Lipolytic and antimicrobial activities of Pseudomonas strains isolated from soils in Phetchaburi Province, Thailand
Purpose: To identify and determine lipolytic and antimicrobial activities, and antibiotic susceptibility of bacterial isolates from soils in Phetchaburi Province, Thailand.
Methods: Bacterial strains were isolated from surface soils by enrichment technique using lipolytic broth (LB) and then identified based on their phenotypic and genetic characteristics. The cell-free culture supernatant was determined for lipase activity by spectrophotometric assay. Disc diffusion assay was used to determine the crude ethyl acetate extract of the culture supernatant for antimicrobial activity and antibiotic susceptibility. The chemical profile of the crude ethyl acetate extract was analyzed by reverse-phase C-18 column high-performance liquid chromatography (HPLC).
Results: On the basis of phenotypic properties and their 16S rRNA gene sequence analysis, five bacterial isolates, P1-2, P1-5, P1-6, P1-10 and P1-20 were identified as strains of Pseudomonas with sequence similarities (99.7 – 100 %). The extracellular lipase activity in LB supplemented with 1 % (v/v) of each of Tween 20, Tween 40, 60 or 80 as the substrate ranged from 11.61 ± 0.61 to 15.09 ± 0.42, 11.79 ± 0.28 to 15.75 ± 0.47, 12.65 ± 0.01 to 14.59 ± 0.87 and 12.71 ± 0.25 to 13.96 ± 0.21 unit/mL, respectively. The crude ethyl acetate extract of isolates P1-5, P1-6 and P1-20 contained quinoline alkaloid compounds and exhibited antibacterial activity against Gram-positive Kocuria rhizophila ATCC 9341 and Staphylococcus aureus strains ATCC 25923, ATCC 6358 and ATCC 25913, but not against Gram-negative Escherichia coli ATCC 25922. All the isolates were susceptible to cefepime, cefotaxime, ceftriaxone, ceftazidime, amikacin, gentamicin, imipeneum, meropeneum and levofloxacin.
Conclusion: The isolates demonstrate high lipolytic activity while the crude extracts exhibit antibacterial activity against Gram-positive bacteria. Thus, this lipase is a potential enzyme for pharmaceutical applications.
Keywords: Antibiotic susceptibility, Antimicrobial activity, Lipolytic activity, Pseudomonas, Thai soil