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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