Negative staining in diagnostic virology

ALD based nanostructured zinc oxide coated antiviral silk fabric

The COVID-19 pandemic has underscored the importance of research and development in maintaining public health. Facing unprecedented challenges, the scientific community developed antiviral drugs, virucides, and vaccines to combat the infection within the past two years. However, an ever-increasing list of highly infectious SARS-CoV-2 variants (gamma, delta, omicron, and now ba.2 stealth) has exacerbated the problem: again raising the issues of infection prevention strategies and the efficacy of personal protective equipment (PPE). Against this backdrop, we report an antimicrobial fabric for PPE applications. We have fabricated a nanofibrous silk-PEO material using electrospinning followed by zinc oxide thin film deposition by employing the atomic layer deposition technique. The composite fabric has shown 85% more antibacterial activity than the control fabric and was found to possess substantial superoxide dismutase–mimetic activity. The composite was further subjected to antiviral testing using two different respiratory tract viruses: coronavirus (OC43: enveloped) and rhinovirus (RV14: non-enveloped). We report a 95% reduction in infectious virus for both OC43 and RV14 from an initial load of ∼1 × 10⁵ (sample size: 6 mm dia. disk), after 1 h of white light illumination. Furthermore, with 2 h of illumination, ∼99% reduction in viral infectivity was observed for RV14. High activity in a relatively small area of fabric (3.5 × 10³ viral units per mm²) makes this antiviral fabric ideal for application in masks/PPE, with an enhanced ability to prevent antimicrobial infection overall.

This study presents an antiviral self-cleaning fabric for masks/PPE applications with protection against human coronavirus.

Imperative role of electron microscopy in toxicity assessment: A review

Electron microscope (EM) was developed in 1931 and since then microscopical examination of both the biological and non-biological samples has been revolutionized. Modifications in electron microscopy techniques, such as scanning EM and transmission EM, have widened their applicability in the various sectors such as understanding of drug toxicity, development of mechanism, criminal site investigation, and characterization of the nano-molecule. The present review summarizes its role in important aspects such as toxicity assessment and disease diagnosis in special reference to SARS-COV2. In the biological system, EM studies have elucidated the impact of toxicants at the ultra-structural level in various tissue in conformity to physiological alterations. Thus, EM can be concluded as an important tool in toxicity assessment and disease prognosis.

Revisiting staining of biological samples for electron microscopy: perspectives for recent research

This review revisits essential staining protocols for electron microscopy focussing on the visualization of active sites, i.e. enzymes, metabolites or proteins, in cells and tissues, which have been developed 50 to 60 years ago, however, never were established as standard protocols being used in electron microscopy in a routine fashion. These approaches offer numerous possibilities to expand the knowledge of cellular function and specifically address the localization of active compounds of these systems. It is our conviction, that many of these techniques are still useful, in particular when applied in conjunction with correlative light and electron microscopy. Revisiting specialized classical electron microscopy staining protocols for use in correlative microscopy is particularly promising, as some of these protocols were originally developed as staining methods for light microscopy. To account for this history, rather than summarizing the most recent achievements in literature, we instead first provide an overview of techniques that have been used in the past. While some of these techniques have been successfully implemented into modern microscopy techniques during recent years already, more possibilities are yet to be re-discovered and provide exciting new perspectives for their future use.

Negative-Stain Transmission Electron Microscopy of Molecular Complexes for Image Analysis by 2D Class Averaging

Negative-stain transmission electron microscopy (EM) is a technique that has provided nanometer resolution images of macromolecules for about 60 years. Developments in cryo-EM image processing have maximized the information gained from averaging large numbers of particles. These developments can now be applied back to negative-stain image analysis to ascertain domain level molecular structure (10 to 20 Å) more quickly and efficiently than possible by atomic resolution cryo-EM. Using uranyl acetate stained molecular complexes of influenza hemagglutinin bound to Fab 441D6, we describe a simple and efficient means to collect several hundred micrographs with SerialEM. Using RELION, we illustrate how tens of thousands of complexes can be auto-picked and classified to accurately describe the domain level topology of this unconventional hemagglutinin head-domain epitope. By comparing to the cryo-EM density map of the same complex, we show that questions about epitope mapping and conformational heterogeneity can readily be answered by this negative-stain method. © 2019 The Authors.

Rapid Viral Diagnosis of Orthopoxviruses by Electron Microscopy: Optional or a Must?

