Klebsiella pneumoniae is among the leading bacteria that cause nosocomial infections. The capsule of this Gram-negative bacterium is a dominant virulence factor, with a prominent role in defense and biofilm formation. Bacteriophages, which are specific for one bacterial strain and its capsule type, can evoke the lysis of bacterial cells, aided by polysaccharide depolymerase enzymes. In this study, we isolated and characterized a bacteriophage against the nosocomial K. pneumoniae 52145 strain with K2 capsular serotype. The phage showed a narrow host range and stable lytic activity, even when exposed to different temperatures or detergents. Preventive effect of the phage in a nasal colonization model was investigated in vivo. Phlyogenetic analysis showed that the newly isolated Klebsiella phage B1 belongs to the Webervirus genus in Drexlerviridae family. We identified the location of the capsule depolymerase gene of the new phage, which was amplified, cloned, expressed, and purified. The efficacy of the recombinant B1dep depolymerase was tested by spotting on K. pneumoniae strains and it was confirmed that the extract lowers the thickness of the bacterium lawn as it degrades the protective capsule on bacterial cells. As K. pneumoniae strains possessing the K2 serotype have epidemiological importance, the B1 phage and its depolymerase are promising candidates for use as possible antimicrobial agents.

The increasing ineffectiveness of traditional antibiotics and the rise of multidrug resistant (MDR) bacteria have necessitated the revival of bacteriophage (phage) therapy. However, bacteria might also evolve resistance against phages. Phages and their bacterial hosts coexist in nature, resulting in a continuous coevolutionary competition for survival. We have isolated several clinical strains of Pseudomonas aeruginosa and phages that infect them. Among these, the PIAS (Phage Induced Antibiotic Sensitivity) phage belonging to the Myoviridae family can induce multistep genomic deletion in drug-resistant clinical strains of P. aeruginosa, producing a compromised drug efflux system in the bacterial host. We identified two types of mutant lines in the process: green mutants with SNPs (single nucleotide polymorphisms) and smaller deletions and brown mutants with large (∼250 kbp) genomic deletion. We demonstrated that PIAS used the MexXY-OprM system to initiate the infection. P. aeruginosa clogged PIAS phage infection by either modifying or deleting these receptors. The green mutant gaining phage resistance by SNPs could be overcome by evolved PIASs (E-PIASs) with a mutation in its tail-fiber protein. Characterization of the mutant phages will provide a deeper understanding of phage-host interaction. The coevolutionary process continued with large deletions in the same regions of the bacterial genomes to block the (E-)PIAS infection. These mutants gained phage resistance via either complete loss or substantial modifications of the phage receptor, MexXY-OprM, negating its essential role in antibiotic resistance. In vitro and in vivo studies indicated that combined use of PIAS and antibiotics could effectively inhibit P. aeruginosa growth. The phage can either eradicate bacteria or induce antibiotic sensitivity in MDR-resistant clinical strains. We have explored the potential use of combination therapy as an alternative approach against MDR P. aeruginosa infection.

Exploitation of engineered nanomaterials with unique properties has been dynamically growing in numerous fields, including the agricultural sector. Due to the increasing resistance of phytopathogenic microbes, human control over various plant pathogens in crop production is a big challenge and requires the development of novel antimicrobial materials. Photocatalytic active nanomaterials could offer an alternative solution to suppress the plant pathogens. In this work, titanium dioxide nanoparticles (TiO2 NPs) with high photocatalytic activity were synthesized by hydrothermal post-treatment of amorphous titania at different temperatures (250 °C or 310 °C) without using any additives or doping agents. The obtained samples were investigated through X-ray diffraction, N2-sorption measurements, diffuse reflectance UV-Vis spectroscopy, transmission electron microscopy, electron paramagnetic resonance spectroscopy, and X-ray photoelectron spectroscopy. The applied hydrothermal treatment led to the formation of TiO2 nanocrystallites with a predominant anatase crystal phase, with increasing crystallinity and crystallite size by prolonging treatment time. The photocatalytic activity of the TiO2 NPs was tested for the photo-degradation of phenol and applied for the inactivation of various plant pathogens such as Erwinia amylovora, Xanthomonas arboricola pv. juglandis, Pseudomonas syringae pv. tomato and Allorhizobium vitis. The studied bacteria showed different susceptibilities; their living cell numbers were quickly and remarkably reduced by UV-A-irradiated TiO2 NPs. The effectiveness of the most active sample prepared at 310 °C was much higher than that of commercial P25 TiO2. We found that fine-tuning of the structural properties by modulating the time and temperature of the hydrothermal treatment influenced the photocatalytic properties of the TiO2 NPs considerably. This work provides valuable information to the development of TiO2-based antimicrobial photocatalysts.

