Improved microtechnique for endotoxin assay by the Limulus amebocyte lysate test

Endotoxemia: methods of detection and clinical correlates

As an assay for endotoxin, the Limulus amebocyte lysate assay has several desirable properties: sensitivity, specificity, and potential for adaptation to a quantitative format. Several modifications have been developed to enhance its potential for clinical application. The modifications that allow quantitative measurement of endotoxin and also improve its application to blood samples are described in this review. In fluids other than blood, the detection of endotoxin with the Limulus amebocyte lysate assay can be used as an aid to identify the presence of gram-negative bacteria, and the assay has established utility. With blood, however, there are a range of factors that interfere with the detection of endotoxemia and there are disparate views with respect to the diagnostic and prognostic significance of the test results. In general, the clinical significance of the finding of endotoxemia broadly parallels the frequency and importance of gram-negative sepsis in the patient groups studied and a decline in endotoxin levels accompanies clinical improvement. However, with therapies designed to reduce levels of endotoxin, or to antagonize its effects, it is unclear whether clinical improvement occurs as a consequence of changes in the levels of endotoxemia.

Influence of high versus low intestinal concentration of gram-negative bacteria and endotoxin on the susceptibility of murine myelopoiesis in bone marrow and spleen to cytostatic treatment with Ara-C

The haematopoietic recovery after i.v. cytarabine was studied in C3H/Law mice as a measure for stem cell susceptibility in relation to the intestinal Gram-negative bacteria (GNB) and endotoxin. Reduction or elevation of GNB and endotoxin was induced by either polymyxin or bacitracin, both non-absorbable antibiotics. Bacitracin caused less suppression of the splenic cellularity after cytarabine, and an advancement of the recovery of femoral nucleated cells. The femoral recovery of CFU-GM exhibited a biphasic pattern. The speed and height of the rebound increase of CFU-GMs were significantly affected by the antibiotics. Thus, (modulation of) the murine intestinal microflora influences the haematopoietic recovery after cytostatic drugs. The mechanisms involved are complex; intestinal endotoxin seems to play a role.

Quantitative Limulus lysate assay for endotoxin and the effect of plasma

The effects of plasma and chromogenic substrate on the kinetics of the endotoxin-activated Limulus amoebocyte lysate (LAL) assay were determined. A linear correlation was observed between the rate of development of turbidity (optical density 405) with the LAL reagent and the concentration of endotoxin over a four log ten-fold range. Like chromogenic substrate, the addition of dilution and heat treated plasma to the reaction resulted in an increase in optical density proportional to the concentration of plasma present. The presence of the treated plasma also resulted in an accelerated increase in optical density with comparable results when testing plasma at different concentrations and, additionally, serum. This accelerated increase in optical density may not be recognised in assays that monitor the progress of the reaction at a single time point and may confound assays of plasma samples that use chromogenic substrate. Plasma obtained from endotoxin sensitive and resistant strains of mice showed similar effects. The use of kinetic methodology means that a quantitative assay for endotoxin in plasma can be achieved, its variability comparable with that seen with semiquantitative serial dilution but with greater economy of the LAL reagent.

Hyaluronic acid in a cardiac myxoma: a biochemical and histological analysis

Cardiac myxoma is the most common primary tumor of the heart. This tumor has a gelatinous stroma that is thought to be composed of glycosaminoglycans, the classical acid mucopolysaccharide ground substance. We examined both biochemically and histologically the hyaluronic acid in a case of cardiac myxoma using a newly developed hyaluronic acid-binding protein probe. We observed that hyaluronic acid was localized in the amorphous stroma and occurred at levels 30 times that found in normal atrial septum.

Recovery of murine myelopoiesis after cytostatic reduction by Ara-C. Effect of bacitracin-induced changes in the intestinal microflora and influence of timing

The influence of intestinal flora modulation by oral bacitracin on the recovery of myelopoiesis after Ara-C was studied in C3H/Law mice. Bacitracin resulted in a 3-5 log increase of Gram-negative bacteria and a 10-fold increase of the intestinal endotoxin concentration. Initiation of bacitracin before Ara-C stimulated the initial rebound increase of colony-forming units for granulocytes and macrophages (CFU-GM) from 23.2 +/- 1.3 to 28.4 +/- 1.4 x 10(3) per femur. Starting the bacitracin after Ara-C advanced the second phase of the rebound CFU-GM increase with 6 days. An important role in the recovery of myelopoiesis after cytostatic drugs in C3H/Law mice is suggested for the intestinal Gram-negative microflora, probably mediated by bacterial endotoxin.