Diagnostic electron microscopy (DEM) was an essential component of viral diagnosis until the development of highly sensitive nucleic acid amplification techniques (NAT). The simple negative staining technique of DEM was applied widely to smallpox diagnosis until the world-wide eradication of the human-specific pathogen in 1980. Since then, the threat of smallpox re-emerging through laboratory escape, molecular manipulation, synthetic biology or bioterrorism has not totally disappeared and would be a major problem in an unvaccinated population. Other animal poxviruses may also emerge as human pathogens. With its rapid results (only a few minutes after arrival of the specimen), no requirement for specific reagents and its "open view", DEM remains an important component of virus diagnosis, particularly because it can easily and reliably distinguish smallpox virus or any other member of the orthopoxvirus (OPV) genus from parapoxviruses (PPV) and the far more common and less serious herpesviruses (herpes simplex and varicella zoster). Preparation, enrichment, examination, internal standards and suitable organisations are discussed to make clear its continuing value as a diagnostic technique.

Accurate virus quantitation using a Scanning Transmission Electron Microscopy (STEM) detector in a scanning electron microscope

A method for accurate quantitation of virus particles has long been sought, but a perfect method still eludes the scientific community. Electron Microscopy (EM) quantitation is a valuable technique because it provides direct morphology information and counts of all viral particles, whether or not they are infectious. In the past, EM negative stain quantitation methods have been cited as inaccurate, non-reproducible, and with detection limits that were too high to be useful. To improve accuracy and reproducibility, we have developed a method termed Scanning Transmission Electron Microscopy - Virus Quantitation (STEM-VQ), which simplifies sample preparation and uses a high throughput STEM detector in a Scanning Electron Microscope (SEM) coupled with commercially available software. In this paper, we demonstrate STEM-VQ with an alphavirus stock preparation to present the method's accuracy and reproducibility, including a comparison of STEM-VQ to viral plaque assay and the ViroCyt Virus Counter.

Microbiological laboratory diagnostics of neglected zoonotic diseases (NZDs)

This review reports on laboratory diagnostic approaches for selected, highly pathogenic neglected zoonotic diseases, i.e. anthrax, bovine tuberculosis, brucellosis, echinococcosis, leishmaniasis, rabies, Taenia solium-associated diseases (neuro-/cysticercosis & taeniasis) and trypanosomiasis. Diagnostic options, including microscopy, culture, matrix-assisted laser-desorption-ionisation time-of-flight mass spectrometry, molecular approaches and serology are introduced. These procedures are critically discussed regarding their diagnostic reliability and state of evaluation. For rare diseases reliable evaluation data are scarce due to the rarity of samples. If bio-safety level 3 is required for cultural growth, but such high standards of laboratory infrastructure are not available, serological and molecular approaches from inactivated sample material might be alternatives. Multiple subsequent testing using various test platforms in a stepwise approach may improve sensitivity and specificity. Cheap and easy to use tests, usually called "rapid diagnostic tests" (RDTs) may impact disease control measures, but should not preclude developing countries from state of the art diagnostics.

The use of convalescent sera in immune-electron microscopy to detect non-suspected/new viral agents

Negative staining electron microscopy methods can be employed for the diagnosis of viral particles in animal samples. In fact, negative staining electron microscopy methods are used to identify viruses, especially in minor species and wild animals, when no other methods are available and in cases of rare, emerging or re-emerging infections. In particular, immune-electron-microscopy with convalescent sera is employed to detect etiological agents when there are undiagnosed clinical outbreaks, when alternative diagnostic methods fail due to the lack of immunological reagents and primers, and when there is no indicative clinical suspect. An overview of immune-electron-microscopy with convalescent sera’s use in the diagnosis of new and unsuspected viruses in animals of domestic and wild species is provided through the descriptions of the following four diagnostic veterinary cases: (I) enteric viruses of pigs: Porcine Rotavirus, Porcine Epidemic Diarrhea Virus, Porcine Circovirus and Porcine Torovirus; (II) Rotavirus and astrovirus in young turkeys with enteritis; (III) Parvovirus-like particles in pheasants; and (IV) Lagoviruses: Rabbit Hemorrhagic Disease Virus and European Brown Hare Syndrome Virus.

Ultrastructure of Felis catus whole fetus (Fcwf-4) cell culture following infection with feline coronavirus

Feline coronavirus (FCoV) consists of two biotypes based on their growth in cell culture and their antigenicity. Infections with FCoV are highly prevalent in the cat population worldwide. In this study, Felis catus whole fetus (Fcwf-4)cell culture was infected with FCoV UPM11C/08. Virus multiplication in cell culture was monitored and examined under the transmission electron microscope. The virus particles revealed the characteristic morphology of feline FCoV represented by envelope viruses surrounded by peplomers. Virus attachment and entry into the cell occurred 15 h post-infection (pi), and the myriad of virus particles were observed both extracellularly and intracellularly after 48 h pi. Thereafter, intracellular virus particles were observed to be present in vacuoles or present freely in the cytoplasm.

