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Understand  –  Bacteria

Bacteria and infections

Throughout history, bacterial infections have played a central role in the lives and deaths of humans.

Bacteria cause many common infections such as pneumonia, wound infections, bloodstream infections (sepsis) and sexually transmitted diseases like gonorrhea. Moreover, they have been responsible for several major disease epidemics. One example from the 1340’s is the plague, also known as the “Black death”, that spread across Asia and Europe along the trading routes, killing millions of people. The disease is now known to be caused by the bacterium Yersinia pestis and is treatable by antibiotics.

When do bacteria cause disease?

Bacteria can be strictly pathogenic, which means that they will cause disease if they manage to overwhelm the human immune system. Other bacteria only cause disease given the right circumstances, these are so-called opportunistic pathogens. Opportunistic pathogens normally do not cause infections in healthy humans, but the risk increases when the immune system is compromised or suppressed by for example cancer chemotherapy, malnutrition or other diseases (like HIV/AIDS). These infections often originate from the individual’s own bacterial flora such as that on the skin or in the gut.

Many bacterial pathogens can spread via water and food, including Salmonella, Campylobacter and E. coli. Sometimes bacteria are transmitted directly or indirectly from animals to humans and cause disease. Such infections are called zoonotic infections. Other bacteria like Neisseria gonorrhea and Chlamydia trachomatis spread via sexual contacts.

Managing bacterial infections

The introduction of antibiotics to treat bacterial infections in combination with improved hygiene and sanitation, use of vaccinations and increased knowledge about bacteria have greatly reduced deaths from bacterial diseases. However, antibiotic resistance is now threatening to again leave us without effective treatments for many common bacterial infections. Resistant bacteria are widespread in most parts of the world and more and more people die from bacterial infections because the antibiotics have stopped working. For information about antibiotic resistance, see Antibiotic resistance, and the sub-sections that follows.

Identifying the disease

Diagnostics are a set of tools used to determine the nature and causes of disease. This information is then used to determine what the appropriate therapy is. It could be, for example, a specific antibiotic, other medicines or bed rest. In the absence of a proper diagnosis, many patients may not get the correct antibiotic treatment when they need it. Another common problem is that patients who do not need antibiotics are given one just in case it is a bacterial infection.

Below are a set of resources about bacterial diseases and their spread.

Selected Resources

Resource Description
What are infectious diseases? Article. Facts about infectious diseases, what they are, and an introduction to the different groups of microorganisms that cause them (bacteria, viruses, fungi and parasites).
Bacteria in medicine (Encyclopaedia britannica) Article about bacterial diseases and their impact. Also provides links to additional pages about specific bacteria.
Understanding Microbes in Sickness and in Health Booklet. Learn about microbes and their role in health and disease in this book written for the general public.
Zoonotic Diseases Fact sheet that explains more about common zoonotic infections – infections shared between animals and humans – and how they can spread (focus on the US). developed by the CDC.
Plague was one of history’s deadliest diseases – then we found a cure Article about “The Black Death”, the plague epidemic in the 1300s.

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