An Overview of Bacterial Infections

MRSA colonies on blood agar plate
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Bacterial infections are common, and their effects vary. There are a number of different bacteria that can cause illness, and you can become exposed to them in a variety of ways.

Bacteria are small organisms that can invade the body, causing illness. These infections usually trigger a protective immune response. You also have innate bacteria in your body that helps digest your food and protect your body from harmful bacteria.

Symptoms

Children and adults of any age can develop a bacterial infection. Bacteria can infect any area of the body, including the skin, bladder, lungs, intestines, brain, and more. A bacterial infection can also spread throughout the blood, causing a condition described as sepsis.

You can experience generalized symptoms, such as fevers, chills, and fatigue as a result of a bacterial infection anywhere in the body.

Localized Symptoms

In addition to generalized symptoms, you can experience local effects of a bacterial infection, which correspond to the affected area or areas of the body. Pain, swelling, redness, and organ dysfunction are common localized symptoms.

Pain is common with bacterial infections, and you can have skin pain with a bacterial skin infection, pain when breathing with a lung infection, and abdominal pain with an intestinal infection.

You can easily identify redness or swelling on visible parts of the body, such as the skin, throat, or ears. Often, internal organs also become red and swollen when you have a bacterial infection, and while you can't see it, you may feel pain or other effects in these areas. For example, you may develop a productive cough, sometimes with thick mucus, with a bacterial infection of your respiratory tract (throat, bronchi, or lungs).

And bacterial infections often cause diminished or altered function of the infected regions of the body. You may have impaired concentration with meningitis (an infection surrounding the brain) or decreased kidney function with pyelonephritis (a kidney infection).

Timing

Different bacterial infections have a characteristic disease course. The symptoms can begin immediately or after a delay due to an incubation period. And the symptoms can worsen rapidly or may progress slowly.

Causes

Bacterial infections are caused by the transmission of bacteria. You can be exposed to bacteria from other people, through the environment, or from eating contaminated food or drinking contaminated water.

Anyone can become sick when exposed to bacteria, but having a weak immune system or taking immunosuppressive medication can make you more susceptible to developing a severe bacterial infection—even from the bacteria that are normally innate to your body.

Types of Bacterial Infections

The severity of bacterial infections depends largely on the type of bacteria involved. Bacterial infections can range from minor illnesses such as strep throat and ear infections to more life-threatening conditions like meningitis and encephalitis.

Some of the most common bacterial infections include:

  • Salmonella is a type of infection often described as food poisoning. It causes severe stomach upset, diarrhea, and vomiting. Salmonella is caused by a non-typhoidal salmonellae bacteria found in the intestinal tracts of humans and other animals, and the most recognized method of infection is through undercooked poultry.
  • Escherichia coli (E. coli) causes gastrointestinal (GI) distress. The infection usually resolves on its own, but it can be severe or even fatal. E. Coli bacteria is commonly spread through contaminated food, including uncooked vegetables.
  • Tuberculosis is a highly contagious disease caused by the Mycobacterium tuberculosis bacteria. It most commonly causes a lung infection, and it rarely affects the brain.
  • Methicillin-resistant Staphylococcus aureus (MRSA) is an antibiotic-resistant bacteria that can be deadly, particularly in people who have compromised immune systems.
  • Clostridium difficile (C. diff) is a bacteria normally found in the intestine. It can cause GI illness when it overgrows due to antibiotic use or an impaired immune system.
  • Bacterial pneumonia is a lung infection that can be caused by an array of different bacteria, including Streptococcus pneumoniae, Klebsiella pneumoniaePseudomonas aeruginosa, and others. These infections are typically spread through air particles from coughing or sneezing.
  • Bacterial vaginosis is an infection of the vagina which can cause itchiness, discharge, and painful urination. It is often caused by sexually transmitted infections, such as chlamydia, or trichomoniasis.
  • Heliobacter pylori (H. pylori) is a type of bacteria associated with stomach ulcers and chronic gastritis. The environment of the GI system can change due to reflux, acidity, and smoking, which predisposes to this bacterial infection.
  • Gonorrhea is a sexually transmitted infection caused by the bacteria Neisseria gonorrhoeae.
  • Vibrio vulnificus is a rare, "flesh-eating" bacteria that can be found in warm seawater.

