Adaptation of the staphylococcal coagglutination technique for detection of heat-labile enterotoxin of Escherichia coli

Coagglutination test for rapid detection of Salmonella enterotoxin

The Staphylococcal Coagglutination (CoA) test using Staphylococcus aureus (Cowan type-1) cells coated with antiserum against purified Salmonella enterotoxin was standardized and carried out to screen Salmonella serotypes for their enterotoxigenicity. Of the 101 cell-free culture supernatants from an equal number of Salmonella strains belonging to 15 different serotypes tested, 76 were found to be enterotoxigenic. All of the 24 strains which gave positive reactions in the rabbit ligated ileal loop test were also positive with this test. As little as 7.5 ng of purified Salmonella enterotoxin could be detected by the CoA test. The presence of enterotoxin in polymyxin B extract of cells and cell-free preparation of a S. typhimurium strain was detected as early as after 1.5 and 3.0 h of incubation, respectively. Besides the test standardized with the antiserum to purified V. cholerae toxin (CT) could detect purified toxin in a quantity as little as 5.0 ng and also enterotoxigenicity in an E. coli strain (LT+). The usefulness of the test as a routine, rapid and economic one for the detection of enterotoxin of Salmonella, Vibrio cholerae and E. coli is discussed.

Evaluation of the Biken test to detect heat-labile (LT) enterotoxin produced by porcine and human Escherichia coli strains

Fifty-seven strains of enterotoxigenic Escherichia coli isolated from humans and pigs and producing thermolabile (LT) enterotoxin were used to ascertain the efficiency of the Biken test compared to the passive immune haemolysis test (PIH), considered as very sensitive for detecting that enterotoxin. The two assays were carried out using anti-porcine (anti-LTp), anti-human (anti-LTh), anti-cholera toxin (anti-CT) and anti-choleragenoid (anti-Cg) antisera. Our results showed that the Biken test was very irregular, with many false-negative results. Positive results (ranging from 78.9 to 22.8) were dependent upon the antiserum used. Conversely, the PIH test was much more efficient in the detection of LT, since 100% of the LT+ strains were positive in this test whatever the antiserum used.

Assay for heat-labile Escherichia coli enterotoxin using sandwich erythroimmunoassay

We investigated the possibility of using a sheep erythrocyte-antibody conjugate as reagent in a sandwich erythroimmunoassay (SERIA) procedure to detect and titrate Escherichia coli heat-labile enterotoxin (LT) with the naked eye. In this assay, which is based on the immunological similarity between Vibrio cholerae toxin (CT) and LT, rabbit anti-CT IgG was used as immunosorbent, and sheep erythrocytes, sensitized with the rabbit anti-CT antibodies, were used as indicator. The sensitivity of the test was demonstrated by a comparative study using an enzyme-linked immunosorbent assay (ELISA). The results obtained by SERIA with 130 samples correlated well with those of a Vero cell assay and a GM1-ELISA. The test is easy, relatively cheap and as sensitive as other standard techniques; it is particularly suited for field laboratories, especially in tropical countries, and a large number of strains may be examined daily.

Comparison of a coagglutination test with the GM1-ELISA and the Y-1 adrenal cell assay for the detection of heat-labile enterotoxin from Escherichia coli

A number of different assay methods has been developed for the detection of the heat-labile enterotoxin (LT) of ETEC strains isolated from humans and animals. In the present study 40 Escherichia coli strains were subject of a comparative study of the staphylococcal coagglutination (Coa-LT) test, the GM1-ELISA and the Y-1 adrenal cell test. All but two of 20 "LT-ST" or "LT-only" producing ETEC strains gave identical results in both the Coa-LT test and the bioassay. None of the 14 "ST only" producing ETEC strains gave false positive results. It is concluded that the Coa-LT test is a simple and rapid assay method for the routine diagnosis of LT producing ETEC strains.

Improvements in the microtitre GM1 ganglioside enzyme-linked immunosorbent assay for Escherichia coli heat-labile enterotoxin

A variant of the microtitre GM1-ELISA for Escherichia coli heat-labile enterotoxin was studied. The test was improved by both reducing the assay time from 2 1/2 d to 8 h and by determining the most appropriate GM1 coating concentration. Coating the plates with greater than or equal to 3 micrograms of GM1/ml yielded a maximal sensitivity and ensured a linear relationship between the enterotoxin concentration and the extinction observed when using the final assay-procedure. Thus an optimal accuracy was obtained. This ELISA was 4- to 8-times more sensitive than the Vero cell monolayer assay. The sensitivity of this ELISA and of the chinese hamster ovary cell monolayer assay were identical.

