Effect of Klebsiella pneumoniae enterotoxin on intestinal transport in the rat

Tropical sprue and subclinical enteropathy: a vision for the nineties

Aside from infectious intestinal diseases with known etiology, there is a group of gastrointestinal disorders mainly affecting the small intestine of individuals predominantly living in and less often visiting or returning from the Third World, usually the tropics, and ranging from asymptomatic structural and/or functional abnormalities of the gastrointestinal mucosa (subclinical enteropathy, SE) to a fully symptomatic condition highlighted by malabsorption of nutrients with associated nutritional deficiencies responsive to folate and broad spectrum antibiotic treatment (tropical sprue, TS). Mounting evidence supports an infectious cause in many instances. The exact nature of the infection, whether initiated and/or perpetuated by enterotoxigenic coliform bacteria, virus(es) or a combination of these, is not clear. Further studies, including those using molecular techniques, are needed in order to clarify various aspects of these widely prevalent disorders.

A Klebsiella pneumoniae strain that shares a type-specific antigen with Shigella flexneri serotype 6. Characterization of the strain and strain and structural studies of the O-antigenic polysaccharide

A strain of Klebsiella pneumoniae was found as the only isolate with pathogenic potential from the stool of a two-year old patient with diarrhoea. A strong serological cross-reactivity with Shigella flexneri serotype 6 was demonstrated. The cross-reacting antigens were shown to reside in the cell wall lipopoly-saccharide. Studies of the pathogenic potential of the Klebsiella strain showed low level of invasion of HEp-2 cells. However, tests for adherence to HEp-2 cells as well as tests for toxin production were negative. The strain had several small plasmids and was multidrug resistant. These data do not form a sufficient basis for estimating the pathogenic potential of the organism. No K antigen was detected. The structure of the O-antigenic polysaccharide from the K. pneumoniae strain was investigated using methylation analysis, NMR spectroscopy, and Smith degradation as the principal methods. The O-antigenic polysaccharide has the following pentasaccharide repeating unit: -->3)- alpha -L-Rhap-(1-->3)- alpha -L-Rhap-(1-->2)- alpha-L-Rhap- (1-->2)- alpha-L-Rhap-(1-->2)- alpha-L-Rhap-(1-->. This structure is not identical to any of the previously described O-antigens of K. pneumoniae. The strong serological cross-reactivity with the Shigella flexneri serotype 6 O-antigen can most likely be attributed to the structural element alpha-L-Rhap-(1-->2)- alpha -L-Rhap present in the O-polysaccharide repeating unit of this serotype. Antiserum raised against the K. pneumoniae strain also agglutinated S. dysenteriae serotype 1 and strains of all different serotypes of S. flexneri. The Shigella strains contain the structural element alpha-L-Rhap-(1-->3)- alpha-L-Rhap in their O-antigen polysaccharides which may be responsible for the observed cross-reactivity.

Enterotoxigenicity, klebocinogeny and antibiotic resistance pattern of food isolates of Klebsiella pneumoniae

The enterotoxigenicity, klebocinogeny and susceptibility to antibiotics for 100 strains of Klebsiella pneumoniae isolated from various food samples is reported. 49% of the samples supported growth of K. pneumoniae: a high proportion of these strains were isolated from sweets and snacks (51%). Enterotoxigenicity as determined by a coagglutination test with anti-LT4 coated staphylococci was observed in 61 of 100 Klebsiella isolates. 21% of the strains were found to be klebocin producers against the K. pneumoniae WC indicator strain. A significant correlation was observed between klebocinogeny and enterotoxigenicity (p less than 0.05). Most strains (91 and 74% respectively) were inhibited by gentamicin and nalidixic acid. Most of the strains were multiply drug-resistant.

Role of bacterial toxins, bile acids, and free fatty acids in colonic water malabsorption in tropical sprue

Colonic perfusion studies in 10 southern Indian patients with tropical sprue and nine matched healthy adults revealed a defect of water and sodium absorption from the colon in sprue. Heat-labile and heat-stable enterotoxin production was not detected in coliforms cultured from the feces of any of the 19 subjects. The 24-hr fecal bile acid output was increased in patients with sprue, but fecal aqueous bile acid concentrations remained within normal limits, and these did not correlate with defects in colonic water and sodium absorption. Fecal free fatty acid excretion was markedly increased in sprue. There was a negative correlation between fecal excretion of unsaturated free fatty acids and colonic water and sodium absorption.

