Contribution to Carbapenem Resistance and Fitness Cost of DcuS/DcuR, RcsC/RcsB, and YehU/YehT Two-Component Systems in CTX-M-15-Producing Escherichia coli

Roles of two-component regulatory systems in Klebsiella pneumoniae: Regulation of virulence, antibiotic resistance, and stress responses

Klebsiella pneumoniae is an opportunistic pathogen belonging to the Enterobacteriaceae family, which is the leading cause of nosocomial infections. The emergence of hypervirulent and multi-drug resistant K. pneumoniae is a serious health threat. In the process of infection, K. pneumoniae needs to adapt to different environmental conditions, and the two-component regulatory system (TCS) composed of a sensor histidine kinase and response regulator is an important bacterial regulatory system in response to external stimuli. Understanding how K. pneumoniae perceives and responds to complex environmental stimuli provides insights into TCS regulation mechanisms and new targets for drug design. In this review, we analyzed the TCS composition and summarized the regulation mechanisms of TCSs, focusing on the regulation of genes involved in virulence, antibiotic resistance, and stress response. Collectively, these studies demonstrated that several TCSs play important roles in the regulation of virulence, antibiotic resistance and stress responses of K. pneumoniae. A single two-component regulatory system can participate in the regulation of several stress responses, and one stress response process may include several TCSs, forming a complex regulatory network. However, the function and regulation mechanism of some TCSs require further study. Hence, future research endeavors are required to enhance the understanding of TCS regulatory mechanisms and networks in K. pneumoniae, which is essential for the design of novel drugs targeting TCSs.

Rcs phosphorelay affects the sensitivity of Escherichia coli to plantaricin BM-1 by regulating biofilm formation

Introduction: Plantaricin BM-1 is a class IIa bacteriocin produced by Lactobacillus plantarum BM-1 that exerts significant antibacterial activity against many foodborne bacteria. Studies have shown that class IIa bacteriocins inhibit Gram-positive bacteria via the mannose phosphotransferase system; however, their mechanism of action against Gram-negative bacteria remains unknown. In this study, we explored the mechanism through which the Rcs phosphorelay affects the sensitivity of Escherichia coli K12 cells to plantaricin BM-1. Methods and Results: The minimum inhibitory concentrations of plantaricin BM-1 against E. coli K12, E. coli JW5917 (rcsC mutant), E. coli JW2204 (rcsD mutant), and E. coli JW2205 (rcsB mutant) were 1.25, 0.59, 1.31, and 1.22 mg/ml, respectively. Growth curves showed that E. coli JW5917 sensitivity to plantaricin BM-1 increased to the same level as that of E. coli K12 after complementation. Meanwhile, scanning electron microscopy and transmission electron microscopy revealed that, under the action of plantaricin BM-1, the appearance of E. coli JW5917 cells did not significantly differ from that of E. coli K12 cells; however, cell contents were significantly reduced and plasmolysis and shrinkage were observed at both ends. Crystal violet staining and laser scanning confocal microscopy showed that biofilm formation was significantly reduced after rcsC mutation, while proteomic analysis identified 382 upregulated and 260 downregulated proteins in E. coli JW5917. In particular, rcsC mutation was found to affect the expression of proteins related to biofilm formation, with growth curve assays showing that the deletion of these proteins increased E. coli sensitivity to plantaricin BM-1. Discussion: Consequently, we speculated that the Rcs phosphorelay may regulate the sensitivity of E. coli to plantaricin BM-1 by affecting biofilm formation. This finding of class IIa bacteriocin against Gram-negative bacteria mechanism provides new insights.

Regulator RcsB Controls Prodigiosin Synthesis and Various Cellular Processes in Serratia marcescens JNB5-1

Prodigiosin (PG), a red linear tripyrrole pigment normally secreted by Serratia marcescens, has received attention for its reported immunosuppressive, antimicrobial, and anticancer properties. Although several genes have been shown to be important for prodigiosin synthesis, information on the regulatory mechanisms behind this cellular process remains limited. In this work, we identified that the transcriptional regulator RcsB encoding gene BVG90_13250 (rcsB) negatively controlled prodigiosin biosynthesis in S. marcescens Disruption of rcsB conferred a remarkably increased production of prodigiosin. This phenotype corresponded to negative control of transcription of the prodigiosin-associated pig operon by RcsB, probably by binding to the promoter region of the prodigiosin synthesis positive regulator FlhDC. Moreover, using transcriptomics and further experiments, we revealed that RcsB also controlled some other important cellular processes, including swimming and swarming motilities, capsular polysaccharide production, biofilm formation, and acid resistance (AR), in S. marcescens Collectively, this work proposes that RcsB is a prodigiosin synthesis repressor in S. marcescens and provides insight into the regulatory mechanism of RcsB in cell motility, capsular polysaccharide production, and acid resistance in S. marcescens IMPORTANCE RcsB is a two-component response regulator in the Rcs phosphorelay system, and it plays versatile regulatory functions in Enterobacteriaceae However, information on the function of the RcsB protein in bacteria, especially in S. marcescens, remains limited. In this work, we illustrated experimentally that the RcsB protein was involved in diverse cellular processes in S. marcescens, including prodigiosin synthesis, cell motility, capsular polysaccharide production, biofilm formation, and acid resistance. Additionally, the regulatory mechanism of the RcsB protein in these cellular processes was investigated. In conclusion, this work indicated that RcsB could be a regulator for prodigiosin synthesis and provides insight into the function of the RcsB protein in S. marcescens.

[General principles of antibiotic resistance evolution in bacteria (review of literature).]

Currently, the impact of antibiotic resistance on human health is a worldwide problem and its study is of great interest from a molecular genetic, environmental and clinical view-point. This review summarizes the latest data about antibiotic resistance, the classification of microorganisms as sensitive and resistant to the action of antibiotics, reveals the concept of minimum inhibitory concentration from modern positions. The resistance of microorganisms to antibacterial agents can be intrinsic and acquired, as well as being one of the examples of evolution that are currently available for study. Modern methods of whole-genome sequencing and complex databases of nucleotide-tagged libraries give an idea of the multifaceted nature of the mechanisms of intrinsic resistance to antibiotics and are able to provide information on genes encoding metabolic enzymes and proteins that regulate the basic processes of the physiology of bacteria. The article describes the main ways of spreading the resistance of microorganisms, reflects the concepts of "founder effect" and the fitness cost of bacteria, which underlie the emergence and evolution of antibiotic resistance. It is shown that the origin of antibiotic resistance genes that human pathogens currently possess can be traced by studying the surrounding not only clinical, but also non-clinical (ecological) habitats. As well as microorganisms of the surrounding ecosystems are the donors of resistance genes in horizontal gene transfer.