Endolysins are the future against antibiotic-resistant bacteria. These enzymes, produced by bacteriophage viruses, kill bacteria by degrading the peptidoglycan layer that forms the cell wall. Gram-positive bacteria are vulnerable to lysins. However, Gram-negative bacteria have an additional barrier that confers resistance to enzyme action: the outer membrane that protects the peptidoglycan layer. Therefore, there are multiple efforts to engineer endolysins to endow them with the ability to penetrate the outer membrane barrier.
«Some endolysins are capable of breaking this protective wall. We call it intrinsic antibacterial activity», declares Diana Gutiérrez, Chief Technology Officer at Telum Therapeutics. Usually, they carry some features in their structure, such as an amphipathic helix in their C-terminus, the end of their amino acid chain terminated by a free carboxyl group. «LysMK34 is one of these lysins, but its action may be hindered under certain experimental conditions in vitro. Therefore, we considered engineering it by fusing a peptide, termed cecropin A, to its N-terminal end, to improve its antibacterial activity».
Briers’ Lab selected cecropin A because previous screening revealed that the most effective lysin against antibiotic-resistant Acinetobacter baumannii carried the peptide. «Cecropin A is produced by the mosquito Aedes aegypti and constitutes a main part of its immune system. The amphipathic nature of cecropin A, which means that the peptide has both hydrophobic and cationic properties, facilitates the permeabilization and disruption of the outer membrane of Gram-negative bacteria», explains the group in its article. “Moreover, the antimicrobial activity of cecropin A does not decrease under human blood serum conditions. Thus, they hypothesized that fusing LysMK34 with the peptide will result in a more robust lysin».
But, did it work? It appears that, according to the results published in Applied and Environmental Microbiology. Specifically, the engineered LysMK34 killed A. baumannii bacteria faster than the natural lysin. Its activity is also less dependent on experimental conditions and, interestingly, the modification did not increase the toxicity of the lysin. «That was good news since an effective antibacterial compound is of little help in clinical practice if it damages human cells», points Gutiérrez. The study carried out at the University of Ghent, under the direction of Prof. Briers, also provides clues about how lysins can successfully interfere with and permeate the outer membrane, which will pave the way for developing new engineered endolysins.
A. baumannii tops the World Health Organization’s list of priority pathogens for the development of new antibiotics. The pathogen is associated with a wide range of infections, including ventilator-associated pneumonia, the presence of bacteria in the bloodstream, wound infections, and meningitis. Its high ability to acquire resistance genes in addition to its natural resistance to a wide range of antibiotics makes treatment of A. baumannii infections challenging.
Abdelkader K, Gutiérrez D, Tamés-Caunedo H, Ruas-Madiedo P, Safaan A, Khairalla AS, Gaber Y, Dishisha T, Briers Y. Engineering a Lysin with Intrinsic Antibacterial Activity (LysMK34) by Cecropin A Fusion Enhances Its Antibacterial Properties against Acinetobacter baumannii. Appl Environ Microbiol. 2022 Jan 11;88(1):e0151521. doi: 10.1128/AEM.01515-21.