Pathogenic bacteria

Most tiny germs are good. Many live in your gut to help you. Some live on your skin too.

But some germs can make you sick. These are called bad germs. They can get into your blood. They can even get into your lungs.

Bad germs can cause a cut to swell. They can also cause a fever. Some germs make your teeth hurt. They do this by making acid.

Your body has ways to fight back. It tries to stop the germs. But sometimes the germs win. This can happen if you are tired or hurt.

Doctors use special medicine to help. This medicine can kill the bad germs. It helps you feel better again.

Most bacteria are helpful or harmless. Thousands of kinds live in your gut. But some bacteria cause disease. We call these pathogenic bacteria.

These bad germs can invade your body. They may enter through a cut in your skin. Some can travel through your blood. They can even reach your lungs. This can cause sickness like pneumonia.

How do they make us sick? Some germs make toxins. Toxins are poisonous things they let out. Other germs damage cells directly. For example, some germs in your mouth make acid. This acid can cause cavities in your teeth.

Your body has a way to fight back. This is called immunity. It helps you resist germs. But germs can win if you are very tired or hurt. Some germs are opportunistic. This means they wait for your defenses to be weak.

Doctors can use antibiotics to help. These are medicines that fight germs. Some kill the bacteria. Others just stop them from growing.

You can stay safe by washing hands. Cooking food to high heat also helps. This kills germs in your food.

Most bacteria are actually helpful or harmless to us. In fact, several thousand species live in your gut as part of your flora. There are also many beneficial bacteria that grow on your skin. However, some bacteria are different and can cause disease. We call these pathogenic bacteria.

While there are many types of bacteria, fewer than one hundred species are estimated to be harmful to humans. These pathogens are specially adapted to overcome your body's natural defenses. They can invade places where bacteria are not usually found, like your blood.

These bacteria make you sick in a few different ways. Some pathogens damage your cells directly by using them for nutrients. For example, bacteria in your mouth can turn sugar into acid. This acid can then damage your teeth and cause cavities. Other bacteria release toxins, which are poisonous substances. Some toxins are released when the bacteria die and their cell walls break apart. This is called an endotoxin. Sometimes, your own immune response can even cause damage while trying to fight the infection.

Bacteria can enter your body through many different paths. Some might enter through a cut in your skin or through a wound. Others can cause sickness by traveling through your blood or your lymphatic system. Some bacteria are even obligate intracellular parasites. This means they can only grow and multiply inside your living cells. Other bacteria, called opportunistic pathogens, wait for your defenses to be weak. They might cause disease if you are tired, malnourished, or have a disease that makes your immunity low.

Pathogenic bacteria are responsible for many important illnesses around the world. In 2019, bacteria like Mycobacterium tuberculosis caused tuberculosis, which killed 1.4 million people. Most of these deaths happened in sub-Saharan Africa. Other bacteria cause pneumonia, such as Streptococcus or Pseudomonas. Some bacteria cause foodborne illnesses, like Salmonella or Shigella. A large study found that bacterial pathogens contributed to one in eight deaths globally in 2019. This was about 7.7 million deaths in total.

Doctors have many ways to identify and treat these germs. They can grow bacteria in cultures to see what they are. They often use a Gram stain to help identify the species. Once they know the bacteria, they can test which antibiotics will work best. Antibiotics are medicines that fight the infection. Some are bacteriocidal, which means they kill the bacteria. Others are bacteriostatic, which means they just stop the bacteria from growing.

You can also stay safe by cooking food to above 73 °C to kill germs.

Pathogenic bacteria are specific types of bacteria that cause disease in humans. While most bacteria are harmless or even beneficial, these pathogens are specially adapted to overcome the body's natural defenses. For example, the body has an innate resistance to many microorganisms. However, pathogens can invade areas where bacteria are not normally found, such as the blood or tissue fluids.

It is important to distinguish between infection and colonization. Colonization occurs when bacteria are present but cause little to no harm to the host.

These bacteria damage the host through several different mechanisms. Some pathogens cause direct damage by attaching to host cells and using them for nutrients. An example is Streptococcus mutans, which lives in dental plaque. It metabolizes dietary sugar and produces acid as a waste product, which decalcifies teeth to cause dental caries. Other bacteria produce toxins, which are poisonous substances. Endotoxins are lipid portions of lipopolysaccharides found in the outer membrane of Gram-negative bacteria. These are released when the bacteria lyse, or break apart. Exotoxins are secreted into the surrounding medium or released when the cell wall breaks.

Finally, an infection can cause indirect damage. This happens when an excessive or inappropriate immune response inadvertently damages the host's own cells.

Pathogens vary in how they interact with human cells and tissues. Some are obligate intracellular parasites, such as Rickettsia prowazekii, which causes typhus. These organisms can only grow and replicate inside other cells. Other bacteria, such as Salmonella or Listeria, can exist both inside and outside host cells. Some bacteria are opportunistic pathogens. These mainly cause disease in people with immunosuppression or conditions like cystic fibrosis. Examples include Pseudomonas aeruginosa and Burkholderia cenocepacia. Other species might be part of the normal skin microbiota, like certain Staphylococcus species, but can initiate infections if conditions change.

Bacterial infections can target specific parts of the body or act as generalists. For instance, bacterial meningitis is an inflammation of the meninges, which are the protective membranes covering the brain and spinal cord. Bacterial pneumonia specifically affects the lungs. Urinary tract infections are often caused by Escherichia coli, which can ascend into the bladder or kidney to cause cystitis or nephritis. Some bacteria cause skin-specific issues. Impetigo is a highly contagious infection caused by Staphylococcus aureus or Streptococcus pyogenes. Erysipelas is an acute infection of deeper skin layers that spreads via the lymphatic system. Cellulitis is a more diffuse inflammation of connective tissue and skin layers.

To survive inside a human, bacteria must compete for essential resources. Iron is required for the growth of most bacteria. To obtain free iron, some pathogens secrete proteins called siderophores. These proteins bind to iron more tightly than the host's own transport proteins. Once the iron-siderophore complex forms, the bacterium takes it up through surface receptors. Bacteria also need carbon and energy sources. To avoid competing with human cells for glucose, some pathogens, like Haemophilus influenzae, specialize in using other carbon sources like lactate.

Pathogenic bacteria have a massive impact on global health. A GBD study estimated that bacterial pathogens contributed to one in eight deaths globally in 2019. This accounts for approximately 7.7 million deaths, making them the second largest cause of death globally that year.

One specific example is Mycobacterium tuberculosis, which caused 1.4 million deaths in 2019, mostly in sub-Saharan Africa. Other bacteria cause significant disease burdens through pneumonia, foodborne illnesses, or infections like tetanus, typhoid fever, and diphtheria.

Medical professionals use several methods to identify and treat these organisms. Bacteria can be grown in cultures, which may take up to 48 hours, and then identified visually or genomically. Doctors also use a Gram stain to help classify them. Once identified, antibiotics are used for treatment. Antibiotics are classified as bacteriocidal if they kill bacteria, or bacteriostatic if they only prevent growth. Some antibiotics, like chloramphenicol, exhibit selective toxicity by targeting bacterial ribosomes while leaving human eukaryotic ribosomes alone.

Prevention is also possible through sterilization of medical tools, using disinfectants like bleach, and cooking food to temperatures above 73 °C (163 °F).