Molecular typing of isolates from a Shigellosis outbreak by pulse-field gel electrophoresis

Objective:To find genetic relations and variances among isolates from a shigellosis outbreak,and to trace the source of infection.Methods:Fifteen Shigella flexneri 4c isolates from a Shigellosis outbreak in Jingsu province in 2007 and 3 local sporadic isolates were analyzed by pulse-field gel electrophoresis(PFGE) with NotI restriction enzymes.PFGE patterns were clustered by outweighed pair group method using arithmetic averages(UPGMA).Dice coefficient was elected as the similarity coefficient.Results:Fifteen outbreak isolates showed 9 PFGE patterns,in which 2 main patterns accounted for 46.7%.These patterns of outbreak isolates with similarity coefficient from 92% to 100% had differences of three or fewer bands between 336.5bp and 310.1bp.The pattern of a food-processing worker had only a difference of one band from the main pattern CNJZXN11.01,and the similarity coefficient was 97%.Three sporadic isolates showed 3 different patterns,and had the similarity coefficient from 82% to 87% with outbreak isolates.Conclusion:Genetical relation was close among outbreak isolates,and this Shigellosis outbreak was caused by the same clone cluster.A carrier who worked in the food processing site was suspected to be a source of infection.