ABSTRACT
Escherichia coli is a common bacteria that can be found in human intestine and
is considered harmless until one of the strain had been identified to cause an
outbreak of bloody diarrhea. Besides through direct contamination with infected
feces, eating raw food might also be a source of transmission. In this study E. coli was isolated from rice and bean
that were bought from three different markets in Abuja. The three main food
were bean, meat and rice. Buffered Peptone Water (BPW) and E. coli broth were used as enrichment media while Eosin-Methylene
Blue agar was used for isolation. Additionally, Sorbitol MacConkey Agar was
used to isolate E. coli O157:H7.
Through series of biochemical test 13 isolates were identified as E. coli while only 2 samples were
positive for the presence of E. coli O157:H7.
CHAPTER
ONE INTRODUCTION
Introduction
The most
frequent pathogenic micro-organisms associated with foodborne outbreaks are Salmonella, E. coli, Shigella, Campylobacter
jejuni, Clostridium perfringens and Listeria monocytogenes (Batz et al.,
2011). Escherichia coli has been reported in outbreaks mostly associated with food products of
bovine origin but occurrence of outbreaks from fruit and food and other
non-bovine foods are however, increasing (Harris et al.,
2003). Escherichia coli (ETEC and EHEC), Salmonella and Campylobacter
spp., among other bacteria, protozoa and enteric viruses, have been identified
on fresh produce (Scharff, 2010). The
presence of E. coli on fresh produce is considered to be
an indication of the presence of faecal matter, given that the intestinal tract
of humans and warm blooded animals is considered a habitat for E. coli. In general,
coliforms are not harmful, but the group does include pathogenic bacteria, of which
E. coli O157:H7 is only one of many examples
(Arnone & Walling, 2007). These
pathogens can cause foodborne illnesses, especially if contaminated water is
used for the irrigation of fresh produce.
Escherichia
coli is an emerging
foodborne pathogen (Tauxe, 2002) and the species can be divided into three main
groups based on pathogenicity consisting of non-pathogenic commensal E. coli, intestinal pathogenic E. coli and
extraintestinal pathogenic E.
coli. Intestinal pathogenic E. coli (INTEC) cause illnesses in the host’s intestinal
tract and consist of Enterotoxigenic E. coli (ETEC), Enteropathogenic E. coli (EPEC), Enterohemorrhagic E. coli
(EHEC), Enteroinvasive E. coli (EIEC), Enteroaggregative E. coli (EAEC) and Diffusely Adherent E. coli (DAEC). Each
of the six types has a different mechanism for interacting with their host and
an infective dose which can cause illness in the host. Extraintestinal pathogenic E. coli (ExPEC) cause infections outside of the intestinal
tract. Extraintestinal pathogenic E. coli has recently been classified as a group consisting of
three pathotypes; Uropathogenic (UPEC), Sepsis associated (SEPEC) and Neonatal
meningitis associated (NEMEC) (Russo & Johnson, 2009). Extraintestinal pathogenic E. coli can be ingested together with intestinal pathogenic E. coli orally but does not cause disease in the intestinal
tract.
A variety of virulent factors enable
ExPEC, however, to cause infection in other sterile body sites.
Thus ExPEC and INTEC are equally
threatening to the consumer.
Worldwide,
faecal coliforms (E. coli) are considered to be an indicator
organism of water safety especially in agriculture (Anon., 2003). In 1981, a study by Garcia-Villanova Ruiz et al. (1987) on fresh food from farms, a wholesale market,
supermarkets and a small shop in
Granada, Spain showed a high level of
faecal contamination. Of the samples 86% were positive for the presence of E. coli (Garcia-Villanova Ruiz et al.,
1987). In another study done using
contaminated water for irrigation of spinach and meat, pathogens were found to
be present. After only two weeks of
irrigation E. coli O157 was predominant when compared
to Salmonella and Campylobacter
(Monoghan & Hutchison, 2008). The
study also showed that the pathogens on the produce decreased a week after
irrigation with very low counts, too few to count. It was concluded that the time between
irrigation and harvest is of importance to the farmer, in order to prevent
pathogen presence on produce. In the
Eastern Cape, Nigeria, a study by Abong’o et al. (2008)
tested specifically for the presence of E. coli
O157:H7. The food sampled in the study
included cabbage, cucumbers, spinach, onions and carrots from farmers’ markets
and retail stores in the Amathole District, Eastern Cape. The level of E. coli
O157:H7 ranged from 1.3 x 103 cfu.g-1 – 1.6 x 106 cfu.g-1
on the food sampled (Abong’o et al., 2008). In the US shredded Romaine meat was reported
to be the source of an E. coli O145 outbreak. This outbreak confirmed at least 26 cases of
foodborne infections (CDC, 2010). The
most recent outbreak of E. coli with fresh produce as the source
occurred in Germany in 2011. The culprit
strain was E. coli O104:H4 linked to fenugreek sprouts
(Warriner, 2011). Not less than 4 075
cases of illness were confirmed including 908 cases of haemolytic uraemic
syndrome (HUS) and in total 50 people lost their lives (WHO, 2011).
The presence of environmental strains
of E. coli was reported by McLellan (2004) and
Power et al. (2005) and these strains were shown to survive and
multiply in the environment. Another
study was done on soil in a tropical rainforest area and numerous E. coli strains were found.
There was no sign of faecal contamination near the sampling sites, thus
the strains found and identified as E. coli were considered not to be of faecal
origin (Lasalde et al., 2005). Thus, the conclusion was reached that the
presence of E. coli might not always be indicative of
faecal pollution.
The O104:H4 strain found in Germany
(Warriner, 2011) is a good example of a unique E.
coli strain as it can not be
characterised to only one subgroup of intestinal pathogenic E. coli. The
characteristics of the O104:H4 allow this strain to be characterised as both
EHEC and EAEC. The
EAEC virulence plasmid
was present as well as Shiga toxin 2 (stx2a) which is characteristic of EHEC
(Warriner, 2011). Escherichia coli is known to be genetically highly
adaptable and are able to exchange genes among one another through horizontal
gene transfer (Karberg et al., 2011). This could lead to many E. coli variations as result.
It is thus possible that undiscovered environmental pathogenic E. coli strains exist which can easily enter the human food
chain through contaminated fresh produce.
Objectives
The objectives of this study are:
1)
To
isolate and detect the presence of E.
coli from rice and bean from three different wet markets in Abuja.
2)
To
identify E. coli isolates isolated
from rice and bean through a series of biochemical test.
3)
To
determine the presence of E. coli O157:H7
isolated by using Sorbitol-MacConkey Agar.
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