A new method for the quantification of beta-glucan in plasma and its application in the diagnosis of postoperative infection

In order to correctly diagnose and treat severe postoperative infections, it may be critical to detect and differentiate between endotoxin derived from Gram-negative bacteria and/or beta-glucan derived from fungi. In addition to the chromogenic assay, the turbidimetric kinetic assay has been performed for the quantification of endotoxin in plasma using Limulus amebocyte lysate as previously reported. However, it is also known that beta-glucan triggers the coagulation of Limulus amebocyte lysate. In the present study, the differentiation of beta-glucan from endotoxin and its clinical application were studied. Endotoxin was able to be inactivated in plasma using one-tenth dilution by 10 per cent ethanol or distilled water, followed by heating at 100 degrees C for 120 min, without affecting the activity of coexisting beta-glucan. The treated sample was then subjected to the turbidimetric kinetic assay using Toxinometer ET-201. Using this method, as little as 30 pg/ml of beta-glucan in the plasma may be assayed separately, with the amount of circulating beta-glucan in the plasma of normal subjects being less than 50 pg/ml. On the other hand, in patients with a fungal infection, the amount of beta-glucan in their plasma was elevated significantly. Clinically, beta-glucanemia may often occur in severe postoperative infection even if fungi are not detected.

A simple turbidimetric time assay of the endotoxin in plasma

In order to apply the turbidimetric time assay system to the quantitative measurement of endotoxin in plasma, the optimal pretreatment of samples was investigated. After a one-tenth dilution of heparinized plasma followed by heating at 100 degrees C for 10 min, the recovery of added endotoxin was about 90% and a well correlated and reproducible standard curve was obtained in the range 10-1000 pg endotoxin per ml plasma. The amount of endotoxin present in plasma from normal subjects, thus measured, was lower than 10 pg/ml when Escherichia coli 0111:B4 endotoxin was used as a reference. It took no more than 2 h to complete the assay. High values were obtained in cases of liver cirrhosis and severe peritonitis as expected. The present method may be applied for clinical use to quantitate circulating endotoxin, because of its simplicity and high reproducibility.

Effect of selective decontamination of the digestive tract of donor and recipient on the occurrence of murine delayed-type graft-versus-host disease

In the present study we investigated the occurrence of delayed-type graft-versus-host disease (DT-GvHD) after allogeneic bone marrow transplantation (BMT) between two H-2 incompatible mouse strains. BMT was performed on mice with a conventional intestinal microflora as well as on mice in which the Enterobacteriaceae were selectively eliminated from the intestinal microflora by oral antibiotic treatment. None of the conventional or the selectively decontaminated (SD) chimaeric mice suffering from DT-GvHD died of bacteraemia. While DT-GvHD was mitigated when C3H/He recipient mice were SD-treated, this was not the case when C57B1/6J recipient mice were SD-treated. SD-treatment of the digestive tract of donor mice only mitigated DT-GvHD when the recipients were also SD-treated. We conclude that Enterobacteriaceae in the digestive tract may only play a minor role, if any, in the occurrence of DT-GvHD. Instead, we postulate that in this study DT-GvHD was determined by differences in the composition of the resident intestinal microflora (IM) of both mouse strains together with the cellular composition of the bone marrow graft. The interaction between antigenic components of the recipient's IM and the developing donor immune system in the recipient as a possible cause for DT-GvHD is discussed.

Kinetics of endotoxin release by gram-negative bacteria in the intestinal tract of mice during oral administration of bacitracin and during in vitro growth

The release of endotoxin by gram-negative bacteria was studied during bacitracin-induced intestinal colonization in C3H/Law mice and during in vitro growth. The "free" endotoxin concentration was determined by the Limulus amebocyte lysate test in faecal and in culture supernatants, respectively. After oral administration of bacitracin for 2 days a significant (p less than 0.001) increase of the faecal concentration of gram-negative bacteria of 3-4 logs accompanied a significant (p less than 0.001) increase of the faecal endotoxin concentration from 10(1.8 +/- 0.2) to 10(3.3 +/- 0.2) micrograms endotoxin/g faeces. In vitro, however, an increase of the concentration of gram-negative bacteria of 3-4 logs resulted in a 3-4 log increase of the concentration of endotoxin during the exponential and early stationary growth phase. The faecal endotoxin level after 8 days of bacitracin treatment dropped to a value not significantly different from the initial value, regardless of a high faecal level of gram-negative bacteria. Endotoxin determination by the Limulus amebocyte lysate test appeared to be unaffected by the amount of bacitracin present in faecal preparations after oral administration of this antibiotic. In addition, the in vitro release of endotoxin was not influenced by bacitracin. From these results we conclude, that "free" endotoxin is a product of extensive proliferation of gram-negative bacteria. Therefore, the intestinal endotoxin level does not necessarily correlate with the level of gram-negative bacteria, but corresponds with the proliferative activity of these bacteria.

