Accumulation of defense systems in phage-resistant strains of Pseudomonas aeruginosa.

Prokaryotes encode multiple distinct anti-phage defense systems in their genomes. However, the impact of carrying a multitude of defense systems on phage resistance remains unclear, especially in a clinical context. Using a collection of antibiotic-resistant clinical strains of Pseudomonas aeruginosa and a broad panel of phages, we demonstrate that defense systems contribute substantially to defining phage host range and that overall phage resistance scales with the number of defense systems in the bacterial genome. We show that many individual defense systems target specific phage genera and that defense systems with complementary phage specificities co-occur in P. aeruginosa genomes likely to provide benefits in phage-diverse environments. Overall, we show that phage-resistant phenotypes of P. aeruginosa with at least 19 phage defense systems exist in the populations of clinical, antibiotic-resistant P. aeruginosa strains.

Inactivation of RNA and DNA viruses in water by copper and silver ions and their synergistic effect.

Cu and Ag have been used as bactericidal agents since ancient times, yet their antiviral capacity in water remains poorly understood. This study tested the effect of copper (Cu) and silver (Ag) on model RNA and DNA viruses MS2 and PhiX 174 in solution at pH 6-8. Cu caused MS2 inactivation with similar rates at pH 6 and 7 but was inert towards PhiX 174 regardless of pH. Ag inactivated both viruses, causing denaturation of MS2 and loss of capsid spikes in PhiX 174. Ag inactivation rates were pH dependent and increased with increasing pH. At pH 8, 6.5 logs of PhiX were inactivated after 3 h and 3 logs of MS2 after only 10 min. The combined use of Cu and Ag revealed synergy in disinfecting MS2 at pH ≥ 7. Although metal concentrations used were higher than the desired values for drinking water treatment, the results prove a promising potential of Cu and Ag combinations as efficient viricidal agents.