CHARACTERIZATION OF ENDEMIC SHIGELLA-FLEXNERI STRAINS IN SOMALIA - ANTIMICROBIAL RESISTANCE, PLASMID PROFILES, AND SEROTYPE CORRELATION

One hundred twelve Shigella flexneri strains isolated from children wi th diarrheal disease in Somalia in 1983, 1984, 1988, and 1989 were ana lyzed for serotype, plasmid profile, and genetic location of antimicro bial resistance determinants. The prevalent serotypes were 4 (46% of t he isolates), 1b (16%), 2a (16%), 3a (12%), and 6 (8%). Each serotype was associated with a characteristic predominant plasmid profile, wher eas no specific correlation between antimicrobial resistance patterns and single serotypes was found. All but three of the strains were resi stant at least to ampicillin, chloramphenicol, spectinomycin, and tetr acycline. Of these resistant strains, 41 were resistant to sulfonamide and streptomycin and 14 were resistant to trimethoprim or trimethopri m and kanamycin. The genes for resistance to ampicillin, chloramphenic ol, spectinomycin, and tetracycline formed a linkage group located on the chromosome of the strains of all serotypes. The genes for resistan ce to sulfonamide and streptomycin were located on a 6.3-kb plasmid in strains of serotypes 1b, 2a, and 4. Conjugative trimethoprim or trime thoprim and kanamycin resistance plasmids with lengths of 80 to 110 kb were present in strains of serotypes 1b, 2a, 3a, and 4. The systemati c presence of a chromosomal component in this uncommon genetic plasmid -chromosome configuration may play a role in the emergence of increase d genetic stability of resistance patterns in S. flexneri.