Methicillin-resistant Staphylococcus aureus (MRSA) can cause a wide range of infections from mild to life-threatening conditions. Its enhanced antibiotic resistance often leads to therapeutic failures and therefore alternative eradication methods must be considered. Potential candidates to control MRSA infections are bacteriophages and their lytic enzymes, lysins. In this study, we isolated a bacteriophage against a nosocomial MRSA strain belonging to the ST45 epidemiologic group. The phage belonging to Caudovirales, Siphoviridae, showed a narrow host range and stable lytic activity without the emergence of resistant MRSA clones. Phylogenetic analysis showed that the newly isolated Staphylococcus phage R4 belongs to the Triavirus genus in Siphoviridae family. Genetic analysis of the 45 kb sequence of R4 revealed 69 ORFs. No remnants of mobile genetic elements and traces of truncated genes were observed. We have localized the lysin (N-acetylmuramoyl-L-alanine amidase) gene of the new phage that was amplified, cloned, expressed, and purified. Its activity was verified by zymogram analysis. Our findings could potentially be used to develop specific anti-MRSA bacteriophage- and phage lysin-based therapeutic strategies against major clonal lineages and serotypes.

Contamination of meats and meat products with foodborne pathogenic bacteria raises serious safety issues in the food industry. The antibacterial activities of phosphorous-fluorine co-doped TiO2 nanoparticles (PF-TiO2) were investigated against seven foodborne pathogenic bacteria: Campylobacter jejuni, Salmonella Typhimurium, Enterohaemorrhagic E. coli, Yersinia enterocolitica, Shewanella putrefaciens, Listeria monocytogenes and Staphylococcus aureus. PF-TiO2 NPs were synthesized hydrothermally at 250 °C for 1, 3, 6 or 12 h, and then tested at three different concentrations (500 μg/mL, 100 μg/mL, 20 μg/mL) for the inactivation of foodborne bacteria under UVA irradiation, daylight exposure or dark conditions. The antibacterial efficacies were compared after 30 min of exposure to light. Distinct differences in the antibacterial activities of the PF-TiO2 NPs, and the susceptibilities of tested foodborne pathogenic bacterium species were found. PF-TiO2/3 h and PF-TiO2/6 h showed the highest antibacterial activity by decreasing the living bacterial cell number from ~106 by ~5 log (L. monocytogenes), ~4 log (EHEC), ~3 log (Y. enterolcolitca, S. putrefaciens) and ~2.5 log (S. aureus), along with complete eradication of C. jejuni and S. Typhimurium. Efficacy of PF-TiO2/1 h and PF-TiO2/12 h NPs was lower, typically causing a ~2–4 log decrease in colony forming units depending on the tested bacterium while the effect of PF-TiO2/0 h was comparable to P25 TiO2, a commercial TiO2 with high photocatalytic activity. Our results show that PF-co-doping of TiO2 NPs enhanced the antibacterial action against foodborne pathogenic bacteria and are potential candidates for use in the food industry as active surface components, potentially contributing to the production of meats that are safe for consumption.