Antibiotic treatment, intestinal aerobic microflora and experimental sarcoma L-1 growth in Balb/c-mice

The present paper deals with the influence of a 10 days treatment with mezlocillin, piperacillin, cefotaxime, clindamycin or gentamicin on the endogenous intestinal microflora of Balb/c-mice and on the local growth of sarcoma L-1 tumor. Clindamycin and gentamicin demonstrated no influence, whereas cefotaxime and piperacillin caused the eradication of gram-negative resp. gram-positive bacteria but these antibiotics didn't produce a growth inhibition of local L-1 sarcoma tumor. The oral or parenteral application of mezlocillin (a 3 days treatment was sufficient) eradicated the complete aerobic and anaerobic intestinal microflora. This effect was significantly correlated with an increase of the cecum weight and the inhibition of local tumor growth. Possible mechanisms of these effects are discussed.

Comparison of a gelation and a chromogenic Limulus (LAL) assay for the detection of gram-negative bacteria, and the application of the latter assay to milk

When a chromogenic Limulus Amoebocyte Lysate (LAL) assay and a tube gelation LAL assay were compared for the detection of Gram-negative bacteria using a strain of Pseudomonas putida, the detection level (approximately 10(3) cfu/ml) and cost of the assays were approximately the same for both assays but the reading was more precise for the chromogenic substrate assay. A modified chromogenic assay was devised for detection of Ps. putida in milk.

Oral administration of antibiotics and intestinal flora associated endotoxin in mice

The contribution of aerobic and anaerobic gram-negative intestinal bacteria to the release of endotoxin in the intestinal tract was investigated during oral administration of various nonabsorbable antimicrobial drugs to C3H/Law mice. The intestinal endotoxin release was studied by determination of the endotoxin concentration in faecal supernatants with the Limulus amebocyte lysate assay. Selective elimination of aerobic gram-negative bacteria by oral treatment with polymyxin, aztreonam or temocillin resulted in a reduction of the endotoxin concentration of faecal supernatants to 10% of the untreated control. Further decrease of the endotoxin concentration to 1% was achieved by total decontamination of the intestinal tract by oral cephalothin/neomycin treatment. Endotoxin determination with the Limulus amebocyte lysate assay appeared to be unaffected by the antibiotics present in the faecal supernatants after oral treatment. On basis of these experiments, it is concluded that in mice 90% of the faeces derived endotoxin can be ascribed to release of endotoxin by intestinal aerobic gram-negative bacteria.

Myelopoiesis in experimentally contaminated specific-pathogen-free and germfree mice during oral administration of polymyxin

Oral administration of polymyxin to specific-pathogen-free C3H/Law mice which with previously contaminated with gram-negative bacteria resulted in complete suppression of cecal gram-negative bacteria. Suppression of cecal gram-negative bacteria was accompanied by reduction of the cecal endotoxin concentration from 10 to 1 microgram/g of cecal content as measured with a microtechnique for the Limulus amebocyte lysate assay. Endotoxin determination by this assay appeared to be unaffected by the amount of polymyxin present in cecal preparations after oral administration of this antibiotic. In experimentally contaminated specific-pathogen-free mice, the femoral concentration of progenitor cells forming granulocyte-macrophage colonies in vitro (CFU-GM) decreased significantly (P less than 0.001) to 66% of the initial control after 4 days of polymyxin treatment. However, the femoral CFU-GM concentration in germfree mice and splenic CFU-GM concentration in experimentally contaminated specific-pathogen-free and germfree mice was not affected by polymyxin treatment. The kinetic behavior of femoral and splenic CFU-GM in experimentally contaminated specific-pathogen-free and germfree mice was expressed as the in vivo sensitivity to the S-phase-specific cytostatic drug hydroxyurea, i.e., the hydroxyurea kill. Administration of polymyxin to experimentally contaminated specific-pathogen-free mice significantly diminished the hydroxyurea kill of femoral CFU-GM from 29 to 13% (P less than 0.02) and of splenic CFU-GM from 53 to 27% (P less than 0.005). The hydroxyurea kill of femoral CFU-GM in germfree mice was not significantly affected by polymyxin treatment. On basis of these results we conclude that the effect of polymyxin treatment on myelopoiesis is most likely due to elimination of intestinal gram-negative bacteria and may indicate a significant role of intestinal gram-negative bacteria in the regulation of myelopoiesis.

