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Photodynamic inactivation of microorganisms known as antibacterial photodynamic therapy (APDT) is one of the most promising and innovative approaches for the destruction of pathogenic microorganisms. Among the photosensitizers (PSs), compounds based on cationic porphyrins/metalloporphyrins are most successfully used to inactivate microorganisms. Series of meso-substituted cationic pyridylporphyrins and metalloporphyrins with various peripheral groups in the third and fourth positions of the pyrrole ring have been synthesized in Armenia. The aim of this work was to determine and test the most effective cationic porphyrins and metalloporphyrins with high photoactivity against Gram negative and Gram positive microorganisms. It was shown that the synthesized cationic pyridylporphyrins/metalloporphyrins exhibit a high degree of phototoxicity towards both types of bacteria, including the methicillin-resistant S. aureus strain. Zinc complexes of porphyrins are more phototoxic than metal-free porphyrin analogs. The effectiveness of these Zn–metalloporphyrins on bacteria is consistent with the level of singlet oxygen generation. It was found that the high antibacterial activity of the studied cationic porphyrins/metalloporphyrins depends on four factors: the presence in the porphyrin macrocycle of a positive charge (+4), a central metal atom (Zn${}^{2+})$ and hydrophobic peripheral functional groups as well as high values of quantum yields of singlet oxygen. The results indicate that meso-substituted cationic pyridylporphyrins/metalloporphyrins can find wider application in photoinactivation of bacteria than anionic or neutral PSs usually used in APDT.

Bacterial resistance is today a matter of great medical concern, so it is urgent to investigate alternatives to alleviate it. Photodynamic inactivation (PDI) is a method that has been endorsed to inactivate different pathogens, including bacteria, fungi and viruses. PDI is achieved by using a photosensitizer (PS) molecule which generates reactive oxygen species under visible or UV radiation. We use visible light and UV-A radiation to excite four commercial PSs (methylene blue, rose bengal, riboflavin and curcumin), and nanoparticles synthesized in our laboratory. Despite these PSs having been thoroughly studied in the past by other research groups, in order to compare their effects in an appropriate way, we matched the number of photons they absorb. We found that methylene blue leads to the major inactivation of Escherichia coli. Furthermore, we evaluated the production of singlet oxygen and hydroxyl radicals in the photoinactivation process.

Non-point source microbial pollution damages the overall health of marine ecosystems. Beyond their direct effects, contaminating microbes can introduce antimicrobial resistance and virulence genes into resident species by horizontal gene transfer, a process that may be enhanced by co-pollutants such as heavy metals. In this work, a number of heavy metal- and antimicrobial-resistant (AMR) strains of E. coli were isolated from water and sediment samples collected in the Causeway Bay, Hong Kong (22.2833 N, 114.1847 E) and their complete genomes obtained by hybrid assembly using both Illumina MiSeq and Oxford Nanopore MinION sequencing platforms. Genomic analysis showed an abundance of plasmids and mobile elements bearing heavy metal- and AMR genes, such as the mer operon and tetR-tetA efflux system, with these features frequently co-located. In addition, NCBIBLAST–using isolates collected from in-land soil, freshwater, and animal faeces in Hong Kong, as well as the NCBI database – showed that these genes, while common amongst human and animal-derived Enterobacteriaceae, could also be shown present in a number of strains of obligate halophilic Vibrio spp.. Previous water chemistry analysis at this location showed high levels of heavy metal contamination (98 ppm Pb, 0.12 ppm Hg, and 0.4 ppm Cd), which has been shown to promote AMR transfer by selecting for co- resistance. Further isolation and characterisation of marine bacterial species from Hong Kong coastal waters will help to determine the extent of this process.