ABSTRACT
Enterobacter sakazakii, designated a unique species in 1980, has been implicated as the causative organism in a rare but severe form of neonatal meningitis. Dried infant formula milk has been identified as a potential source of the organism. E. sakazakii isolates from dried infant formula available in Canada and clinical isolates obtained from Canadian hospital culture collections were characterised by phenotypic (biotype and antibiograms) and genotypic (ribotyping, random amplification of polymorphic DNA and pulsed-field gel electrophoresis) methods. Three biotypes and four antibiogram patterns were observed in the 18 isolates examined. Ribotyping with the Dupont Riboprinter microbial identification system divided the 18 isolates into 10 ribotypes. Three isolates from the same hospital had indistinguishable ribotyping patterns although each was isolated in a different year, as did three food isolates from one company. Pulsed-field gel electrophoresis (PFGE) and random amplification of polymorphic DNA (RAPD) profiles indicated minor differences between the isolates that were indistinguishable by ribotyping. PFGE (with the restriction endonucleases Xba1 and Spe1) and RAPD gave discrete patterns that enabled easy comparison of E. sakazakii isolates, with a high degree of discrimination. The discriminatory index showed RAPD and PFGE were shown to be the most discriminatory typing schemes for E. sakazakii, followed by ribotyping, biotyping and antibiograms.
Subject(s)
Enterobacter/classification , Enterobacteriaceae Infections/microbiology , Food Microbiology , Infant Food/microbiology , Meningitis, Bacterial/microbiology , Bacterial Typing Techniques , DNA Fingerprinting , DNA, Bacterial/analysis , Electrophoresis, Gel, Pulsed-Field , Enterobacter/drug effects , Enterobacter/genetics , Genotype , Humans , Infant, Newborn , Phenotype , Random Amplified Polymorphic DNA Technique , Restriction MappingABSTRACT
Enterobacter sakazakii, previously referred to as a yellow-pigmented Enterobacter cloacae was designated as a unique species in 1980. This reclassification was based on differences from E. cloacae in DNA relatedness, pigment production and biochemical reactions. E. sakazakii has been implicated in a severe form of neonatal meningitis. Although studies have failed to identify an environmental source for the organism, dried-infant formula has been implicated in both outbreaks and sporadic cases of E. sakazakii meningitis. The high mortality rate (40-80%), the severity of the infection in infants, plus the scarcity of information on the ecology and pathogenicity of this organism warranted a review of the clinical and microbiological features of this putative foodborne pathogen.
Subject(s)
Enterobacter/pathogenicity , Enterobacteriaceae Infections/etiology , Food Microbiology , Meningitis, Bacterial/etiology , Enterobacter/classification , Enterobacter/isolation & purification , Humans , Infant , Infant Food/microbiologyABSTRACT
Enterobacter sakazakii, designated a unique species in 1980, has been implicated in a rare but severe form of neonatal meningitis, with dried-infant formula being implicated as the mode of transmission. The high mortality rate (40-80%) and the lack of information about this organism led to a study of the heat resistance of Ent. sakazakii in reconstituted dried-infant formula. Ten Canadian Ent. sakazakii strains (5 clinical and 5 food isolates) were used to determine the heat resistance of this organism at 52, 54, 56, 58 and 60 degrees C in reconstituted dried-infant formula. D-values of 54.8, 23.7, 10.3, 4.2 and 2.5 min were obtained for each temperature, respectively. The overall calculated z-value was 5.82 degrees C. In a comparison of the D-values of several members of the Enterobacteriaceae in dairy products, Ent. sakazakii appeared to be one of the most thermotolerant organisms. The importance of process control during manufacture and the use of aseptic procedures during the preparation, use and storage of dried-infant formula is discussed.
