Donia Mourali

In the present study, sulfated polysaccharides (SPSs) were isolated from the thermophilic cyanobacterium Leptolyngbya sp. CIN61 was characterized and evaluated for its in vitro antimicrobial and anticancer activities. The SPSs were composed of 71.4% sugars, 17% proteins, and 7.9% sulfates. The monosaccharide composition determined by high‐performance liquid chromatography with a refractive index detector revealed the presence of rhamnose, arabinose, mannose, glucose, and galactose. Structural characterization using Fourier‐transform infrared spectroscopy, ¹ H nuclear magnetic resonance, and correlated spectroscopy confirmed the presence of peptide groups, uronic acids, sulfate groups, and acetylated hexosamine residues. Atomic force microscopy revealed a wave‐like microstructure with irregular, rough surface features while scanning electron microscopy showed uneven, smooth tubular structures with varying shapes, sizes, and orientations. In in vitro bioactivity assays, the SPSs exhibited selective antifungal activity against Aspergillus niger and inhibited the proliferation of colorectal adenocarcinoma DLD‐1 cells, with an IC ₅₀ value of 4.73 mg/mL. These findings suggest that thermophilic Leptolyngbya sp. is a promising source of SPSs with potential for various industrial applications.

Phage therapy is a promising therapeutic weapon in the fight against multidrug-resistant Klebsiella pneumoniae infections. A Klebsiella phage, KpTRp1, was isolated from wastewater sample collected in Tunisia. It exhibited specific lytic activity against a reference strain of K. pneumoniae serotype K2. Phage isolation and enrichment were performed using the double-layer agar method. It was characterized by transmission electron microscopy, physiological investigation and genomic sequence analysis. Transmission electron micrographs of KpTRp1 showed a myovirus morphology. The optimal multiplicity of infection by KpTRp1 was 0.0001 with a latent period lasted for 30 min. Its rise phase showed a burst period of almost 150 min and released a small burst size of about six plaque-forming units per infected cell. KpTRp1 was stable over a broad pH and temperature range. The phage genome sequencing revealed a linear double-stranded DNA genome of 48,003 base pairs with a G + C content of 48.79%, defining a new species of Sircambvirus genus of Jameshumphriesvirinae subfamily. Among the 68 open reading frames identified, about half were hypothetical proteins with unknown functions, the others being involved in DNA replication and metabolism, phage structure, host recognition and lysis. Remarkably, lytic activity of KpTRp1 against K. pneumoniae serotype K2 was confirmed by genomic analysis of life cycle, making it suitable candidate for phage therapy, especially since no antibiotic resistance, or lysogenic genes were detected in the phage genome.

Background: Klebsiella pneumoniae is an opportunistic pathogen that causes a wide range of infections worldwide. The emergence and spread of multidrug-resistant clones requires the implementation of novel therapeutics, and phages are a promising approach. Results: In this study, two Klebsiella phages, KpTDp1 and KpTDp2, were isolated from wastewater samples in Tunisia. These phages had a narrow host range and specifically targeted the hypervirulent K2 and K28 capsular types of K. pneumoniae. Both phages have double-stranded linear DNA genomes of 49,311 and 49,084 bp, respectively. Comparative genomic and phylogenetic analyses placed phage KpTDp2 in the genus Webervirus, while phage KpTDp1 showed some homology with members of the genus Jedunavirus, although its placement in a new undescribed genus may be reconsidered. The replication efficiency and lytic ability of these phages, combined with their high stability at temperatures up to 70 °C and pH values ranging from 3.5 to 8.2, highlight the potential of these phages as good candidates for the control of hypervirulent multidrug-resistant K. pneumoniae. Methods: Phage isolation, titration and multiplicity of infection were performed. The stability of KpTDp1 and KpTDp2 was tested at different pH and temperatures. Genomic characterization was done by genome sequencing, annotation and phylogenetic analysis. Conclusions: The ability of KpTDp1 and KpTDp2 to lyse one of the most virulent serotypes of K. pneumoniae, as well as the stability of their lytic activities to pH and temperature variations, make these phages promising candidates for antibacterial control.