Gentamicin-induced resistance to T7 bacteriophage lysis in Escherichia coli is not due to an extracellularly released factor

The worldwide emergence of antibiotic resistant bacteria necessitates the search for alternative treatments for bacterial infections. A promising potential therapeutic is the use of bacteriophages that can lyse bacteria such as Escherichia coli. However, some antibiotics such as gentamicin have been shown to decrease the lysis rate of bacteriophages in E. coli. This ‘protective factor’ has been theorized to be released from the bacteria, such as outer membrane vesicles that competitively bind phage particles. To determine if the gentamicin-induced protective factor is extracellularly released, E. coli UB1005 was treated with different sub-inhibitory concentrations of gentamicin and cell filtrates were tested for protective ability against T7 bacteriophage. We hypothesized that if we transferred filtrate from gentamicin-treated E. coli to untreated cultures, then the untreated cultures would obtain protection against bacteriophage-mediated lysis, indicating that the protective factor was extracellularly released. We observed that filtrate from gentamicin-treated cultures was not able to confer protection to untreated cultures, refuting our hypothesis and disproving the outer membrane vesicle model of protection.