Exploring K30 capsule production by E. coli E69 as a potential mechanism of resistance to T4 bacteriophage infection

Abstract

Bacterial capsules are extracellular structures located on the outer cell wall, and capsule production has been shown to both promote and inhibit bacteriophage susceptibility, with specific interactions seemingly dependent on the capsule serotype and phage used. Understanding the relationship between bacterial characteristics and phage resistance is valuable to aid in the improvement of phage therapy, which is used to treat illnesses caused by pathogenic bacteria. The aim of our experiment was to investigate if capsule production inhibited T4 bacteriophage infection in group I capsule-producing K-30 strain Escherichia coli E69. The K-12 mutant CWG655 has a triple chromosomal deletion of wza-wzb-wzc, encoding for proteins responsible for surface expression of capsular polysaccharides. Based on prior research indicating that T4 resistance was dependent on the presence of K5 capsule in E. coli strain Nissle 1917, it was hypothesized that the production of capsule in E69 would confer resistance to T4 bacteriophage, while CWG655 would be susceptible to phage infection. A preliminary experiment testing infectivity was carried out using a double agar plaque assay, with plaque formation observed in CWG655 but not in wild-type E69. This may indicate that the capsular polysaccharide (CPS) production in wild-type E69 conferred resistance to T4. Further experiments are needed to confirm these initial findings. The mechanism of T4 phage resistance and interactions of CWG655 with other bacteriophages could also be investigated to further understand bacteriophage resistance dynamics for phage therapy.