Research - MS (Thesis)

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Title: Characterization of Antibacterial Extracellular Product Produced By Airborne Fungi

Author: Esmat Jahan

Supervisor: Wahhida Shumi

Co-Supervisor: Jannatul Ferdouse

Research Field: Medical Microbiology

Batch: 11th


Abstract

Fungal antagonism has been reported for a wide variety of pathogenic organisms. Mechanisms of fungal antagonism and defense often include the production of biologically active products by one species that exerts effects on potential competitors and predators. Fungi are remarkably well suited for dispersal into air. The purpose of the present study was to isolate airborne fungi and to observe the antibacterial activity when they produce extracellular metabolites. The fungi isolated were Aspergillus, Penicillium, Cladosporium and Fusarium. The antibacterial activity of fungi were observed by cup-plate method against five pathogenic microorganisms, two were gram positive bacteria Bacillus cereus, Staphylococcus aureus and three gram negative bacteria Salmonella typhi, Shigella dysentriae and Escherichia coli. The culture filtrate was collected by filtration with Whatman filter paper no.1 and the antibacterial activities against selected bacteria were assayed by disc diffusion method. The culture broth inoculated with isolates were exposed to different environmental condition such as incubation period, temperature, pH, inoculums size, stationary or shaking condition, salt concentration, sugar concentration and medium ingredient contents. Their tolerance to different temperature, acid treatment and alkali treatment and activity at different temperature and diffusion period were also observed.
Of the isolated fungi Aspergillus and Penicillium showed antibacterial activity against the selected bacteria except Escherichia coli. They produce antibacterial extracellular metabolites on the broth and this effect was visual with the change of colour of broth. The required condition for the production of maximum extracellular metabolites include incubation period of 7 days, temperature 29°C, pH 7.0, inoculums size single, non shaking condition, salt concentration 0%, sugar concentration 3% and nutrient content single strand. The culture filtrate of Penicillium showed tolerance against different temperature (10ºC, 30ºC, 37ºC and 45ºC), acid treatment (0%, 0.01% and 0.1% HCl) and alkali treatment (0%, 0.01% and 0.1% NaOH). However the filtrate of Aspergillus showed no tolerance to low (10ºC) and high temperature (45ºC) and acid and alkali treatment. Both the fungi showed different activity at various temperature and diffusion period when their maximum activity were found at incubation period of 30ºC and after 3 hr diffusion period.
Since the extracellular products of Aspergillus and Penicillium have antibacterial activity against gram positive and gram negative, these can be used as the model for antibacterial treatment after further characterization. Besides the product of Penicillium was toleratnt to different temperature, acid and alkali treatment, this property may be used for further biotechnological study as it is an important biotechnological criterion. Gene modification and manipulation of the Penicillium strains the extracellular product can be used future industrial purposes.