Bacterial infections are among the most common reasons people visit a doctor, and they can affect nearly every part of the body. Some are mild and clear up quickly with treatment, while others can become serious if left unchecked. Here’s a look at the most common types, what they feel like, and how they’re treated.
How Bacterial Infections Work
Bacteria are single-celled organisms that can live almost anywhere, including on your skin, in your gut, and throughout the environment. Most are harmless or even helpful. But when harmful bacteria enter tissue where they don’t belong, or when normally harmless bacteria multiply out of control, infection follows. Unlike viruses, which hijack your cells and use them as factories to make copies of themselves, bacteria reproduce on their own. This distinction matters because it determines what kind of treatment works: antibiotics target bacteria specifically and have no effect on viruses.
Strep Throat and Other Respiratory Infections
Strep throat is one of the most recognizable bacterial infections, especially in children and teens. It typically comes on fast: a sudden, painful sore throat with red, swollen tonsils that may have white patches or streaks of pus. You might also notice a fever, swollen lymph nodes at the front of your neck, and tiny red spots on the roof of your mouth. Children sometimes experience headache, stomach pain, nausea, or a rash known as scarlet fever. Symptoms usually appear two to five days after exposure.
A quick swab at the doctor’s office can confirm whether the infection is bacterial or viral, which matters because strep throat needs antibiotics. Without treatment, the bacteria can spread and cause complications including ear infections, sinus infections, abscesses around the tonsils, and in rare cases, rheumatic fever (which can damage the heart, joints, and brain) or a kidney condition called post-streptococcal glomerulonephritis.
Bacterial pneumonia is another common respiratory infection. It inflames the air sacs in the lungs, causing cough, fever, chills, and difficulty breathing. Doctors can diagnose it by testing a sputum sample, where mucus coughed up from the lungs is cultured in a lab to identify the specific bacteria involved.
Skin Infections
Staph bacteria (Staphylococcus aureus) live on the skin or in the nose of about 30% of people without causing any problems. When they do cause infection, the result often looks like a pimple, boil, or red swollen area that may be warm and tender. Cellulitis, a deeper skin infection, causes spreading redness, swelling, and pain. Impetigo, more common in young children, produces crusty, honey-colored sores usually around the nose and mouth.
MRSA (methicillin-resistant Staphylococcus aureus) gets a lot of attention because it resists several common antibiotics, making it harder to treat. But any staph infection can become dangerous, even strains that aren’t resistant. Skin infections that are spreading, warm to the touch, or accompanied by fever need prompt medical attention.
Urinary Tract Infections
UTIs are extremely common, particularly in women. The culprit is usually E. coli, a bacterium that normally lives in the digestive tract but causes trouble when it migrates to the urinary system. A bladder infection (the most common type) brings frequent, painful urination, pelvic pressure, lower belly discomfort, and sometimes blood in the urine.
If a UTI travels upward to the kidneys, the symptoms shift significantly. A kidney infection typically causes back or side pain, high fever, shaking chills, nausea, and vomiting. This is a more serious situation that can require aggressive treatment. A urine culture identifies the exact bacteria and which antibiotics will be most effective against it.
Foodborne and Digestive Infections
Food poisoning is frequently bacterial. Salmonella and Campylobacter are two of the most common culprits worldwide. Campylobacter symptoms usually appear two to five days after eating contaminated food (though the range can stretch from one to ten days) and include diarrhea that is frequently bloody, abdominal pain, fever, headache, nausea, and vomiting. Salmonella causes a similar picture with watery or bloody diarrhea, cramps, and fever.
Most foodborne bacterial infections resolve on their own within a few days with rest and fluids. The main risk is dehydration, especially in young children and older adults. Doctors can confirm a bacterial cause through a stool culture if symptoms are severe or prolonged.
Tuberculosis
Tuberculosis (TB) stands apart from most bacterial infections because it can hide in the body for years without causing illness. In its latent form, TB bacteria are alive but inactive. A person with latent TB feels perfectly healthy, has no symptoms, and cannot spread the infection to others. The only sign is a positive result on a TB skin test or blood test.
Active TB disease is a different story. It usually affects the lungs and causes a persistent cough (sometimes producing blood), chest pain, fatigue, weight loss, fever, and night sweats. People with active TB can spread the bacteria to others through the air. TB requires a long course of treatment, typically six to nine months, because the bacteria are slow-growing and difficult to fully eliminate.
How Bacterial Infections Are Diagnosed
The core diagnostic tool is the bacterial culture. A sample is collected from wherever the infection is suspected: a throat swab for strep, a urine sample for UTIs, blood drawn from a vein for bloodstream infections, or a swab from a wound. The sample goes to a lab, where it’s placed in a dish with nutrients that allow bacteria to grow. After the bacteria are identified, an antibiotic sensitivity test checks which medications will work best against that particular strain. This step is increasingly important as antibiotic resistance grows.
How Antibiotics Treat Bacterial Infections
Antibiotics work by targeting structures or processes that bacteria need to survive. Some, like penicillins and cephalosporins, destroy bacteria by breaking apart their cell walls. Since human cells don’t have cell walls, these drugs can kill bacteria without harming your own tissue. Other antibiotics, like macrolides, work by blocking the machinery bacteria use to build proteins, which stops them from growing and reproducing.
The key to effective treatment is matching the right antibiotic to the specific bacteria. Taking the full prescribed course matters even if you feel better after a few days, because stopping early can leave behind the hardiest bacteria, giving them a chance to multiply and potentially develop resistance.
Antibiotic Resistance
Antibiotic resistance is one of the biggest challenges in treating bacterial infections today. The World Health Organization maintains a priority list of resistant bacteria that pose the greatest threat to public health. The 2024 list covers 24 pathogens across 15 bacterial families. The most concerning include drug-resistant tuberculosis, resistant forms of Salmonella, Shigella, gonorrhea, Pseudomonas (a common cause of hospital-acquired infections), and MRSA. Many of these are resistant to last-resort antibiotics, meaning the backup options are running thin.
When a Bacterial Infection Becomes an Emergency
Sepsis occurs when the body’s response to a bacterial infection spirals out of control, damaging organs and tissues. It can develop from any bacterial infection, whether it started as a UTI, a skin wound, or pneumonia. The warning signs include clammy or sweaty skin, confusion or disorientation, extreme pain or discomfort, fever (or feeling very cold and shivering), a racing heart rate or weak pulse, and shortness of breath. Sepsis progresses quickly, and the combination of fever, increased heart rate, low blood pressure, and difficulty breathing is what doctors look for when making the diagnosis. Early treatment dramatically improves survival.