Immunological properties of purified Klebsiella pneumoniae heat-stable enterotoxin

Klebsiella pneumoniae heat-stable enterotoxin was purified to apparent homogenicity by the same techniques used to purify Escherichia coli heat-stable enterotoxin. The two toxins had the same potency in the suckling mouse assay and showed immunological cross-reactivity in enzyme-linked immunosorbent assay, neutralization of secretory activity by specific hyperimmune antisera, and protection against active challenge in rats immunized with a vaccine containing synthetically produced E. coli heat-stable enterotoxin.

Culture supernatants of Campylobacter jejuni induce a secretory response in jejunal segments of adult rats

Culture supernatants of four Campylobacter jejuni strains induced a net sodium secretory flux (plasma-lumen) and an impaired glucose transport in perfused jejunal segments of adult rats in vivo.

Effects of salicylate on intestinal absorption: in vitro and in vivo studies with enterotoxigenic micro-organisms

This study was done to determine whether salicylate could affect alterations in intestinal absorption induced by preparations of enterotoxigenic micro-organisms. It was found in rats that salicylate increased intestinal monosaccharide uptake in vitro and reversed the inhibitory effects induced by cell-free preparations of Staphylococcus sp., Candida sp. and Klebsiella sp. In vivo, salicylates increased net water absorption in rat jejunum exposed to cell-free preparations of various micro-organisms. Increase in net fluid flux occurred after subcutaneous injection only with bacteria which stimulate adenylate cyclase activity. These observations suggest that the absorptive and anti-secretory effects of aspirin are cyclic nucleotide dependent. The potential clinical role of salicylates as anti-secretory agents in diarrhoeal diseases, particularly in children, requires further investigation.

Bacterial colonization of the upper intestine in mild tropical malabsorption

The bacterial flora of the upper intestine has been examined in symptomatic expatriate adults with mild tropical malabsorption, without steatorrhoea, persisting for many months after return to a western environment. Seven of the 11 patients had enterobacteria in luminal fluid or mucosal samples in numbers ranging from 10(3) to 10(8) per ml or per g. The most common isolate was Klebsiella pneumoniae (in four cases); Citrobacter freundii, Serratia marcescens and Pseudomonas spp. were also detected. The signficance of bacterial colonization in the pathogenesis of mild tropical malabsorption is discussed.

Comparison of assay of coliform enterotoxins by conventional techniques versus in vivo intestinal perfusion

Thirty-six strains of coliform bacteria were tested for enterotoxigenicity both by conventional assays, including the Y-1 adrenal and Chinese hamster ovary cell assays for heat-labile toxin and the suckling mouse assay for heat-stable toxin, and by determining the ability of graded concentrations of ultrafiltrate high- or low-molecular-weight toxin preparations to induce water secretion during in vivo perfusion in the rat jejunum. The ultrafiltrates of all 18 strains isolated from persons with infectious diarrheal disease, including seven of Escherichia coli, seven of Klebsiella pneumoniae, and four of Enterobacter cloacae, contained one (nine strains) or two (nine strains) potent toxin fractions (resembling either heat-labile or heat-stable toxin in terms of apparent molecular weight and heat lability characteristics) that induced water secretion at perfusion concentrations of 10 ng/ml or less. Unconcentrated broth filtrates of five of the E. coli strains and two of Klebsiella reacted positively in one or more of the conventional assay systems. Concentrated ultrafiltrates from two strains that were negative in the in vitro assays for heat-labile toxin were tested and also proved to be inactive in these test systems. None of 18 strains isolated from control sources produced, in the ultrafiltrates, enterotoxins capable of inducing water secretion at low concentrations, and none reacted positively in the conventional assays. These results indicate that some strains of coliform bacteria elaborate potent toxin materials that are capable of inducing water secretion and can be detected by perfusion of concentrated ultrafiltrates but not by conventional assay systems for enterotoxigenicity. Whether this represents quantitative or qualitative differences between the toxin materials that stimulate these different test systems remains to be established.

