A double sandwich monoclonal enzyme immunoassay for detection of hepatitis B surface antigen

Exotoxin diversity of Staphylococcus aureus isolated from milk of cows with subclinical mastitis in Central Russia

Mastitis, a major veterinary problem widespread in many regions, is caused mainly by Staphylococcus spp. However, there is no current reliable information about the role of Staphylococcus aureus and their toxins in the development of mastitis in cows in the territory of the Russian Federation. The aim of this investigation was to determine the profile of exotoxins of S. aureus from cow milk from farms of Central Russia. A total of 60 isolates of S. aureus were obtained from milk samples of cows with the subclinical form of mastitis. The exotoxin genes were identified using 2 types of PCR assays. The diversity of enterotoxin genes was studied by multiplex PCR. The percentage occurrence of enterotoxin genes was as follows: sea, 53.3%; seb, 3.3%; sec, 50%; sed, 4%; see, 46.6%; seg, 70%; sei, 10%; selp, 3.3%; and tsst1, 1.6%. The seh gene was not detected. The genes of pore-forming toxins and phenol-soluble modulins were identified by singleplex PCR and consisted of the following: hlA, 70%; lucS, 46.6%; psmA, 81.6%; psmB, 95%; and hld, 78.3%. The most abundant genes were psm (psmB, 95%), which codes for pore-forming toxins, and seg (70%), which codes for enterotoxins. The production of some enterotoxins in bacterial culture medium was detected by ELISA. The level of toxin production was near 1 ng/mL for SEA, SEE, SEG, SEI, SELP, and TSST-1 and reached a maximal level of 18 ng/mL for SEE. In the present work, we show that subclinical mastitis in cows is associated with S. aureus in the central region of the Russian Federation. Most of the isolates containing enterotoxin genes also had cytotoxin genes.

Laboratory demonstration of a prozone-like effect in HRP2-detecting malaria rapid diagnostic tests: implications for clinical management

Background

Malaria rapid diagnostic tests (RDTs) are now widely used for prompt on-site diagnosis in remote endemic areas where reliable microscopy is absent. Aberrant results, whereby negative test results occur at high parasite densities, have been variously reported for over a decade and have led to questions regarding the reliability of the tests in clinical use.

Methods

In the first trial, serial dilutions of recombinant HRP2 antigen were tested on an HRP2-detectiing RDT. In a second trial, serial dilutions of culture-derived Plasmodium falciparum parasites were tested against three HRP2-detecting RDTs.

Results

A prozone-like effect occurred in RDTs at a high concentration of the target antigen, histidine-rich protein-2 (above 15,000 ng/ml), a level that corresponds to more than 312000 parasites per μL. Similar results were noted on three RDT products using dilutions of cultured parasites up to a parasite density of 25%. While reduced line intensity was observed, no false negative results occurred.

Conclusions

These results suggest that false-negative malaria RDT results will rarely occur due to a prozone-like effect in high-density infections, and other causes are more likely. However, RDT line intensity is poorly indicative of parasite density in high-density infections and RDTs should, therefore, not be considered quantitative. Immediate management of suspected severe malaria should rely on clinical assessment or microscopy. Evaluation against high concentrations of antigen should be considered in malaria RDT product development and lot-release testing, to ensure that very weak or false negative results will not occur at antigen concentrations that might be seen clinically.

Simultaneous detection of seven staphylococcal enterotoxins: development of hydrogel biochips for analytical and practical application

A method of simultaneous analysis of staphylococcal enterotoxins using hydrogel-based microarrays (biochips) has been developed. The method allows simultaneous quantitative detection of seven enterotoxins: A, B, C1, D, E, G, and I in a single sample. The development of the method included expression and purification of recombinant toxins, production of panels of monoclonal antibodies (mAbs) against the toxins, and design and manufacturing of an experimental biochip for the screening of mAbs and selection of optimal pairs of primary and secondary antibodies for each toxin. The selected mAbs have high affinity toward their targets and no cross-reactivity with unrelated enterotoxins. Finally, a diagnostic biochip was designed for quantitative analysis of the toxins, and the analytical protocols were optimized. The sensitivity of the detection reached 0.1-0.5 ng/mL, depending on the type of enterotoxin. The evaluation of the resulting biochip using spiked food samples demonstrated that the sensitivity, specificity, and reproducibility of the proposed test system fully satisfy the requirements for traditional immunoanalytical systems. The diagnostic biochips manufactured on reflecting metal-coated surfaces shortened the time of analysis from 17 to 2 h without loss of sensitivity. The method was successfully tested on samples of food and biological media.

