CHARACTERIZATION OF A LARGE PLASMID ENCODING FOR LIPOPOLYSACCHARIDE SYNTHESIS, DRUG-RESISTANCE AND VIRULENCE CHARACTERS IN SHIGELLA-DYSENTERIAE TYPE-1

A 120 kb plasmid was transfered from N'-methyl-N'-nitro-N'-nitrosoguan idine treated Shigella dysenteriae type 1 (Strain Dt 66, Am(r) Cm(r) T c(r) Nal(s) ) to a plasmidless E.coli K12 KL318 (Am(s) Cm(s) Tc(s) Nal (r) ) strain by conjugation. The Ampicillin, Chloramphenicol, Tetracyc line resistant (Am(r) Cm(r), Tc(r) ) characters of transconjugants wer e found to be encoded by the 120 kb-plasmid. On 0.7% agarose gel elect rophoresis, localization of 120 kb plasmids of transconjugant & donor were found at the same position. In lipopolysaccharide (LPS) biosynthe sis studies, six fold, more LPS was recovered from transconjugant then the recipient. Similarly in SDS-PAGE analysis, the donor showed a cha racteristic ladder like LPS-bands in the molar mass of 67 kD to 10 kD. However, the transconjugants revealed only 38-kD LPS band and recipie nt strain did not show any band. In virulence studies, both the donor and transconjugants showed adherence to HeLa cells but transconjugants exhibited no itracellular invasion. Additionally, transconjugants fai led to produce keratoconjunctivities in guineapig whereas the same was performed by the donor (Shigella dysenteriae type 1).