Tuesday, April 12, 2011

Study: Adaptation Of Plasmids To New Bacterial Species

# 5487



The subject of Plasmids – tiny snippets of DNA that can be easily transferred between different types of bacteria – has been of particular interest since that is one of the modes by which bacteria can acquire antibiotic resistance.


The NDM-1 (New Delhi metallo-ß-lactamase-1) enzyme – which has received considerable attention these past few months -  is one of the types of resistance that can be carried on plasmids, raising concerns that it could spread to other types of bacteria.  


It may help if you think of plasmids as vehicles that can travel between different types of bacteria, and the resistance genes (like NDM-1) as one of its passengers.


Since it requires physical contact between two different types of bacteria for plasmids to transfer, man-made environments where many types of bacteria are thrown together -  such as sewage treatment plants and contaminated water supplies -  are of great interest to microbiologists studying plasmids.



Last week, we learned via a Lancet Study, that resistant bacteria were found in 4 per cent of samples tested from New Delhi’s water supplies and 30 per cent of tested sewage sites (see Lancet Study: NDM-1 In New Delhi Water Supply).


The researchers identified 11 new species of bacteria carrying the NDM-1 gene, including strains which cause cholera and dysentery.



While not looking specifically at NDM-1 plasmid transfer, we’ve a new study published in Nature Communications on evolutionary changes in one common family of Plasmids; IncP-1.


The IncP-1 Plasmid was first identified in 1969 at a Birmingham (U.K.) hospital riding on Pseudomonas aeruginosa and Klebsiella aerogenes bacterial strains, and contained genetic coding that allowed their hosts to survive contact with multiple antibiotics  (cite Spread and survival of promiscuous IncP-1 plasmids).


Since that time IncP-1 has been the subject of interest among microbiologists, but evolutionary information on how it adapts to new bacterial hosts has been sparse.


Today’s open access study seeks to fill in some of those gaps.


The IncP-1 plasmid backbone adapts to different host bacterial species and evolves through homologous recombination

Peter Norberg, Maria Bergström, Vinay Jethava, Devdatt Dubhashi & Malte Hermansson

Nature Communications Volume: 2, Article number: 268 DOI: doi:10.1038/ncomms1267


Plasmids are important members of the bacterial mobile gene pool, and are among the most important contributors to horizontal gene transfer between bacteria. They typically harbour a wide spectrum of host beneficial traits, such as antibiotic resistance, inserted into their backbones.


Although these inserted elements have drawn considerable interest, evolutionary information about the plasmid backbones, which encode plasmid related traits, is sparse.


Here we analyse 25 complete backbone genomes from the broad-host-range IncP-1 plasmid family. Phylogenetic analysis reveals seven clades, in which two plasmids that we isolated from a marine biofilm represent a novel clade.


We also found that homologous recombination is a prominent feature of the plasmid backbone evolution. Analysis of genomic signatures indicates that the plasmids have adapted to different host bacterial species. Globally circulating IncP-1 plasmids hence contain mosaic structures of segments derived from several parental plasmids that have evolved in, and adapted to, different, phylogenetically very distant host bacterial species.

(Continue . . . )




If all of this seems a bit technical (and it is), we have a press release from the University of Gothenburg that helps clear some of it up.


The `money quote’ is:


The research team's findings show that IncP-1 plasmids can move, and have moved, between widely differing bacterial species and in addition have interacted directly with one another, which can increase the potential for gene spreading.


But follow the link below to read the release in its entirety.




Antibiotic resistance spreads rapidly between bacteria

The part of bacterial DNA that often carries antibiotic resistance is a master at moving between different types of bacteria and adapting to widely differing bacterial species, shows a study made by a research team at the University of Gothenburg in cooperation with Chalmers University of Technology. The results are published in an article in the scientific journal Nature Communications.


More and more bacteria are becoming resistant to our common antibiotics, and to make matters worse, more and more are becoming resistant to all known antibiotics. The problem is known as multi-resistance, and is generally described as one of the most significant future threats to public health Antibiotic resistance can arise in bacteria in our environment and in our bodies. Antibiotic resistance can then be transferred to the bacteria that cause human diseases, even if the bacteria are not related to each other.


(Continue . . . )