Antibiofilm activity and synergistic effects of DNase I and Lysostaphin against Staphylococcus aureus biofilms

In recent years, food safety has become the focus of global public health concerns. Microbial contamination is one of the most common food safety issues. Staphylococcus aureus is a common foodborne pathogen that can form biofilms on the surface of food processing equipment, leading to greater resistance to antimicrobial agents than occurs with planktonic bacteria. In this work, recombinant Escherichia coli BL21 (DE3) cells expressing optimised lysostaphin (Lst) were constructed, recombinant Lst was produced and purified, and Lst enzymatic assays were performed, followed by antimicrobial testing of Lst. Finally, a mixture of Lst and DNase I was tested for antibiofilm activity. The protein content of purified Lst was 0.6 mg/mL and the enzyme activity was 240 U/mL. The minimum inhibitory concentration (MIC) of Lst against S. aureus was 0.1 μg/mL. At 1 MIC, Lst exerted an effect on the growth, cell wall integrity and cell membrane permeability of S. aureus. Although Lst alone also showed good inhibition and disruption of S. aureus biofilms, inhibition and disruption of S. aureus biofilms was significantly greater when Lst was mixed with DNase I. This is probably because DNase I removes extracellular DNA, affecting biofilm formation and dispersing mature biofilms, and thereby facilitating penetration of Lst.