CHAPTER ONE
1.0 INTRODUCTION
Bacillus cereus is the cause of two kinds of foodborne diseases, an emetic (vomiting) intoxication due to the ingestion of a toxin (cereulide) pre-formed in the food and a diarrhoeal infection due to the ingestion of bacterial cells/spores which produce enterotoxins in the small intestine (Lubenau .C. 1906). Other Bacillus spp, Bacillus subtilis, Bacillus licheniformis, Bacillus pumilus have more rarely been identified as agents of foodborne diseases characterized by diarrhoea and/or vomiting. Emetic intoxication is caused by a very homogeneous group of strains of Bacillus cereus identified by their ability to produce cereulide. In contrast, Bacillus cereus strains able to cause diarrhoea are not easy to identify because the mechanisms leading to infection are complex and diverse (Kramer, .J.M. and R.J. Gilbert 1989). Very little is known on the virulence mechanisms of other Bacillus spp and therefore it is not possible to identify the strains able to cause foodborne poisoning. In most instances, foodborne diseases caused by Bacillus cereus were associated with 5 log to 8 log cells/spores per g of the food vehicle. However, in some outbreaks, lower numbers in the food (3 – 4 log per g) were reported. Foodborne poisoning caused by other Bacillus spp. has always been linked to high numbers of cells/spores in the food vehicle (equal or more to 6 log per g). Bacillus cereus is ubiquitous and low numbers of its spores, too low to cause
foodborne poisoning, can be found in a wide range of foodstuffs. Spores can germinate and multiply in humid, low acid foods, from 45°C to 55°C (Notermans et al. 1997). However, strains able to multiply below 7°C, and strains able to multiply above 45°C, are not the most common. Emetic Bacillus cereus are presumably unable to grow and produce their toxin cereulide below 10°C, or in the absence of oxygen. Other Bacillus spp. involved in foodborne poisoning cases are also frequent causes of food spoilage. Almost all kind of foods have been implicated in B. cereus foodborne poisoning. However, a majority of reported outbreaks were linked to the consumption of heat treated foods and frequently occurred in restaurant and catering establishments. Failure in refrigeration was frequently suspected. Cooked dishes containing pasta or rice were the main, but not the only, foods implicated in emetic intoxications. The major control measures are to control temperature and to establish Hazard Analysis and Critical Control Point (HACCP) system. Only heat treatments used for canning of low acid foods will ensure a complete destruction of spores of Bacillus cereus. The number of spores in other processed foods must be kept as low as possible by proper cleaning and disinfection of equipment. Rapid cooling is necessary to prevent germination and growth of Bacillus cereus spores. Low pH (below 4.5) would inhibit Bacillus cereus. In other cases, refrigeration below 4°C is necessary to prevent growth of all types of Bacillus cereus, including psychotrophic strains. However, below 10°C, lag time and generation times are significantly increased, particularly whenever other factors (i.e. pH, nutrient content of the food) are not optimum for Bacillus cereus. This should be verified by microbiological testing.
1.1 BACKGROUND
Bacillus cereus is an important cause of food-borne illnesses in humans. It is a ubiquitous bacterium in the environment, and it can thus be present in a wide range of different foodstuffs. Food-borne outbreaks caused by B. cereus have been associated with many types of foodstuffs including both food of animal and plant origin. Also some other Bacillus species, such as B. licheniformis and B. subtilis, have occasionally been reported as a cause of food-borne illnesses in humans.
Several Member States of Food Control have in their national legislation or guidelines, criteria for B. cereus in various foodstuffs. However, current state community legislation does not include any specific provisions on B. cereus or other B. sp. in foodstuffs. Community legislation on food hygiene is currently under revision. In this framework are vision of the microbiological criteria in community legislation is taking place. The revised hygiene legislation provides also, among other things, a legal basis to set specific temperature control requirements for foodstuffs (tuwo) when appropriate.
1.2 JUSTIFICATION
Bacillus cereus spores can be found widely in nature including samples of dust, dirt, cereal crops and water. It is a common contaminant of raw agricultural commodities. Cereal grains such as rice and corn which are raw materials for tuwo are commonly associated with B. cereus toxin outbreak. Due to the preparation process there have been several reported outbreaks. Bacillus foodborne illness occur as a result of the survival of bacterial endospore when food is improperly cooked. The knowledge obtained from this study will enable the appreciation of appropriate cooking temperature in tuwo preparation and help to determine the possibility of the survival of bacterial Bacillus cereus during the processing and prior to the consumption of tuwo, therefore enabling food handlers to identify critical control points in tuwo processing for control rectification.
1.3 AIM OF STUDY
To investigate the incidence of Bacillus cereus from the preparation to consumption of tuwo.
1.4 OBJECTIVES
To obtain the total microbial counts from tuwo samples from different food vendors in Giri village, FCT, Nigeria.
To screen samples for the presence of Bacillus cereus from flour to the final tuwo product.
