Screening a mushroom extract library for activity against Acinetobacter baumannii and Burkholderia cepacia and the identification of a compound with anti-Burkholderia activity.

BACKGROUND: Acinetobacter baumannii and species within the Burkholderia cepacia complex (BCC) are significant opportunistic bacterial pathogens of humans. These species exhibit a high degree of antibiotic resistance, and some clinical isolates are resistant to all currently available antimicrobial drugs used for treatment. Thus, new drugs are needed to treat infections by these species. Mushrooms could be a potential source for new drugs to treat A. baumannii and BCC infections. METHODS: The aim of this study was to screen a library of crude extracts from 330 wild mushrooms by disk diffusion assays for antibacterial activity against A. baumannii and Burkholderia cepacia in the hope of identifying a novel natural drug that could be used to treat infections caused by these species. Once positive hits were identified, the extracts were subjected to bioassay-guided separations to isolate and identify the active drug molecules. MICs were performed to gauge the in vitro activity of the purified compounds. RESULTS: Only three crude extracts (0.9%) had activity against A. baumannii and B. cepacia. Compounds from two of these extracts had MICs greater than 128 microg/ml, and further analyses were not performed. From the third extract, prepared from Leucopaxillus albissimus, 2-aminoquinoline (2-AQ) was isolated. This compound exhibited a modest MIC in vitro against strains from nine different BCC species, including multi-drug resistant clinical isolates (MIC = 8-64 microg/ml), and a weak MIC (128 microg/ml) against A baumannii. The IC50 against a murine monocyte line was 1.5 mg/ml. CONCLUSION: The small number of positive hits in this study suggests that finding a new drug from mushrooms to treat Gram-negative bacterial infections may be difficult. Although 2-AQ was identified in one mushroom, and it was shown to inhibit the growth of multi-drug resistant BCC isolates, the relatively high MICs (8-128 microg/ml) for both A. baumannii and BCC strains suggests that 2-AQ is not suitable for further drug development in its current form.

Antibacterial compounds from mushrooms II: lanostane triterpenoids and an ergostane steroid with activity against Bacillus cereus isolated from Fomitopsis pinicola.

Anti- Bacillus cereus bioassay-guided fractionation of a crude extract of the American mushroom, Fomitopsis pinicola, was performed using thin-layer chromatography, Sephadex LH-20 column chromatography, and preparative-scale HPLC. Five lanostane triterpenoids (1-5) and one ergostane steroid (6) were isolated and identified. Compound 1 is a new lanostane triterpenoid, and its structure was determined using 1D and 2D NMR experiments, HR-MS, and physical data. Each of the purified compounds (1-6) was tested for antibacterial activity against B. cereus using standard MIC assays. Compounds 1-6 had MIC values of 32, 16, 32, 32, 128, and 64 microg/mL, respectively.

Antibacterial compounds from mushrooms I: a lanostane-type triterpene and prenylphenol derivatives from Jahnoporus hirtus and Albatrellus flettii and their activities against Bacillus cereus and Enterococcus faecalis.

Antibacterial bioassay-guided fractionation of two American mushroom species, Jahnoporus hirtus and Albatrellus flettii, led to the isolation and identification of their major antibacterial constituents: 3,11-dioxolanosta-8,24( Z)-diene-26-oic acid (1) from J. hirtus and confluentin (2), grifolin (3), and neogrifolin (4) from A. flettii. Compound 1 is a new lanostane-type triterpene. All purified compounds were evaluated for their ability to inhibit the growth of Bacillus cereus and Enterococcus faecalis using standard MIC assays. Compounds 1- 4 demonstrated MIC values of 40, 20, 10, and 20 microg/mL, respectively, against B. cereus and MIC values of 32, 1.0, 0.5, and 0.5 microg/mL, respectively, against E. faecalis. Thus, one novel compound and three others were shown to possess antimicrobial activities against these gram-positive bacteria employed as surrogates for more virulent and dangerous pathogens.