Development of a Phage Cocktail to Target Salmonella Strains Associated with Swine

Infections caused by multidrug resistant Salmonella strains are problematic in swine and are entering human food chains. Bacteriophages (phages) could be used to complement or replace antibiotics to reduce infection within swine. Here, we extensively characterised six broad host range lytic Salmonella phages, with the aim of developing a phage cocktail to prevent or treat infection. Intriguingly, the phages tested differed by one to five single nucleotide polymorphisms. However, there were clear phenotypic differences between them, especially in their heat and pH sensitivity. In vitro killing assays were conducted to determine the efficacy of phages alone and when combined, and three cocktails reduced bacterial numbers by ~2 × 103 CFU/mL within two hours. These cocktails were tested in larvae challenge studies, and prophylactic treatment with phage cocktail SPFM10-SPFM14 was the most efficient. Phage treatment improved larvae survival to 90% after 72 h versus 3% in the infected untreated group. In 65% of the phage-treated larvae, Salmonella counts were below the detection limit, whereas it was isolated from 100% of the infected, untreated larvae group. This study demonstrates that phages effectively reduce Salmonella colonisation in larvae, which supports their ability to similarly protect swine.

Phage-Choline Kinase Inhibitor Combination to Control Pseudomonas aeruginosa: A Promising Combo

Background: : Pseudomonas aeruginosa is one of the most prevalent opportunistic pathogens in humans that has thrived and proved to be difficult to control in this “post-antibiotic era.” Antibiotic alternatives are necessary for fighting against this resilient bacterium. Even though phages might not be “the wonder drug” that solves everything, they still provide a viable option to combat P. aeruginosa and curb the threat it imposes. Main findings: : The combination of antibiotics with phages, however, poses a propitious treatment option for P. aeruginosa. Choline kinase (ChoK) is the enzyme that synthesizes phosphorylcholine subsequently incorporated into lipopolysaccharide located at the outer membrane of gram-negative bacteria. Recently, inhibition of ChoKs has been proposed as a promising antibacterial strategy. Successful docking of Hemicholinium-3, a choline kinase inhibitor, to the model structure of P. aeruginosa ChoK also supports the use of this inhibitor or its derivatives to inhibit the growth of this microorganism. Conclusion: : Therefore, the combination of the novel antimicrobial “choline kinase inhibitors (ChoKIs)” with a phage cocktail or synthetic phages as a potential treatment for P. aeruginosa infection has been proposed.

Phage Cocktail Development against Aeromonas salmonicida subsp. salmonicida Strains Is Compromised by a Prophage

Aquaculture is a rapidly growing food production sector. Fish farmers are experiencing increasing problems with antibiotic resistance when fighting against pathogenic bacteria such as Aeromonas salmonicida subsp. salmonicida, the causative agent of furunculosis. Phage therapy may provide an alternative, but effective use must be determined. Here, we studied the inhibition of A. salmonicida subsp. salmonicida strains by five phages (HER98 [44RR2.8t.2], HER110 [65.2], SW69-9, L9-6 and Riv-10) used individually or as combinations of two to five phages. A particular combination of four phages (HER98 [44RR2.8t.2], SW69-9, Riv-10, and HER110 [65.2]) was found to be the most effective when used at an initial multiplicity of infection (MOI) of 1 against the A. salmonicida subsp. salmonicida strain 01-B526. The same phage cocktail is effective against other strains except those bearing a prophage (named Prophage 3), which is present in 2/3 of the strains from the province of Quebec. To confirm the impact of this prophage, we tested the effectiveness of the same cocktail on strains that were either cured or lysogenized with Prophage 3. While the parental strains were sensitive to the phage cocktail, the lysogenized ones were much less sensitive. These data indicate that the prophage content of A. salmonicida subsp. salmonicida can affect the efficacy of a cocktail of virulent phages for phage therapy purposes.

