NTU Undergraduates' research April 2014 - Biosciences | Seite 49

Abstract
Bacterial species such as Escherichia coli and Acinetobacter baumannii are well known culprits of
antibiotic resistance due to the acquirement of Extended-Spectrum Beta-Lactamases. It has been
proven that Beta-Lactamase genes existed before the development of antibiotics, however the
emergence of antibiotics has created a selective pressure for these bacterial species to adapt to
survive in the human host and confer pathogenesis.
As a result, the direction of the research was based on the phylogeny of the CTX-M and OXA ESBL
genes to determine the order of evolution and the evolutionary pattern as well as subsequent amino
acid analysis to determine the extent of the evolution that has occurred on a molecular level due to
the emergence of the antibiotic era which has provided a catalyst for mutation to occur.
It was found that although mutation of the CTX-M genes has occurred due to the selective pressure
of antibiotics the mutations are largely synonymous. This suggests that bacteria have had to adapt to
the development of new antibiotics in order to survive in the human host however dramatic changes
have not occurred therefore the bacteria have not yet encountered significant threat as a result of
antimicrobial therapies. Furthermore, the OXA enzymes appear to have undergone more extensive
mutation compared to the CTX-M enzymes, with more recognisable evidence of non-synonymous
mutation, indicating that the OXA enzymes have undergone more dramatic evolution in response to
a stronger selective pressure which has driven mutation to occur.