Combined Bacteria Microarray and Quartz Crystal Microbalance Approach for Exploring Glycosignatures of Nontypeable Haemophilus influenzae and Recognition by Host Lectins

Recognition of bacterial surface epitopes by host receptors plays an important role in the infectious process and is intimately associated with bacterial virulence. Delineation of bacteria-host interactions commonly relies on the detection of binding events between purified bacteria- and host-target molecules. In this work, we describe a combined microarray and quartz crystal microbalance (QCM) approach for the analysis of carbohydrate-mediated interactions directly on the bacterial surface, thus preserving the native environment of the bacterial targets. Nontypeable Haemophilus influenzae (NTHi) was selected as a model pathogenic species not displaying a polysaccharide capsule or O-antigen-containing lipopolysaccharide, a trait commonly found in several important respiratory pathogens. Here, we demonstrate the usefulness of NTHi microarrays for exploring the presence of carbohydrate structures on the bacterial surface. Furthermore, the microarray approach is shown to be efficient for detecting strain-selective binding of three innate immune lectins, namely, surfactant protein D, human galectin-8, and Siglec-14, to different NTHi clinical isolates. In parallel, QCM bacteria-chips were developed for the analysis of lectin-binding kinetics and affinity. This novel QCM approach involves capture of NTHi on lectin-derivatized chips followed by formaldehyde fixation, rendering the bacteria an integrated part of the sensor chip, and subsequent binding assays with label-free lectins. The binding parameters obtained for selected NTHi-lectin pairs provide further insights into the interactions occurring at the bacterial surface.
We gratefully acknowledge financial support from the Spanish Ministry of Economy and Competitiveness (Grants BFU2012-36825, BFU2015-70052-R, SAF2012-31166, and SAF2015-66520-R), the Department of Health of the Navarra Government (ref 359/2012), the CIBER of Respiratory Diseases (CIBERES), an initiative from the Spanish Institute of Health Carlos III (ISCIII), and the Marie Curie Initial Training Networks DYNANO (Grant PITN-GA-2011-289033), GLYCOPHARM (Grant PITN-GA-2012-317297), and WntsApp (GA-No. 608180, FP7-PEOPLE-2013). I.K. and D.P. were funded by Marie Curie contracts from the European Commission.