What is the difference between a virus and bacteria?

A bacterium is a single, but complex, cell. It can survive on its own, inside or outside the body.

Viruses are smaller and are not cells. Unlike bacteria, they need a host such as a human or animal to multiply. Viruses cause infections by entering and multiplying inside the host’s healthy cells.

Bacteria

Not all bacteria are harmful, and some bacteria that live in your body are helpful. For instance, Lactobacillus acidophilus — a harmless bacterium that resides in your intestines — helps you digest food, destroys some disease-causing organisms and provides nutrients.

Many disease-causing bacteria produce toxins — powerful chemicals that damage cells and make you ill. Other bacteria can directly invade and damage tissues.

Viruses

Viruses are much smaller than cells. In fact, viruses are basically just capsules that contain genetic material. To reproduce, viruses invade cells in your body, hijacking the machinery that makes cells work. Host cells are often eventually destroyed during this process.

Antibiotics designed for bacteria have no effect on viruses.

Micro-organisms: Germs and Microbes

Different diseases are caused by different types of micro-organisms. Microbes that cause disease are called pathogens.

It is important to remember that:

• A pathogen is a micro-organism that has the potential to cause disease.
• An infection is the invasion and multiplication of pathogenic microbes in an individual or population.
• Disease is when the infection causes damage to the individual’s vital functions or systems.
• An infection does not always result in disease!

To cause an infection, microbes must enter our bodies. The site at which they enter is known as the portal of entry.

Infectious agents come in many shapes and sizes. Bacteria and protozoans are microscopic one-celled organisms, while viruses are even smaller. Fungi grow like plants, and helminths resemble worms.