Enterotoxigenicity of colonising coliform bacteria in tropical sprue and blind-loop syndrome

The enterotoxigenicity of strains of Klebsiella pneumoniae, Enterobacter cloacae, and Escherichia coli, which represented the predominant coliform species isolated from the jejunum of 12 patients with tropical sprue and 5 with the blind-loop syndrome, was quantitatively assessed in terms of the ability of toxin preparations to induce water secretion as assayed by in-vivo perfusion in the rat jejunum. All 12 patients with sprue harboured 1 or more highly toxigenic strains--14 of the 16 strains isolated from this group produced heat-labile and/or heat-stable toxins which were as potent as toxins derived from strains isolated from persons with acute diarrhoea and documented as toxigenic. None of the 9 strains isolated from patients with the blind-loop syndrome produced potent toxins. This difference between the coliform bacteria in sprue and the blind-loop syndrome probably accounts, at least partly, for the different intestinal response in these two disorders to contamination by these organisms.

Enterotoxigenicity of enteropathogenic serotypes of Escherichia coli isolated from infants with epidemic diarrhea

Enteropathogenic serotypes of Escherichia coli which have been incriminated by epidemiological evidence as responsible for epidemics of acute diarrhea in infants are often found to be nontoxigenic when tested by conventional systems such as Y1-adrenal, Chinese hamster ovary, and suckling mouse assays. Twelve such strains, representing four different enteropathogenic serotypes, were examined for their capacity to elaborate toxic materials which alter water transport. Ultrafiltration fractions prepared to contain either a high-molecular-weight, heatlabile or a low-molecular-weight, heat-stable form of toxin from each strain were perfused through rat jejuna in graded concentrations ranging from 100 mug to 0.1 ng/ml. Ten of the twelve enteropathogenic strains produced one or both toxin forms that induced water secretion at concentrations of 1 to 10 ng/ml. Values in this range are considered indicative of clinically significant enterotoxigenicity in this assay system, and toxins from well-documented toxigenic strains examined in this study were active at these same concentrations. Similar preparations from ten control strains from healthy persons were either inactive or evoked water secretion only at concentrations of 10 to 100 mug/ml. These observations suggest that enteropathogenic serotypes of E. coli isolated from epidemics of infantile diarrhea produce diarrhea by elaborating potent heat-labile and heat-stable toxin forms which alter water transport but which are inactive in conventional assay systems. The manner in which these toxins differ either quantitatively or qualitatively from those which stimulate the conventional test systems is unknown.

Immunological interrelationships between cholera toxin and the heat-labile and heat-stable enterotoxins of coliform bacteria

Cholera toxin (CT) and the heat-labile (LT) toxin of Escherichia coli are known to share antigenic properties. The present study examined the immunological relationship of CT and the LT and heat-stable (ST) toxins of E. coli, Klebsiella pneumoniae, and Enterobacter cloacae. The neutralizing capacity of equine CT antiserum and of antiserum raised in rabbits to the LT toxin of the three species of coliform bacteria was evaluated by determining their capacity to inhibit the action of purified CT and semipurified ultrafiltration preparations of the coliform LT and ST toxins in inducing water secretion as assayed by the in vivo marker perfusion technique in the rat jejunum. One milliliter of antiserum to CT and to E. coli and Klebsiella LT completely neutralized the secretory action of each of these three toxins; effective serial dilutions of CT antiserum extended to 1 to 4, whereas those of the antisera to LT were limited to 1 to 2 in most instances. One milliliter of antiserum to E. cloacae LT partially neutralized each of the three coliform LT toxins; serial dilutions were inactive. Antiserum to E. cloacae LT did not neutralize CT. Antiserum to CT and to each of the three coliform LT toxins also had a weak neutralizing effect on the ST toxins of E. coli and Klebsiella, but they did not affect E. cloacae ST. Adsorption of the antiserum to CT and to each of the three LT toxins by incubation with a heat-inactivated preparation of either the homologous or a heterologous LT toxin completely abolished the neutralizing capacity of the antisera towards both LT and ST. These observations indicate that the immunological interrelationship of CT and E. coli LT extends to the LT toxins of Klebsiella and E. cloacae and, further, that these immunological properties are shared to a lesser extent by the ST toxins of E. coli and Klebsiella.

