Comparison of immunosorbent electron microscopy, enzyme immunoassay and counterimmunoelectrophoresis for detection of human rotavirus in stools

Characterization of rotavirus subgroup-specific monoclonal antibodies and use in single-sandwich ELISA systems for rapid subgrouping of human strains

Two subgroup-specific monoclonal antibodies (MAb) raised in mice against group A human rotavirus were shown to react by immunoblotting with the trimeric form of VP6 of the homologous subgroup and successfully applied to development of new single-sandwich ELISA systems for rapid subgrouping of human strains. All of the 344 strains tested could be subgrouped, but for two of them prior propagation in cell cultures was required.

Rapid detection of human rotavirus strains in stools by single-sandwich enzyme-linked immunosorbent assay systems using monoclonal antibodies

Using murine monoclonal antibodies (MAbs) raised against the common antigen of group A rotavirus (RV), two single-sandwich ELISA systems were developed for detection of RV in stools: one using polyclonal antibody (PAb) as capture and a MAb as detector antibody (referred to as PAb-MAb assay); and the other based on the use of two different MAbs as capture and detector antibodies (referred to as MAb-MAb assay). In each single-sandwich ELISA system, samples and peroxidase-labeled MAb were incubated sequentially (two-step method) or simultaneously (one-step method). Using the two-step procedure on purified RV, 50 pg of protein was detected in the PAb-MAb as well as in the MAb-MAb assay, whereas the one-step method detected 0.4 ng and a conventional double-sandwich ELISA detected 3.2 ng of viral protein. Titration of RV samples from stools and cell cultures showed that single-sandwich ELISA titers were, on the average, 10-100-fold higher than those obtained by electron microscopy (EM), but 10-100-fold lower than those obtained by solid-phase immune EM (SPIEM). However, when 200 stool samples previously examined by EM or SPIEM were tested by the single-sandwich ELISA systems, specificity and sensitivity of these assays were 100%, and comparable to SPIEM. No false positive results were obtained when 54 samples of meconium and 91 stools from newborns in the first five days of life were tested. The two-step procedure appeared to be somewhat preferable over the one-step method, which, although faster, gave a marked prozone with a few samples in the MAb-MAb assay. The use of MAbs in rapid single-sandwich ELISA systems for RV detection in stools appears highly convenient, due to reliable results and short test performance times.

Comparison of a new rapid test (TestPack Rotavirus) with standard enzyme immunoassay and electron microscopy for the detection of rotavirus in symptomatic hospitalized children

We compared a new, rapid, qualitative test for rotavirus (TestPack Rotavirus; Abbott Laboratories, North Chicago, Ill.) with another enzyme immunoassay (Pathfinder Rotavirus; Kallestad Laboratories, Inc., Austin, Tex.) and electron microscopy to determine its clinical utility in a population of symptomatic hospitalized children. In the first part of the study, 100 frozen stool samples were tested. The results after resolution with a blocking reagent showed a sensitivity of only 50% and a specificity of 88% for TestPack Rotavirus. In the second part of the study, we tested TestPack Rotavirus on 100 fresh, unfrozen samples. The results (sensitivity/specificity) were as follows: TestPack Rotavirus, 95/90%; Pathfinder Rotavirus, 84/98%; direct electron microscopy, 63/100%. Although it was not as sensitive or specific as immune electron microscopy, TestPack Rotavirus was more sensitive than direct electron microscopy or Kallestad Pathfinder Rotavirus. TestPack Rotavirus represents a rapid, qualitative method for the detection of rotavirus in stools of symptomatic children.

