Download Staphlococcus Aureus Food Poisoning

Microbiology
by Lance Reeve
Food Safety Risks And Prevention Strategies
taphylococcal food poisoning is one
of the most common causes of reported foodborne diseases in the
U.S. It is caused by eating foods
contaminated with toxins produced by
Staphylococcus aureus (S. aureus)—a grampositive coccal bacterium commonly
found in air, dust, water, milk, and on
the skin and in the nose of up to 25% of
healthy people and animals. Usually it
causes no illness unless it is transmitted
8 JULY/AUGUST 2015 AIB UPDATE
through food. Staphylococci do not form
spores but can contaminare food during
preparation, processing, and handling.
Sick employees and poor hygienic
practices are major causes of staphylococcus foodborne disease outbreaks. Contaminated equipment and environmental
surfaces also can lead to S. aureus infections. Products that are frequently implicated in S. aureus food poisoning include
poultry, meat, dairy products, potatoes,
tofu, eggs, tuna, deli salads, cream-filled
pastries, cream pies, sandwich fillings,
etc. In general, a food product that has
not been kept hot enough (>140°F), cold
enough (<40°F), and/or at room temperatures after preparation are vulnerable
to staphylococcus food poisoning.
S. aureus is capable of growing in
food products and produce staphylococcal enterotoxins (the causative agent of
staphylococcal food poisoning) in a wide
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Staphylococcal foodborne illness puts consumers at risk and imposes
grave economic losses to food manufacturers.
Microbiology
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range of temperatures (45-118ºF; optimum 85-99ºF), pH (4.2-9.3; optimum
7-7.5), and sodium chloride concentration (up to 15% NaCl). S. aureus also is
a desiccation-tolerant organism capable
of surviving in potentially dry and stressful environments such as clothing and
surfaces. All these characteristics favor
the growth of S. aureus in a wide range
of foods and environmental conditions.
Apart from putting consumers at
risk, staphylococcal foodborne illness
imposes grave economic losses to food
manufacturers due to recalls and other
legal expenses. In recent years, livestockassociated methicillin-resistant Staphylococcus aureus (MRSA) has become a
rapidly emerging, devastating human
pathogen associated with high mortality
worldwide. Studies have shown commercially distributed meat products as a
potential vehicle for MRSA transmission
in a farm-to-fork model.
Staphylococcal enterotoxins are produced as a byproduct during the growth
of certain strains of S. aureus. The toxin
production requires considerable growth
by the microbe and is normally not present until the bacterial population reaches
100,000 per gram of food. S. aureus can
produce nine types of toxins that are frequently responsible for foodborne illness
outbreaks worldwide. Staphylococcus enterotoxins are highly stable, heat resistant,
and resistant to environmental conditions
such as freezing, drying, and low pH.
They cannot be destroyed by cooking.
An estimated 0.1 µg of staphylococcus
enterotoxins can cause food poisoning
in humans. The microorganism is readily
destroyed by heat, but the toxin is heat
stable, and still capable of causing staphylococcal foodborne disease outbreaks.
SOURCE OF CONTAMINATION.
Poor sanitation and improper foodhandling practices in the food industry is
the number one cause of staphylococcus
foodborne disease outbreaks. Insufficient
cleaning of the processing equipment or
utensils, storage in unsanitary environments, prolonged exposure of prepared
food at room temperature, inadequate
cold-holding temperature, and slow
Staphylococcal enterotoxins are produced as a byproduct of certain strains of S. aureus.
cooling of the prepared food are other
contributing factors responsible for S.
aureus foodborne disease outbreaks.
Studies have clearly shown that food
handling was responsible for 42% of
staphylococcus foodborne disease outbreaks reported in the U.S. from 19751998. Studies also have shown that S.
aureus can adhere to the surface of gloves
worn by food handlers and be a source of
contamination if not changed frequently.
DETECTION. The conclusive diagnostic
criteria of S. aureus foodborne disease
are mainly based upon detection of the
enterotoxins in food products (using bioassays and immunological techniques),
and by enumerating at least 105 (100,
000) colonies S. aureus per gram.
PREVENTION. The following best
practices can help prevent staphylococcal
foodborne disease outbreaks.
• Cook food thoroughly and keep it at
safe temperatures: the cooking and
refrigerating temperature should be
above 140°F and below 40°F.
• Use safe water and raw materials.
• Wash hands before wearing gloves,
and change gloves frequently.
• Reduce or avoid bare-hand contact
of fresh produce and RTE food.
• Practice routine environmental
cleaning and disinfection of equip-
ment used in food processing.
• Avoid inadequate cooking and
reheating.
• Implement an effective HACCP
(Hazard Analysis and Critical Control Points) plan, GMPs (Good
Manufacturing Practice), and GHPs
(Good Hygienic Practices).
• Train employees to wash hands with
soap and water before entering a
food processing facility and handling
and preparing food products.
• Have people who are infected with
S. aureus seek medical attention and
stay out of food handling.
• Strictly prohibit employees with
wounds or skin infection from foodhandling areas.
If an employee has an active infection,
he or she should be excluded until the
infection is healed. The simple act of
touching or blowing the nose, coughing,
or sneezing is enough to contaminate
food products or food-contact surfaces
with this disease-causing bacteria. If the
employee does not have an active infection, then standard personnel hygienic
practices, such as handwashing, should
prevent transmission, and exclusion from
food handling is not required. AIB
The author is Director, Microbiology, AIB
International.
AIB UPDATE JULY/AUGUST 2015 9