Biological characterization of Enterobacter sakazakii.
|Title:||Biological characterization of Enterobacter sakazakii.|
|Abstract:||Enterobacter sakazakii, a motile peritrichous gram-negative rod, has been implicated in a severe form of neonatal meningitis. Dried-infant formula has been implicated in both outbreaks and sporadic cases of E. sakazakii meningitis. Reported case-fatality rates vary from 40 to 80%. Strains of E. sakazakii were isolated from dried-infant formula available on the Canadian retail market. The prevalence varied from 0--12% in 120 samples evaluated from 5 different companies. Nine clinical E. sakazakii strains were obtained from Canadian hospital culture collections. Minimum growth temperatures of 7.0 to 8.5°C were observed. Average generation times were 40 min at 23°C and 4.98 h at 10°C. E. sakazakii strains did not grow at 4°C and appeared to die-off during storage. Heat resistance studies determined the heat resistance of this organism at 52, 54, 56, 58 and 60°C, obtaining D-values of 54.8, 23.7, 10.3, 4.2 and 2.5 min, respectively. The overall calculated z-value was 5.82°C. Using the standard suckling mouse assay, it was found that four strains (1 food and 3 clinical) produced enterotoxin. Dose response studies indicated that 15 of 18 E. sakazakii strains caused lethality in mice by intraperitoneal injection, two through oral feeding. From the 18 strains examined, 3 biotypes and 4 antibiogram patterns were observed. Ribotyping categorized the test strains into 10 clusters. Two decamer primers were selected for random amplification of polymorphic DNA (RAPD) typing. Banding patterns were similar for three strains isolated from the same hospital, although each strain was isolated in a different year. All three of the food isolates from company A showed similar profiles, while two food strains isolated from Company B formula revealed different profiles. Pulsed-field gel electrophoresis (PFGE) revealed a similar number of bands to that of RAPD (4--13 bands), giving distinguishable patterns that allowed for the comparison of E. sakazakii strains. RAPD and PFGE were the most discriminatory methods for distinguishing clinical and food isolates of E. sakazakii. Overall, the abilities of RAPD and PFGE to differentiate between strains were comparable, followed by ribotyping, biotyping and antibiograms. In conclusion, my studies have found that E. sakazakii is prevalent in dried-infant formula available on the Canadian retail market. This organism can grow at temperatures found in many home refrigerators. Growth studies in reconstituted dried-infant formula indicate a generation time of only 40 min at ambient temperatures. Heat resistance studies indicate that E. sakazakii appears to be one of the most thermotolerant organisms among the Enterobacteriaceae. (Abstract shortened by UMI.)|
|Collection||Thèses, 1910 - 2010 // Theses, 1910 - 2010|