Distribution Of Enterotoxin Genes And Molecular Typing By Pulsed Field Gel Electrophoresis Of Shigella Strains Isolated In Tianjin

ObjectiveTo study Shigella strains isolated in Tianjin from the year 2005 to 2007. The strains are identified by biochemical method,serotyping and susceptibility test. Shigella enterotoxin genes are detected by PCR to know its distribution and these Shigella strains are typed molecularly by pulsed field gel electrophoresis.Methods1. All the strains are identified by biochemical method, serotyping and susceptibility test;2. Virulence genes such as Shigella enterotoxin genes set1A,set1B,sen and ipaH in Shigella are detected by PCR to know the distribution;3. The Shigella strains are typed molecularly by pulsed field gel electrophoresis. Restriction enzyme XbaI is used for the molecular typing. PFGE patterns were analyzed by Bionumerics (Version 6.0) software to perform cluster analysis.Results1. Shigella flexneri were 36 strains and divided into 8 subtype:F1a, F1b, F2a, F2b, F3a, F4a, F6, Fx; they were accounted for 6.45%,6.45%,8.06%,17.74%, 6.45%,8.06%,1.61%,3.23% and 41.94% in order. F2b was the dominance serum group and accounted for 30.56% of Shigella flexneri. Shigella Sonnei were 26 strains without subtype and accounted for 41.94% of all Shigella strains. Shigella inTianjin was multidrug resistant strains.It was resistant to penicillins, TMP-SMZ, gentamicin and still sensitive to quinolones.2. The positive rate of ipaH,set1A,set1B and sen were 95.16%(59/62),40.32% (25/62),37.10%(23/62) & 50%(31/62) in order. The average positive rate of enterotoxin genes were 50% above and most of the genes were presented in F2b,F2a and F4a strains. set1A and set1B were not detected in Shigella Sonnei. The positive rate of sen were only 11.54%.There were large difference between distribution of enterotoxin genes of Shigella flexneri and Shigella Sonnei byχ2-test.There were 6 gene groups of virulence factors, accounted for 80.56%. The groups including all enterotoxins were the the dominance combination, accounted for 41.67%.3. All the strains were divided into 14 genotypes. There were 4 genotypes for Shigella Sonnei; they were SⅠ-SⅣ.The other 10 genotypes belonged to Shigella flexneri; they were FⅠ-FⅩ.Conclusion1. Serum agglutination test showed that the strains mainly were Shigella Sonnei and Shigella flexneri in Tianjin area from the year 2005 to 2007. F2b was the dominance serum group of Shigella flexneri. Shigella Sonnei grew up every year. Shigella sonnei should be given more monitoring and control. Shigella was multidrug resistant strains.It was sensitive to quinolones and we can use it.2. There were large differences on distribution of enterotoxins in different strains. setlA and set1B presented in diverse serum groups of Shigella flexneri, especially in F2b,F2a and F4a strains. sen were presented in all Shigella strains. Combination of the virulence genes referred to the association among the virulence factors.3. Shigella Sonnei strains isolated in Tianjin had very close relationship; S1 was the dominance strain in Tianjin area from 2005 to 2007. Shigella flexneri came from different clones.