Development of protein A-gold immunoelectron microscopy for detection of bovine coronavirus in calves: comparison with ELISA and direct immunofluorescence of nasal epithelial cells

A protein A-colloidal gold immunoelectron microscopy (PAG-IEM) technique was developed for the detection of bovine coronavirus (BCV) in the feces and nasal secretions of infected calves. Feces or nasal swab fluids were incubated sequentially with hyperimmune bovine anti-bovine coronavirus serum and protein A-gold, negatively stained, applied to formvar-coated copper grids and viewed using an electron microscope. The PAG-IEM method specifically identified BCV particles and possible subviral particles in feces and nasal-swab fluids from infected calves. The PAG-IEM method did not label other enveloped enteric viruses or morphologically similar fringed particles commonly found in feces. Detection of BCV using PAG-IEM was compared with ELISA and direct immunofluorescence (IF) of nasal epithelial cells by monitoring fecal and respiratory tract shedding of BCV from two experimentally infected and two naturally infected calves from birth to 3 weeks of age. PAG-IEM and ELISA detected shedding of BCV in fecal (4/4 animals) and nasal (3/4 animals) samples for an average of 5.25 days each. The observed agreement of BCV detection by PAG-IEM and ELISA was 85%. PAG-IEM may be a more sensitive immunoassay for the detection of BCV in diagnostic specimens from infected neonatal calves than ELISA. BCV infection of nasal epithelial cells was detected by immunofluorescence in 4/4 calves, persisted for the duration of the study in 2/4 calves and was sporadic in the other two animals. The observed agreement of BCV detection by PAG-IEM and IF was 57%.

Kinetics of intestinal replication of group B rotavirus and relevance to diagnostic methods

Non-group-A rotaviruses have been implicated with increasing frequency as causes of acute gastroenteritis in humans and other animals. However, the incidence and significance of infection with these agents, as well as appropriate diagnostic strategies for making these determinations, are largely unknown. Studies to make these determinations could be more accurately conducted if the relationship between the viral replication kinetics and the particular diagnostic method used is understood. We thus utilized the murine model of group B rotavirus infection to establish the viral replication kinetics by a variety of commonly used diagnostic methods. Enzyme immunoassay, routine negative-stain electron microscopy, solid-phase immunosorbent electron microscopy, polyacrylamide gel electrophoresis, and a dot hybridization assay were used in these studies. By enzyme immunoassay, 100% of experimentally infected suckling rats tested positive for group B rotaviral antigens at 1, 4, and 5 days postinoculation. However, only 70 and 20% of infected animals tested positive at days 2 and 3 postinoculation, respectively. Dot hybridization with a complementary DNA probe also suggested a biphasic pattern of viral antigen excretion. Evidence of the virus causing infectious diarrhea in infant rats was found only on day 1 postinoculation in samples examined by routine negative-stain electron microscopy and by polyacrylamide gel electrophoresis. Rotaviruslike particles were observed by solid-phase immunosorbent electron microscopy on days 1, 2, and 4 after viral inoculation suckling rats but were clearly the most numerous on day 1. Additionally, the enzyme immunoassay was used to quantitate the kinetics of group B rotaviral replication in the intestines of the experimentally infected animals. Levels of murine group B rotaviral antigens in intestinal samples peaked on days 1 and 4 postinoculation; however, only peak 1 represented actual intraepithelial replication of the virus. These studies thus indicate that early sample collection and selection of the appropriate diagnostic method are critical if the incidence and significance of group B and possibly other non-group-A rotaviral infections are to be accurately assessed.

Comparative evaluation of a commercial enzyme-linked immunoassay and solid-phase immune electron microscopy for rotavirus detection in stool specimens

Using solid-phase immune electron microscopy (SPIEM) as a reference test, we examined 151 stool specimens from infants and young children with acute gastroenteritis for rotavirus detection by a one-step commercial enzyme-linked immunosorbent assay (ELISA) with labeled monoclonal antibody. Of the 83 samples determined to be positive for rotavirus by SPIEM, 82 were detected as positive by the monoclonal antibody ELISA (sensitivity, 98.7%), while 67 of the 68 specimens determined to be negative by SPIEM were correctly detected as negative by the ELISA (specificity, 98.5%). The diagnostic accuracy of the ELISA kit was 98.6%. Thus, the one-step monoclonal antibody ELISA, which can be completed in less than 90 min, appears to be highly suitable for the rapid and reliable detection of rotavirus in stools.

