Tackling Intrinsic Antibiotic Resistance in Serratia Marcescens with A Combination of Ampicillin/Sulbactam and Phage SALSA

Newly isolated Drexlerviridae phage LAPAZ is physically robust and fosters eradication of Klebsiella pneumoniae in combination with meropenem

Due to the spread of multidrug resistance there is a renewed interest in using bacteriophages (briefly: phages) for controlling bacterial pathogens. The objective of this study was the characterization of a newly isolated phage (i.e. phage LAPAZ, vB_KpnD-LAPAZ), its antimicrobial activity against multidrug resistant Klebsiella pneumoniae and potential synergistic interactions with antibiotics. LAPAZ belongs to the family Drexlerviridae (genus: Webervirus) and lysed 30 % of tested strains, whereby four distinct capsular types can be infected. The genome consists of 51,689 bp and encodes 84 ORFs. The latent period is 30 min with an average burst size of 27 PFU/cell. Long-term storage experiments show that LAPAZ is significantly more stable in wastewater compared to laboratory media. A phage titre of 90 % persists up to 30 min at 50 ˚C and entire phage loss was seen only at temperatures > 66 ˚C. Besides stability against UV-C, antibacterial activity in liquid culture medium was consistent at pH values ranging from 4 to 10. Unlike exposure to phage or antibiotic alone, synergistic interactions and a complete bacterial eradication was achieved when combining LAPAZ with meropenem. In addition, synergism with the co-presence of ciprofloxacin was observed and phage resistance emergence could be delayed. Without co-addition of the antibiotic, phage resistant mutants readily emerged and showed a mixed pattern of drug sensitivity alterations. Around 88 % became less sensitive towards ceftazidime, meropenem and gentamicin. Conversely, around 44 % showed decreased resistance levels against ciprofloxacin. Whole genome analysis of a phage-resistant mutant with a 16-fold increased sensitivity towards ciprofloxacin revealed one de novo frameshift mutation leading to a gene fusion affecting two transport proteins belonging to the major facilitator-superfamily (MFS). Apparently, this mutation compromises ciprofloxacin efflux efficiency and further studies are warranted to understand how the non-mutated protein might be involved in phage-host adsorption.

Benefits of Combined Phage–Antibiotic Therapy for the Control of Antibiotic-Resistant Bacteria: A Literature Review

With the increase in bacterial resistance to antibiotics, more and more therapeutic failures are being reported worldwide. The market for antibiotics is now broken due to the high cost of developing new molecules. A promising solution to bacterial resistance is combined phage–antibiotic therapy, a century-old method that can potentiate existing antibiotics by prolonging or even restoring their activity against specific bacteria. The aim of this literature review was to provide an overview of different phage–antibiotic combinations and to describe the possible mechanisms of phage–antibiotic synergy.

Synergy between Phage Sb-1 and Oxacillin against Methicillin-Resistant Staphylococcus aureus

Methicillin-resistant Staphylococcus aureus (MRSA) is a notorious pathogen responsible for not only a number of difficult-to-treat hospital-acquired infections, but also for infections that are community- or livestock-acquired. The increasing lack of efficient antibiotics has renewed the interest in lytic bacteriophages (briefly phages) as additional antimicrobials against multi-drug resistant bacteria, including MRSA. The aim of this study was to test the hypothesis that a combination of the well-known and strictly lytic S. aureus phage Sb-1 and oxacillin, which as sole agent is ineffective against MRSA, exerts a significantly stronger bacterial reduction than either antimicrobial alone. Eighteen different MRSA isolates and, for comparison, five MSSA and four reference strains were included in this study. The bacteria were challenged with a combination of varying dosages of the phage and the antibiotic in liquid medium using five different antibiotic levels and four different viral titers (i.e., multiplicity of infections (MOIs) ranging from 10^-5 to 10). The dynamics of the cell density changes were determined via time-kill assays over 16 h. Positive interactions between both antimicrobials in the form of facilitation, additive effects, or synergism were observed for most S. aureus isolates. These enhanced antibacterial effects were robust with phage MOIs of 10^-1 and 10 irrespective of the antibiotic concentrations, ranging from 5 to 100 µg/mL. Neutral effects between both antimicrobials were seen only with few isolates. Importantly, antagonism was a rare exception. As a conclusion, phage Sb-1 and oxacillin constitute a robust heterologous antimicrobial pair which extends the efficacy of a phage-only approach for controlling MRSA.