Study of isolation and determination of antibiotic resistance, plasmid profiles, protein bands and phenotypic virulence of Shigella flexneri strains

Shigellosis is an acute gastroenteritis caused by Shigella species, including S. dysenteriae, S. flexneri, S. boydi and S. sonnei.The purpose of this study was to isolate and to determine antibiotic resistance, plasmid profile and protein bands by SDS-PAGE, and also phenotypic virulence by Congo red dye among S. flexneri strains. The isolated bacteria were identified by use of standard bacterial and biochemical methods. Antibiotic susceptibility tests were performed according to kirby-Bauer method. Plasmids were isolated by alkaline lysis method. Serological reactions were detected by slide agglutination tests with both polyclonal and monoclonal antisera kits. Virulent strains were isolated on a TSA plate containing Congo red dye. From 350 isolated Shigella spp., 142 (40.57%) were S. flexneri. Of 350 patients 41% were female and 59% male. In 100 S. flexneri isolates, resistance rates to tetracycline, ampicillin, trimethoprim-sulfometoxazol and cephalexin were 95%, 91.3%, 85.6% and 70.3% respectively. All of isolates were sensitive to ciprofloxacin. Most isolates contained multiple plasmid bands (1-5 plasmid's bands). A total of 11 distinct plasmid profile patterns were identified. The results of our study showed that serotype 2 was the most common isolated serotype of S. flexeneri (39%). In this study, 46% of S. flexneri were Congo red positive and haemolysin positive on blood agar plates. A 120 KDa protein band was detected on electrophoresis gel. These data showed, pathogenicities of all S. flexneri isolates are not similar. Health care can prevent bacterial diarrhea due to shigella. Therefore laboratories are recommended to be more concerned about isolation of these bacteria. Congo red dye binding test is cheap, simple and rapid, so, it can be used to determine the virulence properties of S. flexneri. Antibiogram tests are recommended to prevent antibiotic resistance.