RANDOM AMPLIFIED POLYMORPHIC DNA AND PLASMID ANALYSES USED IN INVESTIGATION OF AN OUTBREAK OF MULTIRESISTANT KLEBSIELLA-PNEUMONIAE

Multiresistant Klebsiella pneumoniae strains with plasmid-borne extend ed-spectrum beta-lactamases (ESBL) are increasingly frequent nosocomia l pathogens. A major outbreak of clinical infections, mainly involving patients in the Newborn Services Unit with limited spread to adult pa tients, occurred at our hospital. This epidemic was investigated by ty ping the isolates phenotypically and with random amplified polymorphic DNA analysis (RAPD) and plasmid analysis. Forty-eight isolates, consi sting of 44 consecutive clinical isolates and 4 selected surveillance isolates, were studied. A single decamer primer was used for the RAPD, and this was effective in demonstrating that the majority of isolates (45 of 48) had the same profile. Three other isolates had different R APD patterns identifying them as nonepidemic strains. Plasmids were ex tracted by alkaline lysis with Magic-miniprep kits from 10 isolates se lected to represent the epidemic and nonepidemic strains. This method produced small (<20-kb) plasmids; larger ESBL-carrying plasmids were n ot produced, but the small plasmids nonetheless allowed strain differe ntiation. Antibiotic susceptibility patterns alone were not reliable a s strain indicators, since some isolates with the RAPD pattern charact eristic of the epidemic strains did not express ESBL and therefore wer e susceptible to extended-spectrum cephalosporins. The investigation s howed the predominance of a single epidemic strain that was transmitte d between patients in the Newborn Services Unit. RAPD was the best of the methods used for detecting strain differences, and its speed and a bility to type a wide variety of species suggest that it will be an in creasingly useful molecular epidemiologic tool.