Protracted diarrhoea in infancy. Analysis of 82 cases with particular reference to diagnosis and management

Eighty-two cases of protracted diarrhoea in infancy presenting over a 6-year period have been analysed, with particular reference to diagnosis and management. The patients fell into 1 of 2 categories according to whether a specific diagnosis was established or not. A diagnosis (category 1) was established in 59 (72%), the commonest diagnoses being coeliac disease (33-2%), secondary disaccharide intolerance (12-2%), and cows' milk protein intolerance (12-3%). Other diagnoses included primary sucrase-isomaltase deficiency, Shwachman's syndrome, ulcerative colitis, ganglioneuroma, defective opsonization, staphylococcal pneumonia, and Hirschsprung's disease. Despite intensive investigation in diagnosis could not be established in 23 (28%) infants (category 2). Age of onset of symptoms in this group tended to be earlier than in category 1 patients, and 6 (7%) presented with diarrhoea dating from birth. Of particular interest in these 6 patients was the high incidence of associated extraintestinal anomalies, and of sibs who had died after protracted diarrhoea dating from birth. 4 of these 6 infants died, accounting for a mortality of 5% for the whole series. The remaining 17 (21%) patients in category 2 presented at a mean age of 4-9 weeks with a range of 1-18 weeks. All these 17 patients made an excellent response after institution of a chicken-based dietary formula, the details of which are presented. The pathophysiological mechanisms which may be operating in infants with protracted diarrhoea are discussed.

Inhibition of small-intestinal sugar and amino acid transport by the enterotoxin of Shigella dysenteriae I

The enterotoxin of Shigella dysenteriae I produces fluid and electrolyte secretion in the rabbit ileum. These present studies were designed to evaluate nonelectrolyte transport in rabbit ileal mucosa exposed to Shigella enterotoxin. Both 10 mM galactose and 5 mM L-alanine absorptions were significantly impaired in enterotoxin-exposed ileal mucosa compared with control mucosa. L-Alanine influx was not imparied in two other secretory processes: that induced by cholera enterotoxin and hyperosmolarity. These studies provide evidence that both surgar and amino acid absorptions are diminished in the small intestine by the enterotoxin of S. dysenteriae I.

Assay of Escherichia coli enterotoxins by in vivo perfusion in the rat jejunum

Assay of Escherichia coli enterotoxins by in vitro perfusion in rats was evaluated by examining the effects of variously prepared fractions of heat-labile (LT) and heat-stable (ST) toxins on water transport in this system. The assay was found to respond equally well, in a dose-related manner, to both LT and ST; it was sufficiently sensitive to detect the toxigenic effect of concentrations as small as 1 ng/ml. With the assay, it was found that LT is produced in cultures grown under aerobic, but not anaerobic, conditions; in contrast, ST is elaborated in stationary aerobic and anaerobic broth cultures but not in those grown under agitated aerobic conditions. Both toxins can be precipitated by either ammonium sulfate or acetone. The two toxin forms were completely separated from each other by sequential ultrafiltration. LT alone (thermolabile after exposure to 100 degrees C for 30 min) was retained by a PM-30 membrane, and ST alone was present in UM-2 retentates; ST was retained more effectively by a UM-05 membrane, with a 1,000-fold increase in activity over that of the UM-2 retentate. Washed ultrafiltration retentates containing either LT or ST derived from the proper culture conditions all induced water secretion at concentrations of 100 ng or less per ml. These results indicate that in vivo perfusion in rats is a sensitive, duplicable assay for both the LT and ST forms of E. coli enterotoxin.

