Expression of NanoLuc Luciferase in Listeria innocua for Development of Biofilm Assay

Pneumococcal sialidase promotes bacterial survival by fine-tuning of pneumolysin-mediated membrane disruption

Pneumolysin (Ply) is an indispensable cholesterol-dependent cytolysin for pneumococcal infection. Although Ply-induced disruption of pneumococci-containing endosomal vesicles is a prerequisite for the evasion of endolysosomal bacterial clearance, its potent activity can be a double-edged sword, having a detrimental effect on bacterial survivability by inducing severe endosomal disruption, bactericidal autophagy, and scaffold epithelial cell death. Thus, Ply activity must be maintained at optimal levels. We develop a highly sensitive assay to monitor endosomal disruption using NanoBiT-Nanobody, which shows that the pneumococcal sialidase NanA can fine-tune Ply activity by trimming sialic acid from cell-membrane-bound glycans. In addition, oseltamivir, an influenza A virus sialidase inhibitor, promotes Ply-induced endosomal disruption and cytotoxicity by inhibiting NanA activity in vitro and greater tissue damage and bacterial clearance in vivo. Our findings provide a foundation for innovative therapeutic strategies for severe pneumococcal infections by exploiting the duality of Ply activity.

Listeria motility increases the efficiency of epithelial invasion during intestinal infection

Listeria monocytogenes (Lm) is a food-borne pathogen that causes severe bacterial gastroenteritis, with high rates of hospitalization and mortality. Lm is ubiquitous in soil, water and livestock, and can survive and proliferate at low temperatures. Following oral ingestion of contaminated food, Lm crosses the epithelium through intestinal goblet cells in a mechanism mediated by Lm InlA binding host E-cadherin. Importantly, human infections typically occur with Lm growing at or below room temperature, which is flagellated and motile. Even though many important human bacterial pathogens are flagellated, little is known regarding the effect of Lm motility on invasion and immune evasion. Here, we used complementary imaging and computer modeling approaches to test the hypothesis that bacterial motility helps Lm locate and engage target cells permissive for invasion. Imaging explanted mouse and human intestine, we showed that Lm grown at room temperature uses motility to scan the epithelial surface and preferentially attach to target cells. Furthermore, we integrated quantitative parameters from our imaging experiments to construct a versatile "layered" cellular Potts model (L-CPM) that simulates host-pathogen dynamics. Simulated data are consistent with the hypothesis that bacterial motility enhances invasion by allowing bacteria to search the epithelial surface for their preferred invasion targets. Indeed, our model consistently predicts that motile bacteria invade twice as efficiently over the first hour of infection. We also examined how bacterial motility affected interactions with host cellular immunity. In a mouse model of persistent infection, we found that neutrophils migrated to the apical surface of the epithelium 5 hours post infection and interacted with Lm. Yet in contrast to the view that neutrophils "hunt" for bacteria, we found that these interactions were driven by motility of Lm-which moved at least ~50x faster than neutrophils. Furthermore, our L-CPM predicts that motile bacteria maintain their invasion advantage even in the presence of host phagocytes, with the balance between invasion and phagocytosis governed almost entirely by bacterial motility. In conclusion, our simulations provide insight into host pathogen interaction dynamics at the intestinal epithelial barrier early during infection.

Comparative Analysis of NanoLuc Luciferase and Alkaline Phosphatase Luminescence Reporter Systems for Phage-Based Detection of Bacteria

Reporter phage assays are a promising alternative to culture-based assays for rapidly detecting viable bacteria. The reporter systems used in phage-based detection are typically enzymes and their corresponding substrates that provide a signal following infection and expression. While several reporter systems have been developed, comparing reporter systems based on reported bacteria detection limits from literature can be challenging due to factors other than the reporter system that influence detection capabilities. To advance the development of phage-based assays, a systematic comparison and understanding of the components are necessary. The objective of this study was to directly compare two common enzyme-mediated luminescence reporter systems, NanoLuc/Nano-Glo and alkaline phosphatase (ALP*)/DynaLight, for phage-based detection of bacteria. The detection limits of the purified enzymes were determined, as well as the expression levels and bacteria detection capabilities following engineering of the coding genes into T7 phage and infection of E. coli BL21. When comparing the sensitivity of the purified enzymes, NLuc/Nano-Glo enzyme/substrate system demonstrated a lower detection limit than ALP*/DynaLight. In addition, the expression of the NLuc reporter following phage infection of E. coli was greater than ALP*. The lower detection limit combined with the higher expression resulted in a greater than 100-fold increase in sensitivity for the NLuc/Nano-Glo^® reporter system compared to ALP*/DynaLight when used for the detection of E. coli in a model system. These findings provide a comparative analysis of two common reporter systems used for phage-based detection of bacteria and a foundational understanding of these systems for engineering future reporter phage assays.

Characterisation of a new cell wall teichoic acid produced by Listeria innocua ŽM39 and analysis of its biosynthesis genes

Listeria innocua is genetically closely related to the foodborne human pathogen Listeria monocytogenes. However, as most L. innocua strains are non-pathogenic, it has been proposed as a surrogate organism for determining the efficacy of antimicrobial strategies against L. monocytogenes. Teichoic acids are one of the three major cell wall components of Listeria, along with the peptidoglycan backbone and cell wall-associated proteins. The polymeric teichoic acids make up the majority of cell wall carbohydrates; the type of teichoic acids directly attached to the peptidoglycan are termed wall teichoic acids (WTAs). WTAs play vital physiological roles, are important virulence factors, antigenic determinants, and phage-binding ligands. The structures of the various WTAs of L. monocytogenes are well known, whereas those of L. innocua are not. In the present study, the WTA structure of L. innocua ŽM39 was determined mainly by 1D and 2D NMR spectroscopy and it was found to be the following: [→4)-[α-D-GlcpNAc-(1→3)]-β-D-GlcpNAc-(1→4)-D-Rbo-(1P→]_n This structure is new with respect to all currently known Listeria WTAs and it shares structural similarities with type II WTA serovar 6a. In addition, the genome of strain L. innocua ŽM39 was sequenced and the majority of putative WTA synthesis genes were identified.