Isolation and identification of listeria species along the milk value chain in one region of Tanzania
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Date
2016
Journal Title
Journal ISSN
Volume Title
Publisher
Tanzania Livestock Research Institute
Abstract
Introduction
The genus Listeria contains gram positive, non-spore forming, catalase-positive,
oxidase-negative and facultative anaerobic bacteria. Two species are pathogenic
of which L. monocytogenes represents the only pathogen of public and
veterinary health significance and L. ivanovii is usually restricted to causing
disease in ruminants. L. monocytogenes causes large outbreaks of Listeriosis in
humans, with a mortality rate of 9 – 44%. Most cases are foodborne related and
consumption of unpasteurised milk and dairy products is the major means of
zoonotic transmission. Currently, there is no information in available literature
on the presence of Listeria along the milk value chain in Tanzania. In this study,
the awareness of milk contamination was evaluated, total plate count (TPC) was
quantified and isolation of Listeria species was attempted along the milk value
chain in two districts of Tanga region in Tanzania.
Methods
Study sites included five villages in Handeni district and five villages in Lushoto
district. In total, 114 respondents were interviewed on awareness and
strategies for solving the problem of milk contamination. Then, raw milk
samples were aseptically collected from each of the 114 respondents for
laboratory analyses using the standard ISO procedures for food microbial
analyses — Horizontal methods. Four tests i.e. haemolysis on a sheep blood
agar, CAMP, oxidase and Listeria test kit were carried out to confirm the
presence of L. monocytogenes and other Listeria spp. in test samples against
control cultures. Data were analysed for descriptive statistics and Chi-square
using the Statistical Package for Social Sciences (SPSS) version 17.0. TPC values
were analysed against independent variables using the General Linear Models
(GLM) procedures of the Statistical Analysis System (SAS) version 9.1 for
Windows.
Survey showed poor hygienic practices by the majority of
actors. Most of the farmers were skipping most of the
important safe hand milking steps. Few (11.8%) households
were keeping cattle in well-designed and clean shelters. Only,
12.9% of households and 11.1% of restaurateurs were using
Aluminium vessels/stainless steel containers for milk handling.
Furthermore, very few cooling facilities were observed along
the milk value chain as presented in Table 2.
Results
About 90 percent of all raw milk samples processed showed TPC above
standard acceptable in the Eastern Africa countries (EAC) of 2.0x10 5 CFU/ml
(Grade 2). Also, there was more contamination in milk samples obtained from
the household farms than those which were collected from the milk suppliers
and in the extensive farming system than in the intensive system (P < 0.05).
Three Listeria species namely L. innocua (11.4%), L. ivanovii (1.7%) and L.
monocytogenes (42.1%) were identified. L. monocytogenes were isolated and
identified as the common contaminants in milk along the value chain in the
study region (Table 1).
Conclusion
Poor bacteriological quality of milk indicates poor animal
husbandry practices and poor milk handling practices. Presence
of L. monocytogenes in milk provides evidence on the microbial
status of milk in the Tanzanian milk value chain and insights into
the magnitude and public awareness on the health risks
associated with consumption of raw milk. To ensure milk safety,
the awareness of actors must be improved through training on
animal husbandry practices and public education on general
hygienic practices in milk. Also, Sector policies, organizational
structures and support services must be well concentrated to
stimulate dairy development.
Description
Isolation and Identification of Listeria Species along the Milk Value Chain in one
region of Tanzania
Keywords
Listeria species, Milk value chain, L. monocytogenes, L. ivanovii, Dairy products