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Enterobacteria and bacterial food poisoning 

Enterobacteria and bacterial food poisoning

Enterobacteria and bacterial food poisoning

Hugh Pennington



Accounts have been added of two important recent evolutionary events: the global spread of NDM-1 Enterobacteriaceae, and the enormous outbreak caused by the highly virulent EHEC/EAggEC hybrid E. coli O104:H4.

Updated on 31 May 2012. The previous version of this content can be found here.
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date: 30 March 2017

The worldwide impact of food poisoning is very great. Such infections kill many children in the developing world, where diarrhoeal diseases stunt their physical and cognitive development. The number of illnesses is also large elsewhere: in the United Kingdom the commonest cause of food poisoning, Campylobacter, accounts for about 500 000 cases every year.

The commonest bacterial pathogens are Campylobacter and various members of the Enterobacteriaceae, a large family of Gram-negative organisms, of which Escherichia coli, shigella, and salmonella are considered in this chapter.

Escherichia coli

Pathogenic E. coli include the following:

Enteropathogenic (EPEC)—virulence-positive EPEC are now rare in industrialized countries; food- and water-borne and person-to-person spread occur, resulting in diarrhoeal illness; fewer than 500 cases are recorded annually in the United Kingdom.

Enteroaggregative (EaggEC)—first isolated from malnourished children in Chile suffering from chronic diarrhoea; not routinely tested for in industrialized countries but probably common.

Enterotoxigenic (ETEC)—an important cause of mortality in children under 5 years of age in developing countries, and causes travellers’ diarrhoea; adheres to the mucosal surface of epithelial cells of the proximal small bowel, a process mediated by at least 12 different kinds of pili encoded by transferable plasmids, and produces enterotoxins.

Enteroinvasive (EIEC)—like shigella, for all practical purposes.

Enterohaemorrhagic (EHEC)—the most important EHEC is E. coli O157:H7, which produces a toxin virtually identical to that of Shigella dysenteriae. E. coli O157 is a normal nonpathogenic inhabitant of the gastrointestinal tract of cattle and sheep; most human infections are contracted either by the consumption of foods contaminated with animal manure or by its direct ingestion, probably from hands that have touched contaminated surfaces. Clinical presentation is with diarrhoea (becoming bloody in 90% of cases) and abdominal pain, with a few cases (15% of children <10) going on to develop haemolytic uraemic syndrome (HUS). Diagnosis is by culture. Management is supportive.

EHEC/EaggEC hybrid—caused the serious E. coli O104:H4 outbreak in Germany in May to July 2011; attributed to an organic farm producing fenugreek seed sprouts.


Infections are exclusively human, spread by the faecal–oral route from person to person, and with a very low infectious dose. Shigellosis is endemic in developing countries in tropical areas, and it probably kills about 600 000 annually, mostly young children. Presentation is with watery diarrhoea, fever and malaise, with severe infections (most often caused by S. dysenteriae) progressing to diarrhoea comprising mucus, blood, and pus, along with severe abdominal cramps and tenesmus. Management of mild cases is supportive; severe cases are given antibiotics (ampicillin, co-trimoxazole, tetracycline, ciprofloxacin, others) as guided by local antimicrobial susceptibility data.


There are over 2000 salmonella serotypes, all belonging to the single species Salmonella enterica. Those that cause food poisoning infect both animals and humans, and most infections are food-borne, most often by poultry, with S. enteritidis (strictly a serotype rather than a species) the paradigmatic organism. Clinical presentation is typically with headache, vomiting (not usually a prominent feature), diarrhoea, abdominal pain, and fever. Metastatic infection sometimes occurs, particularly osteomyelitis and in atherosclerotic vessels, abnormal heart valves, and joint prostheses. Management of mild cases is supportive; severe cases are given antibiotics, usually ciprofloxacin.


This is by far the commonest cause of bacterial gastroenteritis in the industrialized world, with an annual incidence of infection perhaps as high as 1 per 100 in the United Kingdom. The organisms are very common in the intestines of wild birds, poultry, cattle, and sheep, but the source of infection in most human cases is unknown. A prodrome of fever and general aching sometimes precedes abdominal pain (sometimes severe) and diarrhoea (frequently bloody). Complications include reactive arthritis (1% of cases) and Guillain–Barré syndrome. Most infections are self-limiting, but aside from supportive care, antibiotics (often erythromycin or ciprofloxacin) are given to severe cases.


Prevention of food poisoning depends on Hazard Analysis and Critical Control Points (HACCP), which identifies hazards, identifies the points in a process where they may occur, and decides which points are critical to control to ensure consumer safety, e.g. in milk pasteurization the critical control points are the temperatures reached during heating, its duration, and the measures taken to prevent subsequent contamination.

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