Assessment of antimicrobial resistance of food-borne enteric pathogens and evaluation of antioxidant, antibacterial and antimalarial potentials of Acacia nilotica extracts. | |
| Author | Sadiq, Muhammad Bilal |
| Call Number | AIT Diss. no.FB-16-01 |
| Subject(s) | Anti-infective agents. Acacia nilotica extracts. Antioxidants. |
| Note | A dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Food Engineering and Bioprocess Technology |
| Publisher | Asian Institute of Technology |
| Abstract | The prevalence of antibacterial resistance is high in foodborne pathogens due to extensive use of antibiotics in animal farming for therapeutic and prophylactic purposes. In South East Asia, pathogenic strains of Escherichia coli and Salmonella are frequently identified from food sources. The management of multidrug resistant bacteria with available antibiotics is becoming an increasingly more difficult task and is of great food safety concern. This could explain the fact that Escherichia coli and Salmonella isolated from poultry and beef meat in current study, were resistant to various commonly used antibiotics. The antibacterial susceptibility testing of E. coli and Salmonella spp. obtained from clinical and food sources demonstrated that clinical isolates of E. coli and Salmonella typhimurium were resistant to various antimicrobial agents as compared to food isolates. E. coli obtained from human clinical isolates was found to be resistant to ampicillin (10 μg), amoxicillin ( 10 μg), chloramphenicol (30 μg), tetracycline (30 μg), ciprofloxacin (5 μg) and ceftriaxone (30 μg). The clinical isolates of Salmonella typhimurium were found resistant to ampicillin ( 10 ~tg), amoxicillin ( 10 μg), tetracycline (30 μg) and streptomycin ( 10 μg). E. coli and Salmonella enterica isolated from poultry meat were found susceptible to all the tested antibiotics. Whereas, E. coli, isolated from beef meat was resistant to ampicillin ( 10 μg), amoxicillin (10 μg), chloramphenicol (30 ~tg) and tetracycline (30 μg); S. typhimurium, isolated from poultry meat was resistant to tetracycline (30 μg), and chloramphenicol (30 μg), and S. enteritidis, isolated from beef meat was resistant to ampicillin (10 μg), amoxicillin (10 μg) and tetracycline (30 μg). Further objective of this study was to identify plant-based natural bioactive extracts for their antibacterial and antimalarial activities. The study was conducted to determine the phytochemical contents, antibacterial, antioxidant and antimalarial activities of leaves, bark and pods of Acacia nilotica. The extracts of acacia were evaluated for total phenolic, flavonoid and protein contents, antibacterial (agar well diffusion and broth dilution methods) and antioxidant (DPPH; 1, 1 diphenyl-2-picryl hydrazyl assay) activities. The characterization and identification of phenolic compounds was carried out by liquid chromatography-tandem mass spectrometry analysis (LC-MS). The MS/MS fragmentation pattern showed the presence of galloylated catechins and gallocatechin derivatives in tested extracts. The results indicated that all parts of the plant, but especially leaves, were effective in inhibiting the growth of antibiotic resistant strains of Escherichia coli and Salmonella species obtained from clinical and food isolates. The leaves were found rich in total phenolic content, proteins and high antioxidant activity as compared to pods and bark. The presence of functional groups of active compounds was confirmed by fourier transform infrared spectroscopy (FTIR) analysis of plant extracts. It was concluded that all tested parts of A. nilotica had antibacterial and antioxidant activities. These properties might be due to the presence of high total phenolic content, proteins, peptides and/or flavonoids. The mechanism of action of acacia extracts against E. coli and Salmonella was elucidated by observing the changes in cell structures and growth patterns using time kill analysis, morphological damages including cell integrity and cell membrane permeability. The clinical isolates of E. coli and Salmonella were found more resistant to tested antibiotics, compared to food isolates. Minimum inhibitory concentration and minimum bactericidal concentration of acacia leaves were in the ranges of 1.56 - 3 .12 mg/ml and 3 .12 - 6.25 mg/ml, respectively. Minimum inhibitory concentration and minimum bactericidal concentration for pods and bark extracts were in the similar range of 3 .12 - 6.25 mg/ml and 6.25-12.5 mg/ml, respectively, against all tested pathogens. The release of electrolytes and essential cellular contents (proteins and nucl eic acids) indicated the breakage of cellular membranes. These changes eventually resulted in cell decomposition and death, corresponded to simultaneous reduction in the growth of viable bacteria. The antimalarial activity of Acacia nilotica extracts (leaves, pods and bark) were determined by schizont maturation inhibition assay followed by the guidelines of World Health Organization (WHO). The ethanol extracts of plants were screened for antimalarial potential against artesunate sensitive strain of Plasmodium falciparum (3D7). The half maximal inhibition concentration (ICso) values representing the concentration of sample required to inhibit 50% of the schizont maturation, were calculated by implementing non-linear regression; inhibitor concentration vs. normali zed response model with a variable slope. The leaves were found more potent against the plasmodium parasite with ICso 1.28 μg/ml, whereas, the pods and bark extracts exhibit ICso values, 4.15 and 4.27 μg/ml respectively. The 5 μg/ml of leaves showed full inhibition of mature schizonts development while, pods and bark extracts showed full inhibition at 10 μg/ml. Fmthermore the parasites were washed three times with RPMI buffer after 48 h of incubation and re-incubate with malarial culture medium (RPMI-1640 supplemented with 0.5% Albumax) for further 48 hours. The results after harvesting at 96 h proved the irreversible inhibition of schizont maturation induced by A. nilotica extracts. This study elaborates the antibacterial and antimalarial activity of A. nilotica extracts, thus A. nilotica can be a potential source of new antimicrobials effective against resistant strains of pathogens |
| Year | 2016 |
| Type | Dissertation |
| School | School of Environment, Resources, and Development (SERD) |
| Department | Department of Food, Agriculture and Natural Resources (Former title: Department of Food Agriculture, and BioResources (DFAB)) |
| Academic Program/FoS | Food Engineering and Bioprocess Technology (FB) |
| Chairperson(s) | Anal, Anil Kumar |
| Examination Committee(s) | Athapol Noomhorm;Thammarat Koottatep;Taming, Joel |
| Scholarship Donor(s) | Higher Education Commission (HEC), Pakistan - AIT Fellowship |
| Degree | Thesis (Ph.D.) - Asian Institute of Technology, 2016 |