CategoryPublic Health - MRSA
Date Full Report Received01/12/2018
Date Abstract Report Received01/12/2018
Rationale: Staphylococcus aureus is an opportunistic pathogen of major concern in both human and animal health. While this bacterium can cause life-threatening illness, it more commonly asymptomatically colonizes the nasal passages and skin of healthy people. S. aureus can also be carried by livestock animals including swine, and there is evidence that S. aureus can be transmitted back and forth between humans and swine. This makes swine a potential reservoir for S. aureus, which may pose a risk to workers in swine production facilities, and potentially to the larger community. Bacteriophages (phages) are bacterial viruses and they are major predators of bacteria in natural environments. The continued emergence of antibiotic resistant bacteria, including resistant strains of S. aureus, has led to increased interest in novel antibacterial strategies, including the use of phages. Objectives: Our preliminary data suggested that swine production environments may be a rich source of phages infecting S. aureus that could be used as antibacterials. The goal of this project was to conduct an initial survey of swine production environments across the US to i) estimate the prevalence and diversity of phages in these environments and ii) assemble a large working collection of S. aureus phages that could potentially be used as antibacterials. Methods: Swab samples were collected from swine barns at 20 sites in 10 states and tested for the presence or absence of phage against a panel of 10 S. aureus strains of both human and animal origin. Phage-positive samples were further processed to isolate individual phages from the samples. Results: Twelve of the 20 sample sites were positive for the presence of phage against at least one of the 10 S. aureus host strains used. Two sites contained phage capable of infecting nine of the 10 host strains tested. Host strains of both human and swine origin were roughly equally susceptible to phages contained in the environmental samples, suggesting that the phages are not “specialized” for swine environments and that there is not a strong distinction between human and swine S. aureus. Eighty-four phage isolates were initially collected from the environmental samples, with 51 of these surviving subculture and storage to allow for characterization. This collection of 51 phages was first analyzed by restriction digestion of phage genomic DNA, which placed the phages into one of five groups. Transmission electron microscopy of 13 phage isolates to date showed that the phages belong to one of three distinct morphological types. Fourteen of the phages have been analyzed by genome sequencing, which also placed them into three major groups. Two of these groups are related to known S. aureus phages. The third group has proved to be refractory to normal DNA sequencing approaches, suggesting it may be a new type of S. aureus phage that contains highly modified DNA bases that interfere with DNA sequencing. Work to obtain DNA sequence for these phages is ongoing.