Levels of complement C3 and C4 components in Amerindians living in an area with high prevalence of tuberculosis

The levels of complement C3 and C4 components were determined in non-indigenous (creoles) and indigenous (Warao) populations, the latter with an extremely high tuberculosis (TB) rate. Serum samples from 209 adults were studied and classified in 4 groups taking into account tuberculin skin tests (TST): (1) the group of Warao patients (58 positive for the TST, WP TST+ and 9 negative for the TST, WP TST-), (2) the group of creole patients (34 positive for the TST, CP TST+ and 9 negative for the TST, CP TST-), (3) the group of healthy Warao controls (38 positive and 14 negative for TST, WC TST+ and WC TST-, respectively), (4) the creole controls (26 positive and 21 negative for the TST, CC TST+ and CC TST-, respectively). With respect to the results concerning the measurement of both complement C3 and C4 components with the exception of the WC TST and the CC groups, the WP TST+ and WP TST- as well as WC TST+ groups showed a significant frequency of individuals with decreased levels of complement C3 component (20.6, 33.3, and 26.3%, respectively) and also C4 component (12.0, 11.1, and 13.3%, respectively) in comparison to both creole patients (CP TST+, 8.82% and CP TST-, 0% and CP TST+, 5.88% and CP TST-, 0%) for C3 and C4, respectively. The study of these parameters carried out in 15 Warao subjects with active infection, before and after anti-TB chemotherapy,statisticallyconfirmedthat the effective chemotherapy did not restore normal levels of the complement C3 and C4 components among Warao patients. Aditional tests for hepatitis B or hepatitis C infection, and the profile of the hepatic proteins were not associated to the deficiency in production of the complement components. In conclusion, the results show that within the Warao population, a high percentage of subjects exhibit decreased levels of both complement C3 and C4 components independent of latent or active infection and the status of TST.

Molecular and serological evaluation of surface antigen negative hepatitis B virus infection in blood donors from Venezuela

Surface antigen negative hepatitis B virus (HBV) infection was evaluated in Venezuela, by molecular characterization of blood samples positive for antibodies to core antigen (anti-HBc) and negative for surface antigen (HBsAg) in blood donors (residual infections). HBV DNA was found in 11/258 samples (4.3%), and was significantly associated with high levels of anti-HBc antibodies (>25 UI/ml, P < 0.05), while no correlation was found between the presence of HBV DNA and the levels of anti-HBs. Synonymous and non-synonymous mutations were found in the HBV surface region (but not vaccine escape mutants) and in the precore/core region (precore mutants in 2/7 samples and 33-45 bp deletions near the N-terminal core region in 4/19 samples). While HBV genotype F prevails among HBsAg positive samples from blood donors in Venezuela, residual infection isolates were mainly genotypes A and D. Phylogenetic analysis of viral surface and core region revealed discrepancies in genotype designation in 6/9 samples, suggesting the presence of mixed infection or recombination. In conclusion, HBV residual infection in Venezuela does not seem to be frequently observed in HBV genotype F. This type of infection is frequently associated with variants exhibiting mutations in the surface gene that might be affecting the correct recognition by commercial tests, with precore mutants and with core internal deletions. These variants do not seem to cause severe liver disease, and on the contrary, were found circulating at low viremia.

