Seventy one strains among the 296 S. flexneri isolates were resistant to chloramphenicol (CM), tetracycline (Tc), streptomycin (Sm) and ampicillin (Ap). Thirty eight strains for the molecular characterizations of nontransferable antimicrobial
resistance.
Elimination of antimicrobial resistance determinants was significnatly high (30 of 38) in modified Bochner's media but very low (less than 2) by treatment with acriflavine, rifampin and sodium dodecyl sulfate.
A ccording to the plasmid patterns, S. flexneri strains were classified into 6 groups. Seventeen strains of group Ⅳ contained 4 plasmids of 2, 1.8, 1.5 and 1.4 megadalton (Mdal) and 14 strains of group Ⅳ had no plasmid. Wild strains and cured
strains
which lost Tc fully antimicrobial resistance did not show change of their plasmid contents.
By R1 plasmid, pSM217 plasmid of CmTcSmAp resistance with 54 Mdal was mobilized and classified into Inc K group. pSM513 plasmind which was mobilized by pGL109 was 59 Mdan and was compatible with all standared plasmid tested. By transfer factor
R641, 20
plasmids ranging 36 to 89 Mdal were mobilized and their resistance patterns were CmTcSmAp, CmSmAp or Tc. Among them, 12 R plasmids were untypable but mutuazlly incompatible. They derived from 5 derived from 5 plasmid profile groups of S. flexneri
strains.
EcoR1 restriction enzyme digestion patterns of mobilized plasmids and their mobilizing plasmids were examined. pSM513 and pGS109 shared fragments of 22.9, 11.2, 5.3, 2.1 and 0.55 Kilobases (Kb). pSM217 and R1 shared fragments of 21.7, 2.1 and
0.59
Kb.
R387 and pSM217, a incompatible plasmids, shared fragments of 0.55 and 0.31 Kb. Three plasmids which were mobilized by R641 and their segregants shared 16 fragments.
It was difficult to find relationship of mobilizing plasmids and mobilized plasmids in HindⅢ and Pstl restriction enzyme analysis.
Nontransferable resistance in S. flexneri was less likely to by common ancestral origin in gene evolution.
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