MICROBIAL EVALUATION OF RAW MILK FROM DAIRY FARM

ABSTRACT

Milk is an important source of nutrient to humans and animals. It is meant to be the first and the only food for the offspring of mammals as it is capable to serve as food. This study evaluated the microbial quality of raw milk from dairy farm. About three raw milk samples were collected from Fulani cattle settlement, Umuahia, Abia State. The samples were analyzed using the microbiological techniques for isolation and identification of isolates.  The microbial load of the samples ranged from 8.2x105 CFU/ml to 6.0 x 105 CFU/ml. About five (5) bacterial genera were isolated which comprised of 3 (25%) Lactobacillus spp., 3 (25%) Listeria spp., 3 (25%) Salmonella spp., 2 (16.7%) Proteus spp. And 1 (8.3%) The presence of bacteria responsible for intoxication such as Staphylococcus aureus may be a public health problem if no precaution is taken against this contamination.

TABLE OF CONTENTS

Title page                                                                                                                    i

Certification                                                                                                               ii

Dedication                                                                                                                  iii

Acknowledgment                                                                                                       iv

Table of contents                                                                                                        v

List of tables                                                                                                               vii

Abstract                                                                                                                      viii

CHAPTER ONE

1.0       Introduction                                                                                                    1         

1.1       Aims and objectives of the study                                                                   5

CHAPTER TWO

2.0       Literature review                                                                                            6

2.1       Definition and composition of milk                                                               6

2.2       General overview of milk production and safety in a dairy farm                6

2.3       Source of microbial contamination of milk                                                   7

2.4       Milkborne infections and pathogenic micro-organisms                                 8

2.5       Hygiene, handling and microbial evaluation of raw milk                              8

2.6       Prevention and control of microbial contamination of milk                          9

2.7       Antimicrobial residues, bacterial resistance and their effects

            to animals and humans                                                                                   9

2.8       Milk-borne infections and pathogenic microorganisms                                 11

2.9       Nigerian policy on food hygiene and safety                                                   13

2.9.1    National legislations                                                                                       13

2.10     Dairy development in Nigeria                                                                        14

CHAPTER THREE

3.0       Materials and methods                                                                                    16

3.1       Study area and sample collection                                                                   16

3.2       Sampling of milk/size                                                                                     16

3.3       Milk sample handling                                                                                     16

3.4       Media preparation                                                                                          16

3.5       Inoculation and incubation of the sample                                                       17

3.6       Identification and characterization of isolates                                                17

3.6.1    Gram staining technique                                                                                17

3.7       Biochemical tests                                                                                            18

3.7.1    Catalase test                                                                                                    18

3.7.2    Oxidase test                                                                                                    18

3.7.3    Indole test                                                                                                       18

3.7.4    Citrate utilization test                                                                                     19

3.7.5    Motility test                                                                                                    19

3.7.6    Coagulase test                                                                                                 19

CHAPTER FOUR

4.0       Results                                                                                                            20

CHAPTER FIVE

5.0       Discussion                                                                                                       24

5.1       Conclusion                                                                                                      25

5.2       Recommendation                                                                                            26

REFERENCES

LIST OF TABLES

TABLES                                TITLE                                    PAGES

1                                Characterization and Identification of the bacterial isolates                                    

from the raw milk                                                                                      21

 2                     Total heterotrophic bacterial count (THBC)                                             22

 3                     Prevalence of bacteria isolated from raw milk                                          23

CHAPTER ONE

1.0       INTRODUCTION

Milk is an important source of nutrients to human and animals. It is meant to be the first and the only food for the offspring of mammals as is almost complete food (Pandey and Voskuil, 2011). Almost 87% of milk is composed of water and the remaining part comprises total solids (carbohydrates, fat, proteins and minerals) contained in a balanced form and digestible elements for building and maintaining the human and animal body. Other milk ingredients include immuno-globulins which protect the newly born against a number of diseases (Pandey and Voskuil, 2011). Milk has a complex biochemical composition and its high water activity and nutritional value serves as an excellent medium for growth and multiplication of many kinds of microorganisms when suitable conditions exists (Parekh and Subhash, 2008).

Milk meant for human consumption must be free from any pathogenic organisms (Bertu et al., 2010). Microbial contamination in milk may cause milk-borne diseases to humans while others are known to cause milk spoilage. Many milk-borne epidemics of human diseases are spread through milk contamination. Sources of microbial contamination in milk include primary microbial contamination from the infected or sick lactating animal. The secondary causes of microbial contamination occurs along the milk value chain which may include contamination during milking by milkers, milk handlers, unsanitary utensils and/or milking equipments and water supplies used in sanitary activities. Other secondary sources of microbial contamination occur during milk handling, transportation and storage. There is tertiary microbial contamination which occurs mainly due to re-contamination of milk after being processed due to unhygienic conditions and/or poor or improper handling and storage of milk during consumption (Parekh and Subhash, 2008). The quality of milk is determined by its composition and overall hygiene. However, consumption of contaminated food like milk may lead to food-borne diseases (FBDs).

