The antibiotic susceptibility of Salmonella typhi and Salmonella paratyphi isolates to ten selected antibiotics, plasmid DNA profiles and conjugative ability in Zaria, Nigeria were investigated. Blood samples collected from presumptive typhoid fever patients in the different locations were cultured for Salmonella species and identified by standard procedures. Susceptibility testing and minimum inhibitory concentration determination were performed using appropriate microbiological methods. Conjugative experiment was carried out with multiple antibiotics resistant isolates of Salmonella species. The resistant test bacteria strains were subjected to DNA isolation and characterization. Susceptibility study of test bacteria to ten selected antibiotics showed high percentage resistance to nine antibiotics such as Ampicillin, Amoxicillin, Augumentin, Chloramphenicol, Co-trimoxazole, gentamicin, Nitrofurantoin and Tetracycline (40 - 100%). Antibiotics resistance profile of S. paratyphi isolates were observed to be considerably higher than S. typhi isolates. The result of conjugation studies of multiple antibiotics resistant Salmonellaspecies with Ofloxacin sensitive Escherichia coli ATCC 25722 showed that eight of the 18 Ofloxacin resistant Salmonella species isolates possess transferable resistant trait. The multiple antibiotics resistant (MAR) of test bacteria showed transferable plasmid sizes of 23.13 and 0.145 kb conferring resistance to the ten selected antibiotics. The findings from the plasmid analysis showed that the antibiotic sensitive S. typhi strains could acquire the R-plasmid from any resistant enteric bacteria such as E. coli, to undergo a suitable adaptation for survival in the changing antibiotic environment.
Key words: Plasmid, antibiotics, resistance, Salmonella species.
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