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Objective. To study the antibacterial activity of lysostaphin against staphylococci various species, as well as its effect on the viability of Vero cells. Materials and Methods. Lysostaphin was obtained by genetic engineering. Purification of the protein was carried out on SP-sepharose, the purity was determined by electrophoresis in PAGE by Lamley. The susceptibility to lysostaphin of 9 species 175 strains of staphylococci was studied. Identification was performed by MALDI-TOF MS, antibiotic susceptibility by EUCAST (v. 11.0). The MIC of lysostaphin was studied by the method of serial dilutions with concentrations between 0.015 and 512 mg/l. For 72 hours, the viability of Vero cells with lysostaphin at concentrations of 0.5-32.0 mg/l was determined by the MTT method with counting of living cells according to their growth curve. The results were analyzed by ANOVA followed by Dunnett's test. Results. A kinetic study of S. aureus growth in the presence of revealed an inhibitory effect of endopeptidase (MIC 0.06 mg/l). Lysostaphin was characterized by pronounced activity against clinical methicillinsensitive S. aureus. The MIC ranged between 0.03 and 0.5 mg/l and the MIC50/90 was 0.125/0.5 mg/l. For methicillin-resistant S. aureus MIC50/90 0.25/0.5 mg/l. The MIC50 for MRSE was 2 times higher than for MSSE – 1 mg/l. The maximum MIC value was determined against isolates of S. warneri and S. hominis – 64 mg/l, the lowest for S. saprophyticus – 0.5 mg/l. MIC50 of lysostaphin against MRSA was 4 times lower than that of vancomycin, MIC90 was 3 times lower. Differences in viable cells depending on the concentration of lysostaphin were not found. Conclusions. Significant activity of lysostaphin against staphylococci was revealed, which is several times higher than vancomycin against MRSA. Lysostaphin was also effective against methicillin-resistant S. aureus. The high anti-staphylococcal activity and cytocompatibility of lysostaphin are promising for its further study in the prevention and treatment of staphylococcal orthopedic infections.

Objective. To study effects of bacteriophages on biofilm formation and formed biofilm by S. aureus isolated from patients with orthopedic infection. Materials and Methods. A total of 50 clinical strains of S. aureus were tested. Species identification was performed by MALDI-TOF MS, antibiotic susceptibility – in accordance with the EUCAST v21. Isolates susceptibility to bacteriophages «Sextafag» (Microgen, Russia) was determined by MPA medium. The antibacterial activity of phages against S. aureus ATCC 29213 and S. aureus ATCC 43300 was evaluated by growth kinetic curves. Biofilms of bacteriophage-sensitive S. aureus strains were formed according to the protocol described by O’Toole. Isolates were divided into categories in accordance with the Stepanovic criteria. The effects of bacteriophages on the formation of S. aureus biofilm were studied by co-incubation of phages and bacteria followed by calculation of the percentage inhibition relative to the control without the introduction of the phages. The effect of phages on 24-hour biofilms formed by staphylococci was also evaluated in comparison with the control. Results. Out of 50 clinical S. aureus strains studied, 43 isolates (86%) were susceptible to phages, including 22 MSSA and 21 MRSA. All phage-susceptible cultures were characterized by biofilm-forming ability of varying degree: 28% – weak biofilm producer, 35% – moderate, 37% – strong. Inhibition of biofilm formation was determined in all tested MRSA strains, while in 73% of isolates the index of biofilm formation inhibition was more than 80%, which exceeded this indicator for MSSA by 2.5 times. In turn, the destruction of the formed biofilm under the action of the bacteriophage was 72% for all S. aureus. In 57% of MSSA strains, the decrease in biofilm biomass in comparison with the control was more than 80%, while this indicator was 2 times higher than for MRSA. Conclusions. The results demonstrated a high in vitro efficacy of bacteriophages against biofilm formation in S. aureus.

Objective. To evaluate the resistance rate and production of carbapenemases in Klebsiella pneumoniae with phenotypic resistance to carbapenems isolated from patients with orthopedic infection. Materials and Methods. The materials for the study were tissue samples, aspirates and removed orthopedic devices of patients with orthopedic infection at the Vreden Russian Research Institute of Traumatology and Orthopedics, between 2017 and 2019. K. pneumoniae strains were identified in Microlatest by iEMS ReaderMF. These strains were tested for susceptibility to 15 antimicrobial agents by disk diffusion methods, as described by the EUCAST. The carbapenemase genes were investigated by RT-PCR. Results. Of 858 isolated cultures, 6.8% were resistant to carbapenems. Molecular genetic analysis showed that 43.1% of the cultures had blaNDM gene and 24.1% blaOXA-48. All isolates of K. pneumoniae were characterized by resistance to cefotaxime, moxifloxacin and ciprofloxacin. OXA-48-strains were MDR in 50.0% of cases, XDR in 42.9%, PDR in 7.1%. Strains with NDM-carbapenemases were XDR in 68.0% and PDR in 32.0% of cases. The most effective antibiotic was fosfomycin. Thus, 66.7% of NDM-isolates demonstrated sensitivity to fosfomycin. One isolate was PDR with both NDM and OXA-48. Conclusions. Over the period of three years, carbapenemase-producing K. pneumoniae were isolated in the orthopedic hospital. These isolates were not only resistant to carbapenems, but also to a number of other antimicrobial agents. Isolates differed in resistance phenotypes depending on the presence of carbapenemases group, while strains with gene blaNDM were more resistant than those with blaOXA-48.

