First Advisor

Justin Courcelle

Date of Award

Spring 6-2025

Document Type

Thesis

Degree Name

Bachelor of Science (B.S.) in Biology and University Honors

Department

Biology

Language

English

Subjects

Biofilm, Escherichia coli, Natural Competence, Antibiotic Resistance

DOI

10.15760/honors.1644

Abstract

Escherichia coli is a species not known for natural competence; however, specific growth conditions can induce the process in this bacterium due to the presence of homologous competence genes. These conditions could be met with biofilm formation through an active growth phase in the two-layer architecture. Therefore, my thesis examined whether natural competence is exhibited in E. coli during biofilm formation as determined by the genetic transfer of ampicillin and chloramphenicol-resistance genes between two separate strains. The experiments were broken into three aims to determine the morphology of the biofilm in inter-strain co-cultures and cell-DNA mixes, the effect of media supplementation on antibiotic resistance marker transfer, and the role of biofilm formation on genetic exchange. I found distinct "pink, dry, and rough" (pdar) morphology for inter-strain co-cultures and cell-DNA mixes when at least one of the strains was able to synthesize cellulose for biofilm formation. Co-cultures and mixes with strains unable to synthesize cellulose only displayed irregular concentric circles of growth around the periphery. The types of growth medium influenced the morphology and growth rate of biofilms with co-cultures grown on CaCl2 -supplemented Congo Red medium displaying distinct pdar and wrinkled morphology and faster growth on double selective plates (ampicillin/chloramphenicol). Mixing purified genomic DNA from a strain containing one antibiotic resistance marker with an intact bacterial strain with the opposite marker resulted in a higher occurrence of doubly resistant bacterial colonies compared to co-cultures made through mixing of two intact bacterial strains. However, whole genome sequencing of a colony isolate from ampicillin and chloramphenicol double selection showed the presence of only one of the two antibiotic resistance markers, indicating the transfer of genetic markers might be transient or non-recombinogenic. Further research is required to determine the mechanism for the presentation of double antibiotic resistance.

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Persistent Identifier

https://archives.pdx.edu/ds/psu/43697

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