The use of a model ileum to investigate the effects of novel and existing antimicrobials on indigenous porcine gastrointestinal microflora: using vancomycin as an example

Abstract

The modification of an existing in vitro model of the porcine ileum is described, together with its initial validation in terms of specific bacterial content, resistance to transient pathogen colonisation and test antimicrobial exposure. With the primary aim of producing a standardised test system requiring a low animal cost, a single-stage continuous culture fermenter inoculated with porcine faecal material was shown to be capable of establishing and maintaining a microflora comparable to that of the porcine ileum. Such comparison was based upon total aerobic and anaerobic bacterial population magnitude, total Bacteroides, Bifidobacterium and Enterococcus spp., Escherichia coli and lactic acid bacteria numbers and E. coli strain complexity. The robustness of the model was demonstrated through resistance to transient pathogen ( Salmonella poona) exposure. Test glycopeptide exposure (vancomycin) served both to verify the simulated microflora response as comparable with that reported elsewhere in vivo and to demonstrate the model’s value in the assessment of dietary antimicrobial activity. The trends observed under antibiotic exposure illustrate the influence of vancomycin treatment on the enteric commensal microflora, inhibiting potentially probiotic bacteria that may be vital to the competitive exclusion of the gut and favouring the selection of opportunistic pathogens. Despite the limitations of such a model system, the in vitro porcine ileum produced highly repeatable data at a low cost, with complete control and containment. Given a comparable seeding inoculum the model proved capable of yielding data reproducible over time, describing the test antibiotics influence on the ileal microflora in a form suitable for comparison elsewhere.