23-08-2012, 04:19 PM
Prevalence of Some Milk Borne Bacterial Pathogens Threatening
Camel Milk Consumers in Egypt
Prevalence of Some Milk Borne Bacterial Pathogens Threatening.pdf (Size: 219.82 KB / Downloads: 46)
Abstract:
Camel milk represents the principal milk for consumers in the arid and sub-arid areas where camels
present the main animal source. Regular consumption of camel’s milk in those areas is mainly occurred in raw
state. So the present work was planned to investigate the possibility of transmission of 3 milk borne pathogens
including Salmonella spp., E. coli and Listeria monocytogenes in a total of 185 camel’s milk samples collected
from Sinai, Aswan and Sharqia Governorates. Conventional diagnosis revealed isolation and identification of
5 Salmnella spp. with special interest to presence of S. enteritidis, S. typhi S. typhimurium and S. anatum and
12 E. coli isolates, with special consideration to presence of E. coli O157:H7 and E. coli O26:H11. Two
isolates of Listeria monocytogenes had been detected. Multiplex PCR assay found to be rapid, economic and
sensitive tool for accurate detection of the three organisms concurrently. In addition, this selected multiplex
PCR assay detected virulence genes (InvA, Eae and ActA) of Salmonella spp., E. coli and Liseria
monocytogenes, respectively enhancing evaluation of the pathogenicity of these pathogenic strains present
in milk samples. Finally, it was concluded that for improving quality of raw camel’s milk, enhancing the milking
protocols and sanitizing programs associated with camel’s milk production should be carried out.
Key words: Camel milk % Listeria monocytogenes % E. coli spp. and Salmonella spp.
INTRODUCTION
Escherichia coli and it is pathogenic [6]. Contamination
Camel milk is one of the most valuable food resources the udder may be caused by salmonellae strains, which
for pastoral people in arid and semiarid areas. In the last produce many outbreaks of enteritis [7]. Listeria
years milk consumption among urban population has monocytogenes, Shiga toxin-producing E. coli (STEC) and
been increased [1, 2]. Nowadays, public health concern serotypes of Salmonella are considered as important food
associated with microbial food safety has arisen [3]. borne pathogens [8, Numerous epidemiological reports proved that, non-heat Listeria monocytogenes has been recognized as a
treated milk and raw-milk products represent the major cause of disease in humans and animals and has been
factors responsible for illnesses caused by food borne responsible for listeriosis outbreaks in past years [10, 11].
pathogens [4]. Camel milk and meat are the principal Various reports showed that Listeria spp. can be found in
animal foods in arid and semi-arid areas of the African and dairy products [12], meat and poultry [13]. Raw milk and
Asian countries [3]. FAO [5] has reported that, more than dairy products made from unpasteurized milk have been
18 million camels around the world support the survival of responsible for E. coli outbreaks including strain O157:H7
millions of people. [14, 15].
Raw camel milk may contain microorganisms The detection methods for milk borne pathogens
pathogenic for man and their source may lie either within generally involve: (a) colony isolation on selective media,
or outside the udder. Pathogenic bacteria may present in (b) use of biochemical tests and © serotyping using
raw milk as a direct consequence of udder disease. antibodies against specific bacterial antigens [15, 16].
Among the organisms commonly producing mastitis is These procedures are cumbersome and time consuming.
of raw milk by pathogenic bacteria from source external to
Global Veterinaria, 8 (1): 76-82, 2012
77
In certain cases, it takes several days to establish the Isolation of Salmonella, E. coli and L. monocytogenes:
identity of particular bacteria. Therefore, new approaches
in milk safety are needed for fast and efficient detection of
low numbers of bacteria likely to be present in milk.
Several methods were tested in recent years to facilitate
the identification of bacteria in foods.
Molecular techniques, such as PCR, have been used
extensively for several years for identification and
characterization of bacteria in food samples including
meat and dairy products [17, 18]. However, these assays
used selective enrichment techniques to recover bacteria
in food samples and they take 48-72 hrs before the
identity of bacteria can be established.
The detection of pathogenic bacteria is a fundamental
objective of food microbiology ensuring food quality.
Regarding this, PCR technology has successfully
shortened analysis time and has been widely applied for
the detection of food borne pathogens [19]. Several of
these PCR- based methods were developed for the
detection of L. monocytogenes involving a pre-enrichment
step [20, 21].
E. coli frequently contaminates food and it is a
good indicator of fecal pollution [25-27]. Presence of
E. coli in milk products indicates the presence of
enteropathogenic microorganisms, which constitute a
public health hazard. Enteropathogenic E. coli can cause
severe diarrhea and vomiting in infants and young
children [28].
Salmonella is one of the main causes of food borne
diseases worldwide, in humans and animals [29]. The
infective dose of Salmonella can be as low as 15 to 20
cells, depending upon age and health of host. Although
most outbreaks are associated with the consumption of
egg products, there are also reports of outbreaks related
to the consumption of milk and ice cream [30]. The study
was planned to elucidate the safety status of camel’s milk
for Egyptian consumers. The study was directed to detect
specific pathogens including Salmonella spp., E. coli
spp. and L. monocytogenes by conventional and
molecular assays.
MATERIALS AND METHODS
Collection of Samples: A total of 185 raw camel milk
samples was collected from Sinai (42 samples), Aswan
(73 samples) and Sharquia (70 samples), the samples were
transported to the laboratory in an insulated ice box
without delay until being examined.
It was carried out according to protocols described by
APHA [31].
Strains presenting a biochemical profile suggestive of
Salmonella were submitted to additional biochemical
tests [32]. The strains confirmed as Salmonella spp. in the
Central Laboratory of Egyptian Ministry of Health were
differentiated serologically into species and subspecies as
described by Popoff [33].
Colonies suspected to be E. coli were examined
according to Ewing [32] and Orskov and Orskov [34].
E. coli were selected for subculture and sero-grouping.
Determination of the EPEC sero-groups (O antigens and
H antigens) was performed by agglutination tests using
polyvalent and monovalent sera against O antigens
(O26, O55, O82, O111, O113, O119, O126, O125, O126,
O127, O128, O142 and O157) and flagellar H antigens
(H1 to H 56) according to the instructions of the
manufacturer (Bio-Rad Co and Statens Serum institute,
Copenhagen, Denmark), respectively.
For testing samples for Listeria spp., 25 ml milk of
each sample was homogenized with 225 ml of enrichment
broth (Oxoid, Hampshire, United Kingdom) for 2 min.
The enrichments were incubated at 37°C for 48 hrs. A
loopful of the enrichment culture was streaked onto
Oxford Listeria spp. selective agar (Oxoid) and incubated
for 48 hrs at 37°C and examined for typical Listeria spp.
colonies.