Novel quorum-quenching agents promote methicillin-resistant Staphylococcus aureus (MRSA) wound healing and sensitize MRSA to β-lactam antibiotics

Abstract

The dwindling repertoire of antibiotics to treat methicillin-resistant Staphylococcus aureus (MRSA) calls for novel treatment options. Quorum-quenching agents offer an alternative or an adjuvant to antibiotic therapy. Three biaryl hydroxyketone compounds discovered previously (F1, F12, and F19; G. Yu, D. Kuo, M. Shoham, and R. Viswanathan, ACS Comb Sci 16:85-91, 2014) were tested for efficacy in MRSA-infected animal models. Topical therapy of compounds F1 and F12 in a MRSA murine wound infection model promotes wound healing compared to the untreated control. Compounds F1, F12, and F19 afford significant survival benefits in a MRSA insect larva model. Combination therapy of these quorum-quenching agents with cephalothin or nafcillin, antibiotics to which MRSA is resistant in monotherapy, revealed additional survival benefits. The quorum-quenching agents sensitize MRSA to the antibiotic by a synergistic mode of action that also is observed in vitro. An adjuvant of 1 μg/ml F1, F12, or F19 reduces the MIC of nafcillin and cephalothin about 50-fold to values comparable to those for vancomycin, the antibiotic often prescribed for MRSA infections. These findings suggest that it is possible to resurrect obsolete antibiotic therapies in combination with these novel quorum-quenching agents.

FIG 1

Chemical structure of biaryl hydroxyketone compounds F1, F12, and F19.

FIG 2

Cytotoxicity measurements of compounds F1, F12, and F19 on mouse macrophage cell line J774.2. Toxicity was assessed by measuring lactate dehydrogenase (LDH) leakage from cells at 490 nm. There is no statistically significant LDH leakage beyond that of the vehicle control for any of the three compounds up to a concentration of 200 μM. The positive control is 1× lysis control solution from the Promega CytoTox 96 assay kit, and the vehicle control is 1% DMSO, 1% ethanol, 1% Kolliphor.

FIG 3

Average percent healing of wounds in mice compared to wound status on the first day postinoculation. Wounds were treated with compound F1 or F12 at 20 mg/kg 1 h after inoculation. Treatment was repeated twice daily for 7 days. (A) Wounds infected with 10 μl of 1 × 10⁷ MRSA USA300. (B) Uninfected wounds.

FIG 4

Photographs of wounds in mice 8 days after the onset of the procedure. Wounds were treated with compound F1 or F12 at 20 mg/kg 1 h after inoculation. Treatment was repeated twice daily for 7 days. (A) Wounds infected with 10 μl of 1 × 10⁷ MRSA USA300. (B) Uninfected wounds.

FIG 5

Survival curves of MRSA-infected insect larvae in the presence of compound F12 and cephalothin. Caterpillars were injected with 2 × 10⁷ CFU of MRSA strain USA300. Untreated infected larvae died within 12 h. The mortality rate of uninfected and untreated larvae is 20% at the conclusion of the experiment, the same rate as that of F12-treated uninfected larvae (curves in the upper right corner). Treatments were initiated right after inoculation and repeated every 6 h at the doses indicated. Cephalothin is a cephalosporin β-lactam antibiotic to which MRSA USA300 is resistant, as shown by the solid black curve. The administration of compound F12 at 20 mg/kg increased the survival from 12 to 42 h (broken line). The combination of F12 (20 mg/kg) with cephalothin (30 mg/kg) further increased survival to 84 h (solid broken line). This result indicates a synergism between F12 and an antibiotic, indicating resensitization of MRSA to the antibiotic in the presence of the quorum-quenching compound. Similar results were obtained with compounds F1 and F19.