A spontaneously produced lipopolysaccharide biosynthetic defect which causes both pleiotropic phage resistance and mucoid colony morphology in Salmonella anatum.

A spontaneously derived mutant of the smooth bacterial strain, Salmonella anatum A1, specifically blocks the DNA ejection function of bacteriophage E15 during infection. The mutant, AE15R-5, exhibits mucoid colony morphology but no evidence of colanic acid biosynthesis. It is resistant not only to bacteriophage E15, but also to all other smooth- and rough-specific phages which have been tested. Chemical, immunological and gel electrophoretic analyses indicate that its lipopolysaccharide (LPS) molecules fall into two categories: they are either highly truncated (probably heptoseless) or extremely large (complete LPS molecules with O-polysaccharides containing 80 or more repeat units). The antibiotic resistance pattern of AE15R-5 is roughly intermediate between that of a known heptoseless mutant, S. anatum MG4, and that of the parent strain, S. anatum A-1.