Lauren St. Germaine | 2026 I.S. Symposium
Name: Lauren St. Germaine
Title: A Good Virus: Investigating Increased Antibiotic Sensitivity in Pseudomonas chlororaphis 14B11 Induced by PC2 Bacteriophage Resistance
Major: Biochemistry & Molecular Biology
Advisor: Stephanie Strand
In the past decades, overuse and misuse of antibiotics have led to an abundance of antimicrobial resistance (AMR), making it harder for scientists to develop new antibiotics. Currently, alternative therapies are being researched to treat AMR infections, such as the combined strategy of bacteriophages and antibiotics, known as bacteriophage therapy. Bacteriophages represent a promising alternative because they can induce a notable fitness trade-off of increased antibiotic sensitivity, after bacterium evolve phage resistance. Previous studies have assessed this trade-off in virulent species of bacteria, such as Pseudomonas aeruginosa; however, there is limited research on these interactions in non-pathogenic species such as Pseudomonas chlororaphis 14B11. Furthermore, there is little understanding of the bacterial protein structures involved in conferring phage resistance and supporting a fitness trade-off. In this study, antibiotic susceptibility to ampicillin (AMP) and tetracycline (TET) was tested before and after P. chlororaphis 14B11 evolved phage resistance. Minimum Inhibitory Concentration (MIC) assays of the phage resistant mutants showed a 2.5-fold increase in antibiotic sensitivity to AMP, however there was a decrease in sensitivity to TET. Additionally, gene sequencing was utilized to determine if an outer membrane protein (OprM), is conserved in P. chlororaphis 14B11 and is altered after phage resistance is induced. Sequencing revealed no mutations in the target nucleotide sequence of the mutant colonies; therefore, whole-genome sequencing will be performed in the future to identify other mutations in the genomes of the phage-resistant mutants that may explain the results observed in this study. Future analysis of sequencing data may provide insight into the genomic mechanisms underlying phage-driven fitness trade-offs, potentially exploitable for therapeutic usage of bacteriophages.
Posted in Symposium 2026 on May 1, 2026.
