E¡ects of plasmid curing on antibiotic susceptibility, phage type, lipopoly saccharide and outer membrane protein pro¢les in local Salmonella isolates B. _ Ic° gen, G.C. Gˇrakan and G. Úzcengiz* Five di¡erent Salmonella isolates (four Salmonella enteritidis and one Salmonella havana) of human, chicken or egg origin which all expressed smooth lipopolysaccharide were subjected to plasmid cur- ing. Upon this treatment, four isolates lost at least one of their resident plasmids while all ¢ve isolates became rough in their LPS pro¢les. 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 PT21was 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 OMPof 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. # 2001Academic Press Introduction Poultry, cattle and dairy products are the ma- jor sources of Salmonella contamination in foods that cause human salmonellosis (Wege- ner et al. 1997).There has been an increased in- cidence of gastrointestinal infections caused by Salmonella enteritidis, which has become the predominant serotype in many countries (Thong et al. 1995). Although Salmonella havana is the second most frequently isolated species in Iran, it is rarely isolated in other countries (Katouli et al. 1992). A high percentage of S. enteritidis strains contain a serovar-speci¢c 36 -MDa plasmid that increases the virulence of the strains in mice (Nakamura et al. 1985).The virulence plas- mids are of di¡erent sizes, ranging from 30 to 62 MDa, with a serotype-speci¢c plasmid of ap- proximately 38MDa being common to the ma- jority of strains of S. enteritidis (Helmuth et al. 1985). Phage typing is used to subdivide strains within a particular serotype, and typing schemes have been developed for the most com- mon Salmonella serotypes, including S. enteriti- dis (Threlfall and Frost 1990). Acquisition of plasmids encoding for drug resistance has been associated with a change in phage type (PT) of S. enteritidis (Frost et al. 1989). The ORIGINAL ARTICLE *Corresponding author. Fax: 90-312-2101289; E-mail: ozcengiz@metu.edu.tr Received: 28 February 2001 Middle EastTechnical University, Department of Biotechnology, 06531, Ankara,Turkey 0740-0020/01/060631 +05 $35.00/0 r 2001 Academic Press Food Microbiology, 2001, 18, 631^635 doi:10.1006/fmic.2001.0437 Available online at http://www.idealibrary.com on