Candida tropicalis

Antimicrobial activity of the plant extract was evaluated using Staphylococcus aureus (ATCC 25923), Clostridium perfringens (ATCC 13126), Pseudomonas aeruginosa (ATCC 27853), Enterococcus faecalis (ATCC 29212), Escherichia coli (ATCC 25922), Staphylococcus epidermidis (ATCC 12228), Bacillus cereus (ATCC 13061) and the fungal species Candida albicans (ATCC 90028) and Candida tropicalis (ATCC 756). All the bacterial and fungal species were supplied by the National Health Laboratory Services, Bloemfontein, South Africa. All the microbial species were maintained in Mueller Hinton agar plates at temperatures of 4 °C. Prior to antimicrobial testing, the microorganisms were inoculated in Mueller Hinton broth and placed in a shaking incubator (100 rpm) for 24 h at 37 °C. Thereafter, a microbial suspension was prepared by diluting one millilitre of the culture in 100 ml of Mueller Hinton broth (1:100).

The antimicrobial potency of all the synthesized compounds was assessed in vitro in accordance with the guidelines of Clinical Laboratory and Standards Institute [22 ] against four representative Gram positive bacteria, namely, Bacillus subtilis (ATCC 6633, NCIM 2063), Bacillus cereus (ATCC 10876, NCIM 2156), Staphylococcus epidermidis (ATCC 12228, NCIM 2493), and Staphylococcus aureus (NCIM 2079); Gram negative bacteria, namely, Escherichia coli (ATCC 8739, NCIM 2065), Klebsiella pneumoniae (NCIM 2706), Proteus mirabilis (NCIM 2241), and Pseudomonas aeruginosa (ATCC 19429, NCIM 2036); and two fungal strains Candida albicans (ATCC 2091, NCIM 3102) and Candida tropicalis (ATCC 13803, NCIM 3556). The microbial strains employed for the activity were procured from National Collection of Industrial Microorganisms (NCIM), Pune, India. Ciprofloxacin was used as the standard antibacterial drug and fluconazole as the standard antifungal drug.

The microorganisms Escherichia coli (ATCC 25922), Pseudomonas aeruginosa (ATCC 27853), Klebsiella pneumoniae (ATCC 10031), Staphylococcus aureus (ATCC 29213), Staphylococcus epidermidis (ATCC 12228), Enterococcus faecalis (ATCC 29212), Candida albicans (ATCC 90028), and Candida tropicalis (ATCC 13803) were obtained at the Clinical Microbiology Laboratory at UFRN and maintained in nutrient agar at 4 °C. Antimicrobial assays were performed using the microdilution method in Mueller Hinton broth (MHB); inoculums of 10⁵ CFU/mL for bacteria and 10⁴ CFU/mL for yeast were prepared as mentioned in the Clinical and Laboratory Standards Institute (CLSI) guidelines [80 ,81 ]. COSs (0.25–2 mg/mL) were added in 96 well-plates together with the inoculum in MHB. Then, plates were incubated at 35 ± 2 °C at 200 rpm for 24 or 48 h. Microbial growth was measured by the optical density at 595 nm in a microplate reader (Epoch Biotek, Winooski, VT, USA). Wells containing only microorganism suspensions or sterile saline solution 0.9% (w/v) were used as a positive and negative control of growth, respectively. The minimal inhibitory concentration (MIC) was defined as the lowest concentration of the sample capable of inhibiting the visible growth of the microorganism.