Tropical Milky White Mushroom, Calocybe indica (Agaricomycetes): An Effective Antimicrobial Agent Working in Synergism with Standard Antibiotics

Abstract

Synergistic effect of mushroom extracts with standard antibiotics against pathogenic bacteria is beneficial for treating infectious diseases. The present investigation tested the antibacterial activity and synergistic effect from an edible mushroom, Calocybe indica, with standard antibiotics. The minimum inhibitory concentration (MIC) of different extracts from C. indica was checked against pathogenic and opportunistic pathogenic bacteria such as Escherichia coli, Pseudomonas aeruginosa, Klebsiella pneumoniae, Staphylococcus aureus, S. epidermidis, and Bacillus subtilis using the broth dilution and agar well diffusion method. The agar disc diffusion method, checkerboard study, and growth curve analysis were used to test synergism. The preliminary mechanism of action regarding cellular morphology, membrane permeability, and damage to protein and DNA were evaluated. Maximum antimicrobial activity was found in the methanolic crude extract (MCE) from C. indica, with a MIC value ranging from 5 to 10 mg/mL. It showed a significant increase in the efficiency of ciprofloxacin (CIP) acting synergistically. The fractional inhibitory concentration index (FICI) of MCE was significant for E. coli and S. aureus with values of 0.46 and 0.45 respectively. Results showed an increase in the loss of cell viability, damage to cell membrane permeability, and damage to bacterial protein and DNA as the probable synergistic mechanism of action for the MCE and the antibiotic. HR-LCMS analysis of the MCE showed the presence of phenolic acid, terpenoids, fatty acid ester, and carboxylic acid, which, in combination, increased the bacterial susceptibility. The present study is significant because it considered the methanolic crude extract from C. indica as complementary medicine for infectious diseases.