Survival of Mycobacterium bovis BCG oral vaccine during transit through a dynamic in vitro model simulating the upper gastrointestinal tract of badgers.

Gareth A. Williams,Paul Wheeler,Marjorie E. Koenen,Robert Havenaar,Sonya Gowtage,Mark A. Chambers,Sandrine Lesellier,Riccardo Manganelli

doi:10.1371/journal.pone.0214859

Abstract

In developing an oral bait BCG vaccine against tuberculosis in badgers we wanted to understand the conditions of the gastrointestinal tract and their impact on vaccine viability. Conditions mimicking stomach and small-intestine caused substantial reduction in BCG viability. We performed in vivo experiments using a telemetric pH monitoring system and used the data to parameterise a dynamic in vitro system (TIM-1) of the stomach and small intestine. Some BCG died in the stomach compartment and through the duodenum and jejunum compartments. BCG survival in the stomach was greatest when bait was absent but by the time BCG reached the jejunum, BCG viability was not significantly affected by the presence of bait. Our data suggest that from a starting quantity of 2.85 ± 0.45 x 108 colony-forming units of BCG around 2 log10 may be killed before delivery to the intestinal lymphoid tissue. There are economic arguments for reducing the dose of BCG to vaccinate badgers orally. Our findings imply this could be achieved if we can protect BCG from the harsh environment of the stomach and duodenum. TIM-1 is a valuable, non-animal model with which to evaluate and optimise formulations to maximise BCG survival in the gastrointestinal tract.

Highlights

European badgers (Meles meles) are hosts of Mycobacterium bovis and represent self-sustaining wildlife reservoirs of potential tuberculosis transmission to farmed cattle and other animal species [1]
We wanted to ascertain whether these conditions would cause a significant reduction in Bacillus Calmette-Guerin (BCG) viability and could have a detrimental effect on the protective efficacy of an oral BCG vaccine
A similar reduction in viability was seen on incubation of BCG with ox bile, where a reduction in viability of 80% occurred after 100 min of incubation, despite BCG originally being derived from virulent M. bovis using medium containing ox bile [32]

Summary

Introduction

European badgers (Meles meles) are hosts of Mycobacterium bovis and represent self-sustaining wildlife reservoirs of potential tuberculosis transmission to farmed cattle and other animal species [1]. Tuberculosis (TB) infection in livestock has a significant economic impact on farming and UK taxpayers. Since badgers are protected animals under UK law, vaccination is one possible approach to managing the disease in wild badger populations and forms part of the TB eradication strategy for England [2] and Wales [3]. BCG vaccine survival through an in vitro gut model environment-food-rural-affairs. Defra did not play a role in the study design, data collection and analysis, or preparation of the manuscript.

Methods

Results

Conclusion