Acidophilic Actinobacteria: Isolation, Taxonomic Characterization and Bioactivity against Multidrug Resistant Pathogens


Muhammad Numan
Maira Saleem
Shahid Nawaz
Sabahat Nosheen
Imran Sajid

Actinobacteria are known as potent bioactive microbes capable of producing large number of therapeutic compounds. They are playing a significant role in fight against Multidrug-Resistant (MDR) pathogens. In this study, we isolated 29 actinobacterial strains from acidic soil of various industrial sites in Lahore. The isolated strains were subjected to various morphological and biochemical characterization followed by antibacterial and cytotoxicity screening. The methanolic extracts of strains, obtained by small-scale laboratory fermentation, were screened for activity against clinically isolated MDR bacterial pathogens including Klebsiella pneumoniae, Escherichia coli, Bacillus spp., methicillin-resistant S. aureus (MRSA) Acinetobacter spp., and Pseudomonas aeruginosa. The Grampositive test pathogens were inhibited by 53% of the actinobacterial extracts and Gram-negative test strains were inhibited by 92% of the extracts. The extracts of two actinobacteria strains; N-100 and N-87, exhibited antibacterial activity against all the test pathogens. The test strain E. coli was inhibited by 55% of extracts which was the highest inhibition percentage among all test strains. The Diphenyltetrazolium bromide (MTT) assay was performed for cytotoxicity analysis and it was observed that the strain SS-4 exhibited highest cytotoxicity with up to 77% mortality at 80µg/ml concentration. Overall, the extracts of eleven strains resulted in 40% viability against A549 Adenocarcinoma human alveolar basal epithelial cell line. The Thin Layer Chromatography (TLC) analysis was performed for chemical analysis and different bands were visualized under long and short UV. The 16S rRNA gene sequencing of two most promising strains, N-87 and N-100, revealed them to be Streptomyces coeruleofuscus (97.44%) and Streptomyces iakyrus (97.84%) with query length of 1217 and 1187 base pairs, respectively. This study indicates that acidophilic soil actinobacteria have great potential to harbour novel strains and to produce bioactive secondary metabolites against MDR pathogens.


Keywords: Acidophile, Actinobacteria, Multi-drug resistance, Antibacterial activity, Cytotoxicity

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