Virulence Factors of Uropathogenic Escherichia coli

Uropathogenic Escherichia coli (UPEC) strains are those that cause infections in the urinary tract. They acquired virulence factors which enable them to survive in the urinary tract and elicit pathogenicity. The virulence factors are classified into two categories: (i) bacterial cell surface virulence factors and (ii) bacteria secreted virulence factors. Adhesins, toxins and iron up-take systems are major groups of virulence factors. The variety of virulence factors of UPEC is presented in this chapter.

Evaluation of a Temperature-Induced Chitosanase Bacterial Cell Surface Display System for the Efficient Production of Chitooligosaccharides

Objective To establish a temperature-induced chitosanase bacterial cell surface display system to produce chitooligosaccharides (COSs) efficiently for industrial applications. Results Temperature-inducible chitosanase CSN46A bacterial surface display systems containing one or two copies of ice nucleation protein (InaQ-N) as anchoring motifs were successfully constructed on the basis of Escherichia coli and named as InaQ-N-CSN46A and 2InaQ-N-CSN46A. The specific enzyme activity of 2InaQ-N-CSN46A reached 886.33±0.81 U/g cell dry weight, which was 45.6% higher than that of InaQ-N-CSN46A. However, few proteins were detected in 2InaQ-N-CSN46A hydrolysis system. Therefore, 2InaQ-N-CSN46A had higher hydrolysis efficiency and stability than InaQ-N-CSN46A. GPC revealed that under the optimum enzymatic hydrolysis temperature, the final products were mainly chitobiose and chitotriose. Chitopentaose accumulated (77.62%) when the hydrolysis temperature reached 60 ℃. FTIR and NMR analysis demonstrated that the structures of the two hydrolysis products were consistent with those of COSs.Conclusions In this study, chitosanase was expressed on the surfaces of E. coli by increasing induction temperature, and chitosan was hydrolysed directly without enzyme purification steps. This study provided a novel strategy for industrial COSs production.

The Role of Complement System and the Immune Response to Tuberculosis Infection

The complement system orchestrates a multi-faceted immune response to the invading pathogen, Mycobacterium tuberculosis. Macrophages engulf the mycobacterial bacilli through bacterial cell surface proteins or secrete proteins, which activate the complement pathway. The classical pathway is activated by C1q, which binds to antibody antigen complexes. While the alternative pathway is constitutively active and regulated by properdin, the direct interaction of properdin is capable of complement activation. The lectin-binding pathway is activated in response to bacterial cell surface carbohydrates such as mannose, fucose, and N-acetyl-d-glucosamine. All three pathways contribute to mounting an immune response for the clearance of mycobacteria. However, the bacilli can reside, persist, and evade clearance by the immune system once inside the macrophages using a number of mechanisms. The immune system can compartmentalise the infection into a granulomatous structure, which contains heterogenous sub-populations of M. tuberculosis. The granuloma consists of many types of immune cells, which aim to clear and contain the infection whilst sacrificing the affected host tissue. The full extent of the involvement of the complement system during infection with M. tuberculosis is not fully understood. Therefore, we reviewed the available literature on M. tuberculosis and other mycobacterial literature to understand the contribution of the complement system during infection.

Fe(iii)-complex mediated bacterial cell surface immobilization of eGFP and enzymes

A facile and reversible method to immobilize His6-tagged proteins on the E. coli cell surface through the formation of an Fe(iii)-complex.

The N2N3 domains of ClfA, FnbpA, and FnbpB in Staphylococcus aureus bind to human complement factor H, and their antibodies enhance the bactericidal capability of human blood

In the complement system, the opsonin C3b binds to the bacterial cell surface and mediates the opsonophagocytosis. However, the cell wall protein SdrE of Staphylococcus aureus inhibits the C3b activity by recruiting the complement regulatory protein factor H (fH). SdrE binds to fH via its N-terminal N2N3 domain, which are also found in six other staphylococcal cell wall proteins. In this study, we report that not only the N2N3 domain of SdrE but also those of ClfA, FnbpA, and FnbpB can bind to fH. When immobilized on a microplate, the N2N3 domains recruited fH and enhanced the factor I (fI)-mediated cleavage of C3b. When mixed with fH and S. aureus cells, the N2N3 domains inhibited the fH binding to S. aureus cells and reduced the fI-mediated C3b cleavage on the bacterial cell surface. The F(ab)′2 fragments of the rabbit N2N3 antibodies also inhibited the fH-binding to the S. aureus cell surface. When added to human blood, the N2N3 antibodies or the N2N3 domain proteins significantly increased the bactericidal activity. Based on these results, we conclude that, in S. aureus, not only SdrE but also ClfA, FnbpA, and FnbpB can contribute to the inhibition of C3b-mediated opsonophagocytosis.

The LuxI/LuxR-Type Quorum Sensing System Regulates Degradation of Polycyclic Aromatic Hydrocarbons via Two Mechanisms

Members of the Sphingomonadales are renowned for their ability to degrade polycyclic aromatic hydrocarbons (PAHs). However, little is known about the regulatory mechanisms of the degradative pathway. Using cross-feeding bioassay, a functional LuxI/LuxR-type acyl-homoserine lactone (AHL)-mediated quorum sensing (QS) system was identified from Croceicoccus naphthovorans PQ-2, a member of the order Sphingomonadales. Inactivation of the QS system resulted in a significant decrease in PAHs degradation. The QS system positively controlled the expression of three PAH-degrading genes (ahdA1e, xylE and xylG) and a regulatory gene ardR, which are located on the large plasmid. Interestingly, the transcription levels of these three PAH-degrading genes were significantly down-regulated in the ardR mutant. In addition, bacterial cell surface hydrophobicity and cell morphology were altered in the QS-deficient mutant. Therefore, the QS system in strain PQ-2 positively regulates PAH degradation via two mechanisms: (i) by induction of PAH-degrading genes directly and/or indirectly; and (ii) by an increase of bacterial cell surface hydrophobicity. The findings of this study improve our understanding of how the QS system influences the degradation of PAHs, therefore facilitating the development of new strategies for the bioremediation of PAHs.