Escherichia coli that cause diarrhoeal disease are classified into virotypes based on virulence
properties, mechanisms of pathogenicity, clinical syndromes and distinct O:H serotypes.
These virotypes include enteropathogenic E. coli (EPEC), enteroinvasive E. coli (EIEC),
enterotoxigenic E. coli (ETEC), enteroaggregative E. coli (EAggEC), diffuse adhering E. coli
(DAEC) and verocytotoxin-producing E. coli (VTEC) also known as Shiga toxin -producing
E. coli (STEC) which includes the most virulent subgroup, the enterohaemorrhagic E. coli
(EHEC). The most predominant EHEC is E. coli O157:H7. Cattle are the principal reservoir
for diarrhoeagenic E. coli (DEC) and ground beef products are the major vehicle for their
transmission.
The aim of this study was to determine the incidence of DEC in minced beef and boerewors
and to investigate the growth, survival and thermal inactivation of E. coli O157:H7 in
boerewors. In the first part of this study, a survey was conducted on 30% of butcheries in the
Bloemfontein District and isolated virotypes were identified by serotyping. More minced
beef samples were positive for DEC (38.10%) compared to boerewors samples (28.57%).
Enteropathogenic E. coli were the most frequently isolated virotype while VTEC were the
most virulent virotype recovered from both samples, hence highlighting the potential of
ground meat products as vehicles of transmission of DEC. An enrichment step enabled
optimal recovery of DEC on chromocult⢠chromogenic agar (Merck 1.10426).
In the second part of this study, boerewors with and without sulphur dioxide preservative
were manufactured following a typical commercial procedure and inoculated with E. coli
O157:H7 at low (3.5 log cfu/g) and high (7.5 log cfu/g) inoculum size, and stored at 0 o C, 4
o C and 10 o C followed by evaluation of growth and survival every 48 hours for 10 days.
Boerewors with preservative had significantly lower recoveries compared to boerewors
without preservative at all the three storage temperatures. The low and high inocula with
preservative had significant (p<0.001) reductions in recoveries at 0 o C, declining to below detectable limits at days 8 and 10 respectively. At 4 o C, the low and high inocula with
preservative recoveries declined significantly (p<0.001) to below detectable limits and to
1.01 log cfu/g respectively at day 10. At 10 o C, significant (p<0.001) increases of 1.85 log
cfu/g and 2.35 log cfu/g respectively were observed from day 0 to day 10. At 0 o C, the low
and high inocula without preservative treatments had declines in recoveries of 1.21 log cfu/g
and 1.45 log cfu/g respectively. Insignificant (p<0.001) increases of 0.19 log cfu/g and 0.26
log cfu/g respectively were noted at 4 o C while significant (p<0.001) increases of 1.97 log
cfu/g and 1.84 log cfu/g respectively were noted at 10 o C from day 0 to day 10. The
combination of sulphur dioxide preservative and low temperature (0 o C and 4 o C)
demonstrated the best efficacy against the sur vival of E. coli O157:H7.
It was established that thermal inactivation end point temperatures of E. coli O157:H7
inoculated into boerewors with preservative at 7.00 log cfu/g, was 60 minutes at 60 o C, 80
seconds at 65 o C and 60 seconds at 70 o C. This study demonstrated that E. coli O157:H7 can
survive in boerewors with and without preservative, stored at 0 o C, 4 o C and 10 o C and is
more sensitive to heat treatment at 70 o C.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:ufs/oai:etd.uovs.ac.za:etd-09292005-151550 |
| Date | 29 September 2005 |
| Creators | Charimba, George |
| Contributors | Dr CJ Hugo, Dr A Hugo |
| Publisher | University of the Free State |
| Source Sets | South African National ETD Portal |
| Language | en-uk |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | http://etd.uovs.ac.za//theses/available/etd-09292005-151550/restricted/ |
| Rights | unrestricted, I hereby certify that, if appropriate, I have obtained and attached hereto a written permission statement from the owner(s) of each third party copyrighted matter to be included in my thesis, dissertation, or project report, allowing distribution as specified below. I certify that the version I submitted is the same as that approved by my advisory committee. I hereby grant to University Free State or its agents the non-exclusive license to archive and make accessible, under the conditions specified below, my thesis, dissertation, or project report in whole or in part in all forms of media, now or hereafter known. I retain all other ownership rights to the copyright of the thesis, dissertation or project report. I also retain the right to use in future works (such as articles or books) all or part of this thesis, dissertation, or project report. |
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