B-Milk-borne intoxication:
Among the milk–borne illnesses, intoxications have been extensively studied and
are of serious public health concern as they lead to frequent food-poisioning
outbreaks. Some very common types of food intoxications through milk and milk
products are discussed below.
I-Staphylococcal poisoning:
Among the very common types of food intoxication through milk and milk
products .Infection of milk by some strains of Staphylococcus aureus leads to the
elaboration of enterotoxins by them that cause gastroenteritis in human beings.
Some Scientists reported outbreaks of food poisoning due to consumption of milk
and isolated 169 strains of coagulase positive Staphylococci .
Toxins of Staphylococci:
Staphylococci are able to elaborate several metabolic products like:
1-Haemolysins(Alpha, Beta, Gamma and Detta) or Staphylolysins.
2-Leukocidin.
3-Necrotizing factor.
4-Lethal factor.
5- Enterotoxin.
6- Coagulase.
Among all these, the toxin which is of importance in Staphylococcal food
poisoning is enterotoxin. It is concluded from various food poisoning outbreaks
that there might have been an opportunity for a massive build-up of Staphylococci
in the food product at some stage. Staph. aurus is capable of growing and
producing enterotoxins in raw milk at a concentration of 10 6 cells/ml. However,
not all the strains of this organism are capable of producing enterotoxins. The toxin
production is faster in milk with low count. In poor quality milk, competition with
other organisms and changes brought about by them, e.g. acidity, depletion of
nutrients inhibit toxin production.
Nature of enterotoxins:
Staphylococcal enterotoxins are protein in nature. They are heat stable and are not
destroyed even after boiling for 15 minutes.The purified entertoxins are fluffy,
snow white materials that are hygroscopic and readily soluble in water and salt
solutions.Toxigenic strains produce six antigenically distinct enterotoxins
designated as A, B, C, D, E, and F. A and B are responsible for majority of food
poisoning outbreaks in
man. Two types of enterotoxin C from different
Staphylococcus strains have been purified and classified as C1 and C2 on the basis
of their isoelectic points (8.6 and 7 respectively). Enterotoxin F is of recent origin
and has been found to be associated with toxic shock syndrome (TSS) rather than
food poisoning.
The enterotoxins are single polypeptide chains which contain relatively large
amount of lysine, aspartic acid, glutamic acid and tyrosine. The enterotoxins are
resistant to proteolytic enzymes such as trypsin, chymotrypsin, rennin and papain.
The molecular weight of different enterotoxins are 34000d (Dalton) for A; 30000 d
for C1 & C2 respectively. A few enterotoxin-producing strains of Staph .aureus are
found in cattle, but most Staphylococcal food poisoning derives from human
carriers. At least 5x106 cfu /gm of cheese are required to produce significant
problems of food poisoning in cheese. During the aging period of cheese, the
staphylococci slowly die off, but enterotoxins produced will remain. The most
important factor in the growth of Staphylocci in cheese is failure of the lactic acid
starter culture to develop normally, usually due to the presence of inhibitory
substances such as antibiotics and sulphonamides.
Table 15: Incidence of Staphylococcal enterotoxins in samples of milk
and its
products
Type of sample
Raw milk
source
Cattle
yard
Cheddar cheese
Dairy
factory
Skim
milk Dairy
powder
factory
Baby food
Market
NO. of
samples
affected
out
of
the total
tested
1/5
Staph.
count
cfu/gm
or cfu/ml
Type
Enteotoxins
of
A
B
C
D
11x105
+
-
-
-
1/17
14x103
+
-
-
-
2/17
10x102
50x101
17x102
+
+
-
-
+
-
-
-
1/11
Heat Stability of Staphylococcal entertoxins:
Biological activity of Staphylococcal enterotoxins exhibits rather remarkable
thermal stability. Pasteurization of raw milk was ineffective in the destruction of
enterotoxins.