The WHO has described FBDs as illnesses of an infectious or toxic nature caused by, or thought to have been caused by the consumption of food and water (Adams and Motarjemi, 1999), which conceivably represents the most common health problem of recent days, thus reducing significantly economic productivity (Mukhola, 2000). It is estimated that up to a third of people in developed countries are affected by FBDs (WHO, 2009). FBDs are caused by the consumption of foods exposed to hazards that may be biological or pathogenic (e.g. viruses, bacteria, parasites), chemical (e.g. heavy metals and toxins), and others physical (e.g. glass fragments, bone chips) (Schmidt et al., 2003). Etiological information suggests that the frequency of occurrence from microbial or pathogenic origin is by far higher (WHO, 2009). According to the WHO, 62% of all human pathogens are zoonotic (Taylor et al., 2001). This is in agreement with the WHO that 75% of all emerging human diseases originate from animal reservoirs (Vallat, 2007). Consequently, animal sourced foods have been found guilty for the majority of FBDs (De Buyser et al., 2001) and incidences increase with increasing access to such foods especially without adequate hygiene, inspection for safety or satisfactory heating to kill pathogens (McCrindle, 2008).

Specifically, human may be infected with milk-borne pathogens through consumption of infected raw or unpasteurized milk and milk products (Bertu et al., 2010). Sometimes consumption of contaminated or spoiled milk and dairy products may cause milk-borne diseases in humans. Indeed, FBDs are a serious threat to people in Africa, responsible for 33-90% cases of deaths in children (Flint et al., 2005). Although milk and milk products are a minor constituent in most diets but contaminated milk are responsible for up to 90% of all dairy related diseases of humans (De Buyser et al., 2001). A study by Shirima et al. (2003) documented several pathogens resulting to milk-borne zoonotic diseases including brucellosis, tuberculosis and enterotoxaemia. The risk of infection by milk-borne zoonotic diseases is one of the reasons for public health regulations, which discourages the informal milk markets and consumption of raw or unpasteurized milk (Kang’ethe et al., 2000).

Pathogenic microorganisms commonly isolated from milk and milk products pose a serious threat to human health. Some of these pathogens include Escherichia coli, Staphylococcus aureus, Salmonella spp., Listeria moncytogens, Brucella abortus, Mycobacterium spp., Campylobacter spp., Leptospira spp., Clostridium spp., Pseudomonas aeruginosa and Proteus spp. (Shirima et al., 2003; Al-Tahiri, 2005; Donkor et al., 2007; Lei et al., 2008; AlAll et al., 2012). Raw milk is known to be a major vehicle that serves as means of transmission of these milk-borne pathogens to humans.

On the other hand, raw milk apart from being potential carrier of pathogens can also cause serious health risk to consumers due to antimicrobial residues (Omore et al., 2005; Kivaria et al., 2006a). Antibiotic residues are remnants or small amounts of antimicrobial drugs or their active metabolites which remain in milk after treating lactating cows (Shitandi, 2004; Syit, 2008). Antimicrobial agents especially antibiotics are normally used in dairy cattle for treatment and prevention of bacteria and associated infections (Syit, 2008; Nonga et al., 2010; Sharma et al., 2011). Inappropriate use of these antibiotics by small-scale livestock keepers at farm level may lead to various bacterial pathogens developing resistance to most commonly used antibiotics which in turn increases bacterial resistant to almost all existing antibiotics (Kivaria et al., 2006b; Sharma et al., 2011). The outcome of random use of antimicrobial agents in animals is expansion of antimicrobial resistant bacteria that may be transferred from animals to humans through contact, contaminated environment or milk and milk products (Syit, 2008; Sharma et al., 2011). The side effects associated with antibiotic residues in milk include the risk of allergic reactions to sensitive people, increased selection of resistant bacteria pathogens towards commonly used antibiotics for human illnesses and inhibition of starter cultures used in production of different milk products (Aboge et al., 2000; Shitandi, 2004; Kurwijila et al., 2006). Presence of antibiotic residues in milk may be the result of failure to observe the mandatory withdrawal periods, incorrect dosage levels and/or illegal or extra-label use of drugs (Syit, 2008).

Despite the existence of milk evaluation control measures and regulations at different points before processing and consumption, majority of milk such as over 75% of milk marketed in many developing regions (including East Africa) is sold raw or unpasteurized through informal channels (Bertu et al., 2010; Oliver and Murinda, 2011). Milk is consumed raw at household and/or village level especially to pastoral and agro-pastoral communities who do not believe that milk could be a potential source of human infections and they are not ready for any kind of treatment (Bertu et al., 2010). This poses health risks to consumers and the general public especially for those who consume raw or unpasteurized milk and milk products. Concerns about human health risks from the market pathways need to be addressed in the context of consumer practices, such as boiling, to reduce or eliminate potential infection by milk-borne health hazards without discouraging the markets through which the majority of smallholders’ dairies and livestock keepers sell their milk (Kang’ethe et al., 2000).

This study has quantified and identified some bacteria species that are common contaminants of milk from small-scale livestock keepers. It further attempted to establish the risk factors for microbial contamination of milk at farm level. The study further determined the susceptibility of the bacterial isolates to commonly used antibiotics in veterinary and human practices. Information that have been obtained from this study will be useful in knowing the status of microbial contamination in milk, the common species of bacteria involved and their susceptibility to antibiotics. Also the public will be enlightened and educated on the importance of knowing the microbial quality of milk they consume and this can give the evidence-based advice on the likely dangers of consuming raw or unpasteurized milk.

1.1       AIMS AND OBJECTIVES

      i.         To isolate, characterize and identify microorganisms associated with raw milk (cow).

     ii.         To access the total bacterial load of raw cow milk from farm.

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