AN EPIDEMIOLOGIC-STUDY OF SERRATIA-MARCESCENS ISOLATES FROM NOSOCOMIAL INFECTIONS BY ENZYME ELECTROPHORESIS

Serratia marcescens isolates from 164 patients with suspected nosocomi al infection in several hospitals in the greater Paris region were inv estigated by analysis of the electrophoretically demonstrable allelic variations of gene loci coding for five esterases and five other enzym es. All the loci were polymorphic and the mean number of alleles per l ocus was 6.1. A total of 72 distinctive electrophoretic types (ETs) re presenting multilocus genotypes was distinguished. The isolates were d ivided into two groups according to their resistance to antibiotics: 8 2 multiresistant isolates (MRI) and 82 relatively susceptible isolates (RSI). Seventy-two MRI (88%) were in four genetically related ETs: ET 1, ET2, ET8 and ET9; ET1 was found in 48 isolates, whereas the remaini ng MRI were in 10 ETs, and all RSI in 61 ETs. Three ETs contained both MRI and RSI. The mean coefficients of genetic diversity for the 10 en zyme loci among ETs and isolates were smaller for MRI than for RSI, wh ile the modal ET of MRI resembled that of RSI. The epidemiological sig nificance of isolates varied according to their ET. Thus, isolates bel onging to ET1, ET2 and ET8 were responsible for outbreaks or for spora dic infections, whereas isolates of other ETs were responsible for onl y sporadic infections. The temporal distribution of ET1 isolates among hospitals identified seven outbreaks in seven clinical departments.