STABILITY OF PLASMIDS IN 5 STRAINS OF SALMONELLA MAINTAINED IN STAB CULTURE AT DIFFERENT TEMPERATURES

Four strains of Salmonella berta and one of Salm. enteritidis were sto red as stab cultures in sugar-free agar at 5 degrees, 22 degrees and 3 0 degrees C and in 15% glycerol at -80 degrees C. The stability of the plasmid profiles in each of the strains was monitored over a period o f 2.5 years. Plasmid profiles were stable in all strains stored at -80 degrees C, and only six of 450 colonies examined from strains kept in sugar-free agar at 5 degrees C had lost plasmid molecules. Seventy of 440 colonies from stab cultures that were kept at 22 degrees C, and 7 1 of 440 colonies at 30 degrees C showed changed plasmid profiles. The total number of plasmids lost increased with time, and occasionally, more than one plasmid molecule was lost in the same strain. The virule nce associated plasmid of Salm. enteritidis was remarkably stable as i t was maintained in all colonies examined at all temperatures investig ated. Likewise, no change in SmaI restriction profile was observed in this plasmid molecule at any temperature.