Genotypic and phenotypic analysis of Enterobacter sakazakii strains from an outbreak resulting in fatalities in a neonatal intensive care unit in France

Abstract

In 1994, an outbreak of Enterobacter sakazakii infections occurred in a neonatal intensive care unit in France from 5 May to 11 July. During the outbreak, 13 neonates were infected with E. sakazakii, resulting in 3 deaths. In addition, four symptomless neonates were colonized by E. sakazakii. The strains were subjected to 16S rRNA gene sequence analysis, genotyped using pulsed-field gel electrophoresis, and phenotyped for a range of enzyme activities. E. sakazakii was isolated from various anatomical sites, reconstituted formula, and an unopened can of powdered infant formula. A fourth neonate died from septic shock, attributed to E. sakazakii infection, during this period. However, 16S rRNA gene sequence analysis revealed that the organism was Enterobacter cloacae. There were three pulsotypes of E. sakazakii associated with infected neonates, and three neonates were infected by more than one genotype. One genotype matched isolates from unused prepared formula and unfinished formula. However, no pulsotypes matched the E. sakazakii strain recovered from an unopened can of powdered infant formula. One pulsotype was associated with the three fatal cases, and two of these isolates had extended-spectrum beta-lactamase activity. It is possible that E. sakazakii strains differ in their pathogenicities, as shown by the range of symptoms associated with each pulsotype.

FIG. 1.

Dendrogram generated from PFGE profiles of E. sakazakii isolates (n = 30) by Bionumerics software, version 3.5. Clustering was done with UPGMA by using the Dice coefficient. Pulsotypes are identified on the left. The tolerance in the band was 1.5%, with an optimization of 1.5%.