolutionary force. Perhaps the best example of human driven selection is the rapid evolution of antibiotic resistance in a wide range of bacterial pathogens. Continued antibiotic use has resulted in the assembly of complex DNA molecules composed of diverse resistance determinants and mobile elements, each with independent phylogenetic origins. These novel plasmids, transposons, integrons and genomic islands are xenogenetic, in that they have arisen in human-dominated ecosystems as a direct result of human activity. Xenogenetic elements are being released via human waste streams along with significant quantities of selective agents and other xenobiotic compounds, creating environmental reactors that foster even more complex interactions between genes, mobile elements and diverse bacterial species. Saturation of the environment with selective agents is also likely to increase the basal rates of mutation, recombination and lateral gene transfer in all bacterial species. Consequently, the antibiotic revolution may now be having unintended, second order consequences that will affect the entire microbial biosphere.

Event Date: 
Wednesday, August 27, 2014 - 18:00 - 18:15
Institution: 
USyd
Title: 

Bowel movement: resistance plasmid transfer in the gut

Abstract: 

The treatment of endogenous infections caused by commensal Escherichia coli are often complicated by antibiotic resistance. Strains of resistant E. coli in the gastrointestinal tract serve as a reservoir of resistance determinants, and dissemination of resistance genes is often facilitated by conjugative plasmids. It is important to understand these plasmids in order to track the movement of resistance determinants between populations.
 
Three faecal E. coli isolates from a healthy adult were examined. Two of these (838-98B and -3B) were resistant to ampicillin (Ap), streptomycin (Sm) and sulphamethoxazole (Su). The other (838-50A) was susceptible. 838-50A and -3B were indistinguishable by biochemical and molecular analysis (API20E, phylogenetic group PCR, RAPD). 838-98B was a distinct strain. B/O plasmid replicons were detected in both resistant isolates using PCR-based plasmid replicon typing. A B/O replicon was not detected in the susceptible strain. This suggested that a plasmid bearing a B/O replicon might be responsible for ApSmSu resistance. Conjugation experiments with a laboratory adapted E. coli strain (UB5201) confirmed that the movement of a B/O plasmid from both 838-98B and -3B conferred ApSmSu resistance. Plasmid sequencing revealed that an identical B/O plasmid, p838B-R (94.8kb), was present in 838-98B and -3B, and carried ApSmSu resistance determinants. p838B-R was also observed to mobilise small plasmids, allowing the direction of in situ transfer to be determined.
 
The observed transfer of antibiotic resistance plasmid p838B-R between two unrelated strains in the gastrointestinal tract highlights the important role commensal bacteria play in the spread of resistance determinants. While not well documented, the association of B/O-type plasmids with antibiotic resistance is evident not only through p838B-R but also other available plasmid sequences. Further studies will allow us to determine the extent to which these plasmids influence antibiotic resistance in commensal E. coli

Event Date: 
Wednesday, January 29, 2014 - 18:00 - 18:15
Institution: 
UC Davis
Title: 

Hi-C Metagenomics: Strain- and plasmid-level deconvolution of a synthetic metagenome by sequencing proximity ligation products

Abstract: 

Metagenomics is a valuable tool for the study of microbial communities but has been limited by the difficulty of “binning” the resulting sequences into groups corresponding to the individual species and strains that constitute the community. Moreover, there are presently no methods to track the flow of mobile DNA elements such as plasmids through communities or to determine which of these are co-localized within the same cell. We address these limitations by applying Hi-C, a technology originally designed for the study of three-dimensional genome structure in eukaryotes, to measure the cellular co-localization of DNA sequences. We leveraged Hi-C data generated from a synthetic metagenome sample to accurately cluster metagenome assembly contigs into a small number of groups that differentiated the genomes of each species. The Hi-C data also associated plasmids with the chromosomes of their host and with each other orders of magnitude more frequently than to other species. We further demonstrated that Hi-C data is highly informative for resolving strain-specific genes and nucleotide substitutions between two closely related E. coli strains, K12 DH10B and BL21 (DE3), indicating such data may be useful for high-resolution genotyping of microbial populations. Our work demonstrates that Hi-C sequencing data provide valuable information for metagenome analyses that are not currently obtainable by other methods. This application of Hi-C has the potential to provide new perspective in the study of thefine-scale population structure of microbes, how antibiotic resistance plasmids (or other genetic elements) mobilize in microbial communities, and the genetic architecture ofheterogeneous tumor clone populations.

Event Date: 
Wednesday, February 27, 2013 - 18:00 - 18:30
Institution: 
University of Sydney
Title: 

A tale of two clones; multiple antibiotic resistance in Acinetobacter baumannii .

Abstract: 

The importance of Acinetobacter baumannii in causing nosocomial infections was only recognised in the mid 1980s, making it the least studied of the bacteria that are now resistant to most of the antibiotics that are most important for treatment of such infections. We assembled a large collection of A. baumannii isolates recovered between 1999 and 2011 at hospitals in Sydney, Canberra, Brisbane, Melbourne, Newcastle and Adelaide. All but a few of those that are resistant to multiple antibiotics belong to one of two clonal groups that have recently been found to be globally distributed. Hence, these clones, global clone 1 and 2, have been in Australia at least since the mid 1990s.
Representatives of hospitals and of groups with different carbapenem and aminoglycoside resistance patterns in our collection have been sequenced together with the GC1 and GC2 reference strains from the early 1980s. Trees based on single nucleotide polymorphisms reveal significant diversity in the Australian isolates from one clone and little in the other. Most of the genes conferring resistance to older antibiotics are in the chromosome clustered in one island in GC1 and two in GC2 isolates. However, each of these islands is continually evolving, losing and gaining resistance genes. Further variation arises from the acquisition of different plasmids carrying further resistance genes. Other major but unexpected differences arising within the clones affect the exopolysaccharides. The capsule is an important virulence determinant, and substitution of large chromosomal segments leads to many distinct loci for capsule biosynthesis in each clone.

Event Date: 
Wednesday, November 24, 2010 - 18:15 - 18:30
Institution: 
USyd
Title: 

Active partitioning by S. aureus conjugative multiresistance plasmids.

Syndicate content