Murgia, Manuela (2008) Caratterizzazione molecolare e studio dell'antibiotico-resistenza in ceppi di Salmonella enterica. Doctoral Thesis.
Salmonellosis still remains the most frequent foodborne disease worldwide especially in developing countries. The emergence of antimicrobial resistance in Salmonella isolates from food can compromise the treatment of these infections. In this study 134 strains of S. enterica isolated from food in Morocco and Libya were analyzed by using serotyping, antimicrobial testing, plasmid profiling and macrorestriction profiling by Pulsed- Field Gel Electrophoresis (PFGE). Genetic determinants of antibiotic-resistance were also investigated. Twenty-two different serotypes were identified among isolates, including Infantis, Bredeney, Braenderup, Blokley, M Bandaka and Typhimurium. Macrorestriction analysis defined 49 genotypes among the analyzed serotypes. PFGE subtypes cluster analysis showed a correlation of serotypes to PFGE subtypes. Forty percent of isolates were resistant to at least one antibiotic. Resistance to tetracycline was the most common (19%), followed by resistance to kanamycin (16%), nalidixic acid (15%) and ampicillin (12%). Multidrug resistance (MDR) was seen in 26% of the isolates. The analysis of plasmid content showed the presence of high and low molecular weight plasmids in 42% of the isolates. The molecular characterisation of antibiotic resistance determinants allowed to identify integrons of Class 1 in seven isolates and the presence of TEM-1 gene, encoding a narrow-spectrum - lactamase, in six isolates. Resistance to nalidixic acid was associated to mutations both in gyrA and parC genes. Finally, Salmonella Genomic Island 1 was detected in five S. Typhimurium isolates. The study point out the need of control of antibiotic resistance in Salmonella isolated from food to avoid the spread of MDR.
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