PHAVES #21: Molecular multitasking: inhibition of phage infection by aminoglycoside antibiotics, a seminar by Aël Hardy (September 7, 2021)

YouTube video

Highlights of Aël’s talk

Background and Overview

Aminoglycosides (AGs) are bacterial antibiotics derived from Streptomyces, a genus of gram-positive bacteria. An antibiotic widely used today, known as streptomycin, was the first AG isolated. Five different phages were isolated in 2018 with activity against Streptomyces and previous reports and observations indicated the potential inhibition of phage infection by AGs.

Aminoglycosides can inhibit a range of phages

• To determine the interaction between AGs and phages, AG-resistant bacterial strains were challenged with phage in the presence and absence of different AGs. This experiment determined that:

1. In the absence of AGs there was plaque formation observed, however,
2. In the presence of AGs, there was no plaque formation, even when the same phage was used.

• Therefore, this indicates that AGs inhibit phage infection.
• These experiments conducted using a wide range of bacterial hosts and a wide range of phages. Similar results were observed across the board indicating that AGs inhibit phage infection in a wide range of hosts (both gram-positive and gram-negative).
• Similar experiments were also conducted using liquid cultures. When phage infection occurs, there is a large decrease in the concentration of bacterial cells. However, when AGs were added, the normal bacterial growth curve was restored, with an increase in concentration of bacterial cells.
• Apramycin, a class of AGs were found to completely inhibit Alderaan (a Streptomyces phage) infection of Streptomyces.
• Further experiments were conducted where phages were added to the spent medium of AG producers. The spent medium of an apramycin producer showed the same effect as a purified apramycin producer indicating that spent mediums of apramycin can also inhibit phage infection.

Apramycin Functions by Preventing Replication and Transcription of Phage Genome

• To determine which step of the phage life cycle is inhibited by AGs, a variety of experiments were performed.

1. First, a potassium efflux assay was conducted to look at whether AGs impacted the injection of phage DNA. They found that apramycin did not have an effect on phage adsorption or DNA injection.
2. Second, qPCR allowed the researchers to look at whether AGs impacted phage replication. Using qPCR they were able to measure the intracellular phage DNA concentration overtime and found that while generally phage DNA concentration increases exponentially overtime, when apramycin was added, the concentration of phage DNA increases earlier and to a lesser extent overall.
3. Whole genome sequencing was also used during phage infection to look at transcriptional profiles. Results showed a significant difference in transcription readouts between the control and apramycin groups. These two experiments allowed the researchers to determine that apramycin prevents replication and transcription of the phage genome, which was further supported by fluorescent microscopy.

• AGs inhibit phage through the direct impact on the phage lifecycle and not through their other antibacterial activity.

Significance and future steps

• AGs are just one of the types of antiphage molecules recently described, and future work should explore more antiphage molecules, as such molecules may have negative implications for phage therapy.
• Phage sensitivity to AGs should be tested for when considering a phage’s suitability as a treatment component.

Many thanks to Atif Khan and Stephanie Lynch for finding and summarizing this week’s phage news, jobs and community posts, and to Stephanie Lynch for editing!