#19-051

Complete

Date Full Report Received

11/15/2020

Date Abstract Report Received

11/15/2020

Investigation

Institution:
Primary Investigator:

Funded By

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: Preliminary data suggested the previously isolated S. aureus phages could be effective in combatting S. aureus prevalence in swine production environments. To evaluate the utility of these phage the goals of this project were to i) determine the ability of S. aureus phages to control S. aureus biofilms in the presence of biofilm-disrupting agents such as alpha-amylases, proteases and nucleases and ii) bacteriophages and other antibiofilm agents will be evaluated for their ability to reduce the burden of S. aureus biofilms. Results: The phage collection was further characterized by genome sequencing and comparative genomics. New DNA sequencing approaches revealed a novel clade of “jumbo” phages in the phage collection; these phages have broad host ranges and are able to transduce S. aureus DNA. Biofilm 96-well plate assays for 15 S. aureus isolates showed large variation in the biofilm formation ability of all isolates tested. These strains were compared to positive biofilm control strain, S. aureus ATCC 25923 and
Staphylococcus epidermidis negative control strain, ATCC 12228. The strain with the strongest biofilm formation ability besides the positive control was human isolate NRS70, which is an ST5, USA100 and SccMec type II strain. The strongest biofilm former of the swine isolates tested in this assay was “PD18” which is a ST9 methicillin-sensitive (MSSA) nasal swine strain isolated in North Carolina. Overall, the biofilm formation of all S. aureus strains tested was far lower than the positive control. Treatment of both human and swine isolated S. aureus biofilms on a plastic surface with α amylase, trypsin, DNase I and phage K at two different time points revealed that phage K was able reduce biofilm mass by ~37% S. aureus strains after 6 hours. However, DNase I treatment for both 4 and 6 hour treatments showed the most effective degradation of all S. aureus biofilms. This suggests the assayed isolates are forming biofilms which are constructed at least partially from extracellular DNA (eDNA).
KEY FINDINGS
• DNA sequencing of S aureus phages in the collection identified a novel clade of “jumbo” phages that have not been previously described for S. aureus.
• Phages were identified that are able to move DNA between S. aureus strains, which may provide a mechanism for movement of antibiotic resistance genes in the production environment.
• Swine and human S. aureus isolates were found to be variable in their ability to form biofilms in vitro.
• A broad host-range phage could reduce mature biofilm burden, but was not as effective as the enzyme DNaseI, suggesting that DNA makes up a major component of S. aureus biofilm in the model system.