Development of interpretive criteria and quality control limits for broth microdilution and disk diffusion antimicrobial susceptibility testing of Streptococcus pneumoniae

Cladonia verticillaris lichen lectin (ClaveLL) was purified using a previously established protocol and then evaluated for its potential antimicrobial activity. Initially, the autochthonous lichen was submitted to extraction with sodium phosphate buffer pH 7.0, followed by filtration and centrifugation to obtain crude extract. A salt fractionation was performed with 30% ammonium sulfate. After centrifugation, the protein fraction was loaded onto molecular exclusion chromatography using Sephadex G-100 matrix to purify active lectin. ClaveLL showed antibacterial activity against Gram-positive (Bacillus subtilis, Staphylococcus aureus, and Enterococcus faecalis) and Gram-negative (Escherichia coli and Klebsiella pneumoniae) assayed strains, with greater inhibitory effect on growth of E. coli (MIC of 7.18 μg mL−1). The lowest minimum bactericidal concentration (MBC, 57.4 μg mL−1) was detected against E. faecalis. The antifungal assay performed with Trichophyton mentagrophytes, Microsporum gypseum, Trichophyton rubrum, Trichosporon cutaneum, and Trichosporon asahi evaluated crude extract, fraction, and ClaveLL preparations. ClaveLL was the most active against T. rubrum with an inhibition percentage of 35% compared to negative control (phosphate buffer). Extract and fraction showed better activity on growth inhibition of T. mentagrophytes (35%). The results indicate the potential of ClaveLL and other C. verticillaris preparations as antimicrobial agents useful for applications focusing on human health.