Urogenital disorders

III./2.4.: Escherichia coli, the most important pathogen of infectious peritonitis

III./2.4.1.: General characteristics

Escherichia coli (E. coli) is the most important member of the aerob bacterial flora of the gastrointestinal system. It settles in the human colon not long after birth, where besides its role played in the organism’s vitamin supply it also contributes to the balance of the intestinal flora. E. coli is a short, 2-3-micron-long, 0.5-micron- wide, Gram-negative, rod-shaped bacterium with peritrichous flagella. The undemanding bacterium can be grown on simple culture, both aerobically and semi-aerobically. The bacterial colonies are reddish-purplish with a metallic shine. E. coli obscures the liquid broth evenly. Some bacterial strains cause beta haemolysis.

The bacterium has hundred and fifty seven ’O’-, hundred and three ’K’- and fifty-five ’H’ antigens. The O antigen is the deeper; the K antigen is the more superficial cellular wall antigen, while the protein-natured H antigen is a flagellin antigen. Three subtypes of K antigen can be differentiated based on their heat sensitivity. They surround the bacterium like a capsule and prevent the agglutination of living bacteria in a serum containing O antibodies. The O antigen is a lipopolysaccharid-polipeptide-lipoid complex located in the bacterial cellular wall, which is responsible for the bacterium’s immunobiological functions and toxicity.

III./2.4.2.: Pathogenity

In spite of being part of the normal intestinal flora, E. coli can be a potential pathogen in some extra-intestinal processes, while some of its serogroups and members with a pathogenic factor are clearly enteropathogenic.

Pathophysiological grouping:

• 1. E. coli dyspepsia. It causes an enteritis in infants younger than one year old, with a characteristic age-specific susceptibility, i.e. the younger the infant, the more severe the illness. Water loss developing with the enteritis can lead to severe complications in case of infants with an unstable fluid and salt homeostasis. The pathogenic E. coli strains can be differentiated from the normal members of the intestinal flora biochemically or with a pathogenicity assay. Their identification is based on the determination of antigen structures. Around eleven serogroups are accepted as dyspepsia agents. In order to prevent dyspepsia epidemics the faeces of infants admitted to hospitals has to be tested. Healthy carriers or sick patients have to be isolated and with the transmission hindered aimed antibiotic therapy has to be initiated early.

• 2. Dysenteriform coli. The members of certain E.coli serogroups cause a dysenteriform disease similar to the one caused by Shigellae, but with less severe symptoms. Age-related susceptibility is not present. It is striking that all of these E.coli serogroups show an antigenic structure identical to Shigella types, and that they also provide a positive pathogenicity probe typical of Shigellae (keratoconjunctivitis caused in guinea pigs). From the epidemiological point of view it is important that they often play a role in epidemics caused by drinking water (sometimes by food).

• 3. Enterotoxic E.coli. Some E.coli strains are able to cause cholera-like disorders of different severity. These non-invasive microbes produce a heat-stable and a heat-labile toxin (see above). Some bacteria only produce one of the toxins, but most of them produce both. For the producing of symptoms another virulence factor is needed as well: fibriae with a so-called adhesive function. Fibriae make the attachment to the small intestine mucosa possible. In enterotoxic strains pathogenic for humans two types of adhesive factors are known. The enterotoxigenic E.coli strains also form specific serogroups.
• 4. Our knowledge regarding E.coli strains with extraintestinal roles are deficient. In some cases (e.g. peritonitis after perforation) special characteristics are maybe not even needed, while sometimes they ensure an advantage for the development of infections. (a) E. coli strains isolated from urogenital infections are able to cause haemolysis in a strikingly high proportion. Data suggest that adhesive factors have an important role in this organ system as well. (b) Neonatal sepsis, meningitis. E. coli strains isolated from septic cases carry a Co1V plasmid. It has recently been described that this plasmid encodes a so-called chelin, which is important in the iron-ion transfer of the microbe (e.g. from ferritin). This is said to be explaining the serum resistance of these strains. A significant part of strains cultured from neonatal meningitis carry K1 or K92 antigens. These K antigens are chemically identical to B- or C-type polysaccharide of Neisseria meningitidis.

III./2.4.3.: Laboratory diagnosis, treatment

Since E. coli is a member of the normal intestinal flora easy to culture, their presence in our neighbourhood, food, drinking water can be considered as a faecal indicator, and therefore used in hygienic investigations. In everyday practice different norms define the maximal quantity of E. coli germs food or drinking water can contain. The treatment is based on antibiograms, unfortunately the number of resistant or polyresistant strains is constantly growing.

III./2.4.4.: Of enteric pathogens

Bacterial infections of the gastrointestinal tract represent a large number of infectious diseases. These disorders of different clinical severity range from mild gastroenteritis to generalized infections with bacteraemia through more severe inflammations of the small and large intestines. Among the well defined disorders neonatal E. coli enteritis (E.coli dyspepsia) of infants usually younger than a year old, enterocolitis caused by Y. enterocolica, and two, pathogenetically distinct disorders both caused by bacteria from the Salmonella strain, the enteric fever (which can be typhus abdominalis, i.e. abdominal typhus and paratyphus) and the gastroenteritic salmonellosis can be listed.

Dysentery caused by Shigellae and the severe disease, cholera caused by V. cholerae are distinct disorder groups. Besides these pathogens several other bacteria (Citrohacter, Enterobacter, Proteus, Clostridium perfringens, Campylobacter) can cause inflammatory disorders of the gastrointestinal tract, especially due to the shifted balance of the intestinal flora, because of a change in its components (dysbacteriosis). These disorders can occur sporadically or as an epidemy. Clinical symptoms developing after the infection (fever, leukopenia, decreased blood pressure, shock) are caused by the lipopolysaccharide present in the bacterial wall (the so-called endotoxin), which is released after the disintegration of bacteria.

Sick people, healthy carriers and infected food or water are the most important sources of the disease. The identification of these pathogens, which can most often be isolated from faeces, is possible based on their culturing on selective and differentiating culture media, on their biochemical characteristics and on the serological determination of their antigen structure. Most of these pathogens belong to the Enterobacteriaceae family and are morphologically very similar, rod-shaped Gram-negative bacteria. Some of them (E. coli, Proteus, Klebsiella, Enterobacter) are part of the human and animal intestinal flora.