Faecal endotoxin and activity of the gut-associated lymphoid tissue in patients with malignant (B-cell) lymphoma

On the basis of previously obtained evidence that Gram-negative bacteria may influence the activity of leukaemia, a study of the composition of the flora, the immune stimulation by the Gram-negative bacteria and the endotoxin concentration in faeces was conducted in patients with low-grade malignant B-cell lymphoma as well as in patients with acute leukaemia. In these patients it was investigated whether the number of facultative anaerobic Gram-negative bacteria in the faeces correlated with endotoxin concentration. In addition, IgA coating of Gram-negative bacteria in the faeces was determined and the titre of circulating antibodies to endogenous Enterobacteriaceae species from the faeces of the corresponding patient was studied. No clear difference was found to exist in the percentage of IgA-coated Gram-negative bacteria in the faeces and in the circulating antibody titres to endogenous Enterobacteriaceae between healthy control persons, lymphoma patients and patients with acute leukaemia. Antimicrobial treatment to establish selective decontamination (SD) of Enterobacteriaceae species from the digestive tract did cause a significant decrease in the faecal endotoxin concentration in a subset of patients treated for SD with polymyxin.

Hollow-fiber dialyzers and their pyrogenicity testing by Limulus amebocyte lysate

Aqueous extracts of cellulose hollow fibers (CHF) exhibit positive reactions in some Limulus amebocyte lysate (LAL) tests. However, in spite of LAL activity, the extracts produce no fever reaction in rabbits. A comparison of lysates from different suppliers shows pronounced activity differences when extracts of cuprammonium-derived CHF are tested. One of the lysates, which is fully reactive against standard endotoxin, shows no reaction with such extracts, nor do CHF extracts diminish its sensitivity to standard endotoxin. Investigations of the cuprammonium process have shown that endotoxins introduced by the linters are degraded and washed out. Other endotoxin introduction, particularly by the process water, has been excluded. Oxidative or acidic degradation of cellulose does not result in the formation of LAL-reactive material (LAL-RM). On the other hand, sterile cotton wool shows LAL reactivity, and cellulose acetate regains LAL reactivity when it is saponified. Thus, it appears likely that the LAL-RM found in CHF is of purely cellulosic origin and crossreacts with a number of commercially available lysates.

Immunogenicity of Pseudomonas aeruginosa outer membrane antigens examined by crossed immunoelectrophoresis

By crossed immunoelectrophoresis 36 different anode-migrating antigens were demonstrated in sonicated antigen preparations of Pseudomonas aeruginosa. We numbered these antigens to establish a reference precipitin pattern. Antigen no. 31 was identified as the lipopolysaccharide (LPS) antigen, because it was found to be responsible for the O-group specificity and because it reacted with anti-LPS monoclonal antibodies and with Limulus amoebocyte lysate. Purified outer membrane proteins F (porin), H2, and I used as antigens formed precipitins with the reference antibodies, thus establishing their antigenicity. LPS that copurified with protein F and slightly contaminated protein H2 was detectable as an extra precipitin (antigen no. 31). The use of monoclonal antibodies specific for smooth LPS and rough LPS revealed different antigenic determinants in the LPS molecule and suggested that antigen no. 5 could be the core region of the LPS which is equivalent to the rough LPS. Antibodies against these outer membrane antigens were detected in patients with chronic P. aeruginosa pneumonia and in patients with acute P. aeruginosa bacteremia. Antibodies with the same specificity were also found in rats chronically infected with P. aeruginosa 7 days postinfection. This demonstrates the surface accessibility and antigenic reactivity of outer membrane antigens.

Modified micromethod of the Limulus amoebocyte lysate assay for endotoxin

A Limulus amoebocyte lysate microtechnique performed in petrolatum wells on a microscope slide is described. Injection of a dye solution in ethanol directly into the wells leads to an unambiguous interpretation of the results. Twelve samples can be tested on a single slide, and compact storing of the samples is possible.