Sources of the causative organisms:
The following sources may contribute Staphylococcus aureus in milk and milk
products.
I- Human handlers are the main source of contamination as the organism is
frequently present in the nose, skin, wounds, pimples and boils of the people.
2-Animals: Milk animals may also harbour the organism in udders as it is
also
responsible for mastitis.
Staphylococcal poisoning (Syndrome and its diagnosis):
1-Symptoms: The symptoms are nausea, vomiting, abdominal cramps
diarrhea,
sweating, headache, prostration etc.
2-Incubation period: It is generally varies from 1-16 hours. Unpleasant
illness
usually last of approximately 24 hours duration.
3-Duration: Symptoms last for 24-48 hr.
4- Mortality rate: It is very low.
5-Immunity: This illness does not give immunity for reoccurrence.
6-Diagnosis: for the diagnosis of the Staphylococcal intoxications, the
methods can be used:
a- Biological methods.
b- Serological methods.
c- Coagulase test.
d- Thermonuclease (DNase)test.
following
Prevention and control:
The control measures used against Staphylococcal intoxications through milk and
milk products are given below:
a- Adequate heating destroy Staphylococci but not entertoxins, so heating
within few hours of production would inhibit the multiplication of
Staphylococci and hence no toxin production.
b- Adequate cooling immediately after production of milk also inhibits
multiplication of Staphylococci. It should be kept cooled until processed.
c- Post-pasteurization contamination should be avoided.
d- Infected handlers should not be allowed to handle milk and milk products.
e- Animals having mastitis should be isolated.
2-Botulism: (A common type of food intoxication):
Botulism poisoning is the severest of all the food-poisoning as it affects the
nervous system and is often extremely fatal. However, milk and milk products are
rarely involved in the causative of botulism .Fluid milk is not a suitable substrate
because the causative organism is anaerobic and thus cannot grow. In sour milk,
Clostridium botulinum
cannot survive due to low pH. But, it is quite prevalent in
canned products like condensed milk and processed cheeses. In view of the
existing anaerobic conditions favourable for its growth, as a result of this, the cans
bloat due to gas production. Other types of canned foods can also be implicated in
botulinum poisoning.
Toxins: Although the organism is heat resistant, it produces a variety of heat
labile toxins which can be destroyed at 100 °C within few minutes. However, the
toxins produced by Cl. botulinum are extremely potent. Several types of toxin (A
to G) are produced by the organism and out of these at least four A, B, E and F are
known to affect man. These toxins are lethal in small doses. It is estimated that
0.1µg of toxin, if given to an individual may cause death and only 1mg of the
purified toxin is sufficient to kill one million people. Toxin is produced by the
growing cells but the resting cells are also reported to produce toxin. Botulinum
toxins are protein in nature.
Sources of the causative organism:
The important source is soil as the organism is an inhabitant of
soil. Water is
another source of this organism. Serotype E is known to exist in water, especially
marine water but its number in soil and water is very low.
Botulism syndrome and its diagnosis:
1-Symptoms: The symptoms are nausea, vomiting, fatigue, dizziness, headache
and dryness of skin, mouth and throat. As it acts on central nervous system, it leads
to paralysis of muscles, double vision and respiratory failure resulting finally into
death.
2-Incubation period: It varies from 12-96 hours (usually 18-36hr).
3-Duration: It is generally 1-10 days.
4-Mortality rate: Mortality rate is very high.
5-Diagnosis: Laboratory diagnosis involves microscopic examination,
inoculation and cultural identification.
animal
Preventaion and control:
1-Adequate heating of the products (100°C /10-20 minutes) destroys toxins.
2-Hygienic conditions should be adopted during production of milk.
3-Chilling after production should be essentially practiced.
4-Acidity inhibits the causative organisms.
5- Rejection of Bulged cans and spoiled foods.
