Fig 1.
Multistep resistance selection for ebselen and mupirocin against two strains of S. aureus.
Ebselen and mupirocin were passaged against (a) S. aureus ATCC 6538 and (b) methicillin-resistant S. aureus (MRSA USA300) for 14 days. The broth microdilution assay was used to determine the minimum inhibitory concentration (MIC) of ebselen and mupirocin after each passage. Data are presented as fold change in MIC relative to the initial MIC determined at passage 0.
Table 1.
Postantibiotic effect of ebselen (tested at 5 × MIC) against three different strains of Staphylococcus aureus.
Fig 2.
Evaluation of ebselen or mupirocin treatment of infected pressure ulcers in obese and diabetic TALLYHO/JngJ mice.
The skin of female (obese) and male (diabetic) TALLYHO/JngJ mice (n = 5) were exposed to magnets to form pressure ulcers that were subsequently infected with MRSA USA300. Approximately 48 hours later, PUs were treated with oral linezolid (10 mg/kg, only for obese mice), topical mupirocin (2%), topical ebselen (2%) or vehicle alone (petroleum jelly) twice daily for either five (obese mice) or four (diabetic mice) days. Mice were humanely euthanized 12 hours after the final treatment dose and the infected PUs were aseptically removed to determine bacterial burden. (a) Reduction in burden of MRSA USA300 in pressure ulcers after treatment with the vehicle alone, linezolid, mupirocin, or ebselen in female obese TALLYHO/JngJ mice. (b) Reduction in burden of MRSA USA300 in pressure ulcers after treatment with the vehicle alone, mupirocin, or ebselen in male diabetic TALLYHO/JngJ mice. Data are presented as log10 (total MRSA CFU per wound) for each mouse and were evaluated using a one-way ANOVA with post-hoc Dunnet’s test for multiple comparisons. An asterisk (*) indicates statistical difference for test agents relative to petroleum jelly (negative control, P < 0.05) while a pound sign (#) indicates statistical difference between mice treated with mupirocin compared to ebselen (P < 0.05).
Fig 3.
Histological evaluation of infected pressure ulcers in diabetic TALLYHO/JngJ mice.
(a) Negative controls (vehicle alone) were characterized by dense thick carpets of superficial bacterial colonies (arrows) and full thickness necrosis, extending into the deep subcutis (image acquired at 2× magnification). Scale bar represents 1 mm. (b) On closer view, bacteria extend deep into the dermal tissue and are innumerable, forming thick aggregates (dashed boxes, image acquired at 20× magnification). Scale bar represents 100 μm. (c) Mupirocin-treated diabetic animals had a diminished bacterial burden, confined to the deep dermis and subcutis (arrows) surrounded by wound contraction (circle), indicating early wound healing, absent in negative controls. Inflammation extends deep into the subcutaneous tissue (dashed boxes) in contrast to untreated controls (image acquired at 2× magnification). Scale bar represents 1 mm. (d) On closer view, bacteria are less numerous and form small clusters compared to negative controls and collagen fibers are visible (dashed box). Scale bar represents 100 μm. (e) Ebselen-treated animals had a pronounced decrease in bacterial burden compared to the negative control, with few scattered aggregates in the deep dermis (arrows) and normal collagen fiber architecture in between. Inflammation was sparse compared to mupirocin treatment and present only at the deep tissue margin, indicating tissue clearing and early wound healing (dashed boxes) (image acquired at 2× magnification). Scale bar represents 1 mm. (f) Bacteria are sparse and markedly decreased compared to the negative control, with few colonies in between collagen fibers and occasionally forming clusters (arrows) (image acquired at 20× magnification).
Table 2.
Minimum inhibitory concentration (MIC in μg/mL) of ebselen and mupirocin determined against three strains of Staphylococcus aureus in the presence of different pH and high bacterial inoculum.