CHARACTERISTICS OF THE ANTIBIOTIC-RESISTANCE PLASMID IN SALMONELLA-TYPHI ISOLATED IN TUNIS IN 1990

A multiresistant Salmonella typhi (S typhi, strain 302) was isolated f rom a blood culture of a patient in the Infectious Diseases department of Rabta Hospital in Tunis. The following tests were carried out: ant ibiotic susceptibility testing by the agar diffusion method; determina tion of the minimum inhibitory concentration against four beta-lactam antibiotics (amoxicillin, ceftriaxone, ceftazidime, imipenem), chloram phenicol, gentamicin, and amikacin by the agar dilution method; conjug ation with E coli K12 for study of transferability of resistance marke rs; and electrophoresis of plasmid DNA extracts on agarose gel. S typh i 302 was resistant to amoxicillin, streptomycin, tetracycline, chlora mphenicol, and sulfamide-trimethoprim, and this resistance was transfe rable in toro with a frequency of 10(-4). The MICs of amoxicillin and chloramphenicol were, respectively, 1024 (due to the production of TEM -1 beta-lactamase) and 256 mg/l. These resistance markers were carried by a plasmid of about 40 kb, similar to the Salmonella wien plasmid. The easy acquisition of a multiresistance plasmid by S typhi suggests that epidemiological monitoring of this serovar should be carried out.