Bioherbicides are expected to be a supplement to integrated pest management, assisting in the control of problematic weed species. For instance, bioherbicides (Phoma and BioPhoma) were recently registered in Canada and the USA for the control of some perennial dicotyledonous weeds in lawns. These products are based on strains of the fungus Didymella macrostoma (syn. Phoma macrostoma ) that causes white tip disease (WTD) in Canada thistle ( Cirsium arvense ). In this study, WTD was reported for the first time in the Russian Federation. Analysis of the internal transcribed spacer (ITS) region of nuc rDNA and secondary metabolite profiling confirmed the identity of Russian WTD isolates to Canadian biocontrol strains identified as D. macrostoma . Multilocus phylogenetic analysis based on sequencing of the ITS region, partial large subunit nuc rDNA region (28S), RNA polymerase II second largest subunit gene ( rpb2 ), and partial β-tubulin gene ( tub2 ) has differentiated the WTD isolates from C. arvense and D. macrostoma isolates from other plant hosts. Based on phylogenetic, morphological, and chemotaxonomic features, these WTD isolates were described as a new species named Didymella baileyae , sp. nov. This study also demonstrated the low pathogenicity of the ex-type D. baileyae isolate VIZR 1.53 to C. arvense seedlings and its asymptomatic development in the leaves of aboveground shoots. The organic extracts from mycelium and culture filtrate of D. baileyae , as well as macrocidin A and macrocidin Z, displayed phytotoxicity both to C. arvense leaves and seedlings. Macrocidin A was only detected in the naturally infected leaf tissues of C. arvense showing WTD symptoms. Macrocidins A and Z demonstrated low antimicrobial and cytotoxic activities, exhibiting no entomotoxic properties. The data obtained within this study on the pathogenicity and metabolites of D. baileyae may be important for the rational evaluation of its prospects as a biocontrol agent.

In the grave environment, microorganisms are major ecological participants in the successional decomposition of vertebrates and could infiltrate the skeleton/skeletal material during taphonomic processes. The diversity of archaeological skeleton-associated microbial assemblages and the impact of various factors are poorly understood. This study aimed to evaluate the taxonomic microbial composition of archaeological human bone and teeth samples from the 7th to 11th centuries AD from two burial sites in Latvia. Samples were analysed by a shotgun metagenomics-based approach. The results showed a strong presence of the environmental DNA in the samples, and variability in microbial community structure between individual samples. Differences in microbial composition were observed between bone and tooth samples, as well as between different burial sites. Furthermore, the presence of endogenous ancient DNA (aDNA) in tooth samples was detected. Overall, compositions of microbial communities associated with archaeological human remains in Latvia dated 7-11th century AD were influenced by the sample type and burial location. These findings indicate that, while the content of historical DNA in archaeological samples is low, the comparison of archaeological skeleton-associated microbial assemblages across time and space, along with aDNA damage profile analysis, is important and could help to reveal putative ancient microorganisms., (© 2023 The Authors. Environmental Microbiology Reports published by Applied Microbiology International and John Wiley & Sons Ltd.)

Natural sciences provide several modern methodologies that could be successfully applied in archaeological studies. In this pilot study, archaeological human remains from two Iron Age cemeteries (7th-twelfth centuries AD), Lejasbitēni and Čunkāni-Dreņģeri, which are located in different regions of Latvia, were studied. We applied ancient DNA (aDNA) and tooth enamel peptide analysis to determine the biological sex of the individuals. In addition, aDNA analysis was used to perform mtDNA haplogroup analysis. In most cases, the results of aDNA analysis regarding the biological sex of individuals coincided with the gender assigned based on grave orientation and grave goods. The results of sex determination using peptide analysis in all four individuals for whom data were available matched the possible gender. Of the 17 samples that had sufficient DNA for sequencing, seven samples had enough reads to perform mtDNA haplogroup analysis. The H2a2a, I4a1, H2a2a1, and H16c mtDNA haplogroups were identified in the individuals from the Lejasbitēni cemetery, while the T2b and K1a + 150 mtDNA haplogroups were identified in the individuals from the Čunkāni-Dreņģeri cemetery. Overall, the obtained results demonstrated the feasibility of applying aDNA and tooth enamel peptide analysis for biological sex determination within archaeological studies. The availability of human aDNA data will be highly useful for investigating the demographic history and social structures in Iron Age Latvia., (© 2022. The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature.)

