Bacterial Diseases

Medically Reviewed By William C. Lloyd III, MD, FACS
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What are bacterial diseases?

Bacterial diseases include any type of illness caused by bacteria. Bacteria are a type of microorganism, which are tiny forms of life that can only be seen with a microscope. Other types of microorganisms include viruses, some fungi, and some parasites.

Millions of bacteria normally live on the skin, in the intestines, and on the genitalia. The vast majority of bacteria do not cause disease, and many bacteria are actually helpful and even necessary for good health. These bacteria are sometimes referred to as “good bacteria” or “healthy bacteria.”

Harmful bacteria that cause bacterial infections and disease are called pathogenic bacteria. Bacterial diseases occur when pathogenic bacteria get into the body and begin to reproduce and crowd out healthy bacteria, or to grow in tissues that are normally sterile. Harmful bacteria may also emit toxins that damage the body. Common pathogenic bacteria and the types of bacterial diseases they cause include:

  • Escherichia coli and Salmonella cause food poisoning.

  • Helicobacter pylori cause gastritis and ulcers.

  • Neisseria gonorrhoeae causes the sexually transmitted disease gonorrhea.  

  • Neisseria meningitidis causes meningitis.

  • Staphylococcus aureus causes a variety of infections in the body, including boils, cellulitis, abscesses, wound infections, toxic shock syndrome, pneumonia, and food poisoning.

  • Streptococcal bacteria cause a variety of infections in the body, including pneumonia, meningitis, ear infections, and strep throat.

Bacterial diseases are contagious and can result in many serious or life-threatening complications, such as blood poisoning (bacteremia), kidney failure, and toxic shock syndrome.
Seek prompt medical care if you suspect that you have a bacterial disease. Seek immediate medical care (call 911) if you, or someone you are with, have critical symptoms of a bacterial disease, such as high fever, lethargy or unresponsiveness.

What are the symptoms of bacterial diseases?

Symptoms of bacterial diseases vary depending on the type of bacterial infection, the area of the body that is infected, and other factors, such as the patient’s age and health history. The symptoms of bacterial diseases can also resemble symptoms of other diseases, such as colitis, influenza, and viral infections. The classic symptom of a bacterial infection is a fever, although not all people with a bacterial infection will have a fever.

Bacterial disease symptoms can include:

In infants, signs of a bacterial disease can also include:

  • Bulging of the soft spot on the top of the head 

  • Difficulty with feeding

  • Excessive crying or fussiness

  • Excessive sleepiness

Serious symptoms that might indicate a life-threatening condition

In some cases, bacterial diseases can result in serious or life-threatening complications, such as sepsis or kidney failure. Seek immediate medical care (call 911) if you, or someone you are with, have any of the following symptoms:

  • Confusion or delirium

  • Deep, wet chest cough that produces yellow, green or brownish phlegm

  • Difficulty breathing, wheezing or shortness of breath

  • High fever (higher than 101 degrees)

  • Inappropriate change in alertness or level of consciousness

  • Infants: sunken fontanel (soft spot) on the top of the head, lethargy, no tears with crying, and few or no wet diapers

  • Lethargy or unresponsiveness

  • Not urinating or urinating small amounts of tea-colored urine

  • Seizure

What causes bacterial diseases?

Bacterial diseases are caused by harmful bacteria (pathogenic bacteria). The vast majority of bacteria do not cause disease, and many bacteria are actually helpful and even necessary for good health. Bacterial diseases occur when pathogenic bacteria get into an area of the body that is normally sterile, such as the bladder, or when they crowd out the helpful bacteria in places such as the intestines, vagina or mouth. Less common, bacterial infections can occur when healthy bacteria multiply uncontrollably. 

Various ways pathogenic bacteria can enter the body

Pathogenic bacteria can enter the body through a variety of means including:

  • Contamination of bites, cuts, rashes, abrasions and other breaks in the skin, gums and tissues

  • Eating  contaminated food

  • Getting bitten by an infected insect

  • Having sexual contact with an infected person

  • Inhaling contaminated air-borne droplets into the nose and lungs

  • Kissing an infected person

  • Sharing needles for tattooing or drug use

  • Through the eyes, ears or urethra

  • Touching infected feces or body fluids, and not washing your hands before eating or touching your mouth, eyes or nose

Once bacteria enter the body, a healthy immune system will recognize the bacteria as foreign invaders and try to kill or stop the bacteria from reproducing. However, even in a healthy person, the body is not always able to stop the bacteria from multiplying and spreading. As the harmful bacteria reproduce, they can crowd out healthy bacteria and microorganisms and emit toxins that damage the cells of the body.

