Modulation of Staphylococcus aureus Biofilm Matrix by Subinhibitory Concentrations of Clindamycin

Abstract

Staphylococcus aureus biofilms are extremely difficult to treat. They provide a protected niche for the bacteria, rendering them highly recalcitrant toward host defenses as well as antibiotic treatment. Bacteria within a biofilm are shielded from the immune system by the formation of an extracellular polymeric matrix, composed of polysaccharides, extracellular DNA (eDNA), and proteins. Many antibiotics do not readily penetrate biofilms, resulting in the presence of subinhibitory concentrations of antibiotics. Here, we show that subinhibitory concentrations of clindamycin triggered a transcriptional stress response in S. aureus via the alternative sigma factor B ( B ) and upregulated the expression of the major biofilm-associated genes atlA, lrgA, agrA, the psm genes, fnbA, and fnbB. Our data suggest that subinhibitory concentrations of clindamycin alter the ability of S. aureus to form biofilms and shift the composition of the biofilm matrix toward higher eDNA content. An understanding of the molecular mechanisms underlying biofilm assembly and dispersal in response to subinhibitory concentrations of clinically relevant antibiotics such as clindamycin is critical to further optimize antibiotic treatment strategies of biofilm-associated S. aureus infections. Staphylococcus aureus is a major cause of both health care-related and community-associated (CA) infections. The Grampositive human-pathogenic bacterium produces and secretes a range of toxins and enzymes leading to acute infections such as bacteremia and skin abscesses (1, 2). In addition, most S. aureus strains are capable of biofilm formation and can persist in host tissues such as the bone, leading to chronic osteomyelitis, or on implanted medical devices such as vascular catheters, vascular grafts, heart valves, and prosthetic joints (3-5). Biofilm-associated infections are extremely difficult to treat, and these chronic or relapsing infections typically require prolonged antibiotic treatment or removal of the device (6-8). Antibiotic resistance of bacteria within a biofilm may result from slow growth, phenotypic heterogeneity, persister cell formation, and inactivation or reduced penetration of the antibiotic (9, 10). Diffusion of the antibiotic through biofilm cell clusters is dependent on the thickness and the composition of the extracellular polymeric matrix (9, 11). The slow transport within biofilms suggests that the bacteria may encounter subinhibitory concentrations of antibiotics. Previous studies have shown that low doses of different antibiotics trigger biofilm formation (12, 13) and lead to dramatic alterations in bacterial gene expression in S. aureus (14).Biofilm formation proceeds in at least three phases: initial attachment, biofilm maturation, and dispersal (15, 16). Initial surface attachment is dependent on bacterial surface molecules such as the S. aureus murein hydrolase AtlA, teichoic acids, and fibronectin-binding proteins (FnBPs) (17)(18)(19)(20). After attachment to the surface, the bacteria multiply and produce the extracellular...

Modulatory Effects of a Subinhibitory Concentration of Clindamycin in Community-Acquired Methicillin-Resistant Staphylococcus aureus Strains of Sequence Type 30

“…1a). In agreement with the biofilm findings and a previous study (1,3), agrA and sarA were upregulated at a subinhibitory concentration of clindamycin. An increase in the relative levels of expression of ␣-type PSMs 1 to 4 (PSMs␣ 1-4) was also noted (Fig.…”

Cinnamaldehyde Inhibits Staphylococcus aureus Virulence Factors and Protects against Infection in a Galleria mellonella Model

“…Additionally, different antimicrobial agents may be able to induce biofilm formation at sub-inhibitory concentrations (Kaplan et al, 2012; Schilcher et al, 2016). This effect is suggested to be strain-specific and related to the induction of stress pathways in S. aureus that in turn, lead to the expression of biofilm-associated genes (Schilcher et al, 2016).…”

“…This effect is suggested to be strain-specific and related to the induction of stress pathways in S. aureus that in turn, lead to the expression of biofilm-associated genes (Schilcher et al, 2016). Herein, as in other reports (Kaplan et al, 2012; Schilcher et al, 2016), biofilm formation was evaluated by the crystal violet assay. This method is widely used for this purpose, however, crystal violet stains both viable and dead cells, in addition to the extracellular matrix (Xu et al, 2016).…”

Increased resistance of a methicillin-resistant Staphylococcus aureus Δagr mutant with modified control in fatty acid metabolism

“…In addition, PSMs have been shown to exert other functions, including acting as regulators in persister cells and biofilm formation (Periasamy et al 2012;Xu et al 2017). Following agr activation, PSMs are produced to develop the biofilm structure and disperse the biofilm by forming a complex with eDNA, extracellular polysaccharides, and proteins, or by taking advantage of its surfactant characteristics (Schilcher et al 2016). Regulation of agr is also a trigger for changing the antibiotic resistance of MRSA.…”