In response to increasing frequencies of antibiotic-resistant pathogens, there has been a resurrection of interest in the use of bacteriophage to treat bacterial infections: phage therapy. Here we explore the potential of a seemingly ideal phage, PYOSa, for combination phage and antibiotic treatment of Staphylococcus aureus infections. This K-like phage has a broad host range; all 83 tested clinical isolates of S.aureus tested were susceptible to PYOSa. Because of the mode of action of PYOSa, S. aureus is unlikely to generate classical receptor-site mutants resistant to PYOSa; none were observed in the 13 clinical isolates tested. PYOSa kills S. aureus at high rates. On the downside, the results of our experiments and tests of the joint action of PYOSa and antibiotics raise issues that must be addressed before PYOSa is employed clinically. Despite the maintenance of the phage, PYOSa does not clear populations of S. aureus. Due to the ascent of a phenotyically diverse array of small-colony variants following an initial demise, the bacterial populations return to densities similar to that of phage-free controls. Using a combination of mathematical modeling and in vitro experiments, we postulate and present evidence for a mechanism to account for the demise–resurrection dynamics of PYOSa and S. aureus. Critically for phage therapy, our experimental results suggest that treatment with PYOSa followed by bactericidal antibiotics can clear populations of S. aureus more effectively than the antibiotics alone.

For studies of antibiotics and how they work, the most-often used measurement of drug efficacy is the MIC. The MIC is the concentration of an antibiotic needed to inhibit bacterial growth.

In response to increasing frequencies of antibiotic-resistant pathogens, there has been a resurrection of interest in the use of bacteriophage to treat bacterial infections: phage therapy. Here we explore the potential of a seemingly ideal phage, PYO Sa , for combination phage and antibiotic treatment of Staphylococcus aureus infections. (i) This K-like phage has a broad host range; all 83 clinical isolates of S.aureus tested were susceptible to PYO Sa . (ii) Because the mode of action of PYO Sa S. aureus is unlikely to generate surface mutants resistant to PYO Sa ; none were observed in the 13 clinical isolates tested. (iii) PYO Sa kills S. aureus at high rates. On the downside, the results of our experiments and tests of the joint action of PYO Sa and antibiotics raise issues that must be addressed before PYO Sa is employed clinically. Despite the maintenance of the phage, due to the ascent of potentially pathogenic small colony variants, PYO Sa does not clear populations of S. aureus; following an initial demise the bacterial populations return to densities similar to that of phage-free controls. Bacteriostatic antibiotics prevent PYO Sa from replicating on S. aureus and bactericidal antibiotics are antagonistic to the action of PYO Sa . Using a combination of mathematical modeling and in vitro experiments, we postulate and present evidence for a mechanism to account for the demise-resurrection dynamics of PYO Sa and S. aureus. Critically for phage therapy, our experimental results suggest that treatment with PYO Sa followed by bactericidal antibiotics can clear populations of S. aureus more effectively than the antibiotics alone Significance StatementThe increasing frequency of multiply antibiotic-resistant pathogens has fostered a quest for alternative means to treat bacterial infections. Prominent in this quest is a therapy that predates antibiotics: bacteriophage. This study explores the potential of a phage, PYO Sa , for treating Staphylococcus aureus infections in combination with antibiotics. On first consideration, this phage, isolated from a commercial therapeutic cocktail, seems ideal for this purpose. The results of this population dynamic study identify a limitation and potential liability of using PYO Sa for therapy. Due to the production of potentially pathogenic small colony variants, PYO Sa alone cannot eliminate S. aureus populations. We demonstrate that by following the administration of PYO Sa with bactericidal antibiotics, this limitation and potential liability can be addressed.

One major concern in hospitalized patients is infections with pathogens borne on surfaces, patients, and healthcare workers. Fundamental to controlling nosocomial infections is identifying the sources of pathogens, monitoring the processes responsible for their transmission, and evaluating the efficacy of the procedures employed for restricting their transmission. Here we present a method using the bacteriophage Lambda (λ) to achieve these ends. Defined densities of multiple genetically marked λ phages were inoculated at known hotspots for contamination on high-fidelity mannequins. Healthcare workers (HCWs) then entered a pre-sanitized simulated hospital room and performed a series of patient care tasks on the mannequins. Sampling occurred on the scrubs and hands of the HCWs, as well as previously defined high-touch surfaces in hospital rooms. Following sampling, the rooms were decontaminated using procedures designed and demonstrated to be effective. Following the conclusion of the simulation, the samples were tested for the presence, identity, and densities of these Lambda phages. The data generated enabled the determination of the sources and magnitude of contamination caused by the breakdown of established infection prevention practices by HCW. This technique enabled the standardized tracking of multiple contaminants during a single episode of patient care. While our application of these methods focused on nosocomial infections and the role of HCW behaviors in their spread, these methods could be employed for identifying the sources and sites of microbial contamination in other settings.