Bacterial organisms tend to target certain areas of the body— it is rare for syphilis, which is a sexually transmitted infection, to affect the stomach or lungs. And Haemophilus Influenzae Type B (Hib) causes ear, throat, and lung infections, but does not harm the skin or bladder.

Diagnosis

Your bacterial infection can usually be diagnosed based on the pattern of your symptoms. The location, timing, and severity of your symptoms may be very characteristic of a certain bacterial infection.

Your medical team may also want to verify your diagnosis before prescribing an antibiotic (antibacterial medication). This can be done with a fluid sample that is sent to a laboratory for examination.

A swab from your throat or ear can be sent for an evaluation. Infected areas of skin can also be swabbed, or pus can be examined. Similarly, sexually transmitted infections can be identified with a fluid sample from the affected area.

A urine sample can identify bacterial infections of the bladder and kidneys. In some situations, a fecal sample may be helpful in identifying a bacterial cause of persistent gastrointestinal (GI) upset.

Blood Tests

Sometimes, blood tests can be used to identify infectious bacteria. Often, with a bacterial infection, you may have an elevated number of white blood cells (WBCs), which can be detected on a complete blood count (CBC).

Your medical team may send a CBC with differential to see whether certain types of WBCs have increased in your blood. A number of different types of WBCs work together to help defend you from infections. Different infections induce the increase of different types of WBCs, and this pattern can help your medical team identify which infection you have.

Imaging Studies

If there is a concern that you could have a bacterial abscess (an enclosed, puss filled area) in or near your internal organs, you may need an imaging study to help identify it.

Bacteria and Other Infectious Organisms

There are other infectious organisms besides bacteria. Viruses, parasites, protozoa, fungi, worms, and prions (infectious protein particles) can all cause infections.

Viruses are 10 to 100 times smaller than bacteria, while parasites, protozoa, and fungi are larger than bacteria. These organisms all look different under a microscope and behave differently in the body. For example, parasites often have a complicated life cycle, in which the eggs enter the body and hatch, giving rise to infectious wormlike organisms that invade human tissue. Fungi are often long-lasting, slow-growing infections.

The most important difference between different infectious microorganisms is that they are treated differently. For example, antibiotics are medications that kill bacteria, but they cannot affect other infectious organisms.

Treatment

Often, bacterial infections resolve quickly, even without treatment. However, many bacterial infections need to be treated with prescription antibiotics. You may also need supportive care for effects such as fever, pain, swelling, coughing, or dehydration.

Untreated bacterial infections can spread or linger, causing major health problems. While it is rare, untreated bacterial infections may even be life-threatening.

Antibiotics

Antibiotic selection is based on the type of bacteria involved. Most antibiotics work against more than one type of bacteria, not against all of them.

There are different ways that you can take antibiotics. They are available to take by mouth, topically (superficially, on the skin or eye), and intravenously (IV).

If you are using a prescription antibiotic, be sure to use it as directed. For example, do not use a skin antibiotic on your eyes. And it is important to take your medication for the complete duration of your prescribed therapy.

Supportive Care

Your doctor may prescribe pain medication or anti-inflammatory medication to reduce pain and swelling from your bacterial infection. If you have a fever, your doctor may also recommend medication to lower your fever. Non-steroidal anti-inflammatories (NSAIDs) often reduce fevers, swelling, and pain.

If you have a painful cough, your doctor may recommend anti-cough medication. And you may need IV fluids if you are becoming dehydrated.

Drainage

If you have an abscess, you may need to have it surgically treated. This can be a simple procedure for a superficial abscess in the skin. An abscess located deep in the body, such as in the intestines or in the brain, may require removal with surgical intervention.

A Word From Verywell

You are likely to have a few bacterial infections throughout your life. These infections can cause a wide range of symptoms and effects. Some can worsen and cause severe illness.

Your doctor can diagnose a bacterial infection based on a number of clinical features, as well as diagnostic testing. Sometimes, these infections require prescription medications. It is never a good idea to use an antibiotic "just in case" you have a bacterial infection or to reuse an old prescription—your infection could get worse if you use the wrong medication, or you could develop bacterial resistance if you use the medication unnecessarily.

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