Abstract
Staphylococcal biofilms are problematic and play a critical role in the persistence of chronic infections because of their abilities to tolerate antimicrobial agents. Thus, the inhibitions of biofilm formation and/or toxin production are viewed as alternative means of controlling Staphylococcus aureus infections. Here, the antibiofilm activities of 560 purified phytochemicals were examined. Alizarin at 10 μg/ml was found to efficiently inhibit biofilm formation by three S. aureus strains and a Staphylococcus epidermidis strain. In addition, two other anthraquinones purpurin and quinalizarin were found to have antibiofilm activity. Binding of Ca2+ by alizarin decreased S. aureus biofilm formation and a calcium-specific chelating agent suppressed the effect of calcium. These three anthraquinones also markedly inhibited the hemolytic activity of S. aureus, and in-line with their antibiofilm activities, increased cell aggregation. A chemical structure-activity relationship study revealed that two hydroxyl units at the C-1 and C-2 positions of anthraquinone play important roles in antibiofilm and anti-hemolytic activities. Transcriptional analyses showed that alizarin repressed the α-hemolysin hla gene, biofilm-related genes (psmα, rbf, and spa), and modulated the expressions of cid/lrg genes (the holin/antiholin system). These findings suggest anthraquinones, especially alizarin, are potentially useful for controlling biofilm formation and the virulence of S. aureus.
Highlights
Staphylococcal biofilms are problematic and play a critical role in the persistence of chronic infections because of their abilities to tolerate antimicrobial agents
Further experiments showed that the addition of alizarin (0, 1, 2, 5, 10, 50, or 100 μ g/ml) at the beginning of bacterial culture dose-dependently inhibited biofilm formation by all three S. aureus strains (MSSA 6538, methicillin-sensitive S. aureus strains (MSSA) 25923, and methicillin-resistant S. aureus (MRSA) MW2) and a S. epidermidis strain (ATCC 14990) (Fig. 1a–d)
Alizarin decreased biofilm formation by all three S. aureus strains by ≥ 90%, whereas in the case of S. epidermidis, 50 μ g/ml was required to inhibit biofilm formation by ≥ 70%
Summary
Staphylococcal biofilms are problematic and play a critical role in the persistence of chronic infections because of their abilities to tolerate antimicrobial agents. Binding of Ca2+ by alizarin decreased S. aureus biofilm formation and a calciumspecific chelating agent suppressed the effect of calcium These three anthraquinones markedly inhibited the hemolytic activity of S. aureus, and in-line with their antibiofilm activities, increased cell aggregation. S. aureus, examples include; magnolol[10], ellagic acid[11], tannic acid[12], quercetin[13], ginkgolic acids[14], eugenol[15], and flavonoids[16] It has been reported staphylococcal biofilm formation is inhibited by several plant essential oils[17,18,19,20,21,22]. The identification of active compounds in plant extracts and essential oils often requires extensive investigation to identify active components, and only a limited number of organic biofilm inhibitors have been identified
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