Streptococcus pneumoniae is one of the leading pathogens that cause a variety of mucosal and invasive infections. With the increased emergence of multidrug-resistant S. pneumoniae , new antimicrobials with mechanisms of action different from conventional antibiotics are urgently needed.

Three Bacillus bacteriophage-derived endolysins, designated PlyP56, PlyN74, and PlyTB40, were identified, cloned, purified, and characterized for their antimicrobial properties. Sequence alignment reveals these endolysins have an N-terminal enzymatically active domain (EAD) linked to a C-terminal cell wall binding domain (CBD). PlyP56 has a Peptidase_M15_4/VanY superfamily EAD with a conserved metal binding motif and displays biological dependence on divalent ions for activity. In contrast, PlyN74 and PlyTB40 have T7 lysozyme-type Amidase_2 and carboxypeptidase T-type Amidase_3 EADs, respectively, which are members of the MurNAc-LAA superfamily, but are not homologs and thus do not have a shared protein fold. All three endolysins contain similar SH3-family CBDs. Although minor host range differences were noted, all three endolysins show relatively broad antimicrobial activity against members of the Bacillus cereus sensu lato group with the highest lytic activity against B. cereus ATCC 4342. Characterization studies determined the optimal lytic activity for these enzymes was at physiological pH (pH 7.0–8.0), over a broad temperature range (4–55 °C), and at low concentrations of NaCl (<50 mM). Direct comparison of lytic activity shows the PlyP56 enzyme to be twice as effective at lysing the cell wall peptidoglycan as PlyN74 or PlyTB40, suggesting PlyP56 is a good candidate for further antimicrobial development as well as bioengineering studies.

Bacillus cereus, a Gram-positive bacterium, is an agent of food poisoning. B. cereus is closely related to Bacillus anthracis, a deadly pathogen for humans, and Bacillus thuringenesis, an insect pathogen. Due to the growing prevalence of antibiotic resistance in bacteria, alternative antimicrobials are needed. One such alternative is peptidoglycan hydrolase enzymes, which can lyse Gram-positive bacteria when exposed externally. A bioinformatic search for bacteriolytic enzymes led to the discovery of a gene encoding an endolysin-like endopeptidase, LysBC17, which was then cloned from the genome of B. cereus strain Bc17. This gene is also present in the B. cereus ATCC 14579 genome. The gene for LysBC17 encodes a protein of 281 amino acids. Recombinant LysBC17 was expressed and purified from E. coli. Optimal lytic activity against B. cereus occurred between pH 7.0 and 8.0, and in the absence of NaCl. The LysBC17 enzyme had lytic activity against strains of B. cereus, B. anthracis, and other Bacillus species.

Enterotoxigenic Escherichia coli (ETEC) is a leading cause of diarrhea in travelers and children in resource-limited countries. ETEC colonization factors, fimbrial tip adhesins and enterotoxins are key virulence factors, and thus have been studied as vaccine candidates. Some prevalent colonization factors, including CFA/I and CS17, belong to the class 5 family. We previously found that passive oral administration of hyperimmune bovine colostral IgG (bIgG) raised against dscCfaE (donor strand complemented CFA/I tip adhesin) protected volunteers against CFA/I⁺ ETEC challenge, while anti-dscCsbD bIgG (CS17 tip adhesin) did not confer protection. These findings led us to develop and optimize a panel of alternative CsbD-based vaccine candidates based on allele matching and in silico protein engineering. Physicochemical characterizations revealed that an optimized vaccine candidate dscCsbD_LSN139(P218A/G3) had the greatest thermal stability among the six tested dscCsbD adhesins, whereas the overall secondary structures and solubility of these adhesins had no obvious differences. Importantly, dscCsbD_LSN139(P218A/G3) elicited significantly higher CS17⁺ ETEC hemagglutination inhibition titers in sera from mice intranasally immunized with the panel of dscCsbD adhesins, while no significant difference was observed among heterologous neutralizing titers. Our results strongly advocate for the incorporation of these modifications into a new generation of CsbD-based ETEC vaccine candidates.

Background: Tick-borne encephalitis virus (TBEV) is a flavivirus that causes a range of clinical presentations including severe neurological complications in humans. In Mongolia, TBEV is primarily transmitted by the Ixodes persulcatus tick, which serves as both a vector and reservoir. Historically, TBEV in Mongolian ticks has been predominantly described in the forested regions of the Bulgan and Selenge aimags (provinces). Methods: In 2021 and 2024, I persulcatus ticks (n = 240) were collected from Bulgan and Tuv aimags in northern Mongolia, respectively, and pooled into 52 groups of 1 to 7 ticks. Using polymerase chain reaction, we identified the presence of TBEV RNA in six pooled samples, which were subjected to sequencing. Results: Two full genomes of Siberian TBEV were sequenced and assembled from tick pools collected in Tuv aimag, signifying the closest documented occurrence of this pathogen to the capital of Ulaanbaatar (83 km away). An additional partial Siberian genome was sequenced from a tick pool from Bulgan aimag. Conclusions: This finding indicates an elevated risk for TBEV transmission near Mongolia's largest urban center. The detection of TBEV in I persulcatus ticks in new geographic and ecologic areas underscores the necessity for continuous surveillance of tick populations, especially in densely populated regions.

Crimean-Congo hemorrhagic fever virus (CCHFV) is an orthonairovirus that can be found in Hyalomma spp. ticks. It can cause fatal disease in humans, with the potential for person-to-person transmission in clinical settings. To further characterize CCHFV within Mongolia, small (S), medium (M), and large (L) segments of viral genome were amplified. Adult unfed Hyalomma asiaticum were hand collected from the environment in Bayankhongor, Dornogovi, Dundgovi, Govi-Altai, and Umnugovi aimags (provinces) located in southern Mongolia. Seven of 184 pools tested positive for CCHFV using conventional PCR targeting the S segment. Through next-generation sequencing, a full genome from a single tick pool (n = 5 ticks) collected from Dornogovi in 2022 was detected, with phylogenetic analysis of all three segments indicating the genome fell within the Asian genotype IV. The closest identity (>98%) of all three sequences were to CCHFV viral genomes identified from H. asiaticum collected within China in 2015 and 2016. Given that the Dornogovi aimag directly borders the Inner Mongolia region of China, the sequence similarity is likely attributable to the geographic proximity. Continued surveillance and genetic characterization of CCHFV within Mongolia is vital for disease surveillance as the growing threat of CCHFV in this region is compounded by the expansion of trade and risk of cross-border transmission.