Pathogenic Bacteria

Pathogenic Bacteria - Food Safety Auditing & Inspection - picture of Agar Jelly in dish

Pathogenic Bacteria

What causes many common food-borne illnesses?

Ingestion of Pathogenic Bacteria or toxins that can result in infection and/or the production of toxic by-products in the human gut.

Pathogenic Bacteria

  • A single celled organism that lives independently, invisible to the naked eye and to see them requires a microscope with a magnification of 1000 times or more. 400 million bacteria are equal to the size of a grain of sugar

What do pathogenic bacteria need to survive?

  • Moisture – (aw) at least 0.91 and very a very important consideration for food quality and safety.
  • Nutrients – all bacteria require energy to live and grow. Energy sources such as sugars, starch, protein, fats and other compounds provide the nutrients.
  • Temperature – bacteria are capable of growing over a wide range of temperatures and are usually classified according to the temperature at which they grow.
  • Psychrophilic (cold-liking) bacteria (responsible for food spoilage in refrigerators, grow rapidly at room temp.) – Growth range 0°C to 25°C – Optimum temperature 20°C to 25°C
  • Psychrotrophic bacteria are those that are capable of growing at 0°C to 35°C but their optimum is 25°C. They cause spoilage in foods stored under refrigeration. Several pathogenic bacteria are psychotrophic.
  • Mesophilic Most bacteria are capable of growing at 10°C to 55°C and belong in this group. Most pathogenic bacteria grow at these temperatures.
  • Thermophilic These microorganisms grow at higher temperatures such as 40°C to 80°C. Temperature is the most widely used method of controlling bacterial growth. Bacteria grow slowly at temperatures below 7°C and thermal destruction occurs at temperatures above 60°C. But in the temperature danger zone — between 5°C and 63°C — many bacteria are not controlled.

Each of the factors listed above plays an important role, the interaction between the factors ultimately determines whether a microorganism will grow in a given food. Often, the results of such interaction are unpredictable, as poorly understood synergism or antagonism may occur.

An advantage is taken of this interaction with regard to preventing the outgrowth of C. botulinum. Food with a pH of 5.0 (within the range for C. botulinum) and an aw of 0.935 (above the minimum for C. botulinum) may not support the growth of this bacterium.

Certain processed cheese spreads take advantage of this fact and are therefore shelf stable at room temperature even though each individual factor would permit the outgrowth of C. botulinum.

Therefore, predictions about whether or not a particular microorganism will grow in a food can only be made through experimentation. Also, many microorganisms do not need to multiply in food to cause disease.

Where are pathogenic bacteria found?

Pathogenic bacteria are found everywhere: In air, soil and water. In the intestines and faeces of animals and humans and on the hands, skin, hair and clothing of people. It is important to note that not all bacteria are bad, they are actually quite the opposite.  Only a small fraction of pathogenic bacteria actually cause disease, they usually attack already dead matter. Many bacteria are vital for our health.

For example, without saprophytic bacteria (organism which gets its energy from dead organic matter ) to decompose the dead matter, it would continue to accumulate indefinitely.  Bacteria also enrich the soil.  For example, the nitrogen fixers convert nitrogen gas from the air into nitrate, that plants need to live, and a number of cyanobacteria help fix the levels of nitrogen in the atmosphere.  These photosynthetic bacteria also contribute large quantities of oxygen to the atmosphere.  Bacteria also break down the matter in compost heaps, which are used for fertilizer.

Some other beneficial bacteria which are important:

  • Bacteria are important to some industries such as the production of cheese, yogurt, buttermilk, vinegar, and sauerkraut.
  • They are used in the preparation of antibiotics such as Streptomycin.
  • They are used in the tanning of leather and hides
  • Methane-producing bacteria are used in sewage treatment plants to convert the sludge into methane gas.
  • They help cattle, sheep and goats to digest the tough cellulose in grass.
  • Archaebacteria (previously categorised as extremophiles)supports ecosystems in hot springs and deep sea vents, because many organisms use them for a food source.
  • Bacteria in the human intestine help to produce vitamin K.

Next article: Viruses.

Robert Elsey

Pennine Training Services

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