Detection by a staphylococcal coagglutination test of heat-labile enterotoxin-producing enterotoxigenic Escherichia coli

For detection of heat-labile enterotoxin-producing enterotoxigenic Escherichia coli, the staphylococcal coagglutination test reported by Brill et al. (J. Clin. Microbiol. 9:49-55, 1979) was modified to give better results. Staphylococcal cells were sensitized with anti-heat-labile enterotoxin antiserum and suspended in phosphate-buffered saline containing 0.5% bovine serum albumin, 0.05% Tween 80, 0.01% gelatin, and 0.02% NaN3. The test strain was cultured in 0.25 ml of Biken broth no. 2 in a test tube (12 by 100 mm) stood at an inclination of about 10 degrees to the horizontal. After incubation for 5 h at 37 degrees C, the cells were collected by centrifugation at 2,500 rpm for 15 min and suspended in 50 microliters of polymyxin B solution (20,000 IU/ml). The suspension was then incubated for 1 h at 37 degrees C and centrifuged at 2,500 rpm for 15 min, and 10 microliters of the supernatant was used for the test on a slide. The results of the modified test correlated completely with those obtained by the Biken test. The modifications of the staphylococcal coagglutination test described here allow for detection of heat-labile enterotoxin-producing enterotoxigenic E. coli within 6 to 7 h after inoculation of a test strain.

Detection of heat-labile (LT) enterotoxin of enterotoxigenic Escherichia coli by the radial immune hemolysis test: a modification for clinical use

An adaptation for clinical purposes of a radial immune hemolysis test for the detection of the heat-labile (LT) enterotoxin of the enterotoxigenic Escherichia coli is described. The results correlated well with those from Vero cell assay and the passive immune hemolysis test. Because the test is easy, relatively cheap, and as sensitive as other standard procedures, for LT detection, it is particularly suitable for less-equipped laboratories. Also, a large number of E. coli strains may be examined daily by this technique.

Enzyme-linked immunosorbent assay for detection of Salmonella typhi Vi antigen in urine from typhoid patients

Because typhoid fever continues to be a major cause of illness in many developing countries, there is a clear need for a sensitive and specific test that will permit rapid laboratory diagnosis of the disease. An enzyme-linked immunosorbent assay (ELISA) has recently been developed and tested, both in the laboratory and in a clinical situation, for its ability to detect Vi antigen in urine. The ELISA was capable of detecting as little as 1 ng of purified Vi antigen per ml in urine, compared with 100 ng/ml detectable by a previously tested coagglutination method. It could also detect antigen in urine diluted as much as 1:1,024 in normal urine. In tests of urine specimens from six stool culture-positive persons in a small typhoid outbreak in the United States, the ELISA detected antigen in specimens from four of the six patients. The ELISA also proved to be specific, giving no false-positive results for specimens from 50 persons who did not have typhoid fever. The apparent high sensitivity and specificity of this ELISA make it a promising test for rapid diagnosis of typhoid fever.

A simple and rapid test for the identification of clinical herpes simplex virus isolates

A simple procedure is described which permits the rapid identification of clinical herpes simplex virus isolates. The test utilizes Staphylococcus aureus to which anti-viral immunoglobulins had been adsorbed. Adherence of the antibody-coated bacteria to virus-infected cells is readily seen by light microscopy. Indirect immuno-fluorescence and the S aureus adherence reaction were found to be approximately of equal sensitivity for the detection of virus antigens.

Cytotonic enterotoxin from Aeromonas hydrophila

Aeromonas hydrophila produces two hemolysins and an enterotoxin during growth. Enterotoxin, separated from the hemolysins, gave positive reactions in the rabbit intestinal loop test, the rabbit skin test and the adrenal Y1 cell test. Neutralization experiments in the rabbit loop, rabbit skin and Y1 cell tests failed to demonstrate any immunological relationship between Aeromonas enterotoxin and cholera toxin or Escherichia coli heat-labile enterotoxin. Prior incubation of Aeromonas enterotoxin with gangliosides did not inhibit the positive test results in these systems. A co-agglutination test with antiserum to purified cholera toxin was negative for Aeromonas enterotoxin, which therefore seems to be immunologically distinct from cholera toxin. The Aeromonas enterotoxin induced steroid secretion in adrenal Y1 cells and increased the intracellular cyclic adenosine monophosphate (cAMP) content of Y1 cells as well as of rabbit intestinal epithelial cells. It thus seems to act via the adenylate cyclase-cAMP pathway and should be classified as a cytotonic enterotoxin according to the classification of Keusch and Donta (1975).

