Investigating the use of Bdellovibrio bacteriovorus as a 'living antibiotic' to control Salmonella in pigs.

Globally, non-typhoidal Salmonella spp. is responsible for 93 million human infections perannum, ~27% due to consuming contaminated pork. Salmonella is also a pathogen of pigs, and costs the EU pig industry ~Euro 600 million per annum. Multidrug resistant (MDR) strains of Salmonella are increasingly responsible for infections in pigs, and are associated with higher morbidity and mortality in humans1. Alternative approaches to antibiotics are desperately needed. One such approach is the use of the predatory bacterium Bdellovibrio bacteriovorus.Bdellovibrio preys upon a range of Gramnegative bacterial pathogensincluding Salmonella spp..

We previously demonstrated that Bdellovibrio can significantly reduce Salmonella Enteritidis in the caeca of chickens; accompanied by improvements in clinical symptoms2. Subsequently, Bdellovibrio has been applied to treat infections caused by Yersinia3, Shigella4, Klebsiella5 and Vibrio6. Bdellovibrio has advantages over antibiotics:
they are self replicating and self-limiting; replicating only within susceptible bacteria;
and resistance is a transient event linked to phenotypic plasticity7.

Bdellovibrio does not harm animals during therapeutic trials8, at worst eliciting a mild and temporary inflammation9. Bdellovibrio is present, at least transiently, in the intestinal tracts of animals and humans10,11; we have evidence that Bdellovibrio can be isolated from the intestinal tract of pigs.

The aim of this project is to move towards applying Bdellovibrio therapeutically in pigs: by isolating Bdellovibrio from the intestine of pigs, characterising these bacteria with respect to prey preference and determining their survival and predatory efficiency against Salmonella in ex-vivo models of different pig intestinal compartments. In addition, the delivery of Bdellovibrio into the intestinal tract will be optimised by testing a range of micro- and nano-encapsulation techniques.Main objectives:1. Isolation of Bdellovibrio from different gut compartments of pig intestine samples (obtained from commercial and on-site abattoirs). 2. Genetic and phenotypic analysis of Bdellovibrio isolates, including prey
range and predation efficiency on a range of porcine-derived Salmonella spp.. 3. Testing Bdellovibrio predation on Salmonella in ex-vivo gut models. Also analysis of Bdellovibrio preparation methods including micro and nano-encapsulation to optimise Bdellovibrio delivery.4. Determining the effect of Bdellovibrio on the microbiota of the pig intestine by metagenomics analyses before and after Bdellovibrio treatment.This project will broaden our knowledge about Bdellovibrio's ability to colonise themammalian intestine, and affect target pathogenic species in a complex environment. It will allow us to further explore the effect of Bdellovibrio on the intestinal microbiota of pigs and help
us to optimise Bdellovibrio preparations for use in an in vivo therapeutic trial (outside the scope of this project). Given the increasing presence of multi-drug resistant Salmonella in both pigs and humans, this project may lead to a new, alternative treatment for such infections which may be recalcitrant to conventional antibiotic chemotherapy.

References1.Parisi, Foodborne Pathog. Dis.(2018).doi:10.1089/fpd.2017.2403; 2.Atterbury, Appl Env Microbiol (2011)77,5794-5803; 3.Russo, Microorganisms 2018).doi:10.3390/microorganisms7010002; 4.Willis, Curr. Biol. (2016).doi:10.1016/j.cub.2016.09.067; 5.Shatzkes, MBio (2016).doi:10.1128/mBio.01847-16; 6.Li,
Int. J. Food Microbiol. (2011).doi:10.1016/j.ijfoodmicro.2011.07.036; 7.Shemesh, Environ. Microbiol. (2004). doi:10.1046/j.1462-2920.2003.00530.x; 8.Westergaard, Appl Env Microbiol (1977) 34,506- 511; 9.Shatzkes, Sci. Rep. (2015). doi:10.1038/srep12899; 10.Schwudke, Syst. Appl. Microbiol. (2001).doi:10.1078/0723-2020-00042; 11.Iebba, PLoS One (2013).doi:10.1371/journal.pone.0061608.