Emergence of New Delhi Metallo-β-lactamase-9 (blaNDM-9) gene in Carbapenem-Resistant Acinetobacter baumannii Clinical Isolates in Africa

Imagine the human body as a bustling city, and inside it, tiny invaders called bacteria are constantly trying to set up camp. Usually, our immune system is the police force that keeps them in check. But sometimes, these bacteria evolve into super-criminals, learning to ignore the police and even the heavy-duty weapons we use to stop them. This is the world of antibiotic resistance. Think of antibiotics as the city's special weapons—like a master key that unlocks and destroys the bacteria's protective walls. For decades, doctors have had a "super-key" called carbapenems that works even when the bacteria have learned to ignore the older keys. However, the bacteria are smart; they are building their own "anti-keys," called enzymes, which can break the super-key before it even touches the wall.

The most dangerous of these anti-keys are called carbapenemases. One specific type, known as NDM (New Delhi Metallo-β-lactamase), is like a master locksmith that can destroy almost every kind of antibiotic key we have, leaving doctors with very few options left. When this happens, a simple infection can become life-threatening. Scientists around the world are constantly on high alert, watching for new versions of these "super-enzymes" to see if they are spreading to new places or changing their shape to become even stronger. This is the story of a new discovery in that ongoing battle.

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The New Super-Villain Arrives in Africa

In a recent study, a team of scientists from the Walter Reed Army Institute of Research and the Kenya Medical Research Institute uncovered a new chapter in this bacterial arms race. They found a very specific, dangerous version of the NDM enzyme, called NDM-9, hiding inside a bacterium called Acinetobacter baumannii. This bacterium is notorious for causing infections in hospitals, particularly in patients with skin wounds or throat issues. The researchers discovered this new threat in four patients across three different hospitals in Kenya, with samples taken between 2025 and 2026.

To understand why this is a big deal, imagine the bacteria as a fortress. Inside this fortress, the bacteria usually carry a few "locks" that make them hard to kill. The most common locks in this specific bacterium are called OXA enzymes. But in these four new cases, the bacteria weren't just using the old locks; they had acquired a brand-new, high-tech weapon: the NDM-9 gene. This gene is a variation of the famous NDM-1, but with a tiny tweak (a single change in its code) that makes it even more effective at destroying certain powerful antibiotics, including some of the newest ones doctors were hoping would work.

How the Bacteria Hid the Weapon

The scientists didn't just find the gene; they figured out exactly how it was hiding. Usually, dangerous genes travel on little floating rings of DNA called plasmids, which can jump from one bacterium to another like a virus. However, in this case, the NDM-9 gene wasn't on a floating ring. Instead, it was firmly planted in the bacterium's main instruction manual (its chromosome), locked inside a mobile "package" called a transposon.

Think of this transposon as a self-contained moving truck. The truck is called Tn125, and it is flanked on both sides by "insertion sequences" (like ISAba125) that act as the truck's wheels and engine. These wheels allow the truck to drive itself out of one spot in the DNA and park itself in another. The researchers found that in three of the four bacteria, this truck was a full-sized 10,099 base pairs long. In one case, the truck was slightly shorter (9,945 base pairs) because it had lost a small part of its cargo (a gene called groES), but it was still fully functional and carrying the dangerous NDM-9 gene.

What's fascinating is where this truck parked. In a previous report from France, this same type of truck parked on a floating ring (a plasmid). But in these Kenyan cases, the truck parked directly inside a gene that makes a protein called a LysM domain protein. It's as if the bacteria decided to build their super-weapon right inside the wall of their own house, disrupting the house's original blueprints to make room for the new defense.

The "Super-Resistant" Package

These bacteria weren't just carrying one weapon; they were carrying an entire arsenal. The study showed that these four bacteria were "clonal," meaning they were all essentially identical twins, suggesting they came from the same source and spread through the hospitals. They belonged to a high-risk family known as ST2, which is famous for being tough to kill and good at forming sticky films (biofilms) on medical equipment.

Beyond the NDM-9, these bacteria also carried:

• OXA-23 and OXA-66: The older, more common "locks" that already make them resistant to many drugs.
• A "Biocide" Shield: They carried a gene called qacEΔ1. This is a special gene that helps the bacteria resist not just antibiotics, but also the cleaning chemicals and antiseptics (like bleach or alcohol) that hospitals use to scrub surfaces clean. It's like the bacteria wearing a raincoat that protects them from the rain and the firehose.
• A "Gene Collector": They had a structure called an integron that acted like a filing cabinet, holding multiple other resistance genes for drugs like gentamicin and sulfonamides.

What This Means for the Future

The researchers tested these bacteria against a long list of antibiotics, and the results were grim: the bacteria were resistant to everything they tested, including the powerful carbapenems (meropenem) and even the newest "last-resort" drugs. The presence of NDM-9 is particularly worrying because this specific version has been shown to break down even the newest antibiotics designed to stop NDM enzymes, such as cefepime/taniborbactam and cefiderocol.

The study concludes that this is the first time NDM-9-producing Acinetobacter baumannii has been found in Africa. Because these bacteria are so similar to each other and were found in different regions, it suggests they are spreading. The fact that they carry genes to resist both antibiotics and cleaning chemicals means they are perfectly adapted to survive in hospital environments, making them very hard to get rid of.

The authors emphasize that while they have identified this new threat, the situation is urgent. They call for better monitoring (surveillance) to track how these "super-bacteria" move and to ensure that doctors know which drugs might still work. Without this vigilance, the effectiveness of our last-line treatments could be compromised, leaving patients with infections that are incredibly difficult to treat.