Detection of Enterobacter sakazakii in South African food products
Date
2005-12
Authors
Kemp, Francisca
Journal Title
Journal ISSN
Volume Title
Publisher
Stellenbosch : University of Stellenbosch
Abstract
It is estimated by the World Health Organisation (WHO) that thousands of millions of
cases of foodborne diseases occur world–wide every year. Enterobacter sakazakii is
a member of the family Enterobacteriaceae and has been identified as an occasional
contaminant of powdered infant formula milk (IFM). Enterobacter sakazakii is an
opportunistic emerging pathogen and has the ability to cause a severe form of
neonatal meningitis. This organism was referred to as “yellow pigmented
Enterobacter cloacae” until 1980 after which it was renamed as E. sakazakii.
The current method for the detection of E. sakazakii is very time consuming
and includes pre–enrichment, enrichment in Enterobacteriaceae enrichment broth,
subsequent plating on violet red bile glucose agar and subculturing on tryptone soy
agar. In this study a polymerase chain reaction (PCR) method was developed for the
identification of the presence of E. sakazakii in infant food products. A part of the 16S
ribosomal RNA (rRNA) gene from E. sakazakii was amplified using the primer pair
Esak2 and Esak3.
An internal amplification control (IAC) was constructed as part of the PCR
detection method. The 850 base pair (bp) E. sakazakii PCR product was digested
with AluI and the two fragments containing the primer binding sites were ligated,
resulting in a 240 bp IAC. During this study a positive band for both the target DNA
(850 bp) and the IAC (240 bp) was simultaneously observed when the IAC was
added to the PCR mixture at a concentration of 0.72 pg.ml-1.
Four of 22 South African food products tested positive for the presence of
E. sakazakii, using both the PCR and recommended culturing methods. The PCR
method was used successfully for the detection of E. sakazakii within three days and
thus provides a possible alternative and improvement on the recommended current
culturing methods. Other microorganisms present in the products tested included
Escherichia coli, Klebsiella pneumoniae, Raoultella terrigena (“Klebsiella terrigena”)
and Chryseomonas luteola.
Since E. sakazakii is usually present in low numbers in food products, it is
possible that these few cells are unevenly distributed in the products, making it important to take multiple samples when evaluating IFM and thereby ensuring that
even low numbers of this pathogen are detected.
Description
Thesis (Msc Food Sc (Food Science))--University of Stellenbosch, 2005.
Keywords
Dissertations -- Food science, Theses -- Food science, Enterobacter, Enterobacteriaceae, Infant formulas -- Contamination, Polymerase chain reaction, Infant formula industry -- South Africa