A 5,000-year-old Yersinia pestis genome (RV 2039) is reconstructed from a hunter-fisher-gatherer (5300-5050 cal BP) buried at Riņņukalns, Latvia. RV 2039 is the first in a series of ancient strains that evolved shortly after the split of Y. pestis from its antecessor Y. pseudotuberculosis ∼7,000 years ago. The genomic and phylogenetic characteristics of RV 2039 are consistent with the hypothesis that this very early Y. pestis form was most likely less transmissible and maybe even less virulent than later strains. Our data do not support the scenario of a prehistoric pneumonic plague pandemic, as suggested previously for the Neolithic decline. The geographical and temporal distribution of the few prehistoric Y. pestis cases reported so far is more in agreement with single zoonotic events., Competing Interests: Declaration of interests The authors declare no competing interests., (Copyright © 2021 The Author(s). Published by Elsevier Inc. All rights reserved.)

Recent advantages in paleomicrobiology have provided an opportunity to investigate the composition of ancient microbial ecologies. Here, using metagenome analysis, we investigated the microbial profiles of historic dental calculus retrieved from archaeological human remains from postmedieval Latvia dated 16-17th century AD and examined the associations of oral taxa and microbial diversity with specific characteristics. We evaluated the preservation of human oral microbiome patterns in historic samples and compared the microbial composition of historic dental calculus, modern human dental plaque, modern human dental calculus samples and burial soil microbiota. Overall, the results showed that the majority of microbial DNA in historic dental calculus originated from the oral microbiome with little impact of the burial environment. Good preservation of ancient DNA in historical dental calculus samples has provided reliable insight into the composition of the oral microbiome of postmedieval Latvian individuals. The relative stability of the classifiable oral microbiome composition was observed. Significant differences between the microbiome profiles of dental calculus and dental plaque samples were identified, suggesting microbial adaptation to a specific human body environment.

Ancient genomic studies have identified Yersinia pestis (Y. pestis) as the causative agent of the second plague pandemic (fourteenth-eighteenth century) that started with the Black Death (1,347-1,353). Most of the Y. pestis strains investigated from this pandemic have been isolated from western Europe, and not much is known about the diversity and microevolution of this bacterium in eastern European countries. In this study, we investigated human remains excavated from two cemeteries in Riga (Latvia). Historical evidence suggests that the burials were a consequence of plague outbreaks during the seventeenth century. DNA was extracted from teeth of 16 individuals and subjected to shotgun sequencing. Analysis of the metagenomic data revealed the presence of Y. pestis sequences in four remains, confirming that the buried individuals were victims of plague. In two samples, Y. pestis DNA coverage was sufficient for genome reconstruction. Subsequent phylogenetic analysis showed that the Riga strains fell within the diversity of the already known post-Black Death genomes. Interestingly, the two Latvian isolates did not cluster together. Moreover, we detected a drop in coverage of the pPCP1 plasmid region containing the pla gene. Further analysis indicated the presence of two pPCP1 plasmids, one with and one without the pla gene region, and only one bacterial chromosome, indicating that the same bacterium carried two distinct pPCP1 plasmids. In addition, we found the same pattern in the majority of previously published post-Black Death strains, but not in the Black Death strains. The pla gene is an important virulence factor for the infection of and transmission in humans. Thus, the spread of pla-depleted strains may, among other causes, have contributed to the disappearance of the second plague pandemic in eighteenth century Europe.

This research explores oral health indicators and stable carbon and nitrogen isotope data to explore diet, and differences in diet, between people buried in the four different contexts of the St Gertrude Church cemetery (15th- 17th centuries AD): the general cemetery, two mass graves, and a collective mass burial pit within the general cemetery. The main aim is to assess whether people buried in the mass graves were rural immigrants, or if they were more likely to be the victims of plague (or another epidemic) who lived in Riga and its suburbs. The data produced (from dental disease assessments and isotope analyses) were compared within, as well as between, the contexts. Most differences emerged when comparing the prevalence rates of dental diseases and other oral health indicators in males and females between the contexts, while isotope analysis revealed more individual, rather than context-specific, differences. The data suggested that the populations buried in the mass graves were different from those buried in the general cemetery, and support the theory that rural immigrants were buried in both mass graves. Significant differences were observed in some aspects of the data between the mass graves, however, possibly indicating that the people buried in them do not represent the same community.

The aim of this research is to assess the presence of stress in a high status German population from Jelgava, Latvia. The skeletal material used in this study came from a recently excavated church cemetery, with most of the burials dating to the 17-18th centuries. In total, 108 individuals (80 adults and 28 non-adults) were analysed for evidence of scurvy, rickets/osteomalacia and anaemia. The presence of scurvy and healed rickets/osteomalacia could not be confirmed in any adult individual. Among non-adults, a possible diagnosis of scurvy was considered in six individuals, and active rickets was suggested in two others. Cribra orbitalia in adult and non-adult individuals also argued for the presence of childhood stress. These results, combined with previously acquired data on linear enamel hypoplasia, indicated that children in this population suffered from nutritional deficiencies. The presence of childhood stress markers in adult individuals implies that many children survived stress episodes, possibly due to generally good access to resources, as supported by historical accounts and previous studies on stature and dental disease., (Copyright © 2013 Elsevier Inc. All rights reserved.)