Abstract

Biofilm phenotypes were studied in 32 Staphylococcus aureus strains isolated from store-bought meats and 22 from diseased patients in hospitals. Of the meat-associated strains, 21 were methicillin-resistant Staphylococcus aureus (MRSA) and 11 were methicillin-susceptible Staphylococcus aureus (MSSA). The hospital-associated strains included 15 MRSAs and 7 MSSAs. We studied the robustness and composition of the biofilms produced by these strains. We found that on average hospital-associated strains form more robust biofilms than meat associated strains. The model often used to describe S. aureus biofilm composition includes two biofilm types defined by the presence or absence of polysaccharide intercellular adhesin (PIA), PIA-dependent and PIA-independent respectively. In this model, PIA-independent biofilms are structurally reliant on proteins and extracellular DNA (eDNA) and PIA-dependent are structurally reliant on polysaccharides. Enzymatic degradation of the extracellular matrix can reveal which compounds are essential for the structural integrity of the biofilm, and by this model PIA-independent biofilms should be susceptible to both DNase and proteinase K. We found that hospital-associated strains are, on average, more susceptible to degradation by proteinase K. Interestingly, hospital-associated strains are less susceptible to degradation by DNase than meat-associated strains. Finding that proteinase K and DNase susceptibility for these strains are not linked gives evidence to support the idea that S. aureus biofilm composition can vary greatly from strain to strain and that the PIA-dependent and PIA-independent dichotomy of the standard model may be insufficient to describe the variety of S. aureus biofilm composition and may only apply to the extremes of the spectrum. Additionally, we saw no relationship between MRSA or MSSA strains and biofilm robustness, proteinase K degradation, or DNase degradation. Differences in biofilm characteristics between hospital-associated and meat-associated strains reinforce previous findings that these populations are genetically distinct.

Degree

College and Department

Life Sciences; Microbiology and Molecular Biology

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