Evaluation of the Antimicrobial Activity of Cationic Polymers against Mycobacteria: Toward Antitubercular Macromolecules.

Antimicrobial resistance is a global healthcare problem with a dwindling arsenal of usable drugs. Tuberculosis, caused by Mycobacterium tuberculosis, requires long-term combination therapy and multi- and totally drug resistant strains have emerged. This study reports the antibacterial activity of cationic polymers against mycobacteria, which are distinguished from other Gram-positive bacteria by their unique cell wall comprising a covalently linked mycolic acid-arabinogalactan-peptidoglycan complex (mAGP), interspersed with additional complex lipids which helps them persist in their host. The present study finds that poly(dimethylaminoethyl methacrylate) has particularly potent antimycobacterial activity and high selectivity over two Gram-negative strains. Removal of the backbone methyl group (poly(dimethylaminoethyl acrylate)) decreased antimycobacterial activity, and poly(aminoethyl methacrylate) also had no activity against mycobacteria. Hemolysis assays revealed poly(dimethylaminoethyl methacrylate) did not disrupt red blood cell membranes. Interestingly, poly(dimethylaminoethyl methacrylate) was not found to permeabilize mycobacterial membranes, as judged by dye exclusion assays, suggesting the mode of action is not simple membrane disruption, supported by electron microscopy analysis. These results demonstrate that synthetic polycations, with the correctly tuned structure are useful tools against mycobacterial infections, for which new drugs are urgently required.

Identification of the anti-mycobacterial functional properties of piperidinol derivatives.

BACKGROUND AND PURPOSE: Tuberculosis (TB) remains a major global health threat and is now the leading cause of death from a single infectious agent worldwide. The current TB drug regimen is inadequate, and new anti-tubercular agents are urgently required to be able to successfully combat the increasing prevalence of drug-resistant TB. The purpose of this study was to investigate a piperidinol compound derivative that is highly active against the Mycobacterium tuberculosis bacillus. EXPERIMENTAL APPROACH: The antibacterial properties of the piperidinol compound and its corresponding bis-Mannich base analogue were evaluated against M. smegmatis and Gram-negative organisms. Cytotoxicity studies were undertaken in order to determine the selectivity index for these compounds. Spontaneous resistant mutants of M. smegmatis were generated against the piperidinol and corresponding bis-Mannich base lead derivatives and whole genome sequencing employed to determine the genetic modifications that lead to selection pressure in the presence of these compounds. KEY RESULTS: The piperidinol and the bis-Mannich base analogue were found to be selective for mycobacteria and rapidly kill this organism with a cytotoxicity selectivity index for mycobacteria of >30-fold. Whole genome sequencing of M. smegmatis strains resistant to the lead compounds led to the identification of a number of single nucleotide polymorphisms indicating multiple targets. CONCLUSION AND IMPLICATIONS: Our results indicate that the piperidinol moiety represents an attractive compound class in the pursuit of novel anti-tubercular agents. LINKED ARTICLES: This article is part of a themed section on Drug Metabolism and Antibiotic Resistance in Micro-organisms. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v174.14/issuetoc.

Survival of the ovine footrot pathogen Dichelobacter nodosus in different soils.

Dichelobacter nodosus (D. nodosus) is the causative agent of footrot in sheep; one of the most important health and welfare issues of sheep worldwide. For control programmes to be effective, it is essential that the transmission cycle of D. nodosus is understood and bacterial reservoirs in the environment are better defined. This study evaluated the survival of D. nodosus in different soils using soil microcosms. Cultivation independent and dependent methods were used to detect D. nodosus over 40 days from seeding in soil. A D. nodosus specific probe was used for quantification by qPCR and viability was assessed by cell permeability to an intercalating dye, PMA, and by culture. Survival varied dramatically depending on soil type, matric potential (MP) and temperature. Our findings indicate that D. nodosus survival was higher at 5 °C compared with 25 °C in all soils and significantly longer at both temperatures in clay soil (>44% clay) compared with other soil types. Survival under all conditions was longer than 30 days for both culture independent and dependent methods, this is substantially longer than previous studies and, if this is an infectious dose, longer than the current recommendation of resting a field for 14 days to prevent onward infection.