Structural basis for the immune recognition and selectivity of the immune receptor PVRIG for ligand Nectin-2.

Nectin and nectin-like (Necl) co-receptor axis, comprised of receptors DNAM-1, TIGIT, CD96, PVRIG, and nectin/Necl ligands, is gaining prominence in immuno-oncology. Within this axis, the inhibitory receptor PVRIG recognizes Nectin-2 with high affinity, but the underlying molecular basis remains unknown. By determining the crystal structure of PVRIG in complex with Nectin-2, we identified a unique CC' loop in PVRIG, which complements the double-lock-and-key binding mode and contributes to its high affinity for Nectin-2. The association of the corresponding charged residues in the F-strands explains the ligand selectivity of PVRIG toward Nectin-2 but not for Necl-5. Moreover, comprehensive comparisons of the binding capacities between co-receptors and ligands provide innovative insights into the intra-axis immunoregulatory mechanism. Taken together, these findings broaden our understanding of immune recognition and regulation mediated by nectin/Necl co-receptors and provide a rationale for the development of immunotherapeutic strategies targeting the nectin/Necl axis.

Unearthing new ccr genes and SCC elements in staphylococci through genome mining.

The SCCmec typing is crucial for investigating methicillin-resistant S. aureus, relying primarily on the combination of ccr and mec gene complexes. To date, 19 ccr genes and 10 ccr gene complexes have been identified, forming 15 SCCmec types. With the vast release of bacterial genome sequences, mining the database for novel ccr gene complexes and SCC/SCCmec elements could enhance MRSA epidemiological studies. In this study, we identified 12 novel ccr genes (6 ccrA, 3 ccrB and 3 ccrC) through mining of the NCBI database, which forming 12 novel ccr gene complexes and 10 novel SCC elements. Overexpression of five groups of novel Ccr recombinases (CcrA9B3, CcrA10B1, CcrC3, CcrC4, and CcrC5) in a mutant MRSA strain lacking the ccr gene and extrachromosomal circular intermediate (ciSCC) production significantly promoted ciSCC production, demonstrating their biological activity. This discovery provides an opportunity to advance MRSA epidemiological research and develop database-based bacterial typing methods.

Breastmilk microbiome changes associated with lactational mastitis and treatment with dandelion extract.

Introduction: Dandelion (Pugongying) is one of the most frequently used Chinese herbs for treating lactational mastitis (LM). Pugongying granules, a patented medication primarily comprised of dandelion extract, have been approved by CFDA for LM treatment in China. The aims of this study were to investigate the etiology of LM and the mechanism by which Pugongying granules decrease LM symptoms, with a particular focus on the microbial communities found in breastmilk. Methods: Participants were recruited from a previously performed randomized controlled trial (Identifier: NCT03756324, ClinicalTrials.gov). Between 2019 and 2020, women diagnosed with unilateral LM at the Beijing University of Chinese Medicine Third Affiliated Hospital were enrolled. In total, 42 paired breastmilk samples from the healthy and affected breasts of the participants were collected. Additionally, 37 paired pre- and post-treatment breastmilk samples from the affected breast were collected from women who received a 3-day course of either Pugongying granules (20 women) or cefdinir (17 women). Clinical outcomes [e.g., body temperature, visual analogue scale (VAS) score for breast pain, the percentage of neutrophils (NE%)] were analyzed pre- and post-treatment, and the breastmilk samples were subjected to 16S rRNA gene sequencing to analyze the alpha and beta diversities and identify significant bacteria. Finally, the relationship between microorganisms and clinical outcomes was analyzed. Results: There was no significant difference in fever and pain between the Pugongying group and cefdinir group. The most prevalent bacterial genera in breastmilk were Streptococcus and Staphylococcus. Compared to healthy breastmilk, microbial diversity was reduced in affected breastmilk, and there was a higher relative abundance of Streptococcus. After Pugongying treatment, there was an increase in microbial diversity with significantly higher abundance of Corynebacterium. A negative correlation was found between Corynebacterium, VAS score, and NE%. Treatment with cefdinir did not affect microbial diversity. Taken together, our results show a correlation between LM and reduced microbial diversity, as well as an increased abundance of Streptococcus in affected breastmilk. Conclusion: Pugongying granules enhanced microbial diversity in breastmilk samples. Given the substantial variation in individual microbiomes, identifying specific species of Streptococcus and Corynebacterium associated with LM may provide additional insight into LM pathogenesis and treatment.

Novel cassette chromosome recombinases CcrA8B9 catalyse the excision and integration of the staphylococcal cassette chromosome mec element.

OBJECTIVES: A defining feature of MRSA is the SCCmec element. The excision and integration of SCCmec elements are catalysed by Ccr recombinases. Currently, seven ccrA, eight ccrB and two ccrC allotypes have been described. However, there have been no recent reports of a novel Ccr recombinase and thus this area should be explored. METHODS: According to the proposed criteria of the International Working Group on the Classification of Staphylococcal Cassette Chromosome Elements (IWG-SCC) committee, novel ccr genes were explored by searching the genome of our laboratory staphylococcal strains, which were isolated from bovine mastitis in Northwest China. The biological activity of the novel Ccr recombinases to excise and integrate SCCmec elements was determined. The distribution of the novel ccr genes in staphylococci was conducted by querying the NCBI nr/nt database. RESULTS: We report a set of novel Ccr recombinases CcrA8B9, which share nucleotide identities of 46.6%-50.2% and 47.4%-52.8% with the ccrA and ccrB alleles, respectively. We used PCR to show that CcrA8B9 can excise and integrate the SCCmec element. Furthermore, using NCBI BLAST we showed that the ccrA8B9 genes exist in other staphylococcal strains. Unlike the common ccr genes, ccrA8B9 is located outside the SCCmec/SCC element. CONCLUSIONS: The novel Ccr recombinases CcrA8B9 can help excise and integrate SCCmec/SCC from the genome and provide a new way to facilitate the transmission of SCCmec/SCC elements among staphylococci.

Inducible Resistance to ß-Lactams in Oxacillin-Susceptible mecA1-Positive Staphylococcus sciuri Isolated From Retail Pork.

Most isolated strains of Staphylococcus sciuri contain mecA1, the evolutionary origin of mecA, but are sensitive to ß-lactams (OS-MRSS, oxacillin-susceptible mecA1-positive S. sciuri). In order to improve the efficacy of antibiotic treatment, it is important to clarify whether the resistance of OS-MRSS to ß-lactams is an inducible phenotype. In this study, three OS-MRSS strains with oxacillin MIC = 1 µg/ml were isolated from 29 retail pork samples. The resistance of OS-MRSS to ß-lactams (MIC > 256 µg/ml) was found to be induced by oxacillin, and the induced resistance was observed to remain stable within a certain period of time. Interestingly, the induced ß-lactam resistance was not caused by mecA1, heterogeneous resistance, or any genetic mutation, but mainly due to increased wall teichoic acid (WTA) synthesis that thickened the cell wall. The induced strains also showed slower growth rate, as well as decreased adhesion ability and biofilm thickness. These phenotypes were found to be achieved through altered gene expression in associated pathways, such as the citrate cycle and pentose phosphate pathway. The results challenge the traditional antibiotic sensitivity test. In the presence of ß-lactam antibiotics, OS-MRSS that was initially sensitive to ß-lactams was observed to gradually develop ß-lactam resistance in several days. This often-neglected phenomenon in antibiotic sensitivity tests requires further research attention.