Treating antibiotic-resistant bacteria requires identifying exactly which drugs the bacteria can still be killed by, then using those drugs strategically, often in combinations or at higher doses than standard infections require. In the U.S., resistant hospital infections rose 20% during the COVID-19 pandemic compared to pre-pandemic levels, and most remained elevated through 2022. The good news: clinicians now have more tools than ever, from newer antibiotics to experimental therapies like virus-based treatments that attack bacteria directly.
Why Resistance Changes the Treatment Playbook
In a typical infection, a doctor can prescribe a common antibiotic and reasonably expect it to work. Resistant bacteria have evolved ways to neutralize those drugs, whether by producing enzymes that break the antibiotic apart, pumping the drug out of the cell before it can act, or altering the cellular target the antibiotic was designed to hit. When one of these mechanisms is present, the standard prescription fails, and the infection persists or worsens.
The bacteria that cause the most concern fall into priority tiers maintained by the World Health Organization. At the top are Gram-negative bacteria resistant to last-resort antibiotics, drug-resistant tuberculosis, and several high-burden pathogens including Staphylococcus aureus (the bacteria behind MRSA), Pseudomonas aeruginosa, Salmonella, and Neisseria gonorrhoeae. Each of these requires a tailored treatment strategy because the resistance mechanisms differ between species.
How Doctors Choose the Right Antibiotic
The single most important step in treating a resistant infection is figuring out which antibiotics still work against the specific strain involved. This is done through antimicrobial susceptibility testing, where a sample of the bacteria is exposed to a panel of drugs in the lab. Traditional methods take 18 to 24 hours of incubation, but newer rapid systems can deliver results in as little as 4.5 to 7 hours. One system tested in a randomized trial returned susceptibility results in about 13.5 hours, compared to nearly 50 hours for the standard approach. That speed matters: every hour of delay in effective treatment increases the risk of complications in serious infections like bloodstream sepsis.
Once the susceptibility profile is known, the treatment approach depends on the type of resistance. For bacteria that produce extended-spectrum beta-lactamases (ESBLs), enzymes that break down many common antibiotics, a class of drugs called carbapenems is the preferred choice for serious infections outside the urinary tract. For simpler urinary tract infections caused by the same bacteria, older antibiotics like nitrofurantoin or trimethoprim-sulfamethoxazole often still work and are preferred to preserve the stronger drugs for when they’re truly needed.
Carbapenem-resistant bacteria represent a harder challenge, since carbapenems are themselves considered a last line of defense. Treatment for these infections often involves combining two antibiotics that work through different mechanisms, essentially attacking the bacteria from two angles simultaneously. For Pseudomonas aeruginosa strains classified as “difficult-to-treat resistant,” specific newer antibiotics are reserved and not used for less severe infections, so they remain effective when they’re most needed.
Combination Therapy and Why It Works
Using two or more drugs together is one of the core strategies against resistant infections. The idea is synergy: drug A makes the bacterial cell more vulnerable to drug B, producing an effect greater than either drug alone. One well-studied approach pairs antimicrobial peptides (small proteins that punch holes in bacterial membranes) with conventional antibiotics. The peptides increase membrane permeability, essentially opening doors that let the antibiotic flood into the cell more effectively.
Beyond direct killing, combination approaches can also disrupt biofilms, the slimy protective layers bacteria build on surfaces like catheters and implants. Biofilms make bacteria up to 1,000 times more tolerant of antibiotics, so breaking them apart is often essential for treatment to succeed. Some combinations also directly block the resistance mechanisms themselves, disabling the enzymes or pumps that would otherwise neutralize the antibiotic.
Newer Antibiotics Approved for Resistant Infections
The antibiotic pipeline has been notoriously thin for decades, but several new drugs have reached patients in recent years. In 2025, the FDA approved two notable antibiotics. Zoliflodacin (brand name Nuzolvence) treats uncomplicated gonorrhea, a significant addition given that Neisseria gonorrhoeae has developed resistance to nearly every antibiotic previously used against it. Gepotidacin (brand name Blujepa) was approved for uncomplicated urinary tract infections and works through a novel mechanism, meaning bacteria haven’t yet encountered it and developed widespread resistance.
These approvals matter because truly new classes of antibiotics are rare. Most “new” antibiotics over the past two decades have been modifications of existing drug classes. A genuinely novel mechanism of action buys time before resistance inevitably develops.
