Plasmid profile analysis of Salmenella strains isolated from food products

Among the gram negative bacteria causing food born enteritis, the most importantorganisms belong to the members of Salmonella genus. In this investigation, threemethods of Serotyping, Resistotyping and Plasmid Profile Analysis were used to studythe Salmonella strains isolated from food products. A total of 50 Salmonella strainsisolated from food products and sent to the Veterinary Organization of Tehran Provinceand pasteur Veterinary Laboratory were studied from April to August 2005. Serotypingwas performed using the Mast Diagnostic Kit. Resistotyping was performed by Kirbyand Bauer disk diffusion method according to the NCCLS criteria. Plasmids were extractedusing Takara kit (Takara company, Japan) and electrophoresed on a 1% Agarosegel. Fifty Salmonella strains belonged to 11 serotypes. S. Durban was the most commonserotype followed by S. Nigeria and S. Thompson. All 50 Salmonella strains were resistantto Ampicillin and Streptomycin. Resistance to three or more antibiotics (MDR)was detected for 58% of the studied strains. Strains showed 6 different resistance patterns.The most common resistance pattern was S. Am. Gm. Cz. Te. All fifty Salmonellastrains contained one to four plasmids and showed 4 different plasmid profiles. All thestrains had a 3.036 MD plasmid and all these serotypes were resistant to Ampicillinand Streptomycin. Serotyping distinguished more strains than did the two other methods.Since our strains contained very few plasmids, this method could distinguish fewstrains. However, the method of Plasmid Profile Analysis showed that all the strainscontained a 3.036 MD plasmid that can be considered as a common characteristic ofSalmonella strains isolated from food products.