Bacteria are single-celled organisms that you can only see with a microscope. They look like balls, rods, or spirals. The vast majority of bacteria do not cause disease, and many bacteria — so-called good bacteria — are helpful and even necessary for good health.
Millions of bacteria live on your skin, in your nose, in your digestive system, and on your genitalia.
Bacterial disease vs. infection
Harmful bacteria that cause disease are called pathogenic bacteria. Bacterial diseases occur when pathogenic bacteria get into the body and infect it. They can reproduce quickly, crowd out healthy bacteria, and grow in tissues that are usually sterile, such as the bladder.
The large load of bacteria that is present while they are replicating can make you sick and cause bacterial disease. Pathogenic bacteria can also cause disease by releasing toxins that damage your body.
Bacteria vs. viruses
Viruses and bacteria can both cause illness, and they share some of the same symptoms. However, they are different pathogens. It can be difficult to tell a bacterial disease from a viral disease.
Bacteria can live on their own, even outside of a person’s body. Antibiotics can usually, though not always, treat bacterial infections successfully.
Viruses can only reproduce in the host — that is, a person or another living thing. Antibiotics do not work against viral infections. Some examples of viral infections include the common cold, COVID-19, and HIV.
Learn more about bacterial vs. viral infections here.
Bacteria are part of the 1,400 human pathogens known so far. Bacterial diseases and the bacteria that cause them can be classified according to the body area they affect.
Often, the bacteria that live on our skin — such as Staphylococcus aureus (S. aureus, or staph) and group A Streptococcus (S. pyogenes, or strep) — are the causes of skin bacterial diseases. However, other bacteria can infect the skin as well. Conditions include:
- boils
- abscesses
- cellulitis
- necrotizing fasciitis
- hot tub folliculitis, which is caused by Pseudomonas aeruginosa bacteria
Symptoms of skin bacterial diseases
Symptoms can include:
- pain and swelling of the affected area
- red or flushed skin
- a rash
- blisters
- sores, which may be oozing pus
- open wounds
Strep, staph, and other bacteria can also cause these bacterial diseases around the eye:
Symptoms of eye bacterial diseases
Symptoms can include:
- swollen eyelids that may extend farther from the eye
- pain with eye movements
- bumps along the eyelid at the base of the lashes
- discharge from the eye or visible sores
- vision changes
- eye redness
Strep bacteria are common causes of ear, nose, and throat infections. Haemophilus influenzae is another common cause of ear infections. Examples include:
- ear infections, including middle and outer ear infections
- sinusitis
- strep throat
Symptoms of ear, nose, and throat bacterial diseases
Symptoms can include:
- a sore throat
- flu-like symptoms
- facial pain and pressure
- a headache
- swollen neck glands
- a stuffy nose
- green or yellow discharge from the nose
- ear discharge
- ear pain
- hearing loss
- a feeling of fullness in the ear
Although viruses commonly cause respiratory diseases, bacteria can too. Conditions include:
Symptoms of respiratory bacterial diseases
Symptoms of pneumonia and bronchitis can include:
- a cough, sometimes a wet cough with sputum from the lungs
- shortness of breath
- fever
- muscle aches
- a headache
Learn more about respiratory infections here.
The central nervous system (CNS) includes the brain and spinal cord. Many kinds of bacteria can infect the CNS, including Neisseria meningitidis, Haemophilus influenzae, strep, Listeria, and Escherichia coli (E. coli). Examples of bacterial CNS diseases include:
- encephalitis
- meningitis
- brain abscess
Symptoms of central nervous system bacterial infections
Symptoms of meningitis can include:
- sudden fever and headaches
- a stiff neck
- nausea, vomiting, light sensitivity, and a rash (possibly)
- irritability, poor feeding, vomiting, a bulging soft spot, and unusual reflexes (in infants)
With encephalitis, there may be changes in vision, speech, and hearing as well as seizures, confusion, and hallucinations.