Electropherotype heterogeneity within serotypes of human rotavirus strains circulating in Italy. Brief report

Using solid-phase immune electron microscopy, 126 of 129 human rotavirus (HRV) strains could be serotyped directly in stools collected in Italy during the period 1981-1985. Prevalence was 70.5 per cent for serotype 1, and 13.2 per cent for each of serotypes 2 and 4. No serotype 3 strain was detected. In parallel, for 39 of 61 HRV strains tested the electropherotype of genomic RNA was successfully determined. Different electropherotypes were detected among strains of the same serotype, whereas the same electropherotype was found in HRV strains of different serotypes. Serotyping and electropherotyping of HRV strains appear to be complementary to each other, and both should be used in conjunction for epidemiological surveys.

Demonstration of calicivirus in human faeces by immunosorbent and immunogold-labelling electron microscopy methods

Immunosorbent electron microscopy (ISEM) and immuno-gold staining (IGS) electron microscopy methods have been applied to human faeces, shown by direct electron microscopy (EM) to contain calicivirus. Caliciviruses were successfully trapped on grids coated with positive rabbit or human antisera against calicivirus, but not with negative sera. Caliciviruses were specifically labelled with gold particles, when treated with positive rabbit or human antisera against calicivirus followed by protein A-gold and goat anti-rabbit or anti-human IgG gold conjugates in an indirect method in suspension. Goat anti-human IgM gold complexes did not react with the available antisera. Attempts to label caliciviruses trapped on the grids were unsuccessful. No cross-reactions were observed with Norwalk agent-like particles, hepatitis A virus or poliovirus type 3 by any of the methods. The results indicate that ISEM and IGS may be useful techniques for detection and identification of small viruses present in low concentrations in faeces.

Use of protein A in the serum-in-agar diffusion method in immune electron microscopy for detection of virus particles in cell culture

A modified technique using protein A in the serum-in-agar (SIA) method for immune electron microscopy (IEM) was presented. Grids coated with staphylococcal protein A were floated on samples mounted on agar containing 2% antiserum and incubated at 37 C, for 60 min. After washing and staining, the grids were observed in an electron microscope. The effects of protein A on virus detection were evaluated using poliovirus and bovine rotavirus infected cell culture fluids. The results showed that the technique using protein A (PA-SIA) had at least 10-fold higher sensitivity for virus detection than the original SIA. The optimal concentration of protein A was 1 to 10 micrograms/ml for coating the grids to trap virus particles. The PA-SIA method was also compared with immunosorbent electron microscopy (ISEM). The former showed higher or at least the same sensitivity and some advantages in detecting antigen-antibody reaction than the latter method. These results indicate that our PA-SIA method may be superior to other IEM techniques presented previously for the detection and identification of viruses.

Use of egg-yolk antibody for detection of respiratory syncytial virus in nasal secretions by ELISA

Egg-yolk immunoglobulins extracted from the eggs of hens immunized with respiratory syncytial virus (RSV) have been used as a reagent in double sandwich ELISA for detecting RSV in nasal secretions. The sensitivity of virus detection was the same in indirect ELISA, using rabbit anti chicken globulin conjugate, as when biotinylated yolk globulin and labeled avidin were used for detection. The specificity of ELISA for detecting RSV using yolk antibody was similar to that achieved by indirect immunofluorescence using commercial reagents of mammalian origin. Purified immunoglobulin was easily extracted from egg yolk; the amount of globulin present in a single preparation obtained from a batch of ten eggs was sufficient to carry out 10(6) ELISA tests for RSV detection.

Enumeration of enterovirus particles by scanning electron microscopy

Enumeration of virus particles requires relatively concentrated and uniformly dispersed virus preparations, which is difficult to achieve by the usual methods of negative staining and transmission electron microscopy. We have developed an electrophoretic method that concentrates enteroviruses onto a polycarbonate membrane for examination by high-resolution scanning electron microscopy. The electrophoretic apparatus comprises three chambers in electrical series, each containing 3.5 ml of dilute buffer. The center chamber is inoculated with virus. A 15-nm porosity membrane, which does not pass virus, separates the center from the side chambers. A constant current is applied, and chilled buffer is pumped past the electrodes for 2 h. The virus suspension is recovered, and changes in titer (or radioactivity if labeled virus is used) due to electrophoresis are measured. Buffer pH, relative to the viral isoelectric points, determines the direction of virus migration. Particle counts are calculated from the mean of 25 randomly chosen fields photographed at 35-60,000 X magnification and related to titers measured by plaque assay.