Phage Therapy: Using Viruses to Kill Bacteria
Bacteriophages are viruses that naturally infect and destroy bacteria. They’re highly specific, typically killing only one species or even one strain, which means they leave beneficial gut bacteria largely unharmed. A systematic review of 59 studies covering over 1,900 patients who received phage therapy found clinical improvement in 78.8% of cases and complete pathogen eradication in 86.7%. A separate retrospective series of 100 consecutive cases reported improvement in 77.2% and eradication in 61.3%.
Most current phage cocktails target Staphylococcus aureus or Pseudomonas aeruginosa, though research is expanding to cover Acinetobacter baumannii, Klebsiella pneumoniae, and other resistant species. In the U.S., phage therapy is available through the FDA’s emergency investigational new drug program, which requires extensive documentation of phage preparation and safety testing. It’s not yet a standard prescription. Patients who receive it typically have infections that have failed all conventional antibiotic options, and the process involves matching specific phages to the patient’s specific bacterial strain.
One of the biggest regulatory hurdles is that phages are living, evolving entities. Traditional drug regulations were designed for static chemical compounds, not biological products that may need to be updated as the target bacteria evolve. Some institutions have established streamlined FDA filing processes to speed access, but widespread availability is still years away.
Restoring the Gut to Fight Resistance
Fecal microbiota transplantation (FMT) takes a different approach entirely. Rather than killing resistant bacteria directly, it floods the gut with healthy bacteria from a donor, which can outcompete and displace resistant strains. In a study of patients with blood disorders who were colonized by antibiotic-resistant bacteria, 75% achieved complete decolonization after FMT. The procedure worked best when patients hadn’t received antibiotics around the time of the transplant (79% success vs. 36% with concurrent antibiotics), which makes intuitive sense: antibiotics would kill off the transplanted healthy bacteria before they could establish themselves.
Researchers found that patients who responded successfully had higher levels of specific beneficial bacterial genera in their gut after the procedure, and this microbial shift was particularly effective at eradicating resistant Klebsiella pneumoniae. No adverse events were reported in the study. FMT is currently best established for recurrent C. difficile infections but is being explored more broadly as a decolonization strategy for people carrying resistant organisms.
Monoclonal Antibodies as an Alternative
Monoclonal antibodies, lab-made proteins that target specific bacterial toxins or surface structures, offer another route around resistance. Because they work by neutralizing toxins or flagging bacteria for the immune system rather than by the mechanisms antibiotics use, bacterial resistance to antibiotics doesn’t affect them. They also have minimal impact on beneficial bacteria, avoiding the collateral damage that broad-spectrum antibiotics cause. Monoclonal antibodies have been approved for preventing and treating inhalational anthrax and are in clinical trials for Staphylococcus aureus and C. difficile infections, the two bacterial targets with the most active development programs.
Infection Control and Decolonization
Treating resistant infections is only half the equation. Preventing their spread, especially in hospitals, is equally critical. Patients known to carry resistant organisms are placed on contact precautions in acute care settings, meaning healthcare workers wear gloves and gowns for all interactions, and the patient is typically in a private room or cohorted with others carrying the same organism.
For MRSA specifically, decolonization is sometimes attempted using a topical antibiotic applied inside the nostrils combined with antimicrobial body washes. This approach is generally reserved for outbreaks or high-prevalence situations rather than routine use, because decolonization doesn’t always stick permanently. In long-term care facilities, the approach is more individualized, balancing infection control with the resident’s quality of life and mobility needs. In outpatient and home settings, standard hand hygiene and wound care precautions are typically sufficient.
What Makes Treatment Succeed or Fail
The biggest factor in successfully treating a resistant infection is time to effective therapy. Every treatment approach described above works better when started early, which is why the shift toward rapid diagnostics is so consequential. Getting susceptibility results in 6 hours instead of 48 can be the difference between a contained infection and one that spreads to the bloodstream.
Source control also plays a major role. If a resistant infection is associated with an infected device like a catheter, prosthetic joint, or implant, removing or replacing that device is often necessary regardless of which antibiotics are used. Biofilms on these surfaces protect bacteria from even the most potent drugs, and no antibiotic regimen can reliably clear an infection while the colonized device remains in place.
The duration of treatment tends to be longer for resistant infections than for their susceptible counterparts, and the drugs involved often have more side effects because they’re stronger or less refined than first-line options. Monitoring kidney function, hearing, and other organ systems during treatment is standard when using these more aggressive regimens.