Harmful Effects of Microorganisms

Hi everyone! We often hear about the "good bacteria" in yoghurt, but what about the not-so-good ones? Microorganisms are all around us, and while many are harmless or even helpful, some can be real troublemakers. In this chapter, we'll explore the "dark side" of microorganisms – how they cause diseases, spoil our food, and what we can do to stop them. Understanding this is super important for staying healthy and keeping our food safe to eat. Let's dive in!


1. How Microbes Make Us Sick (The Principles)

What are Pathogens?

Not all microorganisms cause disease. The ones that do are given a special name: pathogens. A pathogen is any microorganism (like certain bacteria, viruses, or fungi) that can cause illness. Think of them as the villains of the microbial world.

How Do Pathogens Cause Disease?

Once a pathogen gets inside our body, it doesn't just hang around quietly. It wants to survive and multiply, and it can make us sick in two main ways:

1. Damaging Host Cells Directly: Some pathogens act like invaders breaking into a house. They enter our body's cells, multiply rapidly, and eventually cause the cells to burst and die. This direct damage to our tissues is what causes the symptoms of the disease.

Example: The influenza virus infects cells in our respiratory tract, causing them to die, which leads to a sore throat and cough.


2. Producing Toxins: Other pathogens are like tiny factories producing poison. They release harmful chemical substances called toxins. These toxins can travel through the bloodstream and disrupt the normal functioning of our body, causing the symptoms of the disease. Some toxins are released while the bacteria are alive, while others are released only when the bacteria die and break apart.

Example: The bacterium Vibrio cholerae produces a powerful toxin in the small intestine, causing severe diarrhoea, which is the main symptom of cholera.

An Easy Analogy to Remember

Think of a pathogen invasion like an army attacking a city (your body):

  • Direct Damage: The soldiers (pathogens) physically destroy buildings (your cells).
  • Toxin Production: The army releases chemical weapons (toxins) that poison the city's water supply and make everyone sick.
Key Takeaway

Pathogens are disease-causing microorganisms. They make us sick either by directly damaging our cells or by producing poisonous chemicals called toxins.


2. Tummy Troubles: Food-borne Illnesses

We've all had a stomach ache after eating something "off". This is often caused by pathogens in our food. But there's a crucial difference between a food-borne infection and food poisoning. Don't worry if this seems tricky at first, the difference is all about timing and the cause!

Food-borne Infection: The Live Invaders

This happens when you eat food that contains living pathogens.

  • The Cause: The living microorganisms you swallow set up camp in your intestines, multiply, and then start causing trouble (either by damaging cells or producing toxins inside you).
    • - Onset Time: It's usually slower (from several hours to a few days) because the pathogens need time to multiply to a large enough number to make you sick. - Real-world Example: Getting sick from Salmonella bacteria in undercooked chicken or eggs. The live bacteria multiply in your gut and cause illness.

Food Poisoning (Intoxication): The Pre-made Poisons

This happens when you eat food that contains toxins produced by microorganisms. The microbes have already been growing in the food and left their toxic waste products behind.

    - The Cause: You swallow pre-formed toxins. The bacteria that made them might even have been killed by cooking, but the toxins (which can be heat-resistant) remain in the food and make you sick. - Onset Time: It's usually very fast (from 30 minutes to a few hours) because the toxins are already present and can act immediately. - Real-world Example: Sickness from toxins made by Staphylococcus aureus bacteria. This can happen in foods like cream-filled pastries or potato salad that have been left at room temperature for too long.
Quick Comparison

FEATURE
Cause:
Onset Time:
Analogy:

FOOD-BORNE INFECTION
Ingesting live pathogens
Slower (hours to days)
Swallowing tiny invaders that build an army inside you.

FOOD POISONING
Ingesting pre-formed toxins
Faster (minutes to hours)
Swallowing tiny poison bombs that were already left in the food.