3- E.coli poisoning (food intoxication)
E.coli is known to be associated with enteritis in infants and adults as well as with
traveller´s diarrhea and food poisoning. This organism can bring about the disease
syndromes either by invasion or by virtue of its ability to produce two types of
enterotoxins, namely heat labile(LT) and heat stable (ST). Milk and milk products
like ice–cream, dried milks, cheese etc. can be contaminated with toxigenic strains
of E.coli which can elaborate the enterotoxins under favourable conditions .It is
estimated that a minimum of 105 to107
cells
/ gm are required to produce
enterotoxins sufficient to cause food poisoning syndromes when ingested along
with cheese.
Toxins of E.coli:
E.coli strains can produce two types of enterotoxins designated as (LT) and (ST)
toxins based on their ability to withstand heat. The (LT-toxin) is a protein with a
molecular weight around 100,000 daltons and is completely inactivated by a heat
treatment of 65°C for 30 minutes. The ST-toxin on the other hand, has not yet been
well characterized.
Sources of the causative organism:
The common sources of E.coli in milk and milk products are as follows:
1-Water supplies contaminated with faecal matter.
2-Unhygienic practices by the handlers may also introduce the organism in milk
and milk products.
3-Infected animals may also excrete the organisms which may gain
access into
milk (through mastitis).
Disease in relation to man:
Both LT and ST toxins of E.coli can cause food poisoning syndromes in man.
Although children are more susceptible, the sensitive adults may also be affected
with E.coli poisoning through ingestion of contaminated milk and milk products.
Symptoms:
The symptoms produced as a result of ingestion of (LT Toxin) resemble those
of cholera. There is massive watery diarrhea due to accumulation of fluid in the
intestine. In case of ST toxin, the systems include, diarrhea with or without
vomition, which is non-bloody and without inflammatory exudate in the stool.
Fever may be caused in children but not in adults.
Incubation period: It is 8-24 hours.
Prevention and control:
The control of E.coli poisoning is similar to that for any other entric disease.
However, the following precautions should be taken in this connection.
a- The faecal contamination of water supply should be avoided.
b- Handlers should strictly follow hygienic practices.
c- Cross contamination from infected animals should also be avoided.
d- Animals having mastitis should be isolated.
e- Adequate pasteurization of milk and milk products.
4-Cholera: (Food intoxication):
Cholera is one of the acute diarrheal diseases caused by Vibrio
cholera. It
frequently occurs in the form of massive epidemics, and unhygienic practices
appear to be chiefly responsible for the eruption of outbreaks. Although Cholera is
mainly a water-borne illness the involvement of milk and milk products may also
transmit the disease. The organisms adherer to the epithelial cells lining the crypts
of the mucosa in the small intestine where it produces enterotoxin that cause loss
of fluid and electrolytes from the body followed by dehydration.
Causative agent:
Vibrio cholera
Source of the causative organism:
a- Milk may be infected by soiled hands of a patient or a convalescent carrier.
b- Use of infected water for dairy purposes (i.e polluted water with faecal matter).
c- Adulteration of milk with contaminated water may also be one of the causes.
Disease in relation to human being:
Vibrio cholera organisms penetrate the mucosa of the intestines and accumulate in
layers next to sub-mucosa.
Symptoms:
In mild cases of cholera, diarrhea appears to be only symptom. However in severe
cases, the symptoms are diarrhea, vomiting, rice water stools, abdominal pain,
thirst, dehydration symptoms etc. The disease runs a short course terminating in
death, sometimes within 12 hours after the appearance of symptoms.
Incubation period: It is usually for 3 days (few hours to 5 days).
Diagnosis: Vibrio
cholera can be isolated from faeces of both infected
individuals and carriers.
The intraperitoneal inoculation of Guinea pigs with pure cultures results in the
death of the animals within 24 hours.
Susceptibility and immunity:
Natural resistance varies in different individuals. Clinical attacks confer a
temporary immunity which may last for several years. Active artificial immunity
may last for 6-12 months and may be induced by the use of vaccines.