Immunonegative stain techniques for electron microscopic detection of viruses in human faeces

Immune electron microscopy techniques have for some years been applied to detection of viruses in clinical specimens, especially faecal samples, as both sensitivity and specificity are improved by use of specific antibody. The following review describes in detail different preparation methods and illustrates some of the results that may be obtained.

Development of a sensitive protein A-gold immunoelectron microscopy method for detecting viral antigens in fluid specimens

Protein A-colloidal gold immunoelectron microscopy (PAG IEM) has been employed to specifically detect rotavirus and enterovirus antigen in negatively stained fluid specimens. Unlike other IEM methods, PAG IEM can detect not only viral antigen associated with morphologically recognizable particles but also viral antigens of unrecognizable ultrastructure. This rapid and sensitive immunoassay was found to be applicable to virus-infected stool specimens as well as partially purified virus preparations. The sensitivity of viral antigen detection by PAG IEM was 2- to 40-fold greater than direct IEM and 200- to 1,000-fold greater than direct electron microscopy. In addition, PAG IEM appears to offer a more reliable and sensitive alternative to standard IEM for detection and quantitation of viral antibody.

Evidence that a novel rotavirus-like agent of rats can cause gastroenteritis in man

A rotavirus-like agent known to cause gastroenteritis in rats was also found to be associated with diarrhoea in a human population. Serological studies indicated that infection with this virus is prevalent in children and adults living in Baltimore, Maryland. The virus is antigenically and genomically distinct from group A rotaviruses and this should be borne in mind in efforts to develop vaccines for protection against infantile gastroenteritis.

Quantitative microcomplement fixation tests using chicken anti-viral antibody extracted from egg yolk

Yolk immunoglobulins obtained from hens immunized with human rotavirus and two plant virus antigens were used in quantitative microcomplement fixation tests. Difficulties inherent in the use of avian complement were overcome by utilizing a mixture of the C1 component of chicken complement and guinea-pig complement devoid of its own C1. The method is suitable for detecting small quantities of viral antigen and antibody and for detecting antigenic activity present on peptide fragments of viral proteins.

Subgrouping of human rotavirus strains by complement fixation, indirect double-antibody sandwich enzyme-linked immunosorbent assay and solid-phase immune electron microscopy

Complement fixation (CF), indirect double-antibody sandwich (DAS) enzyme-linked immunosorbent assay (ELISA) and solid-phase immune electron microscopy (SPIEM) were compared for their ability to subgroup 73 human rotavirus (HRV) strains from infants and young children with gastroenteritis admitted to one or the other of two different hospitals of Northern Italy. By both indirect DAS ELISA and SPIEM all 73 HRV strains were classified into one or the other of two subgroups. By CF only 67 strains could be subgrouped, as six HRV-positive stools showed anticomplementary activity which could not be eliminated. Indirect DAS ELISA required subgroup-specific, unabsorbed antisera from two different animal species. For SPIEM two antisera from a single animal species were needed, but they had to be absorbed with single-shelled bovine rotavirus for HRV subgrouping to be reliable. Indirect DAS ELISA appeared to be the technique most suitable for extensive application in epidemiological studies of HRV infections by different subgroups. However, SPIEM allowed rapid subgrouping of HRV in stool specimens showing anticomplementary activity in the CF test or non-specific reactions in the ELISA test. In one area of Northern Italy the prevalence of subgroup I HRV infections was 7.8 per cent, while in another it reached 68.1 per cent in the same period.

