Aztreonam Lysine Increases the Activity of Phages E79 and phiKZ against Pseudomonas aeruginosa PA01

Abstract

Pseudomonas aeruginosa is a pernicious bacterial pathogen that is difficult to treat because of high levels of antibiotic resistance. A promising alternative treatment option for such bacteria is the application of bacteriophages; the correct combination of phages plus antibiotics can produce synergistic inhibitory effects. In this study, we describe morphological changes induced by sub-MIC levels of the antibiotic aztreonam lysine (AzLys) on P. aeruginosa PA01, which may in part explain the observed phage–antibiotic synergy (PAS). One-step growth curves for phage E79 showed increased adsorption rates, decreased infection latency, accelerated time to lysis and a minor reduction in burst size. Phage E79 plus AzLys PAS was also able to significantly reduce P. aeruginosa biofilm growth over 3-fold as compared to phage treatment alone. Sub-inhibitory AzLys-induced filamentation of P. aeruginosa cells resulted in loss of twitching motility and a reduction in swimming motility, likely due to a reduction in the number of polar Type IV pili and flagella, respectively, on the filamented cell surfaces. Phage phiKZ, which uses Type IV pili as a receptor, did not exhibit increased activity with AzLys at lower sub-inhibitory levels, but still produced phage–antibiotic synergistic killing with sub-inhibitory AzLys. A one-step growth curve indicates that phiKZ in the presence of AzLys also exhibits a decreased infection latency and moderately undergoes accelerated time to lysis. In contrast to prior PAS studies demonstrating that phages undergo delayed time to lysis with cell filamentation, these PAS results show that phages undergo accelerated time to lysis, which therefore suggests that PAS is dependent upon multiple factors, including the type of phages and antibiotics used, and the bacterial host being tested.

In Vitro Newly Isolated Environmental Phage Activity against Biofilms Preformed by Pseudomonas aeruginosa from Patients with Cystic Fibrosis

“…This promising result provides new insights on possible phage adaptation "training" able to enhance cross-activity against specific patient CF PA strains, also envisaging personalized phage cocktails [32]. In agreement with these intriguing experiments [8,10], we agree with researchers suggesting that the most efficacious lytic phages are those isolated on purpose, personalized, against specific antibiotic-resistant PA strains in patients with CF (sur-mesure, patient-tailored therapy) [33][34][35].…”

Advances in Phage Therapy: Targeting the Burkholderia cepacia Complex

“…Phage–antibiotic synergy (PAS) was first described for bacteriophages infecting certain strains of E. coli , as researchers noticed a significant increase in phage plaque size in the presence of subinhibitory concentrations of certain antibiotics, and this phenomenon was subsequently confirmed in S. aureus , B. cenocepacia , and P. aeruginosa [ 242 , 243 , 244 , 245 , 246 ]. While this plaque-size based approach may still be used to screen phage–antibiotic pairs for potential synergies, the therapeutic applicability of phage–antibiotic combinations exhibiting synergy is now more commonly verified through liquid-growth assays, where growth reductions greater than the sum of the independent growth reductions of the constituent parts may indicate a synergistic effect [ 239 , 240 , 241 , 247 ].…”

The Potential of Phage Therapy against the Emerging Opportunistic Pathogen Stenotrophomonas maltophilia

“…The application of phages in combination with selected antibiotics can also increase the production and/or killing activity of phages, a phenomenon termed phage antibiotic synergy (PAS) [140]. Specifically, subinhibitory concentrations of antibiotics that lead to changes in cell morphology due to affected cell wall synthesis and cell division have been shown to increase the activity of phages targeting E. coli [140], Burkholderia cepacia [141], and P. aeruginosa [142], and combination phage and antibiotic treatments led to decreased mortality in a Galleria mellonella model [141] and increased biofilm clearance [142] compared to phage treatment alone. These examples demonstrate that carefully designed combinations of phages alone or together with antibiotics can increase the efficacy of phage therapy.…”