Five different Salmonella isolates (four Salmonella enteritidis and one Salmonella havana) of human, chicken or egg origin which all expressed smooth lipopolysaccharide were subjected to plasmid curing Upon this treatment, four isolates lost at least one of their resident plasmids while all five isolates became rough in their LPS profiles, Two of the S. enteritidis isolates, CA13 and CE7 were found to convert phage types (PTs) as well. The phage type conversion in CA13 from PT6 to PT21 was found to be accompanied by the loss of a 19.0-MDa plasmid as well as the loss of sulbactam ampicillin and tetracycline resistance. The change in the PTs of the strain CE7 from PT20a to the PT20 variant was accompanied by the loss of two plasmids of 10.9 and 1.45 MDa, Outer membrane protein (OMP) type change occurred only in the isolate CA13, which lost an OMP of 27.2 kDa. The strains, CA13 and CE7 retained their high molecular weight plasmid (36 MDa), which has been very commonly found (77 of 82) among local S. enteritidis isolates. (C) 2001 Academic Press.