Latex immunoassay for rapid detection of rotavirus

A latex agglutination (LA) test was evaluated for the detection of human rotaviruses in stool specimens. Both antiserum and immunoglobulin G (IgG)-sensitized latex particles were used, with IgG-coated beads being more sensitive for human rotavirus antigen detection. Latex beads sensitized with anti-simian-SA-11 IgG were stable for at least 8 months when stored at 4 degrees C. The sensitivity of the test was compared with that of the Rotazyme (Abbott Laboratories, Diagnostics Div., North Chicago, Ill.) test. The least number of particles detected was 9.0 X 10(5) particles by the LA test versus 4.5 X 10(5) particles by the Rotazyme test. When 10 stool specimens were serially diluted for antigen endpoint determinations, the geometric mean titer by the LA test was 592 versus 1,280 by the Rotazyme test. Forty-three stool samples positive by the Rotazyme test were all positive by the LA test, and no false negative results were detected. Unconfirmed false positive reactions ranged between 8 and 24%. The LA test for rotavirus antigen detection is direct, easy to perform, sensitive, quick, and may have application for use in diagnostic laboratories, emergency rooms, and physician's offices.

Human rotavirus detection by counterimmunoelectrophoresis versus enzyme immunoassay and electron microscopy after direct ultracentrifugation

The sensitivity of the counterimmunoelectrophoresis test with NCDV, Wa, and SA-11 rotavirus antisera was 60, 60, and 67%, respectively. The counterimmunoelectrophoresis specificity was greater than 99%, but the low sensitivity is a limiting feature of this test as a first-line immunodiagnostic test for rotavirus detection.

Serotyping of cell culture-adapted subgroup 2 human rotavirus strains by neutralization

Nine human rotavirus strains from stools of infants with gastroenteritis were serially propagated in MA-104 cell cultures. All strains were identified as subgroup 2 rotaviruses by RNA gel electrophoresis, complement fixation, and enzyme-linked immunosorbent assay. The human rotavirus strains were propagated for 15 to 20 passages and then used for immunization of guinea pigs and rabbits. Animal antisera were also raised against a subgroup 1 human strain purified from stools and against the cell culture-adapted Wa strain, a reference subgroup 2 rotavirus of human origin. Cross-neutralization studies revealed the existence of two distinct serotypes within the cell culture-adapted subgroup 2 human rotaviruses: strains related and unrelated to strain Wa were classified as serotypes 1 and 3, respectively. Results with convalescent-phase sera from infants with primary rotavirus infections confirmed the existence of two serotypes within subgroup 2, and the serotypes responsible for primary subgroup 2 infections could be determined on the basis of the neutralizing reactivity of convalescent sera.

Rapid serotyping of human rotavirus strains by solid-phase immune electron microscopy

Nine cell culture-adapted, as well as 30 clinical, human rotavirus (HRV) strains from fecal extracts of children with primary HRV infection were typed by rapid solid-phase immune electron microscopy with protein A and absorbed DS-1 (HRV serotype 2), Wa (serotype 1), and VA70 (assumed serotype 3) rabbit immune sera. As a reference typing test for cell culture-adapted strains, the neutralization assay was used, whereas for noncultivatable strains typing was done for comparison, indirectly, based upon the differential neutralization reactivity of convalescent-phase serum samples from patients with primary HRV infection versus the three reference HRV serotypes. Typing results by solid-phase immune electron microscopy for all strains examined were in complete agreement with those obtained by the neutralization assay, both on cell culture-adapted strains with the three reference rabbit antisera and on three reference HRV strains with human convalescent-phase serum samples. Since adaptation to growth in cell cultures of clinical HRV strains from stool specimens is a time-consuming procedure and is often unsuccessful, solid-phase immune electron microscopy is preferred over the neutralization assay, giving results in about 16 h and also allowing typing of HRV strains from stool specimens low in virus particles. In addition, HRV strains reacting differently from the three reference serotypes may be easily selected by solid-phase immune electron microscopy for further characterization, as was the case for one strain in this study.

