About 20 years ago, Thomas Byrd, MD, a physician-scientist at The University of New Mexico School of Medicine, took an interest in a seemingly inconsequential bacterium: Mycobacterium abscessus (M. abscessus). Driven by “intellectual curiosity,” Byrd said he and his “very talented” collaborators at UNM conducted research that laid the foundation for understanding the organism.

Nowadays, M. abscessus is no longer inconsequential. The slow-growing infection it causes — while uncommon — is multidrug-resistant, tough to kill and can be found around the world, including in New Mexico, Byrd said.

“What’s happened in about the last 15 years is it is an emerging infectious disease, and it causes very severe infections in patients with cystic fibrosis — lung disease — and also skin, joint and wound infections,” said Byrd, now an Emeritus Professor of infectious diseases at the UNM School of Medicine. “The unique thing about it is it’s multidrug-resistant, so that once you get an established infection, it’s extremely difficult to eradicate.”

Antibiotics simply may not work, he said.

Fortunately, the basic science research of Byrd and his colleagues on M. abscessus has made it possible for a different type of treatment to be used: bacteriophage therapy, which may represent the future of treating multidrug-resistant infections.

A Foundational Paper

In 2006, Byrd and his colleagues published a paper that established that M. abscessus can change shape, from having a smooth appearance — also called a “morphotype” — to a rough one, or vice versa.

The smooth variant might form a relatively harmless biofilm in the lung of a patient with lung disease.

However, the “aggressive and virulent” rough shape is more effective at causing infection than the smooth one, and it can exhibit a phenomenon called “serpentine cording,” in which bacteria line up end-to-end, like a snake, Byrd said.

“The moment that this rough variant arises, the disease or the infection becomes much more aggressive,” he said. “The patient gets much sicker and has a much greater chance of dying.”

Microscope images of M. abscessus published in Byrd's 2006 research paper, "Spontaneous reversion of Mycobacterium abscessus from a smooth to a rough morphotype is associated with reduced expression of glycopeptidolipid and reacquisition of an invasive phenotype." The top left image demonstrates the rough morphotype of M. abscessus. The top middle image demonstrates the smooth morphotype. The bottom left image shows serpentine cording. All images copyright 2006 Microbiology Society. Used with permission.

In the 2006 paper, Byrd and his colleagues also identified that a specific molecule, called glycopeptidolipid (GPL), drives what shape is taken by M. abscessus — and therefore helps determine how virulent it is. The smooth variant is coated in GPL, while the rough one is not.

“When you have a conversion from the smooth variant to the rough variant, the production of the GPL is shut off, or there’s a mutation,” he said. “Something causes it to no longer be produced, and then the emerging colonies are this rough variant.”

Targeting Infections with Bacteriophages

Byrd’s 2006 research paper laid the groundwork for scientists to later explore a different treatment option for M. abscessus: bacteriophage therapy.

Bacteriophages are naturally occurring organisms that employ a virus to kill specific bacteria, and they can work in tandem with antibiotics to cure an M. abscessus infection.

Under the powerful magnification of an electron microscope, a bacteriophage looks like a “lunar module,” Byrd said. “The main compartment has what’s essentially a virus, and it’s a virus that infects bacteria.”

Each bacteriophage uses legs to attach to its target bacteria.

“Once it attaches, it has this central structure that basically perforates the bacterial cell wall and injects the viral nucleic acids into the bacteria, and they can either become integrated into the bacterial chromosome, or immediately begin to replicate and destroy the bacteria — that’s the one that’s of clinical interest,” Byrd said. “They’re called lytic phages. They’re the phages that will destroy.”

Byrd explained that countries in Eastern Europe, such as the Soviet Union, Poland and Georgia, studied bacteriophages in the early 20^th century.

“They never quite caught on in the United States,” he said. “Then World War II came along, and you had the discovery of penicillin with World War II, and that pretty much stopped any research at that point on bacteriophages.”

The penicillin discovery eventually gave rise to hundreds of antibiotics.

Now, in 2026, with multiple strains of bacteria — including M. abscessus — becoming increasingly resistant to antibiotics, bacteriophage therapy has taken on a new importance, Byrd said.

Based on a relatively small number of cases, bacteriophage therapy has a 70-80% success rate at curing multidrug-resistant bacterial infections when used with antibiotics, he said.

He described a case from 2019, in which a teenager with cystic fibrosis had a lung transplant, and the rough, virulent form of M. abscessus reoccurred in the transplant. The patient was “pretty close to death” while doctors searched for a bacteriophage that would work on his infection, Byrd said.

“They were able to screen a library of phages against his M. abscessus organism, and found a phage that worked,” he said. “He got billions of phage in multiple doses, and he was cured. They eradicated his infection. He would have died if he didn’t have this.”

Because M. abscessus can change shape, bacteriophage therapy requires a “cocktail” of phages that works on both the smooth and rough variants, Byrd noted.

A Future with Phages

Byrd thinks bacteriophage therapy will become more viable going forward for many types of multidrug-resistant infections.

“My feeling is we’re on the cusp of a revolution in molecular biology,” he said.

Whereas doctors usually search a library of natural bacteriophages to find one that works, they may soon be able to genetically engineer the right bacteriophage for each individual’s infection, he said.

“That’s the hope or the potential that exists for bacteriophage therapy,” he said. “And ideally these phages will become even more effective at eradicating the bacteria.”

As for his pursuit of intellectual curiosity, Byrd said he’s happy with how things turned out with his work on M. abscessus, including its ability to inform clinical treatment.

“I’ve been very satisfied with the work,” he said. “Obviously, now it’s assumed some greater importance, but when I was doing it initially, I was just very happy to have found something unique in nature that I could describe.”