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  The A to Z September 2001

Did You Know?

Dishcloths and sponges can be contaminated with Listeria and other pathogens, which then can spread throughout the kitchen. Be sure to wash dishcloths often in the hot cycle of your washing machine. Or, wipe kitchen surfaces with a paper towel. Then throw away the towel.

List of Terms:  L 
(Return to Comprehensive List of Terms)

> Listeria monocytogenes
Unlike most bacteria, this pathogen can grow slowly at refrigerator temperatures. It can also cause serious problems in vulnerable people, especially pregnant women, newborns, people with weakened immune systems, and the elderly.

Listeria monocytogenes
Listeria monocytogenes

Sources: Listeria monocytogenes is often found in refrigerated, ready-to-eat foods.


Incubation: Most symptoms have been reported 48 to 72 hours after consumption of contaminated food, but can develop from 7 to 30 days after ingestion.

Symptoms: Fever, headache, fatigue, muscle aches, nausea, vomiting, diarrhea, meningitis (a bacterial disease in which any of the 3 membranes that envelop the brain and spinal cord become inflamed), and miscarriages, resulting in a 20% mortality rate in fetuses.

Duration: 1 to 4 days.

> Log Reduction
"Log" stands for logarithm, which is the exponent of 10. For example, log2 represents 102 or 10 x 10 or 100. Log reduction stands for a 10-fold or one decimal or 90% reduction in numbers of recoverable bacteria in a test food vehicle. Another way to look at it is: 1 log reduction would reduce the number of bacteria 90%. This means, for example, that 100 bacteria would be reduced to 10 or 10 reduced to 1.

Food Safety Implication: The 5-log reduction is the value used for some food safety standards. It is an estimate of the potential number of organisms that would contaminate an 8 oz. juice serving and the level of reduction that it would take to render the product safe.

The 5 log refers to 10 to the 5th power or reduction in the number of microorganisms by 100,000-fold. For example, if a juice product contained 100,000 pertinent microorganisms, a 5-log reduction would reduce the number of pertinent microorganisms to 1. (See the Log Reduction Chart below.) While the 5 log is specific to unpasteurized juice, the value has been used by the Food Safety and Inspection Service (FSIS) as a performance standard in roast beef.

Two Practical Ways of Looking at 5-Log Reduction:

  1. Reduction of 100,000 bad bugs in one contaminated serving to 1 bad bug in a serving.
  2. Reduction of 100,000 contaminated servings to 1 contaminated serving.
Log Reduction Chart
Log Reduction % Reduction of Bacteria
1 90
2 99
3 99.9
4 99.99
5 99.999

Food Safety A to Z Reference Guide

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