Preventation & control:
1- Proper pasteurization of milk and milk products.
2- Sanitary disposal of human excreta.
3- Protection of water by boiling.
4- Sanitary preparation and handling of products.
5-Control or destruction of house flies.
6- Education of public in personal cleanliness.
7- Isolation of patients.
8- Disinfection of stools and vomits and articles soiled by these.
9- Food left by patients should be burnt.
10- Room of patient should be thoroughly cleaned and disinfected.
11-Carriers should be isolated.
12-Use of cholera vaccine in exposed population group.
5- Fungal intoxications:
The common types of fungal intoxications that rest through milk and milk
products are those caused by Aspergillus and other mold like penicillium,
Fusarium etc.
A-Aflatoxicosis:
It is a common type of fungal intoxication caused by common molds, Aspergillus
flavus and Aspergillus parasiticus by virtue of their ability to produce Aflatoxin.
The aflatoxin can be present in milk as
preformed toxin or it can be
secreted in milk by the milk animal (cow) which has been fed with aflatoxin
containing feeds. Therefore, ven with an exceptionally satisfactory sanitation and
hygiene observed during production and processing of milk, the mycotoxins can be
transferred to the consumers. Upon ingestion (by the cow),the Aspergillus- toxins
are metabolized by the milk animals (cows) and are secreted into the milk in the
form of M1 and M2 which are also toxic to the milk consumers.
Types of Aflatoxins:
Aspergillus flavus can produce the following distinct types of Aflatoxins in milk
and milk products, apart from M1 and M2 toxins.
1. B1, B2 and B2a: Aflatoxin B1 is the most abundant and most toxic of the
aflatoxins.
2. G1, G2 and G2a: These toxins are extremely heat stable, potent and exhibit
very strong toxicity part from being highly carcinogenic. Raw milk, ice
cream powder, evaporated milks, dried milk and cheese are the common
foods implicated with aflatoxins. The recommended upper permissible limit
of aflatoxins in foods is 90 ppm.
Sources of the causative organisms:
The main sources of Aspergillus species which are capable of producing aflatoxins
are as follows:
1- Environment: Aerial contamination is one of the most important sources of
mold spores.
2- Soil and contaminated foods may also introduce mold spores in milk
and
milk products.
3- Poor storage conditions.
Disease in relation to man and animals:
As a result of ingestion of Aflatoxins through contaminated milk and milk
products, acute aflatoxicosis may result in the consumers.
Symptoms:
The main symptoms of the Aflatoxicosis are liver hyperplasia, tissue
haemorrhage, anorexia, hepatitis and finally death in animals. The vital organs like
splean, pancreas and kidney may also be involved in Aflatoxicosis.
Prevention and control:
The system for controlling aflatoxins in milk and milk products as well as feeds is
essentially the same as for controlling any microbial toxin. In this regard, the
following measures are required to be taken.
1- Prevent contamination of milk and milk products as well as feed by
takingappropriateprecautions.
2- Prevent fungal growth by storing the products under proper
conditions
and by the use of fungistatic agents.
3-Detoxification of Aflatoxins by physical, chemical or biological
agents,
however, this measure is relatively impractical in dairy products.
B-Other Mycotoxicoses:
Apart from Aflatoxins, molds can also produce a variety of other toxins which
can cause other human illnesses or Mycotoxicoses, as results of consumption of
intoxicated milk and milk products. A few such mycotoxins along with the
producing organisms have been given in the following Table 16.
Note: Most fungal toxins including mycotoxins are resistant to heat and are not
destroyed by boiling of food.
