Date of Award


Document Type

Master Thesis

Degree Name

Masters of Science (Research)


Biological Sciences

First Advisor

Dr. Aidan Coffey

Second Advisor

Prof. Seamus Fanning


In this study, 176 isolates of Salmonella were collected from different laboratories in Ireland. All isolates were confirmed to be of the genus Salmonella by performing bacteriological and biochemical tests. Briefly, all isolates were cultured onto XLD agar after which pure cultures were verified and stocked at this institute. Definitive identification was carried out using the API 20-E system and a separate urease test was also performed on all isolates. After confirmation of the genus, all isolates were prepared for antibiotic susceptibility testing and r-types were determined using sixteen antibiotics. Depending on the antibiotic resistance profiles, isolates were selected for different molecular tests. DNA extraction was carried out using two methods, the chloroform method and the boiling method. The quality of DNA from both methods was compared. All isolates with resistance or susceptibility to the quinolone antibiotics were selected and a further quantitative level of resistance was determined using graduated E-test strips. The three recognized mechanisms responsible for in quinolone resistance were investigated in those Salmonella isolates. Briefly, DNA sequences of specific housekeeping genes were screened for specific mutations implicated in quinolone resistance; a plasmid-borne mechanism encoded by the qnr gene was investigated and thirdly, the possible existence of an active efflux system was examined. Integron-bome resistance to the common antibiotics, ampicillin, chloramphenicol, tetracycline, streptomycin, spectinomycin and sulphonamides was also studied. All 176 isolates were screened for the presence of integron-associated genes inti (identifying Class 1 integrons) and int2 (identifying Class 2 integrons). The integrons of int1- and int2-positive isolates were characterized by PCR amplification and nucleotide sequencing. The association of integron-borne resistance linked to Salmonella Genomic Island 1 was also examined.

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