Updates on the Virulence Factors Produced by Multidrug-Resistant Enterobacterales and Strategies to Control Their Infections.

The Enterobacterales order is a massive group of Gram-negative bacteria comprised of pathogenic and nonpathogenic members, including beneficial commensal gut microbiota. The pathogenic members produce several pathogenic or virulence factors that enhance their pathogenic properties and increase the severity of the infection. The members of Enterobacterales can also develop resistance against the common antimicrobial agents, a phenomenon called antimicrobial resistance (AMR). Many pathogenic Enterobacterales members are known to possess antimicrobial resistance. This review discusses the virulence factors, pathogenicity, and infections caused by multidrug-resistant Enterobacterales, especially E. coli and some other bacterial species sharing similarities with the Enterobacterales members. We also discuss both conventional and modern approaches used to combat the infections caused by them. Understanding the virulence factors produced by the pathogenic bacteria will help develop novel strategies and methods to treat infections caused by them.

CRISPRi-mediated suppression of E. coli Nissle 1917 virulence factors: A strategy for creating an engineered probiotic using csgD gene suppression.

Background: Biofilm formation is a complex phenomenon, and it is the causative agent of several human infections. Bacterial amyloids are involved in biofilm formation leading to infection persistence. Due to antibiotic resistance, their treatment is a great challenge for physicians. Probiotics, especially E. coli Nissle 1917 (EcN), are used to treat human intestinal disorders and ulcerative colitis. It also expresses virulence factors associated with biofilm and amyloid formation. EcN produces biofilm equivalent to the pathogenic UPEC strains. Methods: CRISPRi was used to create the knockdown mutants of the csgD gene (csgD-KD). The qRT-PCR was performed to assess the expression of the csgD gene in csgD-KD cells. The csgD-KD cells were also evaluated for the expression of csgA, csgB, fimA, fimH, ompR, luxS, and bolA genes. The gene expression data obtained was further confirmed by spectroscopic, microscopic, and other assays to validate our study. Results: CRISPRi-mediated knockdown of csgD gene shows reduction in curli amyloid formation, biofilm formation, and suppression of genes (csgA, csgB, fimA, fimH, ompR, bolA, and luxS) involved in virulence factors production. Conclusion: Curli amyloid fibers and fimbriae fibers play a critical role in biofilm formation leading to pathogenicity. CsgD protein is the master regulator of curli synthesis in E. coli. Hence, curli amyloid inhibition through the csgD gene may be used to improve the EcN and different probiotic strains by suppressing virulence factors.

CRISPR Interference (CRISPRi) Mediated Suppression of OmpR Gene in E. coli: An Alternative Approach to Inhibit Biofilm.

Biofilm plays an important role in the community and hospital-acquired infections. Especially E. coli biofilm that contributes towards the significant part of medical devices associated with microbial infections. OmpR/EnvZ, a two-component system, is one of the regulatory mechanisms involved in transcription regulation in response to environmental osmolarity changes. The main objective of this study was to elucidate the role of the OmpR/EnvZ two-component system in regulating the biofilm through curli and fimbriae (FimH gene), a contrary approach towards biofilm inhibition. In this study, the CRISPRi technique was used to suppress the expression of the OmpR gene. The RT-PCR assay was performed to quantify mRNA gene expression of curli and biofilm producing genes, and the data were further confirmed by different microscopic, spectroscopic and biofilm quantification assay (Crystal Violet). It is the first time we have shown downregulation of the OmpR gene in biofilm causing clinical isolates of E. coli, which further suppressed the FimH gene, leading to biofilm reduction. The crystal violet assay and microscopic studies also confirmed the biofilm reduction. We conclude that the OmpR gene of the OmpR/EnvZ two-component system could be one of the targets for biofilm mediated infection intervention. Our findings open new vistas to explore the pathways and targets to control biofilm mediated infections.

bolA gene involved in curli amyloids and fimbriae production in E. coli: exploring pathways to inhibit biofilm and amyloid formation.

BACKGROUND: Biofilm formation is a complex phenomenon of bacterial cells, involved in several human infections. Its formation is regulated and controlled by several protein factors. The BolA-like proteins (bolA gene) are conserved in both prokaryotes and eukaryotes. The BolA protein is a transcription factor involved in bacterial cell motility and biofilm formation. This study was initiated to elucidate the role of the bolA gene in the curli biogenesis and amyloid production as well as to observe changes in the expression of fimH, a fimbriae gene. METHODS: Knockdown mutants of Escherichia coli MG1655 bolA gene (bolA-KD) were generated using CRISPR interference. The results obtained, were validated through gene expression using RT-PCR, microscopic analysis and different biofilm and amyloid assays. RESULTS: The bolA knockdown mutants showed a decrement in curli amyloid fibers, in fimbriae production and biofilm formation. We have also observed a reduction in EPS formation, eDNA production and extracellular protein content. Gene expression data showed that bolA downregulation caused the suppression of csgA and csgD of curli that led to the reduction in curli fiber and the amyloid formation and also the suppression of fimH, leading to the loss of fimbriae. CONCLUSIONS: Curli fibers and fimbriae are found to be involved in biofilm formation leading to the pathogenicity of the bacterial cell. BolA is a conserved protein and is found to play a significant role in curli and fimbriae formation in E. coli. This study further proved that CRISPRi mediated suppression of the bolA gene leads to inhibition of biofilm formation through curli and fimbriae inhibition. Hence, it may be proposed as a possible target for intervention of biofilm mediated infections.