Table 16: Some common mycotoxins other than Aflatoxins responsible for
human illnesses
Type of toxin
Toxin producing organsim
Citreovirdin
Citrinin
Penicillium citreoviride
Penicillium citrinum
Penicillium viridicatum
Penicillium islandicum
Aspergillus ochraceus
Penicillium martensii
Penicillium viridicatum
Penicillium cyclopium
Penicillium roqueforti
Penicillium camembertii
Penicillium rubrum
Fusarium tricinctum
Fusarium roseum
Fusarium solani
Luteoskyrin
Ochratoxins
Penicillic acid
Cyclopiazonic acid
Roquefortin
Cammembertin
Ruberatoxin
FusarotoxinT-2
Prevention and control:
The control of different Mycotoxicoses requires the prevention or reduction of
mycotoxin contamination in milk and milk products as has already been discussed
under aflatoxicoses.
C- Milk –borne toxi-infections:
The organisms like Clostridium perfringens and Bacillus cereus cause toxiinfections through milk and milk products.
1-Clostridium perfringens (welchii) poisoning:
The perfringens type of food –poisioning can also occur due to the ingestion of
contaminated milk or canned products. Clostridum perfringens causes gas
gangrene in animals. Since this organism is anaerobic in nature like Clostridum
botulinum, the anaerobic conditions as observed in canned products could be
favourable for this type of toxi-infection. There are at least five antigenically
distinct types of this organism according to the type of toxins it produces, namely
A, B, C, D, and E. Two types of the five types namely A and C can cause food –
poisoning in man by virtue of their ability to produce enterotoxins which are lethal
and emetic.
Sources of the causative organism:
A- Clostridium perfringenes is commonly found in soil and faeces of man and
animals from where it can find its way into milk and its products
through dust,
fodder and unsanitary handling.
B-Water supplies contaminated with sewage or fecal matter may also
this organism into milk.
introduce
As it is a sporeforming organism, the highly resistant spores survive almost
indefinitely in dust and are widely prevalent in cow shed and dairies.
Disease in relation to human beings:
The disease caused in human beings is gastroenteritis which occurs due to the
production of exotoxins / enterotoxins by this organism which are excreted during
sporulation and the release of the spores. The enterotoxin is resistant to intestinal
juices and therefore, affects the intestinal walls. Children are more susceptible. The
Minimum lethal dose (MLD) of the toxin is 2000 mice /mg nitrogen.
Symptoms: Diarrhea, vomiting, nausea, abdominal pain etc. are the common
symptoms of this type of poisoning.
Incubation period: It varies from 8-22 hours and duration is generally one day
or less. However, it is not very fatal.
Pervention and Control:
1- Proper heat treatment of milk.
2- Milk should not be stored under conditions suitable for the spores to
vegetate
and multiply.
3-After pasteurization, a rapid cooling and storage of milk at temperature, below
15°C is required.
4- Environmental hygiene should be observed.
2-Bacillus cereus poisoning
Bacillus cereus poisoning is yet another type of ″Toxi-infection″ which can
occur as a result of ingestion of milk and milk products contaminated with Bacillus
cereus or its spores. Bacillus cereus, the causative agent of this poisoning, is an
aerobic sporeforming organism which occurs in almost all raw milk supplies as
well as in pasteurized milk, evaporated milk, condensed milk, dried milk, cream,
cakes, pastry, confectionary fillings and processed cheese.
Sources of the causative organism:
1-Since
B. cereus is one of the causatives for mastitis, the herd raw milk
sometimes gets B. cereus from mastitic animals.
2-The raw milk may also get spores from animal’s teat and skin and the milking
equipment especially cans.
Symptoms: The main symptoms are nausea, diarrhea, abdominal pain etc.
Incubation period: The incubation period is about 12 hours and the duration is
one day or less (6-12 hours).
Pervention and control:
The following practices should be strictly observed to minimize Bacillus cereus
poisoning through milk and milk products.
I-Prompt cooling of milk / milk products during storage.
2-Environmental hygiene should be maintained and the aerial
contamination
should be avoided.
3-Precautions should be taken during transition of milk.
4-General hygienic conditions should be maintained during production of milk and
marketing of dairy products.