26: Infections of the gastrointestinal tract

Chapter 26 Infections of the gastrointestinal tract

Normal flora

In healthy, fasting individuals, the stomach is either sterile or may contain only a few organisms, because of its low pH and enzymes. The diet has a major effect on the gut flora. The small intestine may be colonized with streptococci, lactobacilli and yeasts (especially Candida albicans); the proportions of these and other organisms vary, depending on dietary habits. In the ileum, a typical Gram-negative flora (e.g. Bacteroides spp. and Enterobacteriaceae) is seen, and the large intestine has a dense population of varied flora. These include members of the Enterobacteriaceae, Enterococcus faecalis, Bacteroides spp., Clostridium spp., bifidobacteria and anaerobic streptococci. The anaerobes outweigh the aerobes by far and comprise the vast majority of the bacteria in the large intestine. Roughly 20% of the faeces contains bacteria, approximately 1011 organisms per gram. As in the oral cavity, the gastrointestinal tract harbours a vast multitude of unculturable, and yet to be discovered organisms.

Common diarrhoeal diseases

Shigella

Shigella causes bacillary dysentery, as opposed to amoebic dysentery caused by intestinal amoebae. It is an important cause of morbidity and death in young children, particularly in the developing world.

Salmonella

A large number of different Salmonella species exist, together with an even more bewildering number (about 1500) of serotypes. Of these, about 14 are important pathogens. The common diarrhoea-causing organism is Salmonella typhimurium. The other major pathogens of this group are Salmonella typhi and Salmonella paratyphi-A, -B and -C, which cause enteric fever, a septicaemic illness in which diarrhoea is a late feature of the disease.

Escherichia coli

E. coli is a normal commensal of the gastrointestinal tract, but certain strains, for some unknown reason, can behave as pathogens. As described in Chapter 15, they produce enterotoxins, and the enteroinvasive strains have the ability to invade the gut mucosa.

Only gold members can continue reading. Log In or Register to continue

Jan 4, 2015 | Posted by in General Dentistry | Comments Off on 26: Infections of the gastrointestinal tract
Premium Wordpress Themes by UFO Themes