The Counts Of Bacteria And Occurrence Of Pathogens

Project and Seminar Material for Biology

The Counts Of Bacteria And Occurrence Of Pathogens

Chapter One

1.0 Introduction

Milk is a complex biological food and by its nature, a good growth medium for many microorganisms, of which bacteria is prominent. Because of the specific production, it is impossible to avoid contamination of milk with microorganisms (bacteria). Therefore, the bacteriological quality of milk is a major factor in determining its safety for consumption (Rojeli, 2003). Bacterial contamination of raw milk can originate from different sources – air, milking equipment, feed, soil, faeces, and grasses ( Coorevits et al., 2008). The number and type of microorganisms in milk immediately after by factors such as animals and equipment cleanliness, season, and animal health (Rojeli, 2003). It is hypothesized that difference in feeding and housing strategies of cows may affect the bacteriological quality of milk (Coorevit et al., 2008). Rinsing water for milking machine and milking equipment washing also involve some of the reasons for for the presence of higher number of microorganisms including pathogen in raw milk (Bramley, 1990).

The condition during storage and transport in refrigerated tanks cause the raw milk micro-biota from predominantly gram’s negative organisms as they grow. Gram’s negative bacteria usually account for more than 90% of the bacterial population in cold raw milk that has been stored. The gram’s negative flora is composed mainly of psychotropic species of Pseudomonas, Achromobacter, Aeromonas, Serratia, Alcaligenes, Chromobacterium, Flavobacterium and Enterobacter (Martins et al., 2006). Organisms unable to grow at refrigeration temperature remains at low number, implying that temperature is an important factor contributing to the prevalence and proliferation of specific organisms in milk. Pasteurization in raw milk is effective in eliminating all, but not thermodeuric organisms of the genera Mycobacterium, Micrococcus, Streptococcus, Lactobacillus, Bacillus, Clostridium, the Coryneforms and occasionally, some gram’s negative rods (Jay,1996).Psychotrophs can grow at refrigeration temperature below 7 degrees Celsius, produces enzymes, toxins and other metabolites. most of these bacteria produces extra-cellular ,proteolytic and lipolytic enzymes that are secreted into the milk –many of these enzymes are not inactivated by pasteurizing at 72 degree Celsius for 15 seconds or by ultra- high temperature treatment (Griffith et al., 1981). Pasteurization cannot guarantee the absence of microorganisms when present in large number in raw milk or due to pasteurization contamination (Salmeron et al., 2002).The contamination of milk and some milk products are due to the production of enzymes/toxins by some bacteria like Staphylococcus aureus and Lactobacillus spp. They can also produce some metabolite like short chain fatty acid and other compound with known toxic effect against undesired microorganisms in the intestinal tracts.

1.1 Background Information

Cow‘s milk has long been consumed as highly nutritious and valuable human food and is consumed by millions daily in a variety of products. Its nutrient composition makes it an ideal medium for bacterial growth and therefore can be considered as one of the perishable agricultural products. Many contaminating organisms only spoil the product, thereby reducing the shelf-life. Some, such as the lactic acid bacteria (LAB) are useful in the milk processing, causing milk to sour naturally. Other bacteria present are pathogenic to man and can transmit disease if the milk is consumed untreated. Unlike meat and meat products,milk is less likely to be subjected to any subsequent heating by the consumer before consumption. Therefore, contaminated milk is potentially more dangerous (Steele et al., 1997).

Raw milk of good hygienic quality is necessary to produce milk product of good quality and adequate shelf-life, and to provide a safe, sound and wholesome food for the consumers. The liquid nature of milk ensables its contact with some type of equipment or surface from the time it was removed from the cow till the time it is consumed. A freshly drawn milk from a disease free udder contains less number of bacteria (500 – 1000 per ml),which is derived from the organisms colonizing the canal. Milk’s quality starts deterioration immediately after milking, due to bacteria entering the milk from a wide variety of source. These bacteria may originate from air, water, soil, the Milker’s hand and faeces that collects on the skin of the cow. Once microorganisms get into the milk, they start multiplying rapidly. Microbial growth can be controlled by cooling the milk, as most microorganisms’ reproduces slowly colder environment. Pathogenic bacteria like Staphylococcus aureus, Escherichia coli and Campylobacter spp. may also be found in raw milk as a direct consequence of clinical or sub-clinical mastitis (Giesecke et al., 1994).

1.2 Statement of Problem

Raw milk is an important vehicle for the transmission of milk borne pathogen to humans,as can easily be contaminated during milking and handling (Addo et al., 2011). Being highly perishable commodity and highly nutritious food,milk serves as an ideal medium for the growth and multiplication of various bacteria (Parekh and Subhash, 2008). Poor or improper handling of milk can exert both a public and economic constraints, thus requiring hygienic vigilance throughout the milk value chain (Swalan Schooman, 2011). Although fresh milk from cow may possess germicidal or bacteriostatic properties, growth of pathogenic bacteria is inevitable unless it is processed and well stored. The main health concern associated with milk include tuberculosis caused by Mycobacterium bovis and M. tuberculosis; and brucellosis caused by Brucella spp.(Ai-tahiri,2005). In some parts of the world including developing countries like Nigeria, milk is still a still a significant source of these infections. It also applies in developed countries. For example, it was reported in England and Wales that there are yearly outbreak of food poisoning from Salmonella spp. and Campylobacter jejuni in milk not receiving heat treatment or imperfectly pasteurized. Therefore, bacteriological assessment of milk essential to establish the degree of contamination and recommend some corrective measures (Parek and Subhash, 2008).

1.3 Aim and Objective of the Study


The aim of the study is to determine the counts of bacteria and occurrence of pathogens.

  1. To assess the bacterial quality of cow’s raw milk obtained from herdsmen in the university of Abuja.
  2. To evaluate the degree of bacteria contamination of cow’s raw milk

1.4 Hypothesis:

H0: There is no difference in bacterial quality 0f cow’s raw milk collected at different milking point at the University of Abuja


H1: There is difference in bacterial quality of cow’s raw milk collected at different milking point at the University of Abuja.

1.5 Justification of the Study

It is obvious that milk is part of human diet that is consumed by many. Due to its nutritional value, it serves as a medium for the growth of bacteria. Hence, contamination can result 0n the basis of several factors, during and after the milking process. Therefore, it is essential that the bacteriological quality of milk be determined and known, to cut down the risk of its infection especially on human.

1.6 Limitation of the Study:

Though there are several bacteriological and biochemical test that can be employed in determining the quality of cow’s raw milk, the scope of this study is limited to the use of a few selected ones

The Counts Of Bacteria And Occurrence Of Pathogens

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The Counts Of Bacteria And Occurrence Of Pathogens


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