[Epidemiological pattern of the resistance of 153 Salmonella strains (S. typhi excluded) isolated in a Tunisian pediatric unit from 1985 to 1990]

Abstract

Since 1985 to 1990, 153 isolates of non typhoidic Salmonella were recovered from pediatric unit of the Charles Nicolle Hospital in Tunis. The epidemiological profile of these isolates was established according to the biochemical and serological characterizations, the antibiotic susceptibility patterns (disk diffusion method) to betalactams and aminoglycosides. 127 isolates of Salmonella spp were from stools and 22 from blood cultures. The main serotypes were S. ser. Wien (108 isolates) and S. ser. Typhimurium (21). A sample of 50 isolates was selected among the different resistance phenotypes for determination of MICs and betalactamase identification by isolelectro-focusing (36 isolates). All of them were resistant to ampicillin and carbenicillin but variable for cephaloridine. Since 1986 appeared the resistance to cefotaxime and in 1990 all the S. ser. Wien isolates were resistant to the 4 betalactams tested including cefotaxime associated to streptomycin, kanamycin, gentamicin, tobramycin and amikacin. All of them had a high level of resistance to amoxicillin and gentamicin (mean MICs > 2048 and > 512 mg/l). The mean MIC of cefotaxime was 43.2 mg/l for S. ser. Wien, 64mg/l for S. ser. Typhimurium and decreased to 1.9 and 0.12 mg/l in combination with 1 mg/l of clavulanic acid. The beta-lactam resistance was mediated to enzymatic mechanism, at first the betalactamase of TEM-1 type alone, then associated to extended-spectrum betalactamase, mainly type SHV-2 since 1986, and other new types in 1990. They were under the control of plasmids with different sizes.