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CONTROL AND PREVENTION OF LISTERIA MONOCYTOGENES IN
THE DAIRY INDUSTRY
Arun K. Bhunia, BVSc, PhD,
Professor of Molecular Food Microbiology, Department of Food Science, Purdue University,
West Lafayette, Indiana-47907, USA
Introduction
Listeria monocytogenes is primarily a soil-borne pathogen; however, its distribution is
ubiquitous. Historically, this pathogen is known for its ability to cause disease in ruminants,
but its significance as a foodborne pathogen was not recognized until early 80’s when several
Listeria-related outbreaks were reported. Since then foodborne listeriosis has been reported
with ready-to-eat meats, hotdogs, smoked fish and dairy products.
Infection and the symptoms
L. monocytogenes is an intracellular pathogen, invades host cells, spread from cell-to-cell and
eventually induces programmed cell death. It primarily infects immunosuppressed population
affecting infants, pregnant women, the elderly and the immunocompromised patients. Thus,
the severity of the disease depends on the immunological status of the host and the fatality is
very high (20-28%). The symptoms of the infection start with a mild fever, leading to
progressive neurological symptoms resulting from meningitis and meningoencephalitis.
Additionally, the intracellular transplacental migration to the fetus in the pregnant women
results in abortions and stillbirths.
Organism and growth conditions
L. monocytogenes is a gram positive rod shaped bacterium and can survive in extreme growth
conditions therefore it is very difficult to eliminate from the products or from the dairy
processing environments. It can grow at refrigeration temperature (4-10ºC) and at high
temperature (48°C). It can tolerate high salt (>10%) and is able to grow in pH rangeof 4 to 9.
These organisms secrete polysaccharides that allow them to form biofilms in the processing
equipments or in the floors, walls or drains.
Significance in dairy industry
In dairy industry, L. monocytogenes presents a major challenge. The organism can be present
in raw milk - primarily remain hidden inside the macrophages. Improper pasteurization or
lack of it, allow the pathogen to be present in the finished product such as ice-cream, cheeses,
cheese-spreads, etc. Listeria can also be transmitted from the dairy cow, milk, personnel, food
handlers, or the trucks used. It is widely found in the farm, processing equipments, floors,
storage facility etc.
Thus, to control L. monocytogenes in dairy industry, proper sanitation and hygienic
practices should be implemented in the farm and milk production facility, which can reduce
Como citar este capítulo:
BHUNIA, A.K. Control and prevention of Listeria monocytogenes In the dairy industry. In: MESQUITA, A.J., DURR, J.W.,
COELHO, K.O. Perspectivas e avanços da qualidade do leite no Brasil. Goiânia: Talento, 2006, v.1, p. 259-260.
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the pathogen loads. Pasteurization can inactivate most pathogens in milk. In spite of the best
practices, Listeria continued to be present in finished ready to consume dairy products which
are thought to be due to post-processing contamination.
Control and Prevention
Control and prevention could be achieved by early detection of pathogen in the farm or in the
product and by employing proper sanitary measures. The dairy farm and the dairy processing
plants should be monitored periodically for the presence of Listeria. The standard culturing
methods outlined by the United States Department of Agriculture (USDA) could be employed
for detection of low numbers of Listeria. Alternatively, some rapid methods and or emerging
biosensor methods could be employed for rapid and specific detection of L. monocytogenes.
Prevention and control of the pathogen in products could be achieved by practicing standard
Pasteurization of the milk, general sanitation of the plant/farm, strict hygienic practices by the
personnel handling the products, and implementation of hazard analysis and critical control
point (HACCP) plans.
Como citar este capítulo:
BHUNIA, A.K. Control and prevention of Listeria monocytogenes In the dairy industry. In: MESQUITA, A.J., DURR, J.W.,
COELHO, K.O. Perspectivas e avanços da qualidade do leite no Brasil. Goiânia: Talento, 2006, v.1, p. 259-260.