Immunosorbent electron microscopy for detection of viruses

This chapter discusses the newer modifications of immunosorbent electron microscopy (ISEM) methods in both plant and animal virology. ISEM methods presented in the chapter include all the techniques where the “solid phase principle” is essential in a way similar to other solid phase immunoassays. These methods include (1) the antibody-coated grid technique (AB-CGT); (2) the protein A-coated grid technique (PA-CGT); (3) the protein A-coated bacteria technique (PA-CBT); and (4) the antigen-coated grid technique (AG-CGT). In all ISEM methods, one of the components of the system is adsorbed to a solid phase. In AG-CGT, PA-CGT, and AB-CGT, one of the reagents is adsorbed to an electron microscopic grid, while in PA-CBT protein A is naturally present on the surface of a bacterium that serves as a solid support. In ISEM methods, the viruses can be statistically evaluated and numerically expressed as number of virions per unit of area, and can, therefore, be statistically evaluated. Thus, these methods optimize the results of a test by quantifying the effects of the quality of the supporting grid, the time of adsorption, the pH, the presence of salts, and the type of staining. The ISEM also permits a detailed study of antigenic variations in the same genus of virus, and thus would visually pinpoint the type or strain differences.

Effect of specimen support film in solid phase immunoelectron microscopy

The type of grid support film used in solid phase immunoelectron microscopy (SPIEM) for poliovirus affected the efficiency of virus trapping. Parlodion/carbon films coated with homologous antiserum were found to be 9 times more efficient in trapping virus than similar grids prepared with Formvar/carbon, and 20 times better than SPIEM grids prepared with pure carbon films. Trapping efficiency could be further improved if support films were pretreated prior to exposure to viral antiserum. Maximum efficiency was obtained with Parlodion/carbon films pretreated with UV light. Almost as efficient were Parlodion/carbon and Formvar/carbon films pretreated with glow discharge ionization.

Comparison of solid-phase immune electron microscopy by use of protein A with direct electron microscopy and enzyme-linked immunosorbent assay for detection of rotavirus in stool

A total of 525 stool specimens collected during 1 year were examined for the presence of rotavirus by direct electron microscopy (EM), enzyme-linked immunosorbent assay (ELISA), and a solid-phase immune electron microscope method (SPIEM) utilizing protein A-coated grids for anchoring of specific viral antisera. Rotavirus was seen in 187 specimens; SPIEM detected 183 (97.8%), whereas direct EM and ELISA detected 161 (86%) and 166 (88.7%), respectively. No false-positive reactions were seen by ELISA. The sensitivity of the methods was evaluated by coded investigation of a dilution series of a positive sample, with a negative fecal specimen as diluent. SPIEM was approximately 30 times more sensitive than direct EM and 10 times more sensitive than ELISA. A study was done to compare the elapsed time for recognition of rotavirus by SPIEM and EM in 25 randomly selected positive specimens. All virus-positive specimens were detected within 2 min by SPIEM, whereas up to 9 min was required for direct EM. SPIEM with protein A is a highly sensitive method, useful for rapid detection of viruses in clinical specimens. Due to the direct visualization of virus particles by electron microscopy, there is no requirement for monospecific antisera for the method.

Comparison of two methods of virus detection by immunosorbent electron microscopy (ISEM) using protein A

The efficiency of two methods of immunosorbent electron microscopy has been compared. The first method consists in trapping virus particles by means of Staphylococcus aureus cells coated with a layer of viral antibodies; the second method consists in trapping virus particles o electron microscope grids coated with specific antibody. A suspension containing 107 antibody-coated bacteria trapped the total number of virions present in 1 ml of a 500 ng/ml virus preparation; the cells were then fully saturated with virions, and approximately 100 virions (of 30 nm diameter) were visible at the periphery of each cell. When 107 cells/ml were used the minimum virus concentration needed to see one virion at the cell periphery was 5 ng/ml. Antibody-coated grids allowed for the detection of approximately the same quantity of virus, but the data obtained with the method were more reproducible and suitable for quantitation.

Solid-phase immune electron microscopy (SPIEM) by use of protein A and its application for characterization of selected adenovirus serotypes

Staphylococcal protein A was used for the anchoring of specific antibodies for a solid-phase immune electron microscope method (SPIEM). More IgG adsorbed to grids in the absence of protein A than in its presence. However, the virus trapping efficiency was markedly improved in the presence of protein A. The specificity of the test was evaluated by use of different adenovirus preparations and matching rabbit hyperimmune sera. The degree of serological reaction was evaluated by counting the number of particles attached to the grid. Type specific reactions and inter- and intrasubgroup reactions were identified.