EPIDEMIOLOGIC TYPING OF ISOLATES FROM AN OUTBREAK OF INFECTION WITH MULTIDRUG-RESISTANT ENTEROBACTER-CLOACAE BY REPETITIVE EXTRAGENIC PALINDROMIC UNIT B1-PRIMED PCR AND PULSED-FIELD GEL-ELECTROPHORESIS

An outbreak of multidrug-resistant Enterobacter cloacae infection last ed for 4 months in a neonatal intensive care unit (NICU). Forty-six is olates from the NICU and 20 epidemiologically unrelated strains were c haracterized by pulsed-field gel electrophoresis (PFGE) and repetitive extragenic palindromic unit b1-primed PCR (REPUb1-PCR) typing. The PF GE patterns after XbaI restriction of the bacterial DNA were analyzed by computer software (Gelcompar) using the UPGMA (unweighted pair grou p method with arithmetic averages) clustering method and the Dice coef ficient. The 46 isolates from the NICU were classified by PFGE typing into five clusters: A (further classified into 7 subtypes, A1 to A7), B, C, D, and E. This outbreak was attributed to multiple genetically r elated strains of cluster A which had a similarity of 85.8% +/- 4.6%. The minor band differences among strains of cluster A were probably du e to minor genetic mutations. The type A1 and A3 strains were isolated from the clinical specimens of patients and hands of nurses. It was p robable that these outbreak strains were transmitted among patients vi a the hands of personnel. REPUb1-PCR typing of the 46 isolates also de monstrated five types, in agreement with results obtained by the PFGE technique, but could not detect the minor mutations among the cluster A strains. Twenty epidemiologically unrelated strains were well distin guished by both PFGE and REPUb1-PCR typing. We conclude that PFGE is a highly discriminately but time-consuming method for epidemiological t yping of E. cloacae and that REPUb1-PCR is a more rapid method with go od reproducibility and discriminatory power comparable to that of PFGE .