CHARACTERIZATION OF A SMALL CRYPTIC PLASMID FROM SALMONELLA-ENTERITIDIS THAT AFFECTS THE GROWTH OF ESCHERICHIA-COLI

We examined the plasmid content of 25 clinical isolates of Salmonella enteritidis, and detected the presence of small plasmids (3-5.3 kb) in 9 of them, alone, or in addition to the large, so-called virulence pl asmid. A 5.3-kb plasmid isolated as unique extrachromosomal DNA from a strain responsible for a high-mortality outbreak was characterized by restriction mapping and cloning. The plasmid replicon was localized i r a 1.7-kb fragment, that hybridized with three of the small plasmids detected in S. enteritidis, and with another small plasmid from Salmon ella typhimurium. A strain of Escherichia coli carrying this plasmid, or a cloned 3.7-kb PvuII restriction fragment, showed a slower growth rate, especially in minimal medium, as well as a noticeable increase i n DNA methyltransferase activity.