Mechanisms of pathogen control in the avian gastrointestinal tract
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The environment of the avian enteric system is complex and dynamic. With many different types of bacteria and up to 1012 viable bacteria/g of digesta, how does the gut maintain a commensal microflora while protecting itself from harmful organisms? Mechanisms by which pathogens are thought to be controlled in the gut include: (i) physiological barriers such as mucin and pH; (ii) competition for enteric attachment sites; (iii) competition with the host and other microbes for nutrients, such as short-chain fatty acids; (iv) production of antimicrobial compounds or agents, including bacteriocins and bacteriophage; and (v) stimulation of the immune system. The intestinal mucosa functions as a primary host defence against the constant presence of antigens from food and the wide variety of beneficial and harmful microorganisms in the gut lumen. There is emerging evidence of a sophisticated 'cross-talk' between the enteric microflora and the host, as well as similar communication between the microbial inhabitants in the intestinal lumen. Understanding the interactions between commensal and pathogenic bacteria and the avian gastrointestinal tract will enhance the discovery of new ways to exploit the potential benefits of this complex and dynamic environment. CAB International 2006.