What are the risk factors for bacterial diseases?

Bacterial diseases can occur in any age group or population, but a number of factors increase the risk of developing bacterial diseases. Not all people with risk factors will get bacterial diseases. Risk factors for bacterial diseases include:

  • Being an infant, child or older adult

  • Eating eggs or meats that are raw or undercooked

  • Eating expired foods, or eating leftovers that have been stored for more than two to three days

  • Having a genetic predisposition to bacterial infection

  • Having a compromised immune system due to an immunodeficiency disorder, HIV/AIDS, diabetes, cancer or cancer treatment, kidney disease, or from taking steroid medications   

  • Having a chronic disease

  • Malnutrition

  • Not washing your hands frequently, especially after using the bathroom, touching pet feces, handling reptiles, or touching raw foods or foods contaminated with bacteria

  • Significant exposure to a person with a bacterial disease

Reducing your risk of bacterial diseases

You can lower your risk of developing or transmitting bacterial diseases by :

  • Avoiding contact with a person who has a bacterial disease or its symptoms, such as fever, vomiting or diarrhea

  • Covering your mouth and nose with a tissue when sneezing or coughing, then washing your hands

  • Defrosting foods in the refrigerator or microwave, not on the counter

  • Refrigerating leftovers right away and eating them within two to three days unless they have been frozen

  • Eating a healthy diet that is high in whole grains, fruits and vegetables and contains adequate low-fat protein and low-fat dairy products or other calcium sources

  • Getting enough rest and minimizing stress

  • Getting recommended vaccines for bacterial diseases, such as meningitis, pneumonia, tetanus and rabies

  • Seeking regular medical care and following your treatment plan for a chronic disease

  • Throwing out expired food or perishable food that has been sitting at room temperature for two hours or longer

  • Using antibacterial products to clean surfaces, such as computer keyboards, telephones and sinks

  • Washing your hands after using the bathroom and after contact with pet feces, reptiles, dirty diapers, raw foods, and people who are ill

  • Washing plates, utensils, and cutting boards that have been exposed to raw meats or poultry in hot soapy water

  • Wearing long pants and sleeves, and using insect repellant when in tall grass or wooded areas

How are bacterial diseases treated?

Bacterial diseases are treated with antibiotics. Antibiotics work by killing the harmful bacteria or by stopping them from reproducing and spreading. Different types of antibiotics are effective for treating specific types of bacteria. Antibiotics may be given orally, intravenously, or by intramuscular injection, depending on the type and severity of bacterial disease and other factors.

General types of antibiotics include:

  • Aminoglycosides
  • Cephalosporins
  • Macrolides
  • Penicillins
  • Quinolones
  • Tetracyclines

Treatment of bacterial infections also includes:

  • Good nutrition

  • Hospitalization and intensive care in some cases, especially if complications occur

  • Increased fluids

  • Rest

People who have had close contact with a person with a serious bacterial disease, such as bacterial meningitis, may also need to be treated and monitored for the disease, even in the absence of symptoms.

Sometimes an antibiotic that used to work in treating a bacterial disease stops being effective. This is called antibiotic resistance. This makes a bacterial disease more difficult to treat and can result in serious complications, such as sepsis, coma and death.

What are the possible complications of bacterial diseases?

In some people, bacterial diseases can lead to serious, even life-threatening complications. Therefore, it is important to visit your health care provider when you experience symptoms of a bacterial infection. Once the underlying infection has been determined, following the treatment plan outlined by your doctor can help reduce any potential complications including:


  1. Understanding Microbes in Sickness and in Health. National Institute of Allergy and Infectious Diseases.
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Medical Reviewer: William C. Lloyd III, MD, FACS
Last Review Date: 2021 Jan 19
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THIS TOOL DOES NOT PROVIDE MEDICAL ADVICE. It is intended for informational purposes only. It is not a substitute for professional medical advice, diagnosis or treatment. Never ignore professional medical advice in seeking treatment because of something you have read on the site. If you think you may have a medical emergency, immediately call your doctor or dial 911.
  1. Understanding Microbes in Sickness and in Health. National Institute of Allergy and Infectious Diseases.