Genetic drift can also be easily replicated with experimental evolution by adapting the directed evolution method. However, mutations were not consistently deleterious between all ten positions: Also in , directed evolution with error-prone PCR was able to recapitulate all four of the natural single mutations that conferred resistance to a combination ampicillin-clavulanate treatment Vakulenko et al. Find articles by Mojtaba Moosavian. Hong Fang ; Karolinska Institutet. Substitutions at E37, S, Q, H, and K largely had no effect on fitness scores compared to the wild type i. Efflux pumps present another route by which Gram-negative bacteria may effectively resist antibiotics.

In contrast, a recent study 56 that assessed diverse antibiotic resistance genes in E. Zinc ions are shown as spheres in light orange, with metal binding residues displayed as sticks. The initial rates of reaction for each MBL-substrate pair. For example, Bahr et al. Nobuhiko Tokuriki, at the University of British Columbia in Vancouver, British Columbia, between and the publication of this thesis.

However, some genetic changes may still be driven by adaptation. A thorough characterization of the mutations was able to reveal the mechanism by which a second-shell ligand mutation GS could alter the substrate specificity of the enzyme and facilitate the increased cephalexin resistance.


Any metaallo variants with altered substrate specificity will be biochemically characterized to determine the mechanisms by which MBLs may modify their substrate specificity to reveal what molecular features grant it in the first place. The biological consequences of this are shown in the enzymes diminished ability to provide strong resistance against these antibiotics.

They also do not account for the myriad of more advanced medical procedures that are now reliant upon the established use of antibiotics i. In the intervening years ghesis their first widespread use and today, significant bacterial resistance has emerged for virtually every clinically approved antibiotic.

Support Center Support Center. Eight variants from each of the three restoration rounds were randomly selected and the cefotaxime, meropenem, and ampicillin MICs were determined and compared to the values from the previous 18 rounds Figure 4. This may reflect the structural and functional constraints placed upon each position. This suggests that mutations in the catalytic domain for these two MBLs may also be affecting the host specificity, in addition to changes in the signal peptide.


Each data point represents the average increase in MIC over the wild type MBL for 6 to 10 variants randomly chosen from selected rounds. Nobuhiko Tokuriki, for creating a stimulating and always challenging research environment that encouraged me to grow and become metalo strong problem solver and capable scientist.

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Antecedents, consequences, and moderators In-line application of electric fields in capillary separation systems On diode-pumped solid-state lasers Popular complementary terms: Parts of Chapter 5 were performed by three undergraduate students in the same laboratory: Every second round in the TOsc trajectory is visualized as a line with each data point representative of the growth of that population at the given concentration of ampicillin compared to its uninhibited growth in duplicate.

The extracted DNA was then used as the template in the next round of genetic drift. On 7 September, Pvt.

thesis on metallo beta lactamase

Those variants that best display the trait are then selected and used as the template for the next cycle of directed evolution, while the remainder is discarded. On average, individual genes from the 40th round for lactamass T10, TOsc, and T trajectories had Indeed, the chromosomal MBL BcII, from Bacillus cereus, consistently provided one of the strongest resistance levels in all three organisms, but has yet to spread to pathogenic bacteria and has never been isolated in clinics.

The enrichment of each variant was then obtained by dividing the frequency of each variant in the selected condition i.

Interestingly, the improvement in the directed evolution appeared to be partially or fully host specific, which suggests that the MBLs were adapting to the host E.

Characterization of carbapenem-resistant Pseudomonas aeruginosa clinical isolates, carrying multiple genes coding for this antibiotic resistance.


thesis on metallo beta lactamase

For example, a gene would lactamaze subjected to mutagenesis lachamase the resulting mutated proteins screened 26 for a desired trait.

Indeed, the active site architecture of the MBLs certainly lends itself to broad specificity: The fitness of the drifted populations in the T high functional threshold T10 low functional threshold, T1 sub-inhibitory threshold, and T0 control trajectories.

For example, the relative enrichment for F61Y and ST under meropenem selection was 4. After transporting the samples to the microbiology laboratory in Medical School, the colonies were again inoculated into MacConkey agar medium and pure colonies were identified as P.

Each variant is represented by a single data point that follows the same scheme as above. Bacteria can also carry multiple versions of the efflux pumps, with some being acquirable through horizontal gene transfer. Steve Withers University Examiner Dr. They were further able to demonstrate that the combination of GS and another one of the mutations, N70S, created an additive effect that further improved resistance and produced a broader substrate spectrum Tomatis et al.

I have also been most fortunate to have two wonderful mentors, Dr.

thesis on metallo beta lactamase

metxllo CENTA activity was measured in duplicate and the MICs were determined by identifying the lowest concentration at which at least three of four replicates did not grow. This indicates that not only is variation increasing throughout the production of the MBLs, but that the relative expression of each MBL can be modified. A map showing the location of mutations identified in the sequenced variants of selected rounds from each genetic drift trajectory Nonetheless, the specific level of [Ep] of each enzyme varies depending on the host organism.