Molecular epidemiological typing of Enterobacter cloacae isolates from a neonatal intensive care unit: three-year prospective study

Since 1992, there has been an increase in the incidence of Enterobacter sep sis in the neonatal intensive care unit (NICU) of the authors' hospital. Fr om 1995 to 1997, a prospective molecular epidemiological survey of the colo nizing and infecting strains isolated from neonates was conducted. Enteroba cter cloacae was the most frequent cause of neonatal sepsis, accounting for 19.2% of all neonatal infections, reaching a peak incidence of 2.2/1000 du ring 1996. Fifty isolates from the NICU and four epidemiologically unrelate d strains were characterized by pulse-field gel electrophoresis (PFGE), rib otyping, enterobacterial repetitive intergenic consensus (ERIC)-PCR and pla smid profiling. PFGE was the most discriminatory technique and identified 1 3 types (two of them classified into two and three subtypes) compared with ERIC-PCR, plasmid profiling and ribotyping that identified 11, 11 and seven types, respectively. A good correlation was found between all techniques. Five different clones caused 15 cases of sepsis. Clones A and B were preval ent in 1995 and 1996, but they were not isolated in 1997, An outbreak cause d by clone G in 1997 was controlled by cohort nursing and hygienic measures , without changing the antibiotic policy. Strains were characterized by the ir antibiotic resistance pattern and divided into three groups. Group I cor related with PFGE types A, B1 and B2, which hyperproduced Bush type 1 chrom osomal beta -lactamase and expressed extended-spectrum beta -lactamases (ES BLs). Group 11 only hyperproduced Bush type 1 chromosomal beta -lactamase a nd correlated with PFGE-types DI, D2, D3 and 1. Finally, Group III, with in ducible P-lactamases, correlated with the rest of PFGE types. The sudden di sappearance of E. cloacae after reinforcement of hygienic measures confirms the importance of patient-to-patient transmission. (C) 2001 The Hospital I nfection Society.