By Marianne Beaulieu

Faculty Mentor: Dr. Lynn Lewis

Abstract

Phage therapy is the practice of treating bacterial infections with bacteriophages, viruses that are virulent to bacterial hosts. Phage therapy is a promising solution to the growing issue of treating antibiotic-resistant bacteria. However, bacteria develop resistance to phages as well. There is literature to suggest that bacteria can lose fitness or their mechanism of virulence in the process of developing resistance to infection by phages. Potentially, phage therapy could work both directly by lysing bacteria and indirectly by attenuating the bacteria. This experiment sought to model the attenuating effect on bacteria by phage therapy using Bacillus thuringiensis subsp. kurstaki (Btk) and a susceptible host, Manduca sexta larvae. I isolated phage-resistant mutant strains of Btk by repeatedly incubating the bacteria with a number of Bacillus phages and picking colonies that continued to grow once plated. Phage resistance assays confirmed phage resistance in three of the isolated strains. A Gram stain confirmed that all three strains were gram-positive rods, as expected for Btk. To test the virulence of the phage-resistant mutants compared to wild type Btk, I saturated the food of Manduca sexta with each of the three strains, as well wild type Btk as a positive control and water as a negative control. The bacterial spores, which contain the toxin against M. sexta, were not present in high enough concentrations for any of the groups (including the positive control) to kill any of the larvae. I generated synthetic data to demonstrate the statistical analysis portion of this project.