Shigella dysenteriae type 1 carrying LPS biosynthesis genes of Salmonella typhimurium affects both Invasive Plasmid AntigenH (IpaH) secretion and invasion

A Shigella dysenteriae 1 strain isolated from an epidemic in West Bengal, I ndia. The strain contained six plasmids including a large virulence plasmid . A plasmid, pPR1347 carrying both the rfb gene cluster and the rfc gene of Salmonella typhimurium has been transferred to this invasive Shigella dyse nteriae 1 strain by triparental cross with a very low frequency. Only five stable (100%) clones were isolated after examining several thousand colonie s. All five transconjugants were Sereny negative and were unable to invade the HeLa cells. Transconjugants exhibited strong cross reactivity with S. d ysenteriae 1 antisera but they showed weak reaction with Salmonella typhimu rium antisera. Plasmid profiles of the transconjugants were unaltered as co mpared with the wild type strain except for the presence of pPR 1347. The t ransconjugants regained their invasive property after elimination (curing) of pPR 1347. However, Shigella-infected convalescent phase serum was able t o detect IpaABCD proteins from whole cell lysate and culture supernatant of transconjugants and cured (pPR 1347) transconjugants. A 60 kDa IpaH protei n was not secreted into the culture supernatant by the transconjugants. Syn thesis of lipopolysaccharides (LPS) of the hybrid strains was increased wit hin the region of 43 to 67 kDa in comparison with the wild type S. dysenter iae 1 strains.