Targeting OprF to Overcome Carbapenem Resistance in Pseudomonas aeruginosa: A New Therapeutic Opportunity

Antibiotic resistance is one of the most pressing public health challenges of the 21^st century. It occurs when bacteria evolve and develop the ability to withstand the effects of antibiotics that were once effective in killing them or slowing their growth. As a result, infections become harder to treat, leading to prolonged illnesses, higher medical costs, and increased mortality rates. Infections by the opportunistic human pathogen, Pseudomonas aeruginosa in particular are difficult to treat due to its high intrinsic and acquired antibiotic resistance. It thrives in hospital settings, where it preys on the most vulnerable patients including people in intensive care, those with weakened immune systems, and individuals with cystic fibrosis. The real danger comes from its ability to resist even the most powerful antibiotics such as carbapenems (imipenem and meropenem as examples), which doctors rely on when other treatments fail. Once this bacterium becomes resistant to carbapenems, the treatment options become severely limited, making infections far more dangerous and difficult to manage. Indeed, WHO designated carbapenem-resistant Pseudomonas aeruginosa as one of three Critical Priority pathogens. It can produce carbapenemase enzymes which break the antibiotics. Moreover, it can shut down a protein channel called OprD, which normally allows carbapenems to enter into the cell. On top of that, this bacterium has efflux pumps that actively push antibiotics out of its system and can even change its membrane structure to make it harder for drugs to get through. This growing resistance has serious consequences for patients. When Pseudomonas aeruginosa becomes resistant to carbapenems, doctors are often forced to use older, more toxic drugs like polymyxins, which can cause significant kidney a neurological damage. Therefore, there is an urgent need to find a solution and researchers are looking for creative ways to restore the effectiveness of existing antibiotics rather than relying solely on developing new ones. To this account, new research paper published in Journal Antimicrobial Agents and Chemotherapy and led by Professor Patrice Nordmann from the University of Fribourg in Switzerland and contributed with Nicolas Helsens, Laurent Poirel, Mustafa Sadek, Dirk Bumann, and Jacqueline Findlay investigated whether removing another outer membrane protein, OprF, could impact carbapenem resistance. While OprD is well known for its role in carbapenem entry, OprF has been mostly seen as a structural protein. However, the researchers suspected that without OprF, the bacteria might compensate by increasing OprD levels or making their membranes more permeable, allowing carbapenems to work more effectively. If this idea proves correct, it could open up entirely new possibilities for treating resistant infections.

The researchers started by engineering different strains of Pseudomonas aeruginosa that lack the OprD or OprF channels or both studied if this could change how the bacteria respond to antibiotics. They used three different bacterial strains: one strain lacked oprD (ΔoprD), another was missing oprF (ΔoprF), and the third had both genes deleted (ΔoprD/ΔoprF). The next step, they introduced various resistance genes that can produce β-lactamases enzyme, which can break down antibiotics like carbapenems, rendering them ineffective. The team selected a range of these enzymes, including some that are commonly found in antibiotic-resistant bacteria in hospitals. To measure this, they performed minimum inhibitory concentration tests, which assess how much of an antibiotic is needed to stop bacterial growth. The authors found that in strains where oprF was deleted, resistance to carbapenems, including imipenem and meropenem, dropped significantly. This effect was particularly noticeable in bacteria producing powerful carbapenemase enzymes such as NDM-5, VIM-2, and OXA-181. In some cases, the authors found that reduction in resistance was so dramatic that the bacteria which had previously been untreatable, became susceptible to carbapenems again. Interestingly, this did not happen when only oprD was deleted which suggest that oprF plays a role in antibiotic resistance that was not previously understood. Moreover, the team examined gene expression levels and found that when oprF was removed, the bacteria responded by increasing oprD production. According to the research team, OprD allows carbapenems to enter the bacterial cell, this could explain why the antibiotics suddenly became more effective. Without oprF, the bacteria appeared to adjust by opening up more pathways for the antibiotics to get inside. Further tests showed that deleting oprF did not affect resistance to other antibiotics like colistin or rifampicin. The researchers also noticed that bacteria lacking oprF grew more slowly which indicate that this deletion might weaken them in other ways.

In conclusion, the research work led by Professor Patrice Nordmann and his team, changes the way we think about antibiotic resistance in Pseudomonas aeruginosa and discovered removing oprF, the bacteria compensated by increasing the production of OprD, which in turn made them more sensitive to carbapenems. This finding reveals a potential weak spot in Pseudomonas aeruginosa, one that could be used to restore the power of these important antibiotics. If scientists can find a way to temporarily block OprF, it might trigger the same effect seen in the study, where bacteria respond by boosting OprD levels. This would allow carbapenems to enter into bacterial cells and become again an effective and reliable treatment. Additionally, the work of Professor Nordmann et al could help doctors make more precise, personalized treatment decisions. For instance, we could know by testing if Pseudomonas aeruginosa are still vulnerable to carbapenems depending on their oprF status and this could help determine the best antibiotic to use.