Rapid presumptive identification of Cryptococcus neoformans by staphylococcal coagglutination

A coagglutination reagent was prepared by sensitizing the Cowan I strain of Staphylococcus aureus with rabbit immune globulin directed against Cryptococcus neofromans A15 and absorbed with C. laurentii. This reagent was evaluated for its usefulness in differentiating C. neoformans from other yeast colonies rapidly. Antigen-containing extracts were prepared form Sabouraud dextrose agar cultures of 48 C. neoformans, 33 other Cryptococcus species, 21 Candida, 4 Torulopsis, 3 Saccharomyces, and 2 Rhodotorula strains. This was done by suspending a 0.001-ml loopful of colony growth in 0.5 ml of phenolized saline, mixing for 30 s, and then centrifuging. Equal volumes (50 microliters) of coagglutination reagent and yeast extract were mixed within marked circles on a glass slide and then mechanically rotated at 180 rpm for 8 min. Forty-five of the 48 strains of C. neoformans produced strong (3+ to 4+) agglutination, and 3 strains of serotype C produced weak (1+ to 2+) agglutination with the reagent. Other Cryptococcus species which reacted positively were 4 C. albidus subsp. diffluens, 7 C. albidus subsp. albidus, and 2 C. terreus strains; however, false-positive errors in identification were circumvented by performing a supplemental rapid test for nitrate utilization which differentiated these yeasts from C. neoformans. None of the other yeasts tested (including 14 C. laurentii, 2 C. luteolus, and 2 C. uniguttulatus strains) produced any degree of agglutination with the reagent. A commercial cryptococcal latex agglutination reagent (Crypto-Test, Microbiological Associates, Walkersville, Md.) proved less reliable for identifying C. neoformans yeast colonies because of cross-reactions which occurred with all other species of Cryptococcus tested.

Modified Elek test for detection of heat-labile enterotoxin of enterotoxigenic Escherichia coli

The Elek test was modified for detection of the heat-labile enterotoxin of enterotoxigenic Escherichia coli. A total of 164 strains of E. coli were tested by the modified Elek test, and the results correlated well with those of the Chinese hamster ovary cell assay and passive immune hemolysis. It is concluded that the modified Elek test is a simple and reproducible assay method for identification of E. coli which produce heat-labile enterotoxin, and is suitable for use in clinical laboratories.

Detection of Escherichia coli enterotoxins in stools

We determined whether enterotoxigenic Escherichia coli diarrhea could be diagnosed by direct examination of stools for heat-labile (LT) and heat-stable (ST) enterotoxins. The Y-1 adrenal cell and an enzyme-linked immunosorbent assay (ELISA) detected LT in 85 and 93%, respectively, of stool specimens obtained from adults with acute diarrhea from whom an LT- and ST-producing organism had been isolated. Furthermore, the ELISA assay detected LT in 8 of 35 stool specimens from which no LT-producing E. coli had been isolated. The infant mouse assay was utilized to detect ST in these stool specimens and was found to be an insensitive method, showing positive results in only 36% of the specimens from which an ST-producing organism was isolated. Further studies are warranted to determine the diagnostic value of direct detection of LT in stools, especially by the ELISA method.

Microtiter ganglioside enzyme-linked immunosorbent assay for vibrio and Escherichia coli heat-labile enterotoxins and antitoxin

We have developed a microtiter enzyme-linked immunosorbent assay method for detecting the heat-labile enterotoxins of Vibrio cholerae and Escherichia coli using GM1 ganglioside as the base coat. This method compares favorably with a similar assay using anticholera toxin as the base coat, and with the Y1 adrenal cell assay. The assay should be useful in detecting enterotoxin production in E. coli and vibrios (including non-agglutinating Vibrio), in quantitating the toxin, and in determining binding properties of enterotoxins to ganglioside. The assay can also be used to quantitate antibodies which block the attachment of the toxin to the ganglioside.

Evaluation of a ganglioside immunosorbent assay for detection of Escherichia coli heat-labile enterotoxin

The GM1 ganglioside enzyme-linked immunosorbent assay (GM1-ELISA), an immunological method for detection of Escherichia coli heat-labile enterotoxin (LT), was quantitatively and qualitatively compared with the conventional adrenal cell test for the identification of LT-producing strains. A micromodification model of the assay was developed. Enterotoxin preparations from 120 E. coli isolates from individuals with diarrhea, which had been previously shown to be enterotoxigenic by the adrenal cell test, and from 44 control strains of E. coli were compared in parallel by the two methods. Quantitatively the covariation of the enterotoxin titers was highly significant (RS = 0.98, P less than 0.001), the GM1-ELISA being somewhat more sensitive than the adrenal cell test. The methodological error was less than 5% in both tests. Qualitatively the overall agreement for positive and negative reactions for the two methods was 89%. The GM1-ELISA is practical for routine use in the diagnosis of enterotoxigenic E. coli, especially in laboratories without facilities for cell culture.