ACD: Antimicrobial chemotherapeutics database.

Antimicrobial resistance is becoming a growing health problem, which has become a challenge for the physicians to control infection and also an economic burden on the healthcare. This increase in resistance to the present antimicrobial agents led the researchers to find some alternative and more efficient drugs which can fight with the resistant microorganisms more effectively. Hence, in silico approach is used to design some novel drugs against various targets of microorganisms. For effective virtual screening of the drugs, there is a need to know about the chemical structure and properties of the antimicrobial agents. Therefore, we have prepared a comprehensive database as a platform for the researcher to search for possible lead molecules. Antimicrobial chemotherapeutics database (ACD) is comprised of ~4100 synthetic antimicrobial compounds as well as ~1030 active antimicrobial peptides. The Antimicrobial peptides are mainly from biological sources but some of them are synthetic in nature. Only those compounds, which are found to be active against either bacteria (both Gram-positive and negative) or fungus, are selected for this database.The ACD database is freely available at URL: http://amdr.amu.ac.in/acd, and it is compatible with desktops, smartphones, and tablets.

Updates on the pathogenicity status of Pseudomonas aeruginosa.

Pseudomonas aeruginosa is a pathogenic bacterial species that causes infections and diseases in both plants and animals, including several human diseases, especially in immune-compromised patients, and many hospital-acquired infections. Given that P. aeruginosa is an opportunistic pathogen, the occurrence of antimicrobial resistance makes it difficult to treat and eradicate. Antimicrobial resistance in P. aeruginosa is categorized as intrinsic, acquired, or adaptive. Here, we different aspects of resistance and pathogenicity in P. aeruginosa, such as the role of outer membrane proteins, transcriptional regulators, efflux pumps, enzymes, and biofilms in antimicrobial resistance. We also highlight quorum-sensing (QS) genes, their protein secretion, and role in pathogenicity; different QS inhibitors; and the influence of QS on the clustered regularly interspaced short palindromic repeats (CRISPR)-Cas system and virulence factor production.

Understanding the mode of binding mechanism of doripenem to human serum albumin: Spectroscopic and molecular docking approaches.

The infections caused by multidrug resistant bacteria are widely treated with carabapenem antibiotics as a drug of choice, and human serum albumin (HSA) plays a vital role in binding with drugs and affecting its rate of delivery and efficacy. So, we have initiated this study to characterize the mechanism of doripenem binding and to locate its site of binding on HSA by using spectroscopic and docking approaches. The binding of doripenem leads to alteration of the environment surrounding Trp-214 residue of HSA as observed by UV spectroscopic study. Fluorescence spectroscopic study revealed considerable interaction and complex formation of doripenem and HSA as indicated by Ksv and Kq values of the order of 104  M-1 and 1012  M-1  s-1 , respectively. Furthermore, doripenem quenches the fluorescence of HSA spontaneously on a single binding site with binding constant of the order of 103  M-1 , through an exothermic process. Van der Waals forces and hydrogen bonding are the major forces operating to stabilize HSA-doripenem complex. Circular dichroism spectroscopic study showed changes in the structure of HSA upon doripenem binding. Drug displacement and molecular docking studies revealed that the binding site of doripenem on HSA is located on subdomain IB and III A. This study concludes that, due to significant interaction of doripenem on either subdomain IB or IIIA of HSA, the availability of doripenem on the target site may be compromised. Hence, there is a possibility of unavailability of threshold amount of drug to be reached to the target; consequently, resistance may develop in the bacterial population.

Non-active site mutation (Q123A) in New Delhi metallo-ß-lactamase (NDM-1) enhanced its enzyme activity.

New Delhi metallo ß-lactamase-1 is one of the carbapenemases, causing hydrolysis of almost all ß-lactamase antibiotics. Seventeen different NDM variants have been reported so far, they varied in their sequences either by single or multiple amino acid substitutions. Hence, it is important to understand its structural and functional relation. In the earlier studies role of active site residues has been studied but non-active site residues has not studied in detail. Therefore, we have initiated to further comprehend its structure and function relation by mutating some of its non-active site residues. A laboratory mutant of NDM-1 was generated by PCR-based site-directed mutagenesis, replacing Q to A at 123 position. The MICs of imipenem and meropenem for NDM-1Q123A were found increased by 2 fold as compare to wild type and so the hydrolytic activity was enhanced (Kcat/Km) as compared to NDM-1 wild type. GOLD fitness scores were also found in favour of kinetics data. Secondary structure for α-helical content was determined by Far-UV circular dichroism (CD), which showed significant conformational changes. We conclude a noteworthy role of non-active-site amino acid residues in the catalytic activity of NDM-1. This study also provides an insight of emergence of new variants through natural evolution.