REPLICON TYPING OF 71 MULTIRESISTANT SERRATIA-MARCESCENS STRAINS

Replicon typing is the identification of plasmids by hybridization with specific DNA probes which contain the genes involved in plasmid maintenance. This new method has been used to classify plasmids into replicon (rep) groups which can often be correlated with incompatibility (Inc) groups. We studied 71 multiresistant Serratia marcescens strains with 19 rep probes constructed from reference plasmid replicons belonging to known Inc groups. These probes are known to react with enteric bacterial plasmids. However, they did not represent the totality of the thirty known Inc groups. For 52 % of the studied strains, plasmids were identified and classified into groups FIB, FIC, FIIA, Hl2, L/M, N, B/O, P, W, Y and Com9. Most (79 %) of the plasmid preparations hybridized with a single rep probe, and 21 % hybridized with two different probes. Electrophoretic analysis of DNA suggested that double hybridization could result from the presence of either two different Inc plasmids in the same strain (e.g. S37) or one single plasmid with a multireplicon (e.g. S113).