Study On The Virulent Genotype And Viruence Of Shigella In Lanzhou City

Objective:To investigate the rate and the type of Shigella spp infection among the patients suffered with the diarrhea in Lanzhou city.To detect the virulent genotype of the Shigella spp separated from the patients lived in Lanzhou city.To measure the virulence of Shigella with different virulent genes in order to investigate their relation among virulent genotype and virulence.Methods:The ordinary and acute diarrheal patients came to the three third A grade hospitals in Lanzhou city were enrolled in the study.The isolated culture, biochemical reaction and serological method were used to identify the rate and the type of Shigella spp infection among the patients in the area.The virulent genes of SHET1(setlA,setlB),SHET2(sen),ipaH,ial and virA of Shigella spp were detected by PCR.The Shigella with different virulent genes was chosen to detect its virulence. The healthy Kunming mouse were chosen as laboratory animal to detect the median lethal dose(LD50)by intraperitoneal injection.Results:1.16 Shigella strains were isolated from 80 diarrheal patients.The positive rate of Shigella was 20%.All the isolated Shigella strains were composed with 9 S.flexneri strains(56.3%),6 S.sonnei strains(37.5%)and 1 S.dysenteriae strain(6.3%).There exit difference in biochemical reaction and antigenicity in different strain among the same Shigella group.2.The virulent genes of virA and setlA were presented in all the Shigella strains. The positive rate of ipaH,ial and sen genes were 93.7%,56.2%and 62.5% respectively.The setlB only presented in some S.flexneri strains and the positive rate were 25%.Except for virA,ipaH and setlA genes,the positive rate of sen in S.sonnei strains were 50.0%.The positive rate of ial were 33.3%.The setlB were not found in the 6 S.sonnei strains.The positive rate of ial,setlB and sen in S.flexneri strains were 66.7%,44.4%and 66.7%respectively.The positive rate of ial,setlB and sen in S. flexneri strains were higher than that in S.sonnei strains.3.The LD50 of the seven Shiglla strains with the different virulent genotype in virA+ipaH+setlA,virA+ial+ipaH+setlA+setlB+sen,virA+setlA,virA+ial+ipaH+ setlA+sen,virA+ipaH+setlA+sen,virA+ipaH+setlA+setlB and virA+ial+ipaH+setlA +setlB were 1.422×10~9 cfu/ml,6.653×10~7 cfu/ml,-,6.653×10~8 cfu/ml,1.422×10~9 cfu/ml,1.422×10~9 cfu/ml and 6.653×10~8 cfu/ml respectively.The LD50 of the quality control S.sonnei 51334 was 3.062×10~9 cfu/ml.Conclusions:1.There were about 20%diarrheal patients infected by Shigella spp.The predominant prevalent species was S.flexneri and the second was S.sonnei.The S. sonnei strain infection was higher in Lanzhou city comparatively with the other place.2.There present virulent genes of virA,ial,ipaH,setlA,setlB and sen among the Shigella strains in Lanzhou city.The virA,setlA and ipaH present stably in the Shigella strain in the area.The positive rate of virulent genes of the S.flexneri strains was higher than that in the S.sonnei strains.There exists setlA in the S.sonnei strains in the area.3.There has good correlation between Shigella virulence and virulent genotype.S. flexneri typeⅣwith virA,ial,ipaH,setlA,setlB and sen have the strongest virulence in all genotype strains.4.The virA,setlA and ipaH can be used as the target genes to detect the Shigella in Lanzhou city.SetlB can be used to select the S.flexneri typeⅣin the area.