S. typhi harbored a large plasmid 122 MDa and most of them contained a second plasmid 63 Mda. The frequency of auto transferable plasmid shifted from 10-8 to 105. The multiple drug resistance was associated with a 122 MDa. Lysotype E1 and E3 were predominant ribotype 3a for 87% of the studied strains. It is concluded a single clonal. Analyses of the quinolone resistance determining region of gyrA in 91 nalidixic acid resistant Salmonella typhi isolates by polymerase chain reaction and DNA sequencing. There was only one point mutation at nucleotide 83 Ser -- Phe (n=87), 83 Ser -- Tyr (n=3) and 87 Asp -- Gly (n=l).
Salmonella ; Epidemiology