It is very important to carry out a microbial examination of a food. Many pathogenic bacteria are transmitted through food. The detection of microbiological quality of food is an essential part for food safety. The quality and safety of foods is important in human health (Adams & Moss 2000).
There are several different methods for microbial examination of a food. In this experiment, the methods are used, included:
1. Plate count: It is the most common method of measuring bacterial populations. One of the advantages of the plate count is that it counts the viable cells. There are two methods of plate count (Tortora, Funk & Case 2010):
A pour plate method: This method carries out by introducing a dilution of bacterial cell suspension into a petri dish. Then, the melted agar is added to the sample. The colonies will grow within the nutrient agar and on the surface of the agar plate. This method is not suitable for sensitive organisms (Tortora, Funk & Case 2010).
A spread plate method: This method carries out by introducing a dilution of bacterial cell suspension into a solidified agar medium. The colonies will grow on the surface of the medium (Tortora, Funk & Case 2010). 2. E.coli/ coliform petrifilm plates: It is a new method of performing count on bacteria. The method based on detecting the presence of coliforms in a food sample. The coliforms refer to aerobic or facultatively anaerobic bacteria that are able to ferment lactose and produce gas. The presence of the coliforms in the food sample indicates a fecal contamination. An example of a predominant fecal coliform is E.coli. E.coli is normally found in the large intestine of animals as a normal flora. It is not pathogenic under normal condition. It can be pathogenic if it is present in a large amount in a food sample (Tortora, Funk & Case 2010).
An enzyme indicator and bile are incorporated into E.coli/ coliform petrifilm plates (Water PDF). The bile is used to ferment lactose and it inhibits the growth of gram positive bacteria (Adams & Moss 2000). Also, an indicator of an enzyme called glucuronidase is incorporated in the plate. If the bacteria produce this enzyme, the colonies will turn blue. E.coli makes glucuronidase and produce CO2 which will be indicated as gas bubbles (Reynolds 2011). 3- APC petrifilm plates: This type of plates is designed to determine total aerobic bacteria populations. The plates contain indicator dye that colors the colonies. The colonies will appear red (Reynolds 2011).
In this experiment, the meat will be analyzed for various foodborne bacteria (Bobbitt 2012). The meat was taken from the muscle of beef. The muscles are normally sterile; this means that the bacteria are absent. However, other parts of the animals such as skin, intestines and respiratory tract contain bacteria. The bacteria live in these parts of the body as a normal flora (FAO 2012).
The meat became contaminated through (FAO 2012):