Clade analysis and surface antigen polymorphism of hepatitis B virus American genotypes

Eight genotypes (A-H) of hepatitis B virus (HBV) have been described, HBV genotypes F and H being autochthonous to America. HBV genotype F has been classified in four clusters. The objective of this study was to gain insight into the molecular epidemiology of HBV American genotypes, as well as to analyze the genotype-related polymorphism in some functional domains of the surface proteins. The sequences of the S region of 106 isolates genotype F and H were analyzed, out of which 47 isolates genotype F circulated in different Venezuelan populations. Most of the Venezuelan isolates genotype F were grouped in cluster III (n = 39) and 7 in cluster II. One isolate obtained from a blood donor could not be classified in any clade and harbored amino acid substitutions characteristic of a vaccine escape mutant (G145R) and a stop codon in the surface antigen. Amino acid analysis of the PreS and S gene products showed unique genetic characteristics in genotype F and H sequences in some important domains involved in the early steps of infection. Out of 30 available sequences, two complete genome sequences of HBV genotype F from Venezuela were obtained. Phylogenetic analysis of these complete genomes confirmed the presence of four clusters inside genotype F, differing in more than 4% nucleotide divergence. Our extended analysis showed that genotype F clades Ia, III, and IV exhibit a restricted geographic distribution (Central America, the North and the South of South America, respectively) while clades Ib and II are found in all the Americas except in the Northern South America and North America respectively.

Hepatitis B virus DNA in blood samples positive for antibodies to core antigen and negative for surface antigen

Anti-hepatitis B core antigen (HBcAg)-positive hepatitis B surface antigen (HBsAg)-negative plasma samples from blood donors were tested by nested PCR. DNA positivity was more significantly associated with high levels of anti-HBcAg than with low levels of anti-HBsAg antibodies. Analysis of a dilution of anti-HBcAg antibodies might result in a more rational exclusion of anti-HBcAg-positive HBsAg-negative samples, reducing the number of donations discarded and enabling more countries to incorporate anti-HBcAg testing.

A comparison of performances of four enzymes used in ELISA with special reference to beta-lactamase

Horse radish peroxidase, alkaline phaosphatase and beta-D-galactosidase are widely used as labels in the development of enzyme immunoassays (EIAs). Enzyme beta-lactamase, though introduced as a label in late seventies has not yet become very popular inspite of having the necessary features of an enzyme to be used in EIAs. The present article reviews assays developed with this enzyme, highlights its salient features and brings out an argument in favour of its wide spread use in EIAs.

Mechanism of the oxidation of 3,5,3',5'-tetramethylbenzidine by myeloperoxidase determined by transient- and steady-state kinetics

Earlier investigations of the oxidation of 3,5,3',5'-tetramethylbenzidine (TMB) using horseradish peroxidase and prostaglandin H-synthase have shown the formation of a cation free radical of TMB in equilibrium with a charge-transfer complex, consistent with either a two- or a one-electron initial oxidation. In this work, we exploited the distinct spectroscopic properties of myeloperoxidase and its oxidized intermediates, compounds I and II, to establish two successive one-electron oxidations of TMB. By employing stopped-flow techniques under transient-state and steady-state conditions, we also determined the rate constants for the elementary steps of the myeloperoxidase-catalyzed oxidation of TMB at pH 5.4 and 20 degrees C. The second-order rate constant for compound I formation from the reaction of native enzyme with H2O2 is 2.6 x 10(7) M-1 s-1. Compound I undergoes a one-electron reduction to compound II in the presence of TMB, and the rate constant for this reaction was determined to be (3.6 +/- 0.1) x 10(6) M-1 s-1. The spectral scans show that compound II accumulates in the steady state. The rate constant for compound II reduction to native enzyme by TMB obtained under steady-state conditions is (9.4 +/- 0.6) x 10(5) M-1 s-1. The results are applied to a new, more accurate assay for myeloperoxidase based upon the formation of the charge-transfer complex between TMB and its diimine final product.

A monoclonal inhibition enzyme immunoassay for detection of antibodies against hepatitis B core antigen: confirmation of an immunodominant epitope

Monoclonal antibodies (mAbs) were raised against hepatitis B virus core produced by a recombinant clone of Escherichia coli (rHBc). The three mAbs recognized rHBc by Western blot, suggesting that they reacted with non-conformational epitopes. Competition experiments between mAbs and human anti-HBc sera confirmed the existence of an immunodominant HBc epitope within the viral antigen. A monoclonal competition enzyme immunoassay using an IgM mAb conjugated to biotin and streptavidin-peroxidase as the detection system yielded 99% sensitivity and 100% specificity, when compared to other commercial assays.