Abstract
BackgroundShigella spp. are major cause of diarrhoeal disease in both developing and developed countries. Shigella sonnei is the serogroup of Shigella most frequently responsible for sporadic and epidemic enteritis in developed countries. In recent years the emergence and spread of S. sonnei biotype g carrying class 2 integron have been frequently reported in many countries. Recently, S. sonnei has been reported as the prevalent serogroup of Shigella in Iran.The present study was carried out to investigate phenotypic and genetic characteristics of Shigella sonnei isolates identified in the years 2002 and 2003 in Tehran, Iran.MethodsBiotyping, drug susceptibility testing, pulsed field gel electrophoresis (PFGE) and analysis of class 2 integrons have been carried out on 60 S. sonnei isolates, including 57 sporadic isolates from paediatric cases of shigellosis occurring in 2002 and 2003, two sporadic isolates recovered in 1984 and the ATCC 9290 strain.ResultsBiotype g and resistance to streptomycin, sulfamethoxazole-trimethoprim and tetracycline were exhibited by 54 of the 57 recent isolates. Of the 54 biotype g isolates, 28 exhibited a class 2 integron of 2161 bp, and 24 a class 2 integron of 1371 bp, respectively. Class 2 integrons were not detected in four isolates only, including the two endemic isolates recovered in 1984 and two strains from recent sporadic cases. PFGE divided the strains into eight pulsotypes labeled A to H, three major pulsotypes – A to C – including the large majority of the recent sporadic S. sonnei isolates. Pulsotypes A and C were the most prevalent groups, accounting for 41.6% and 35.0%, respectively, of the isolates under study.ConclusionThe results suggest that biotype g, class 2 integron carrying S. sonnei are prevalent in our geographic area. S. sonnei isolated in the years 2002 and 2003 could be attributed to a few predominant clusters including, respectively, strains with pulsotypes B and C carrying a 2161 bp class 2 integron, and those having pulsotype A and a 1371 bp class 2 integron. A few epidemic clones are responsible for the apparently endemic occurrence of shigellosis in Tehran, Iran.
Highlights
Shigella spp. are major cause of diarrhoeal disease in both developing and developed countries
Pulsed Field Gel Electrophoresis (PFGE) divided the strains into eight pulsotypes labeled A to H, three major pulsotypes – A to C – including the large majority of the recent sporadic S. sonnei isolates
The results suggest that biotype g, class 2 integron carrying S. sonnei are prevalent in our geographic area
Summary
Shigella spp. are major cause of diarrhoeal disease in both developing and developed countries. In recent years the emergence and spread of S. sonnei biotype g carrying class 2 integron have been frequently reported in many countries. Development and spread of multidrug resistance is becoming a serious threat to Public Health worldwide since the early 1960s [3]. Mobile genetic elements, such as plasmids, transposons, genomic islands and integrons, disseminating via horizontal transfer are exponentially amplifying the problem [4]. Several reports have shown the successful emergence and spread in different countries of S. sonnei biotype g carrying a class 2 integron [4,7,8,9,10,11,12]. Emergence and selective pressure by use of some antimicrobial agents or, alternatively, international trade are under debate as possible epidemiological mechanisms of the successful dissemination of this organism [13]
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