Prevalence Of Escherichia Coli O157:H7, Listeria Monocytogenes And Staphylococcus Aureus In Ready-To-Eat Fresh Milk And Fresh Milk Products Inmilk Markets In Accra
Date
2017-07
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University of Ghana
Abstract
The fresh milk industry in Ghana is a source of livelihood for a significant proportion of smallscale
farming households in the country. However, lack of consumer food safety assurance of fresh
milk and fresh milk products have limited business growth of this sector. Reports on lack of
cooling infrastructure, unhygienic handling, inadequate processing and post-process
contamination contributes to microbial spoilage in dairy products leading to loss of large volumes
of milk in developing countries.
This study therefore sought to assess the microbiological quality and hygiene of raw milk from
assemblers and fresh milk products from five informal milk markets. This was accomplished by
subjecting randomly sampled fresh milk and fresh milk products (22 brukina, 18 boiled milk, 15
raw milk, 8 nunu, 24 yoghurt, 17 raw wagashi and 13 fried wagashi) to standard cultural methods
of microbial assessments. Products were tested for concentration of index and hygiene indicators
including total coliforms, fecal coliforms, Escherichia coli and Staphylococci. Confirmation of
suspected pathogens was done with biochemical tests, API 20E and Matrix-Assisted Laser
Desorption/Ionization Time Of Flight (MADLI-TOF) mass spectrometry. Quantitative
Polymerase Chain Reaction (qPCR) was done to confirm the prevalence of E. coli O157:H7,
Listeria monocytogenes and Staphylococcus aureus in the ready-to-eat (RTE) dairy products
tested. Mean counts were reported in Log cfu/g or Log cfu/ml using Microsoft Excel (2016).
Significant differences between total coliforms, fecal coliforms, E. coli and Staphylococci counts
was determined using Analysis of Variance (ANOVA) with a P value of <0.05 using IBM SPSS
version 21.
The study in general identified insufficient heat treatment used to pasteurize the dairy products,
poor hygienic practices and possible post-process contamination as reasons for the poor
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microbiological quality of the samples tested. The quality of the raw milk had a direct effect on
the quality of the final milk products. There was statistical similarity (P≤0.05) in the coliform
content between raw milk (3.64± 2.56 Log cfu/ml) and boiled milk (3.61± 3.06 Log cfu/ml) which
signified insufficient heat treatment used in processing the boiled milk. The study identified a
general high prevalence of coliform contamination (67%), with raw wagashi having the highest
coliform and Escherichia coli concentrations of 5.90± 3.79 Log cfu/g and 2.61± 2.65 Log cfu/g
respectively. Fried wagashi emerged as the only product which was safe from coliform
contamination. The staphylococci concentration of the products analyzed were within the
acceptable (3.0 Log cfu/ml/g) limits. L. monocytogenes was not detected in any of the products
analyzed using cultural methods. Results from qPCR indicated high prevalence of E. coli O157:H7
in boiled milk (66%), nunu (37%) and brukina (14%). Boiled milk had a 42.8% S. aureus
prevalence and 11.11% prevalence of L. monocytogenes. The results from the viability tests
suggests shortfalls in the processing of the RTE fresh milk products in the local milk markets. The
presence of significant pathogens in the product has implications on food security with respect to
food safety.
Overall microbiological analysis conducted suggests a poor quality of RTE fresh milk products
sold in the informal markets in Accra. This indicates an urgent need for intervention measures with
highlights on effective pasteurization of raw milk and training of the various stakeholders in the
dairy value chain on hygienic handling to prevent post-process contamination.
Description
Thesis (MPhil)
Keywords
Escherichia Coli O157:H7, Listeria Monocytogenes, Staphylococcus Aureus, Ready-To-Eat Fresh Milk, Fresh Milk Products, Inmilk Markets, Accra, Ghana