Key Takeaway

Remember the key difference: Food-borne infection is caused by living pathogens multiplying in your body. Food poisoning is caused by pre-formed toxins already in the food. The main clues are the speed of onset and whether the cause is the microbe itself or its toxic byproduct.


3. Beyond Disease: Microbial Deterioration

What is Microbial Deterioration?

Not all harm caused by microorganisms involves disease. Microbial deterioration is the breakdown or spoilage of materials (like food, wood, paper, and textiles) by microorganisms. In nature, this is a vital process called decomposition, which recycles nutrients. But when it happens to our food or belongings, it's a big problem!

Think of it as tiny, invisible demolition crews (bacteria and fungi) releasing enzymes to digest whatever they are growing on.

Where Do We See It in Daily Life?

Microbial deterioration is happening all around you:

  • Food Spoilage: This is the most common example. Microbes break down the nutrients in food, changing its taste, smell, texture, and appearance, making it inedible or even dangerous.
    • Examples: Greenish-blue mould on bread, milk turning sour and lumpy, fruit becoming mushy and rotten.

  • Damage to Other Materials: Microbes don't just eat our food! They can damage many other things.
    • Examples: Mildew growing on bathroom tiles or shower curtains, fungi causing wood to rot, mould spots on old books or leather jackets stored in a damp place.
Did You Know?

The "old book smell" is actually caused by volatile organic compounds released by fungi and bacteria as they slowly break down the paper and glue in the book!

Key Takeaway

Microbial deterioration is the spoilage and breakdown of food and other materials by microorganisms. It's the reason our food goes bad and why things can get mouldy or rot in damp conditions.


4. Fighting Back: Controlling Microbial Growth

So, how do we stop these tiny troublemakers from making us sick and spoiling our stuff? The key is to create conditions where they can't grow or survive. We use these principles every single day, especially in the kitchen!

Methods to Control or Eliminate Microorganisms

1. Using Temperature

Temperature is one of our best weapons. We can either turn up the heat to kill them or turn down the cold to slow them down.

  • High Temperature (Killing microbes): - Cooking: Thoroughly cooking food to a high enough temperature kills most pathogens. - Pasteurisation: A process of gentle heating (e.g., milk heated to 72°C for 15 seconds) that kills harmful pathogens without significantly changing the taste. It does NOT kill all microbes, so pasteurised milk still needs to be refrigerated. - Sterilisation: Using very high temperatures to kill ALL microorganisms and their tough, dormant spores. UHT (Ultra High Temperature) milk is an example – it can be stored for months at room temperature before opening.

  • Low Temperature (Slowing growth): - Refrigeration (e.g., 4°C): This doesn't kill microbes, but it dramatically slows down their growth and reproduction. It's like putting them in slow motion. This is why we keep fresh food in the fridge. - Freezing (e.g., -18°C): This stops microbial growth almost completely by turning water into ice, making it unavailable for them. Be careful – many microbes survive freezing and will start growing again once the food is thawed!
2. Removing Water (Dehydration)

All living things, including microbes, need water to survive and grow. By removing water, we can preserve food for a very long time.

  • Drying: This is one of the oldest methods of food preservation.

    Examples: Dried fruits, beef jerky, milk powder, instant noodles.

3. Using Chemical Preservatives

We can add substances to food that make the environment hostile for microbes.

  • Adding Salt or Sugar: High concentrations of salt or sugar create a solution with a very low water potential. By osmosis, water is drawn out of any microbial cells, killing them or stopping their growth.

    Examples: Jam (high sugar), salted fish (high salt), soy sauce.

  • Adding Acid: Most microbes cannot grow in highly acidic (low pH) conditions.

    Examples: Pickling vegetables in vinegar (acetic acid), using lemon juice as a preservative.

Key Takeaway

We can control microorganisms by creating environments they don't like. The main methods involve using high temperatures to kill them, low temperatures to slow their growth, removing water, or adding preservatives like salt, sugar, and acid.