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

Abstract

Since 1992, there has been an increase in the incidence of Enterobacter sepsis in the neonatal intensive care unit (NICU) of the authors' hospital. From 1995 to 1997, a prospective molecular epidemiological survey of the colonizing and infecting strains isolated from neonates was conducted. Enterobacter 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 during 1996. Fifty isolates from the NICU and four epidemiologically unrelated strains were characterized by pulse-field gel electrophoresis (PFGE), ribotyping, enterobacterial repetitive intergenic consensus (ERIC)-PCR and plasmid profiling. PFGE was the most discriminatory technique and identified 13 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 prevalent in 1995 and 1996, but they were not isolated in 1997. An outbreak caused by clone G in 1997 was controlled by cohort nursing and hygienic measures, without changing the antibiotic policy. Strains were characterized by their antibiotic resistance pattern and divided into three groups. Group I correlated with PFGE types A, B1 and B2, which hyperproduced Bush type 1 chromosomal beta-lactamase and expressed extended-spectrum ?-lactamases (ESBLs). Group II only hyperproduced Bush type 1 chromosomal beta-lactamase and correlated with PFGE-types D1, D2, D3 and I. Finally, Group III, with inducible beta-lactamases, correlated with the rest of PFGE types. The sudden disappearance of E. cloacae after reinforcement of hygienic measures confirms the importance of patient-to-patient transmission.