Horizontal gene transfer plays an important role in the spread of antibiotic resistance, in which plasmid-mediated conjugation transfer is the most important mechanism. While sub-minimal inhibitory concentrations (sub-MIC) of antibiotics could promote conjugation frequency, the mechanism by which sub-MIC levels of antibiotics affect conjugation frequency is not clear. Here, we used Klebsiella pneumoniae SW1780 carrying the multi-drug resistance plasmid pSW1780-KPC as the donor strain, to investigate the effects of sub-MICs of meropenem (MEM), ciprofloxacin (CIP), cefotaxime (CTX), and amikacin (AK) on conjugational transfer of pSW1780-KPC from SW1780 to Escherichia coli J53. Our results showed that the transfer frequencies increased significantly by treating SW1780 strain with sub-MIC levels of MEM, CIP, CTX and AK. Transfer frequencies at sub-MIC conditions in a Galleria mellonella were significantly higher than in vitro. To investigate gene expression and metabolic effects, RT-qPCR and LC–MS-based metabolome sequencing were performed. Transcript levels of T4SS genes virB1, virB2, virB4, virB8, and conjugation-related genes traB, traK, traE, and traL were significantly upregulated by exposure to sub-MICs of MEM, CIP, CTX, and AK. Metabolome sequencing revealed nine differentially regulated metabolites. Our findings are an early warning for a wide assessment of the roles of sub-MIC levels of antibiotics in the spread of antibiotic resistance.

A carbapenem-resistant hypermucoviscous Klebsiella pneumoniae isolate was recovered from human sputum. Whole genome sequencing of this isolate was carried out to reveal its clonal background, antimicrobial resistance determinants and virulence factors. Virulence assays were performed using wax moth larvae. The transfer of blaNDM-5 between bacterial strains was tested using conjugation. 59 genome assemblies of ST29 K. pneumoniae and 230 IncX3 plasmids regardless of the carriage of resistance gene were employed for phylogenetic analysis, respectively. The strain carried a virulence plasmid pVir-SCNJ1 bearing the virulence gene rmpA and exhibited a high virulence in wax moth. This hypervirulent strain belongs to sequence type 29 and carries blaNDM-5, which is located on a conjugative plasmid, designated pNDM5-SCNJ1, belonging to type IncX3. pNDM5-SCNJ1 was fully sequenced and shows high similarity with pNDM_MGR194, except some deletion inside the ISAba125 region. Phylogenetic analysis of IncX3 plasmids revealed that although blaNDM-5 can be evolved from blaNDM-1 via point mutations within some IncX3 plasmids, most of blaNDM-5-carrying IncX3 plasmids probably have acquired blaNDM-5 in multiple events. In this study, we characterized a blaNDM-5-positive hypervirulent K. pneumoniae of sequence type 29 in China. Our results highlight the need for active surveillance on this lineage of carbapenem-resistant K. pneumoniae.

To resolve the growing problem of drug resistance in the treatment of bacterial and fungal pathogens, specific cellular targets and pathways can be used as targets for new antimicrobial agents. Endogenous riboflavin biosynthesis is a conserved pathway that exists in most bacteria and fungi. In this review, the roles of endogenous and exogenous riboflavin in infectious disease as well as several antibacterial agents, which act as analogues of the riboflavin biosynthesis pathway, are summarized. In addition, the effects of exogenous riboflavin on immune cells, cytokines, and heat shock proteins are described. Moreover, the immune response of endogenous riboflavin metabolites in infectious diseases, recognized by MHC-related protein-1, and then presented to mucosal associated invariant T cells, is highlighted. This information will provide a strategy to identify novel drug targets as well as highlight the possible clinical use of riboflavin.

Rhinosinusitis is a common inflammatory disease of the sinonasal mucosa and paranasal sinuses. The pathogenesis of rhinosinusitis involves a variety of factors, including genetics, nasal microbiota status, infection, and environmental influences. Pathogenic microorganisms, including viruses, bacteria, and fungi, have been proven to target the cilia and/or epithelial cells of ciliated airways, which results in the impairment of mucociliary clearance, leading to epithelial cell apoptosis and the loss of epithelial barrier integrity and immune dysregulation, thereby facilitating infection. However, the mechanisms employed by pathogenic microorganisms in rhinosinusitis remain unclear. Therefore, this review describes the types of common pathogenic microorganisms that cause rhinosinusitis, including human rhinovirus, respiratory syncytial virus, Staphylococcus aureus, Pseudomonas aeruginosa, Aspergillus species, etc. The damage of mucosal cilium clearance and epithelial barrier caused by surface proteins or secreted virulence factors are summarized in detail. In addition, the specific inflammatory response, mainly Type 1 immune responses (Th1) and Type 2 immune responses (Th2), induced by the entry of pathogens into the body is discussed. The conventional treatment of infectious sinusitis and emerging treatment methods including nanotechnology are also discussed in order to improve the current understanding of the types of microorganisms that cause rhinosinusitis and to help effectively select surgical and/or therapeutic interventions for precise and personalized treatment.

Human pathogenic fungi are ubiquitous in the environment and induce an expanding repertoire of devastating diseases globally. Upon fungal invasion, fungus adopt multiple strategies to adapt to, or eliminate, hostile environmental conditions, which immune checkpoints serve as one of the mechanism for fungal evasion. Programmed death receptor-1 (PD-1), an immunosuppressive molecule, transmits inhibitory signals upon binding to its ligand PD-L1. During infection, aberrant activation of the PD-1/PD-L1 pathway has been proven to facilitate immune evasion by the pathogen. In this review, we summarize the roles of PD-1/PD-L1 in fungal infection. First, the molecular structures and function of PD-1 and PD-L1 are described. Then, we highlight the dynamic expression patterns and regulatory mechanisms of PD-1/PD-L1 during fungal invasion. Potential therapeutics based on PD-1/PD-L1-blocking to enhance antifungal immunity and improve clinical outcomes are also discussed. These insights reveal future directions regarding PD-1/PD-L1 and immune checkpoint-based therapies for preventing pathogenic fungi infections.