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

Abstract

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.

Fig. 1

Dendogram showing percent similarity calculated by the Dice similarity index of PFGE restriction endonuclease digestion profiles among the 66 Salmonella isolates: (a), S. Anatum; (b), S. Enteritidis; (c), S. Corvallis. The different patterns, sources, year of isolation and number of strains are indicated.

Fig. 2

PFGE patterns of XbaI digests of chromosomal DNA of S. Typhimurium. The numerical prefix was used to designate the serovar of the strain. The alphabetical suffix was to designate the code of the strain in our laboratory. Salmonella enterica serovar cholereasuis ATCC14028 strain was used as a control. M, lambda DNA ladder; lane 1, S. Choleraesuis ATCC14028; lane 2, ST21(01); lane 3, ST1031(01); lane 4, ST2157(01); lane 5, ST1161(02); lane 6, ST179(03); lane 7, ST299(03).