The molecular epidemiologic analysis was used to characterize the Inc FIR plasmids derived from Shigella isolates.
Five R plasmids resistant to chloramphenicol(Cm), tetracycline(Tc), streptomycin(Sm), sulfamethoxazole(Su), ampicillin(Ap), trimethoprim(Tp), and kanamycin(Km), were derived from one of S. flexneri and 4 of S. sonnei, and had molecular weight
ranging I
from 66 to 81 megadaltons(MDa).
Resistance patterns of the rest 4 R plasmids derived from S. flexneri were CmTcSmSuAp, SmSuApTpKm, and Tc, and their molecular weight ranged from 76 t 84 MDa. The molecular weight of some plasmids in E. coli transconjugants were same as those of
Shigella but the others showed more or less changes in size during resistance transfer or long preservations of bacterial stock. The variations of molecular weigh did not necessarily correspond with the presence of transfer plasmid or some drug
resistance determinants.
The restriction endonuclease analysis with EcoR I, HindⅢ, and Pst I showed similar fragments pattern among 4 plasmids derived from S. sonnei. Three of 5 plasmids from S. flexneri showed different DNA fragment patterns but 2 plasmids with
identical
resistance pattern(SmSuApTpKm) and molecular size(84 MDa) showed identical restriction pattern.
By southern blot hybridization. Tc1 pKYo1405 S8, used as a probe, showed homology with fragments less than 4.8 kilobase of all Tc1 plasmids tested and with 6.6 kilobase strongly except pKY01403.
All of the Ap1 plasmids produced TEM-1 type β-lactamase.
These results indicate that most of the Inc FIR plasmids derived from Shigella isolates were highly related evolutionlly.
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