Nilsson, O. R. | Search bioRxiv

bioRxiv2020

Bacterial protein domains with a novel Ig-like fold bind human CEACAM receptors

Streptococcus agalactiae, also known as group B Streptococcus (GBS), is the major cause of neonatal sepsis in humans. A critical step to infection is adhesion of bacteria at mucosal surfaces. Though several GBS adhesins have been identified, the host receptor targets of these adhesins remain unknown. We report here that surface-expressed {beta} protein from GBS binds to human CEACAM1 and CEACAM5 receptors. A crystal structure of the complex showed that the IgSF domain in {beta} represents a novel Ig-fold subtype called IgI3, in which unique features allow binding to CEACAM1. Bioinformatic assessments revealed that this newly identified IgI3 fold is not exclusively present in GBS. Instead, the IgI3 fold is predicted to be present in adhesins from other clinically important human pathogens. We confirmed the interaction between CEACAM1 and the predicted IgI3-containing adhesin in two different streptococcal pathogens. Overall, our results indicate that the IgI3 fold could provide a broadly applied mechanism for bacteria to target CEACAMs.

microbiology↗

bioRxiv2019

Highly reproducible murine model of oral Salmonella infection via inoculated food

Oral infection of mice with Salmonella Typhimurium is an important model system. In particular C57Bl/6 mice, which are susceptible to Salmonella, are used to study both systemic and gastrointestinal pathogenesis. Pretreatment with streptomycin disrupts the intestinal microbiota and results in colitis resembling human intestinal Salmonellosis. Oral gavage is typically used for delivery of both antibiotic and bacteria. Although convenient, this method requires a moderate level of expertise, can be stressful for experimental animals, and may lead to unwanted tracheal or systemic introduction of bacteria. Here, we demonstrate a simple method for oral infection of mice using small pieces of regular mouse chow inoculated with a known number of bacteria. Mice readily ate chow pieces containing up to 108 CFU Salmonella, allowing for a wide range of infectious doses. In mice pretreated with streptomycin, infection with inoculated chow resulted in less variability in numbers of bacteria recovered from tissues compared to oral gavage, and highly consistent infections even at doses as low as 103 Salmonella. Mice not treated with streptomycin, as well as resistant Nramp1 reconstituted C57Bl/6J mice, were also readily infected using this method. In summary, we show that foodborne infection of mice by feeding with pieces of chow inoculated with Salmonella results in infection comparable to oral gavage but represents a natural route of infection with fewer side effects and less variability among mice.

microbiology↗