Tiny Natural Pirates Fight Multi-Resistant Pathogens

Bacteriophages Offer New Strategic Options in Battling Multi-Resistant Achromobacter xylosoxidans

Infections with the often multi-resistant pathogen Achromobacter xylosoxidans are reported more and more frequently. This opportunistic pathogen is for example involved in cystic fibrosis, a metabolic disorder for which no cure exists. Bacteriophages (phages for short) are natural enemies of bacteria and might provide an alternative way of effectively fighting infections, in particular hospital-acquired infections. Johannes Wittmann, a researcher at Leibniz Institute DSMZ – German Collection of Microorganisms and Cell Cultures, Braunschweig (Brunswick), Germany, has isolated and thoroughly studied various phages targeting Achromobacter xylosoxidans. His is the first study presenting a large number of diverse phages that might be used to fight this pathogen. Further studies investigating their therapeutic potential are under way. Initial results have just been published in the scientific journals PLOS One and Virology Journal.

Viruses targeting bacteria are referred to as bacteriophages, or phages for short. They have become a focus of scientific interest for rather practical reasons: As antibiotics are losing, at an alarming rate, their effectiveness in fighting multi-resistant bacterial pathogens, these natural enemies of bacteria are becoming more and more important. This is where current basic research at DSMZ, conducted by a team led by scientists Johannes Wittmann and Christine Rohde, comes into play.
“As the name bacteriophages (which is derived from the Greek ‘phagos,’ meaning ‘glutton’) suggests, these viruses ‘devour’ bacteria, effectively destroying them,” as Johannes Wittmann, a postdoctoral researcher at DSMZ, explains. “They achieve this by using a sophisticated system. The virus injects its genetic material into the bacterial cell where it is ‘read’ by the protein-making mechanisms of the bacterium, essentially reprogramming it. In this way, the phages, like tiny pirates, ‘hijack’ the bacterial cell. The result is the production of countless new phages. Eventually, the host cell bursts, releasing hundreds of these viruses, which in turn may destroy more bacteria.”


A new strategy for battling multi-resistant pathogens

This effective mechanism of action employed by phages, plus the fact that they are harmless to humans, might make bacteriophages a weapon in the fight against various multi-resistant infectious agents. “Phages are particularly suited to fighting pathogens because they each target only one specific species of host bacteria”, says Johannes Wittmann. “You might think of them as ‘intelligent’, self-limiting medications. They will replicate only at the site of bacterial infection, and they will do so only until all host bacteria have been used up.”

At the center of this first comprehensive scientific study of phages at DSMZ is the mobile gram-negative rod-shaped bacterium Achromobacter xylosoxidans, an opportunistic pathogen that so far has not been sufficiently investigated. Achromobacter xylosoxidans is wide spread in our natural environment, occurring both in soil and various water sources. While often harmless, it may cause severe infections, such as endocarditis, bacteriemia, and meningitis, in people with compromised immune systems.

“In medicine, the often multi-resistant pathogen Achromobacter plays a not to be ignored role in cystic fibrosis, a tragic metabolic disorder for which no cure exists today,” says Johannes Wittmann. “In patients with cystic fibrosis, this bacterium is one of several species forming biofilms in the affected lungs. These biofilms are more accessible to phages than to antibiotics. It is just these opportunistic pathogens that have hospital staff worried. We therefore consulted on this project with Charité, the Berlin university hospital.”

“We are seeing an increase in patients with opportunistic infections in recent years,” comments Professor Martin Witzenrath of the Department of Infectious Diseases and Respiratory Medicine at Charité. “In this context, pathogens that are resistant to common antibiotics such as penicillin, macrolides, and cephalosporins, present us with major therapeutic challenges. From a clinical point of view, Achromobacter is problematic as well, in particular in patients with cystic fibrosis, and we fear that we will see it much more often in the future. This illustrates an urgent unmet need for fighting pathogens that are resistant to antibiotics. Wittmann’s current study presents an important example of a new alternative strategy.”


New phages targeting Achromobacter

“Phages are best found in the same places that are inhabited by the pathogens that we suspect them to be effective against, e.g., in waste water. We have been able to readily isolate phages targeting Achromobacter from municipal water treatment plants. For screening purposes, we incubated filtrates from the plant with the host bacteria,” recalls Johannes Wittmann. “Plaques forming in the bacterial lawn on the agar plates then showed us where we would find the matching phages.”

A widely diverse range of more than 60 strains of the genus Achromobacter was used as host bacteria. They were taken from the DSMZ’s own collection as well as from culture collections in Sweden, the Czech Republic, Belgium, and Canada. Most of the strains had been isolated from clinical samples such as sputum, blood, and urine, or from the environment. They all exhibited resistance to antibiotics commonly used in hospitals.

A total of 34 phages were isolated and characterized, and some of their genetic material has already been sequenced at DSMZ. “We were very surprised to discover that two phages belong to the rare family of N4-like phages”, says Wittmann.

“More studies are needed to test Achromobacter targeting phages for their usefulness as therapeutic phages. Then they would be added to the collection of therapeutic phages at DSMZ,” explains Christine Rohde, head of the working group. “These studies include the sequencing of the entire phage genome in order to exclude genes encoding for undesirable properties.”


For more informatione please visit the website of the DSMZ