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article imageUnpacking the clues as to why some bacteria resist antibiotics

By Tim Sandle     Jan 22, 2015 in Science
Phoenix - Scientists are seeking to find out the different processes used by bacteria to survive destruction from antimicrobial peptides within the natural environment. The hope is to find new ways to kill pathogenic organisms.
To kill bacteria, antimicrobial peptides target the bacterial membrane. This makes it difficult for bacteria to develop resistance, unlike the processes that occur with conventional antibiotics. Antimicrobial peptides (also called host defense peptides) are part of the innate immune response and are found among all classes of life. The peptides kill bacteria by triggering a rupture to the cell membrane leakage and this causes eventual cell destruction.
Many of these peptides occur naturally. For example, frogs can survive quite happily in pond water that contains bacteria which would kill most other creatures. The reason for this is because the skin of the frog contains peptides that kill bacteria on contact. For such reasons scientists have been keen to explore these peptides and to find ways to utilize them in medicine, especially to eliminate those bacteria that have developed resistance to antibiotics.
However, sometimes bacteria can shield themselves from peptides. One means is through the use of multi-drug pumps which are capable of removing antimicrobial peptides from the bacterial cell. This is described as a two-component system (officially “CpxR/CpxA”). The system is seen as a development by certain bacteria to counteract the peptides.
This is not an insurmountable obstacle for scientists are of the view that if the internal pump can be disabled then no pathogenic bacteria would be able to remove the peptides and they would therefore be killed.
Researchers have been studying specific genes with the bacterium Escherichia coli that allow it to counteract peptides. The researchers examined 115 bacterial strains for this purpose. Through this the researchers identified a gene called tolC. This gene is an important constituent for removing peptides from the cell and therefore it acts as part of the bacterial defence mechanism.
The results of the research provide a useful insight into mechanisms of bacterial resistance to antimicrobial peptides and it provides clues as to how the system could be disrupted.
The research was performed by Center for Infectious Diseases and Vaccinology at Arizona State University's Biodesign Institute. The research results have been published in the Journal of Biological Chemistry. The paper is headed “The CpxR/CpxA Two-component Regulatory System Up-regulates the Multidrug Resistance Cascade to Facilitate Escherichia coli Resistance to a Model Antimicrobial Peptide.”
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