Fundamental Food Microbiology, Third Edition - Fuad Fathir

370 FUNDAMENTAL FOOD MICROBIOLOGY
and subjected to proper sanitation (hazard analysis critical control point; see Appendix
D) until products free of Lis. monocytogenes are produced. Because of the effectiveness
of current regulatory procedures, it is possible that in the future the current
stringent zero-tolerance may be slightly relaxed. 10–14
In addition to the control measures in processing facilities, regulatory agencies
have stressed on consumer education to reduce foodborne listeriosis. This includes
thoroughly cooking raw foods of animal origin; thoroughly washing raw vegetables
before eating; keeping uncooked meats separate from vegetables, cooked foods, and
ready-to-eat foods; not consuming raw milk or foods made with raw milk; and
washing hands, knives, and cutting boards after handling uncooked foods. In addition,
there are special recommendations for high-risk individuals: avoid soft cheeses
(Mexican style, Feta, Brie, Camembert, blue-veined, cream or cottage cheeses);
reheat (until steaming) all refrigerated leftover foods and ready-to-eat foods before
eating; avoid foods from the delicatessen (recommended for pregnant women, elderly
people, and immunocompromised people). 10–14
H. Detection Method
The most commonly used method involves preenrichment and enrichment steps in
recommended broths and streaking on specific selective-differential agar media
plates. Suspected colonies are then tested for biochemical and serological profiles.
Several rapid methods have also been developed based on immunological characteristics
and nucleic acid base sequences (see Appendix E).
I. Case Study
In December 1988 in Oklahoma, a cancer patient developed septic listeriosis after
consumption of turkey franks following heating in a microwave oven. 15 Lis. monocytogenes
serotype 1/2a was isolated from the patient, from the remaining franks in
the opened package (in high numbers) in the refrigerator, and several other foods
in the same refrigerator. Isolation of the same serotype from unopened packages (in
low numbers) of the same brand of turkey franks led the regulatory agency to believe
that the contaminated turkey franks were the cause of this foodborne listeriosis.
Subsequent investigations by the regulatory agencies after 4 months revealed that
the plant processing this brand of franks had the same serotype of Lis. monocytogenes
(as well as other serotypes) in the processing environment, and the heated franks
were recontaminated from the conveyor belt following peeling of casings and before
repackaging (see Chapter 28).
This incident reveals several important aspects of foodborne human listeriosis: (1)
the person affected with listeriosis is immunocompromised; (2) ready-to-eat franks
were the source of the pathogenic serotype; (3) microwave heating, the way used by
the individual, did not kill the pathogen; (4) the pathogen grew during refrigerated
storage in the franks; (5) several other foods in the same refrigerator were also crosscontaminated;
(6) the pathogenic strain was present in the processing environment
(along with other serotype) even after 4 months; and (7) recontamination of franks
following heating occurred from contaminated equipment before packaging.