Abstract
Staphylococcus aureus is one of the most common pathogens in biofilm-associated chronic infections. S. aureus living within biofilms evades the host immune response and is more resistant to antibiotics than planktonic bacteria. In this study, we generated S. aureus with low and high levels of biofilm formation using the rbf (regulator of biofilm formation) gene and performed a BioTimer assay to determine the minimum inhibitory concentration (MIC) and minimal bactericidal concentration (MBC) of various types of antibiotics. We showed that biofilm formation by S. aureus had a greater effect on MBC than MIC, probably due to the different growth modes between planktonic and biofilm bacteria. Importantly, we found that the MBC for biofilm S. aureus was much higher than that for planktonic cells, but there was little difference in MBC between low and high levels of biofilm formation. These results suggest that once the biofilm is formed, the bactericidal activity of antibiotics is significantly reduced, regardless of the degree of S. aureus biofilm formation. We propose that S. aureus strains with varying degrees of biofilm formation may be useful for evaluating the anti-biofilm activity of antimicrobial agents and understanding antibiotic resistance mechanisms by biofilm development.
Highlights
A biofilm is a conglomeration of one or more types of microorganisms attached to a surface, in contrast to the planktonic state in which bacteria exist as individual organisms (Flemming et al 2016; Rumbaugh and Sauer 2020)
The CYL1106 strain showed a more than fourfold higher ability to form biofilms than the CYL1135 strain (Fig. 2B). These results demonstrate that the rbf gene is involved in biofilm formation by S. aureus
We measured the antimicrobial activities of several classes of antibiotics against planktonic and biofilm bacteria
Summary
A biofilm is a conglomeration of one or more types of microorganisms attached to a surface, in contrast to the planktonic state in which bacteria exist as individual organisms (Flemming et al 2016; Rumbaugh and Sauer 2020). There is a positive correlation between drug resistance and biofilm development in clinical S. aureus isolates (Kwon et al 2008; Martins et al 2007). Shin et al J Anal Sci Technol (2021) 12:41 of biofilm formation are thought to contribute significantly to the search for novel antimicrobial agents effective against chronic biofilm-associated infections and to understand antibiotic resistance mechanisms due to biofilm development. Staphylococcus aureus, a major cause of communityacquired infections and nosocomial infections, can form biofilms on the surfaces of various medical devices used in hospitals, leading to chronic and persistent infections (Ando et al 2004; Baltch et al 2008; Cirz et al 2007; Villain-Guillot et al 2007). One of the most significant problems with biofilm formation by S. aureus is the development of resistance to antibiotics (Kranjec et al 2021; Lin et al 2019). Different degrees of S. aureus biofilm formation can be generated by targeting the rbf gene
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