Conjugation in escherichia coli : an investigation on plasmid-mediated antimicrobial resistance

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Conjugation in escherichia coli : an investigation on plasmid-mediated antimicrobial resistance


Author: Yao, Mianzhi
Title: Conjugation in escherichia coli : an investigation on plasmid-mediated antimicrobial resistance
Degree: M.Sc.
Year: 2016
Subject: Plasmids.
Escherichia coli.
Hong Kong Polytechnic University -- Dissertations
Department: Dept. of Health Technology and Informatics
Pages: vii, 102 pages : color illustrations
Language: English
InnoPac Record:
Abstract: Background: Carbapenems are unique class of β-lactam because they possess the broadest spectrum antimicrobial activity and greatest potency against many Gram-negative bacteria among the currently available β-lactams. The raise of antimicrobial resistance is driven and facilitated by a number of risk factors in which some are naturally observed phenomenon and others are bacteria independent. Bacterial conjugation is on the basis of plasmid-mediated mechanism, which involves transfer of a copy of a conjugative plasmids to another bacterial cell. The main objective for this study was to investigate the plasmid transfer frequency among E. coli strains by means of various conjugal mating procedures. The effects of bacterial growth phases on the transfer frequency and the survival of E. coli transconjugants grown on various material surfaces were also investigated. Methodology: Wild type E. coli strain was induced to resistant to gentamicin and served as the recipient for the conjugal experiments. The gentamicin resistant E. coli strain together with several imipenem and cefotaxime resistant E. coli strains underwent different conjugal mating experiments (solid, liquid, and filter) with different donor-to-recipient ratio. Growth curves of each E. coli strains were determined. The effects of growth phases on transfer frequency were determined by the dynamic monitoring the transfer frequency at each bacterial growth phase. E. coli transconjugants were spotted on various surface material to determine their survival. Results: The highest transfer frequency was obtained by using the filter mating procedure, and the intermediate transfer frequency was observed using the solid mating procedure. For all the three mating procedures, the highest transfer frequency was observed when the donor-to-recipient ratio was to be 10:1. Dynamic monitoring the transfer frequency at each growth phases showed that all the three mating pairs had the highest transfer frequency during lag phase. Stainless steel supported significant longer survival when compared with clay and marble. Conclusions: Higher transfer frequency observed by use of filter mating revealed that tighter cell-to-cell contact favors the transfer of plasmids. Higher donor cell density facilitates the transfer frequency, which was reflected on the finding that higher transfer frequency was observed when the conjugal mating was performed under higher donor-to-recipient ratio. Highest transfer frequency observed during lag phase revealed that bacterial conjugation takes place more likely when the cells are in their steady state. The E. coli transconjugants survived longer on stainless steel suggested that antiseptic procedures should be taken more frequent on stainless steel.

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