Evaluation of a pre-harvest bacteriophage therapy for control of Salmonella within bovine peripheral lymph nodes

A series of proof of concept studies were developed to determine if a commercial bacteriophage (phage) cocktail could be utilized for the mitigation of Salmonella in bovine peripheral lymph nodes (LN). The first objective sought to determine if exogenous phage could be isolated from the LN following administration. If successful, the second objective sought to determine if once in the LN, could the phage effectively reduce Salmonella . Salmonella Montevideo was inoculated intradermally in multiple sites and administrations, later followed by delivery of the phage cocktail subcutaneously in two injections around each of the right and left prescapular and subiliac LN. At the conclusion of each study, animals were euthanized and the popliteal and above LN examined. The first study was successful, in that transmission electron microscopy revealed the presence of phage in the LN of the treated cattle, that were identical to the strains in the cocktail. Concentrations of phage were increased ( P < 0.01) in the pre-scapular and subiliac LN in the phage-treated versus control cattle. Subsequent studies modified the protocols to increase Salmonella and phage concentrations within the LN. Overall concentrations of Salmonella were increased in the LN compared to the first study and phage treatment decreased ( P < 0.01) Salmonella in the some of the LN. Phage concentrations were numerically ( P = 0.12), but not statistically, increased in the treated cattle. The final study was modified, hypothesizing that a 48h post-mortem period prior to LN removal would facilitate phage/ Salmonella interaction, however, there were no differences ( P > 0.10) in Salmonella concentrations among treatments. Results demonstrated that Salmonella- specific phages administered to live cattle can translocate to the LN, however once in the LN they had limited to no effect on Salmonella within these nodes.

132. Evaluation Phage Cocktails in Combination with Ciprofloxacin Against Multidrug-Resistant Pseudomonas aeruginosa Overexpressing MexAB-OprM Efflux Systems

Background Multidrug-resistant (MDR) Pseudomonas aeruginosa infections are increasing in prevalence and cause significant mortality. The MexAB-OprM efflux system confers resistance to a wide range of drugs, including β-lactams, fluoroquinolones, tetracyclines, and macrolides. Obligately lytic bacteriophages (phages) are viruses that infect and kill bacteria. Phage therapy has been suggested as an alternative treatment option in combination with traditional antibiotics. The objective of this study was to determine the ability of a phage cocktail in combination with ciprofloxacin (CIP) to improve bacterial killing and/or prevent the emergence of phage resistance in MDR P. aeruginosa. Methods Initial bacterial susceptibility to phage was evaluated with three newly isolated phages (phages EM, LL, and A6) against ten clinical MDR P. aeruginosa isolates. Theoretical multiplicity of infection (tMOI) optimization was performed with two phages with the broadest initial susceptibility (tMOI: 1.0 chosen for further analysis). A preliminary evaluation was performed with P. aeruginosa R9316 (carbapenem-resistant clinical strain with MexAB-OprM overexpression, as determined previously by quantitative real-time PCR). Synergy for phage cocktail combinations (≥ 2-log10 CFU/mL kill compared to most effective single agent at 24 h), bactericidal activity for all samples (≥ 3-log10 CFU/mL reduction at 24 h compared to starting inoculum), and phage resistance development were evaluated in time kill analyses (TKA). Results R9316 is a MDR P. aeruginosa isolate with a CIP MIC of 2 mg/L. Phage cocktails as monotherapy had little impact on bacterial eradication (reduction: 1.19 log10 CFU/mL). However, the addition of CIP to phage cocktails of EM and LL phages led to synergistic and bactericidal effects (reduction: 3.92 log10 CFU/mL). Furthermore, phage resistance was observed in the phage monotherapy regimens. Whereas the addition of CIP was shown to prevent the emergence of phage resistance in some regimens. Conclusion Our results show synergistic activity and prevention of phage resistance with phage cocktail-antibiotic combinations against MDR P. aeruginosa. Further research is needed to determine the impact of phage cocktail therapy on additional strains and clinical outcomes. Disclosures Michael J. Rybak, PharmD, MPH, PhD, Paratek Pharmaceuticals (Research Grant or Support)

Evaluation of Bacteriophage Cocktails Alone and in Combination with Daptomycin Against Daptomycin-Nonsusceptible Enterococcus faecium

Enterococcus faecium ( E. fcm ) is a significant multidrug-resistant pathogen. Bacteriophage cocktails are being proposed to complement antibiotic therapy. After a screen of 8 E. fcm strains against 4 phages, two phages(113, 9184) with the broadest host ranges were chosen for further experiments. Transmission electron microscopy, whole-genome sequencing, comparative genome analyses, and time-kill analyses were performed. Daptomycin(DAP) plus phage cocktail(113:myophage;9184:siphopage) showed bactericidal activity in most regimens, while DAP addition prevented phage 9184 resistance against daptomycin non-susceptible E. fcm .