Monolaurin inhibits antibiotic-resistant Staphylococcus aureus in patients with atopic dermatitis

Abstract

Frequent use of antibiotics increases the incidence of antimicrobial-resistant Staphylococcus aureus in atopic dermatitis (AD), which prompts the search for new treatments. Monolaurin is a chemical byproduct found in coconut oil and has anti-bacterial properties. This study aimed to investigate the inhibitory effect of monolaurin on antimicrobial-resistant S. aureus. Thirty children and thirty adults diagnosed with AD were recruited and swabbed at three different sites: lesion, non-lesion, and nasal mucosa. Methicillin resistance and high-level mupirocin resistance in S. aureus were identified using mecA and mupA PCR, respectively, whilst fusidic acid resistance were detected by fusA gene sequencing. The broth microdilution method and tetrazolium bromide assays were used for monolaurin susceptibility and cellular cytotoxicity, respectively. We show that S. aureus was frequently isolated from lesions of both children and adults with AD. One isolate of methicillin-resistant S. aureus (MRSA) harboring mecA, one isolate of mupirocin-resistant S. aureus harboring mupA, and four isolates of fusidic acid-resistant S. aureus with novel point mutations of fusA were found in the children group. In silico molecular docking showed that these mutants interacted weakly with fusidic acid, explaining the mechanism of drug resistance. Monolaurin inhibited these antimicrobial-resistant S. aureus isolates with a minimal inhibitory concentration of 2 µg/mL without cytotoxicity to cultured epidermal and dermal cells. These data show that monolaurin could potentially be used to inhibit antimicrobial-resistant S. aureus in AD patients.

Fig. 1

The chemical structure and purity of monolaurin. The spectral signals of monolaurin demonstrated by (a) proton (¹H NMR) and (b) carbon (¹³C-NMR) Nuclear Magnetic Resonance (NMR).

Fig. 2

S. aureus and coagulase-negative Staphylococci (CoNS) clinical isolates found in a) children (n=30) and b) adults (n=30) with AD.

Fig. 3

All known fusidic acid-resistance mutation sites in Supplementary Table S6 online were mapped onto S. aureus EF-G structure which was visualized and modeled by PyMOL [DeLano, 2002] (PyMOL Molecular Graphics System, Version 1.2r3pre, Schrödinger, LLC.). (a) The mutation sites are shown as H457Y (Domain III), P404Q (Domain III), Q505H (Domain IV), S238A (Domain I), and C258W (Domain I). Molecular docking of fusidic acid (orange, red and white) in the active site of (b) wild type EF-G and (c) mutant EF-G of S. aureus (mEF-G). Hydrogen bonds are represented as green dotted lines and numbers represent the bond distance. The wild type EF-G structure was extracted from rcsb.org/ (PDB: 2XEX) and the mutant form was modeled by PyMOL [DeLano, 2002] (The PyMOL Molecular Graphics System, Version 1.2r3pre, Schrödinger, LLC.).

Fig. 4

Cytotoxicity assay of cells treated with different concentrations of monolaurin (2-32 µg/ml). The percentage of cell viability of a) HEKn (primary epidermal keratinocytes) (n=3). b) dermal fibroblasts (n=3).***p-value = 0.0005, ****p<0.0001.