Dissemination ofanAntibiotic Resistance Plasmid inHospital Patient Flora

isolated atonehospital. Eight plasmids withthegeneforthis enzymepurified fromdifferent strains and species isolated atdifferent times hadsimilar EcoRIdigestion fragments, indicatingthatthegenehaddisseminated ononeplasmid without transposition. This 56.5-megadalton plasmid ofincompatibility groupM,whichalsocarried three other resistance genes, spread, atfirst, largely inonestrain ofKlebsiella pneumoniae, whichlater disappeared. Ittransferred tosomestrains whichtended not tocolonize other patients andlater circulated predominantly inSerratia marcescens. Computer surveillance ofroutine hospital laboratory results wasableto detect andtrace thegeneandtheplasmid andmeasure their effect onresistance prevalence. Anantibiotic resistance genemaytranspose fromoneplasmid toanother, maytransfer ona plasmid fromonebacterial cell toanother, or mayremain inabacterial cell whichleaves one person andcolonizes another (8). Inclinical settings, however, ithasproven difficult toobserve movementofresistance genes relative toplasmids, bacteria, andpeople because ithasbeen difficult toidentify individual genes, plasmids, andstrains ofbacteria atthesametime. We describe hereanoccasion onwhichsuchobservations werepossible. Theyshowthedissemination ofasingle plasmid intomultiple strains andspecies ofEnterobacteriaceae isolated from manypatients inonehospital.