Gastrointestinal diseases that can be caused by bacteria include:
Symptoms of gastrointestinal bacterial diseases
Symptoms of these conditions can include:
- diarrhea
- a change in stool color
- blood in the stool
- nausea
- vomiting
- a loss of appetite
- unexplained weight loss
- generally feeling ill
- abdominal pain, which may be cramp-like
- fever
Foodborne diseases are commonly known as food poisoning because consuming foods or liquids contaminated with the bacteria can cause them. Many types of bacteria can cause it, including:
- Salmonella
- Campylobacter
- Staphylococcus
- E. coli
- Clostridium perfringens
Food poisoning symptoms
Symptoms can include:
Sexually transmitted infections (STIs) caused by bacteria include:
Symptoms of sexually transmitted infections
Symptoms of chlamydia and gonorrhea can include:
- discharge from the vagina or penis
- pain or burning with urination
- fever
- lower abdominal pain and pain with vaginal intercourse (in females)
Symptoms of early stage syphilis include a painful lesion, known as a chancre, on the genitals, rectum, or mouth. The second stage is marked by flu-like symptoms and rashes.
Learn about the most common STIs here.
Bacterial diseases can involve the urethra, bladder, ureters, and kidneys. A variety of bacteria can cause these conditions, including E. coli, Klebsiella pneumoniae, and S. aureus. Urinary tract infections (UTIs) and diseases include:
- bladder infection
- kidney infection
- poststreptococcal glomerulonephritis (caused by group A Streptococcus)
Symptoms of UTIs
Symptoms can include:
- a sudden urge to urinate
- burning with urination
- cloudy urine
- malaise
- fever
- back pain
- flank pain
Bacteria can also enter and multiply in the bloodstream. Known as bacteremia or septicemia, this condition is very serious because bacteria in the bloodstream can easily trigger widespread inflammation in your body, known as sepsis. Bacteria and bacterial diseases that most commonly lead to bloodstream infections include:
- Neisseria meningitidis
- Streptococcus species
- S. aureus
- Listeria monocytogenes
- E. coli
- K. pneumoniae
- carbapenum-resistant Enterobacterales bacteria
Learn more about septicemia here.
Bacteria can enter the body through a variety of means, including:
- having breaks in the skin or mucous membranes — including the nose, mouth, and urinary tract — such as from bites, cuts, rashes, abrasions, or needle injections, including tattooing and drug use
- eating contaminated foods or touching infected feces or bodily fluids and not washing your hands before eating
- having sexual contact with a person who has an infection
- inhaling contaminated airborne droplets or kissing a person with an infection
- sharing needles for tattooing or drug use
- touching infected body fluids and then touching the eyes, ears, or urethra
Although less common, bacterial infections can also occur when bacteria already in the body begin to multiply too much. For instance, taking a course of antibiotics to treat another bacterial infection can trigger gut bacteria such as Clostridium difficile to overmultiply. This can cause serious harm in the digestive tract.
Learn more about C. diff here.
Medical professionals may prescribe antibiotics for bacterial diseases. These drugs work by stopping the bacteria from reproducing and spreading. Different types of antibiotics are effective for treating specific types of bacteria.
Some bacterial infections do not need antibiotics, according to the Centers for Disease Control and Prevention (CDC). These include bacterial ear and sinus infections because they may resolve on their own in time.
Antibiotics come in different forms, including pills, liquids, eye drops, creams, and injections. Depending on the type and severity of the infection or disease you have, you may need IV antibiotics administered in a healthcare setting.
General types of antibiotics include:
- cephalosporins
- macrolides
- penicillins
- quinolones
- sulfanilamides
- tetracyclines
The length of treatment depends on your condition, age, and overall health as well as the antibiotic. A standard course of antibiotics is 10 days, but a short course of 5–7 days may be sufficient under certain circumstances. However, treatment can take much longer for some infections. For example, antibiotic treatment for active tuberculosis is 6–12 months.
Antibiotic resistance
Sometimes, an antibiotic that used to work in treating a bacterial disease stops being effective. This is called antibiotic resistance.
Antibiotic resistance is becoming a global public health problem because resistant bacterial diseases — sometimes called “superbugs” — become more difficult to treat. This can result in serious complications, such as sepsis, coma, and death.
Millions of antibiotic-resistant bacterial infections happen every year in the United States, and more than 35,000 people die from these infections annually.
Learn more about superbugs here.
Contact your doctor right away if you develop new or worsening symptoms or do not feel better within 48–72 hours after starting your antibiotic treatment. Possible reasons for continued symptoms include the antibiotic not being the right choice for the particular bacteria or the bacteria not being the cause of the symptoms.
Although a course of antibiotics can easily treat some infections, certain bacterial diseases are serious enough to require hospitalization and even intensive care.
You can reduce your risk of getting a bacterial disease by preventing infections by:
- practicing good hygiene
- handling food properly
- cleaning all wounds, cuts, and incisions
- getting all recommended immunizations