Partial purification and properties of Enterobacter cloacae heat-stable enterotoxin

Cell free preparations of the whole-cell lysate and ultrafiltration (UF) fractions of broth cultures of a strain of Enterobacter cloacae, isolated from a Puerto Rican with tropical sprue, were assayed for their ability to induce in vivo net water secretion in the rat jejunum. The whole-cell lysate and UM-10 retentate of broth cultures were inactive. The UM-2 retentate and filtrate were active at a concentration of 100 mug/ml or more; the toxigenic activity was entirely retained, and increased to 1 mug/ml, by a UM-05 membrane; washing this retentate yielded a fraction with an activity of 10 ng/ml. Stationary aerobic culture conditions yielded the most active UF fractions when ammonium sulfate was used as the precipitating agent, whereas anaerobic culture conditions produced the most active fractions in broth cultures precipitated by acetone. Passage of the active acetone-precipitated UF fractions through a Sephadex G-25 column yielded eluate pools with enhanced toxigenic activity in, or adjacent to, the void volume, but maximum activity of the ammonium sulfate-precipitated UM-05 retentate eluated at a Kav of 0.38 to 0.52. Neither of the most active gel filtration elution fractions of the UM-05 retentates contained detectable carbohydrate, suggesting that the toxin is not associated with endotoxin. Toxigenic activity was unaltered by exposure to a temperature of 100C for 30 min, lowering the pH to 1, or incubation with either Pronase or trypsin. These observations indicate that the strain of E. cloacae under study elaborates a heat-stable enterotoxin htat has approximately the same molecular weight and shares many of the characteristics of the heat-stable enterotoxin produced by some strains of Escherichia coli and Klebsiella pneumoniae.

Purification and properties of Klebsiella pneumoniae heat-stable enterotoxin

The enterotoxic material in cell-free growth preparations of Klebsiella pneumoniae serotype 5 was purified by sequential ultrafiltration and gel filtration (GF) procedures and the fractions were assayed for enterotoxic activity by determining their ability to induce in vivo net water secretion in the rat jejunum. Whole-cell lysates were inactive. Anaerobic broth culture conditions yielded a 10-fold increase in toxin production over aerobic conditions. Enterotoxic activity was absent in the UM-10 retentate of the broth filtrate but present in both the retentate and filtrate of the UM-2 membrane. GF of the two UM-2 ultrafiltration fractions through a Sephadex G-25 column yielded an active eluate, whose potency was increased by 10- or 200-fold, in or adjacent to the void volume. When subsequently passed through a G-50 column, these pools eluted at a Kav of between 0.4 and 0.6 and were further increased in potency by two- or fivefold. A second equally potent fraction was also recovered in the void volume of the G-50 eluate of the UM-2 filtrate; this may represent a polymer. Progressive purification by GF was associated with an increased protein and decreased carbohydrate content of the most active fractions. The most active G-50 eluate of the UM-2 retentate had a minimal effective enterotoxic dose of 5 mug/ml and that of the filtrate was less than 0.1 mug/ml. Heating the active GF eluates to 100 C for 30 min did not abolish enterotoxic activity and lowering the pH to 1 or incubation with either Pronase or trypsin had no effect on activity. These observations indicate that K. pneumoniae heat-stable enterotoxin is probably a single toxin with an apparent molecular weight in the range of 5,000. The elution characteristics during GF as well as the chemical composition of the most purified enterotoxin fractions indicate that the toxin is not associated with endotoxin.

Enterotoxigenic intestinal bacteria in tropical sprue. IV. Effect of linoleic acid on growth interrelationships of Lactobacillus acidophilus and Klebsiella pneumoniae

The factors responsible for colonization of the small intestine by enterotoxigenic coliform bacteria in Puerto Ricans with tropical sprue are unknown, but epidemiological observations have suggested that they may be related to an increased dietary intake of long-chain unsaturated fatty acids, particularly linoleic acid, which is known to exert an inhibitory effect on the growth of gram-positive organisms that normally comprise the flora of the small intestine. We have examined, by using a glucose-limited continuous-culture system, what effect this fatty acid exerts on the growth relationships of enteric gram-positive and coliform bacteria. In this system, colonization by an invading strain of Klebsiella pneumoniae was prevented by the presence of an established culture of Lactobacillus acidophilus, principally by virtue of a lowered pH of the medium that was incompatible with Klebsiella growth. However, when the population density of L. acidophilus was reduced by the presence of a sufficient concentration of linoleic acid, the invading K. pneumoniae successfully colonized the system and, once established, suppressed the growth of L. acidophilus. These observations indicate that, under the conditions of our chemostat, gram-positive enteric bacteria suppress coliform growth and that this effect is reversible by the presence of linoleic acid. It remains to be established, however, what pertinence these in vitro observations have to conditions within the intestinal tract of persons living in the tropics.