R-Factor in Salmonella enterica serovar typhi: transfer to and acquisition from Escherichia coli.

Blood culture isolates of Salmonella enterica serovar Typhi showing high degrees of resistance to ampicillin, chloramphenicol, cotrimoxazole and tetracycline (ACCoT-resistance) transferred their full resistance phenotype to antibiotic-sensitive S. enterica serovar Typhi strains through the primary recipient Escherichia coli C600. Transfer frequencies were 0.80 x 10(-5) and 0.80 x 10(-6), respectively, in the primary and secondary transfer experiments. The Escherichia coli isolates from urinary tract infection cases showing high minimum inhibitory concentration values (microg/ml) to A (2,000-5,000), C (2,000-5,000), Co (250-1,200), and T (500-2,000) also transferred ACCoT-resistance to the antibiotic-sensitive S. enterica serovar Typhi and then to E. coli C600 with transfer frequencies 0.61 x 10(-6) and 0.98 x 10(-5), respectively. Curing experiments revealed the loss of ACCoT-resistance from the original and the transconjugant S. enterica serovar Typhi strains. Results suggest that R-factor from other enteric bacteria is acquired by S. enterica serovar Typhi, and that it (R-factor) is unstable in nature.