Bacterial infections are primarily treated with antibiotics, medications that either kill bacteria directly or stop them from multiplying so your immune system can finish the job. The specific antibiotic, how you take it, and how long you take it all depend on what type of bacteria is causing the infection and where in your body it’s located. Some minor infections clear up with a topical cream, while serious ones may require days of intravenous treatment in a hospital.
How Doctors Identify the Right Treatment
Before choosing an antibiotic, your doctor often needs to figure out exactly which bacteria is causing your infection. This starts with a culture test: a small sample is taken from the infected area (a swab from a wound, a urine sample, blood draw, or throat swab) and sent to a lab. Technicians encourage the bacteria in the sample to grow and multiply, then examine it under a microscope to identify the species.
The lab also runs susceptibility testing, which exposes the bacteria to different antibiotics to see which ones actually work against it. The whole process takes one to five days depending on the type of bacteria. For common, straightforward infections like a urinary tract infection or strep throat, your doctor will often prescribe a standard antibiotic right away based on the most likely cause, then adjust if the culture results come back showing something unexpected.
How Antibiotics Work Against Bacteria
Antibiotics attack bacteria through four main strategies, each targeting a different part of the bacterium’s biology.
Breaking down the cell wall. Bacteria are surrounded by a rigid wall that holds their structure together. Some antibiotics, including penicillin and its relatives, block the construction of this wall. Without it, the bacterium swells and bursts.
Stopping protein production. Bacteria need to constantly build proteins to survive and reproduce. Several antibiotic classes work by attaching to the bacterium’s protein-building machinery (its ribosomes) and jamming the process at different stages. This prevents the bacterium from making the proteins it needs to function.
Blocking DNA replication. To multiply, bacteria must copy their DNA. Certain antibiotics, particularly a class called fluoroquinolones, bind to the enzymes bacteria use to unwind and duplicate their genetic material. This causes the DNA strands to break apart, killing the cell.
Disrupting essential nutrient processing. Bacteria need to produce folic acid to grow. Unlike human cells, which absorb folic acid from food, bacteria have to manufacture it themselves. Some antibiotics shut down that manufacturing process, starving the bacteria of a nutrient they can’t get any other way.
Oral, Topical, and Intravenous Options
Most bacterial infections are treated with oral antibiotics, pills or liquids you take at home. This is the standard approach for infections like strep throat, sinus infections, urinary tract infections, and many types of pneumonia.
For skin infections, minor wounds, or infections around the eyes and ears, topical antibiotics applied directly to the area are often enough. Over-the-counter options typically contain ingredients like bacitracin, neomycin, or polymyxin B. Prescription-strength topical treatments come as ointments, creams, gels, or even adhesive patches that release medication through the skin over time.
Intravenous (IV) antibiotics are reserved for more severe infections, situations where the bacteria have entered the bloodstream, or cases where the infection isn’t responding to oral treatment. These are given in a hospital or sometimes through a home infusion setup for longer courses.
How Long Treatment Typically Lasts
The trend in modern medicine has shifted toward shorter antibiotic courses when the evidence supports it. Shorter treatment means less total antibiotic exposure, which reduces your risk of side effects and lowers the chance of breeding resistant bacteria. For several common infections, studies have shown that shorter courses produce the same outcomes as longer ones.
Here’s what current guidelines from the American College of Physicians recommend for some of the most frequently treated infections:
- Bladder infections (uncomplicated, in women): 3 to 5 days depending on the antibiotic, or in some cases a single dose.
- Community-acquired pneumonia: A minimum of 5 days, extended only if symptoms like fever, appetite loss, or mental fogginess haven’t resolved.
- Kidney infections (uncomplicated): 5 to 14 days depending on the antibiotic chosen and what the bacteria responds to.
The old advice to “always finish your entire course even if you feel better” is being re-examined. For some infections, stopping once symptoms have clearly resolved and clinical markers are stable is now considered appropriate. That said, don’t make that call on your own. Your doctor can tell you whether your specific infection is one where early stopping is safe.
Side Effects to Expect
Antibiotics are not side-effect-free. A Johns Hopkins study found that roughly 1 in 5 hospitalized patients experienced at least one adverse effect from antibiotics, with risk increasing about 3 percent for every additional 10 days of treatment.
The most common problems were gastrointestinal issues like diarrhea, nausea, and stomach cramps, accounting for 42 percent of all reported side effects. Kidney-related effects made up 24 percent, and blood-related changes accounted for 15 percent. About 4 percent of patients developed a secondary infection called C. diff, a difficult-to-treat gut infection caused by antibiotics wiping out the normal protective bacteria in the intestines.
These numbers come from hospitalized patients receiving stronger or longer courses, so the risk for a standard outpatient prescription is generally lower. Still, it underscores why taking antibiotics only when you actually need them matters.
Antibiotic Resistance
One of the biggest challenges in treating bacterial infections today is resistance. Bacteria evolve quickly, and overuse or misuse of antibiotics accelerates the process. When bacteria become resistant, the drugs that once killed them no longer work, leaving fewer treatment options.
The scale of this problem is growing. One particularly dangerous category, carbapenem-resistant bacteria (CRE), caused approximately 12,700 infections and 1,100 deaths in the U.S. in 2020 alone. Between 2019 and 2023, infections from one of the most concerning subtypes of CRE surged by more than 460 percent in the United States, according to a CDC report.
Resistance is a major reason why doctors try to match the right antibiotic to the right bacteria through culture testing rather than prescribing broad-spectrum antibiotics for everything. It’s also why you shouldn’t take leftover antibiotics from a previous illness or someone else’s prescription. Using the wrong antibiotic, or the right one at the wrong dose, gives bacteria a chance to adapt without being fully eliminated.
Experimental Alternatives: Phage Therapy
When antibiotics fail entirely, a small but growing number of patients have been treated with bacteriophages, viruses that specifically infect and kill bacteria. Phage therapy isn’t new (it’s been used in parts of Eastern Europe for decades), but it’s gaining renewed attention in Western medicine as antibiotic resistance worsens.
In the U.S., phage therapy is not yet an approved, standard treatment. It’s currently available only through an emergency process where a physician requests permission from the FDA to use it on a case-by-case basis when conventional antibiotics have failed. Since a landmark 2017 case where phage cocktails saved a patient with a life-threatening antibiotic-resistant infection, this emergency pathway has been used for prosthetic joint infections, heart device infections, lung infections in cystic fibrosis patients, and various bloodstream infections.
The regulatory framework hasn’t caught up to the science yet, which limits how widely phage therapy can be used. For now, it remains a last-resort option rather than something your doctor can routinely prescribe.