Molecular basis of bacterial outer membrane permeability.

Microbial pathogenesis in cystic fibrosis: mucoid Pseudomonas aeruginosa and Burkholderia cepacia.

Since their initial recognition 20 years ago, Shiga toxin-producing Escherichia coli (STEC) strains have emerged as an important cause of serious human gastrointestinal disease, which may result in life-threatening complications such as hemolytic-uremic syndrome. Food-borne outbreaks of STEC disease appear to be increasing and, when mass-produced and mass-distributed foods are concerned, can involve large numbers of people. Development of therapeutic and preventative strategies to combat STEC disease requires a thorough understanding of the mechanisms by which STEC organisms colonize the human intestinal tract and cause local and systemic pathological changes. While our knowledge remains incomplete, recent studies have improved our understanding of these processes, particularly the complex interaction between Shiga toxins and host cells, which is central to the pathogenesis of STEC disease. In addition, several putative accessory virulence factors have been identified and partly characterized. The capacity to limit the scale and severity of STEC disease is also dependent upon rapid and sensitive diagnostic procedures for analysis of human samples and suspect vehicles. The increased application of advanced molecular technologies in clinical laboratories has significantly improved our capacity to diagnose STEC infection early in the course of disease and to detect low levels of environmental contamination. This, in turn, has created a potential window of opportunity for future therapeutic intervention.

Pathogenesis and Diagnosis of Shiga Toxin-Producing Escherichia coli Infections

How does the host sense pathogens? Our present concepts grew directly from longstanding efforts to understand infectious disease: how microbes harm the host, what molecules are sensed and, ultimately, the nature of the receptors that the host uses. The discovery of the host sensors — the Toll-like receptors — was rooted in chemical, biological and genetic analyses that centred on a bacterial poison, termed endotoxin.

Innate immune sensing and its roots: the story of endotoxin

There are four major categories of diarrheagenic Escherichia coli: enterotoxigenic (a major cause of travelers' diarrhea and infant diarrhea in less-developed countries), enteroinvasive (a cause of dysentery), enteropathogenic (an important cause of infant diarrhea), and enterohemorrhagic (a cause of hemorrhagic colitis and hemolytic uremic syndrome). Besides manifesting distinct clinical patterns, these categories of E. coli differ in their epidemiology and pathogenesis and in their 0:H serotypes. Common features (albeit distinct for each category) include plasmid-encoded virulence properties, characteristic interactions with intestinal mucosa, and elaboration of various types of enterotoxins or cytotoxins. A less-well-defined fifth category of diarrheagenic E. coli is that of enteroadherent E. coli, so far identifiable only by their pattern of adherence to Hep-2 cells in tissue culture.

Escherichia coli that Cause Diarrhea: Enterotoxigenic, Enteropathogenic, Enteroinvasive, Enterohemorrhagic, and Enteroadherent

Bacterial hemagglutination and hemolysis.

A study on hemagglutination and hemolysis by Escherichia coli O111 and O55 (rabbit) antisera and on hemagglutination and hemolysis inhibition by E. coli O111 and O55 antigens revealed the following facts.

1. Red blood cells of man, dog, rabbit, guinea pig, sheep, rat, and chicken adsorb E. coli O111 and O55 antigens and thus become specifically agglutinable by the homologous E. coli antisera.

2. The adsorption of these E. coli antigens is a function of the concentration of the antigen, the time (from 5 minutes to 2 hours) of treatment of the red blood cells with the antigen, and the concentration of the red blood cells used.

3. Red blood cells of man and sheep adsorb simultaneously both antigens, as indicated by the fact that both antisera give agglutination of all red blood cells. Complete agglutination does not occur when a mixture of red blood cells treated separately with the two antigens is added to one or the other of the two antisera.

4. Treatment of red blood cells of man with one of the antigens does not block the adsorption of the second antigen. Human cells treated with either or both antigens are still agglutinated by the homologous blood group (A, B, and Rh)-specific antibodies.

5. In the presence of guinea pig complement, E. coli O111 and O55 antisera produce hemolysis of modified human red blood cells in titers of the same order of magnitude as those giving hemagglutination and bacterial agglutination. The same antisera produce hemolysis of sheep cells treated with the identical antigens in titers exceeding by far those giving agglutination of modified human or sheep red blood cells.

6. Both sediment and supernate of a boiled E. coli suspension are capable of modifying red blood cells for E. coli hemagglutination; in contrast, the supernate obtained from an unboiled suspension and then heated does not modify red blood cells for hemagglutination, although it contains the antigen which can specifically adsorb E. coli antibodies, as shown by means of the hemagglutination and hemolysis inhibition tests.

7. Both the unheated and the boiled suspensions of E. coli O111 and O55 inhibit hemagglutination and hemolysis specifically.

8. Rabbit red blood cells modified by either E. coli O111 or 055 antigens, upon intravenous injection into rabbits, engender specific E. coli antibodies.

The significance of the results is discussed.

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Studies on hemagglutination and hemolysis by escherichia coli antisera.

A study on the presence of Escherichia coli 0111, 055, and 026 hemagglutinins and agglutinins in the sera of children and adults selected at random yielded the following results. The E. coli hemagglutination test proved to be far more sensitive for the detection of these antibodies than the conventional bacterial agglutination test. A relationship was found to exist between the presence of E. coli hemagglutinins and the age of the individuals; these antibodies were found in over 90 per cent of human sera selected at random from individuals 12 years of age and older, and less than 14 per cent of sera from infants up to the age of 3 months. Placental transfer of E. coli hemagglutinins was demonstrated in only 3 out of 26 cases, and in these instances the maternal antibody titers were from 4 to 16 times higher than those of the cord blood. These E. coli hemagglutinins were demonstrated also with red blood cells modified with purified lipopolysaccharides, indicating that they react with the somatic antigens of these serogroups of E. coli. The specificity of the hemagglutinins was established by absorption tests, utilizing red blood cells modified by one or the other of the lipopolysaccharides. E. coli 0111, 055, and 026 hemagglutinins were demonstrated in 2 commercial gamma globulin preparations, indicating that these antibodies are not restricted to a population in a small geographical area. The potential diagnostic usefulness of the E. coli hemagglutination test deserves further investigation.

Demonstration of antibodies against enteropathogenic Escherichia coli in sera of children of various ages.

This review deals with immunologic aspects of the effects of endotoxins in susceptible hosts. The subject matter is divided into three sections as follows: (1) biologic effects of endotoxins and immunologic implications, (2) endotoxins as adjuvants, and (3) endotoxins as immuno-suppressants. Not considered is the extensive literature on the antigenic make-up of endotoxins, characterizing the numerous O and R antigens, and endotoxins as immunogens.

Endotoxins and the Immune Response

It is well known that patients with cystic fibrosis are prone to chronic infections of the respiratory tract [1,2]. Increasingly often Pseudomonas aeruginosa is the responsible microorganism in both its nonmucoid and mucoid forms [2, 3]. Its contribution to the pathogenesis of the lung involvement has not been definitely ascertained [3]. It is assumed that active infection rather than surface colonization must take place in order to elicit a specific immune response. Therefore, in this study the antibody response of patients with cystic fibrosis harboring P. aeruginosa was determined and, in addition, all isolates were grouped serologically according to O antigens.

Erwin Neter

Papers

Bacterial hemagglutination and hemolysis.

Studies on hemagglutination and hemolysis by escherichia coli antisera.

Demonstration of antibodies against enteropathogenic Escherichia coli in sera of children of various ages.

Endotoxins and the Immune Response

Serogroups of Pseudomonas aeruginosa and the immune response of patients with cystic fibrosis.