Synergistic Action Between Peptide-Neomycin Conjugates and Polymyxin B Against Multi-Drug-Resistant Gram-Negative Pathogens

Dev Arya^1*Sandra Story²Liuwei Jiang¹

• ¹Clemson University, Clemson, United States
• ²Nubad (United States), Greenville, South Carolina, United States

It is predicted that globally by 2050, 10 million people will die annually caused by infection with drug-resistant bacteria. Considering that antibacterials with novel mechanisms of action have not been developed in over 30 years, there is a surge of interest in combination therapy using existing drugs. The combination of an aminoglycoside and colistin are often used to treat pneumonia cause by multidrug resistant bacteria, however, the additive effect of these drugs can result in toxicity which complicates recovery. The goal of this study is to investigate the relationship of the antibacterial activity of a peptide-neomycin library in combination with polymyxin B in extensively drug resistant and pandrug resistant bacteria. The peptide-neomycin library represented conjugates with one or two amino acids linked to neomycin rendering them unsuitable substrates for aminoglycoside modifying enzymes. Neomycin-susceptible and resistant members of Acinetobacter baumannii, Klebsiella pneumoniae and Pseudomonas aeruginosa were screened for synergy with polymyxin B using the two-way checkerboard and time-kill methods. Most A. baumannii strains were resistant to amikacin, gentamicin, tobramycin and plazomicin and about half were susceptible to neomycin. P. aeruginosa had a similar resistance profile but was more susceptible to plazomicin. K. pneumoniae strains were the most susceptible to a wider variety of aminoglycosides. Bacteria challenged with the combination of neomycin, other aminoglycosides and polymyxin B exhibited an additive to indifferent relationship, whereas synergy was found with several of the neomycin-peptide conjugates containing cysteine, arginine or tryptophan, lowering the minimal inhibitory concentration for the peptide-neomycin conjugate 8 to 64-fold and polymyxin B 2 to 8-fold. Cysteine, arginine or tryptophan conjugates were most effective with A. baumannii and K. pneumoniae carrying a 16S rRNA methyltransferase genes and a pandrug-resistant P. aeruginosa strain. Resistance to the combination of R-, C- or RC- NEO conjugates and PB did not develop over a 14-day period for neomycin-susceptible strains of A. baumannii, K. pneumoniae and P. aeruginosa. Based on this survey of the peptide-neomycin library, circumvention of aminoglycoside modifying enzymes and alluding bacterial resistance is an important step towards the design and development of peptide aminoglycoside-based motifs for antimicrobial drug development.