Quinolone resistance among Salmonella Kentucky and Typhimurium isolates in Tunisia: first report of Salmonella Typhimurium ST34 in Africa and qnrB19 in Tunisia.

AIMS: Characterization of quinolone-resistant Salmonella Kentucky and Typhimurium isolates in Tunisia from various sources, detection of some plasmid-mediated quinolone resistance genes and the genetic relatedness. METHODS: A total of 1404 isolates of S. Kentucky (n = 1059)/S. Typhimurium (n = 345) from various sources from all over Tunisia were tested for quinolone resistance by disk diffusion method. Minimum inhibitory concentrations of nalidixic acid, ciprofloxacin and ofloxacin were determined. Quinolone-resistant isolates were screened for plasmid-mediated quinolone-resistance genes (qnrA,qnrB,qnrS, aac(6')-Ib-cr and qepA) by polymerase chain reaction (PCR). Mutations in the quinolone-resistance-determining regions of the gyrA and parC genes were detected by PCR and DNA sequencing. Pulsed-field gel electrophoresis and multilocus sequence typing were accomplished for isolates harbouring plasmid-mediated quinolone-resistance genes. RESULTS: According to our selection criteria (NAL = resistance phenotype; CIP = resistant with diameter 0, or intermediate), only 63 S. Kentucky/41 S. Typhimurium isolates were investigated: 49% (5/104) were multidrug resistant. Two S. Typhimurium isolates harboured qnrB19 with different PFGE profiles. A mutation was detected in the gyrA gene for each of these two isolates. MLST revealed the presence of ST313 and ST34, an endemic sequence type. CONCLUSION: Our study highlights the presence of quinolone multidrug-resistant Salmonella in humans and animals in Tunisia. This is the first report of S. Typhimurium ST34 in Africa and qnrB19 in Tunisia. SIGNIFICANCE AND IMPACT OF THE STUDY: This is the first report that describes not only the current epidemiological situation of the quinolone resistance in S. Kentucky and Typhimurium isolated from various sources and regions in Tunisia, but also, the genetic resistance determinants associated with phenotypic antibiotic resistance and the molecular mechanisms of their quinolone-resistance. Also, we provide the first report of S. Typhimurium ST34 in Africa, and the first report of qnrB19 in Salmonella in Tunisia.

Survival of Escherichia coli strains in Mediterranean brackish water in the Bizerte lagoon in northern Tunisia.

This study investigated survival and virulence of Escherichia coli strains exposed to natural conditions in brackish water. Two E. coli strains (O126:B16 and O55:B5) were incubated in water microcosms in the Bizerte lagoon in northern Tunisia and exposed for 12 days to natural sunlight in June (231 to 386 W/m2, 26 +/- 1 degrees C, 30 g/L) and in April (227 to 330 W/m2, 17 +/- 1 degrees C, 27 g/L) or maintained in darkness for 21 days (17 +/- 1 degrees C, 27 g/L). The results revealed that sunlight was the most significant inactivating factor (decrease of 3 Ulog within 48 hours for the two strains) compared to salinity and temperature (in darkness). Survival time of the strains was prolonged as they were maintained in darkness. Local strain (E. coli O55:B5) showed better survival capacity (T90 = 52 hours) than E. coli O126:B16 (T90 = 11 h). For both, modifications were noted only for some metabolic activities of carbohydrates hydrolysis. Cytotoxicity of the two strains, tested on Vero cell, was maintained during the period of survival.

Molecular typing of Salmonella enterica serovars Enteritidis, Corvallis, Anatum and Typhimurium from food and human stool samples in Tunisia, 2001-2004.

During the period from 2001 to 2004, a total of 72 isolates of Salmonella enterica serovars: Anatum (n=40), Enteritidis (n=18), Corvallis (n=8), and Typhimurium (n=6), of various origins (mainly food and diarrhoeagenic stool samples), were collected and further characterized by antibiotic resistance, plasmid analysis, and pulsed-field gel electrophoresis (PFGE). Forty-five isolates presented multidrug resistance to antibiotics. Among which one S. enterica serovar Anatum isolate was resistant to 11 antibiotics, and one S. enterica serovar Typhimurium DT104 isolate was resistant to eight antibiotics. Plasmid profiling identified eight plasmid profiles (with 1-5 plasmids) among the isolates, of which one plasmid profile (P01) was predominant. XbaI PFGE analysis revealed the presence of a predominant clone of the four studied Salmonella serovars circulating in Tunisia throughout the years 2001-2004.