Evaluation of various methods for recovering human norovirus and murine norovirus from vegetables and ham

We evaluated and optimized each step in an analytical method for detecting norovirus from various foods. We characterized the buffers needed for eluting norovirus from foods such as ham and lettuce. Two different concentration methods, polyethylene glycol (PEG) precipitation and hollow fiber ultrafiltration (HUF), were compared using both murine norovirus (MNV) and human norovirus (HuNoV). For PEG precipitation, an elution buffer containing 3% beef extract (pH 7.1) was more suitable than 0.05 M glycine plus 0.14 M NaCl (pH 7.5), and the recovery efficiency increased with increasing molecular weight of PEG. To determine the optimal buffer for concentrating norovirus by HUF, glycine buffers with different pH values and ionic strengths were examined as elution buffers. Overall, HUF was more efficient for norovirus recovery than was PEG precipitation. Because there was a significant positive correlation between MNV and HuNoV results, MNV could be a useful surrogate for detecting HuNoV in foods.

Detection limit of negative staining electron microscopy for the diagnosis of bioterrorism-related micro-organisms

Aims:  To determine the detection limit of diagnostic negative staining electron microscopy for the diagnosis of pathogens that could be used for bioterrorism.

Methods and Results:  Suspensions of vaccinia poxvirus and endospores of Bacillus subtilis were used at defined concentrations as a model for poxviruses and spores of anthrax (Bacillus anthracis), both of which are pathogens that could be used for bioterrorist attacks. Negative staining electron microscopy was performed directly or after sedimentation of these suspensions on to the sample supports using airfuge ultracentrifugation. For both virus and spores, the detection limit using direct adsorption of a 10‐μl sample volume onto the sample support was 10⁶ particles per ml. Using airfuge ultracentrifugation with a sample volume of 80 μl, the detection limit could be reduced to 10⁵ particles per ml for spores and to 5 × 10⁴ particles per ml for poxviruses. The influence on particle detection of incubation time, washing and adsorption procedures was investigated.

Conclusions:  The reproducibility and sensitivity of the method were acceptable, particularly considering the small sample volume and low particle number applied onto the sample support.

Significance and Impact of the Study:  Diagnostic negative staining electron microscopy is used for the diagnosis of pathogens in emergency situations because it allows a rapid examination of all particulate matter down to the nanometre scale. This study provides precise detection limit for the method, an important factor for the validation and improvement of the technique.

The role of electron microscopy in the rapid diagnosis of viral infections--review

Electron microscopy (EM) allows fast visualization of viruses in a wide range of clinical specimens. Viruses are grouped into families based on their morphology. Viruses from various families look distinctly and these morphological variances are the basis for identification of viruses by EM. The identification to the family level is often sufficient for the clinician or recognition of an unknown infectious agent. Diagnostic EM has two advantages over enzyme-linked immunosorbent assay and nucleic acid amplification tests. After a simple and fast negative staining, EM allows fast morphological identification and differential diagnosis of infectious agents contained in the specimen without the need for special considerations and/or reagents. Nevertheless, EM has the disadvantage of being unsuitable as a screening method.

Viral Haufen are urinary biomarkers of polyomavirus nephropathy: New diagnostic strategies utilizing negative staining electron microscopy

Haufen, i.e. discrete three-dimensional cast-like polyomavirus aggregates in the urine, mark polyoma BK-virus nephropathy (BKN) with positive and negative predictive values of greater than 95%. They are novel diagnostic biomarkers of BKN, an important infectious complication post kidney transplantation. Here, we describe technical details of Haufen detection by negative staining electron microscopy. We studied more than 400 urine samples from over 180 patients and developed easy-to-follow protocols for optimal specimen preservation and preparation, including sample clarification and concentration. We detail diagnostic clues to detect Haufen and illustrate pitfalls, including "Haufen-look-alikes," which can hamper the interpretation. Urinary Haufen detection by negative staining electron microscopy is a new application of an old, well-established diagnostic technique. The protocols described here are useful for pathologists and electron microscopists to search for Haufen in voided urine samples, to predict BKN noninvasively, and to help clinicians managing renal allograft recipients.

Full-length, glycosylated NSP4 is localized to plasma membrane caveolae by a novel raft isolation technique

Rotavirus NSP4, initially characterized as an endoplasmic reticulum intracellular receptor, is a multifunctional viral enterotoxin that induces diarrhea in murine pups. There have been recent reports of the secretion of a cleaved NSP4 fragment (residues 112 to 175) and of the association of NSP4 with LC3-positive autophagosomes, raft membranes, and microtubules. To determine if NSP4 traffics to a specific subset of rafts at the plasma membrane, we isolated caveolae from plasma membrane-enriched material that yielded caveola membranes free of endoplasmic reticulum and nonraft plasma membrane markers. Analyses of the newly isolated caveolae from rotavirus-infected MDCK cells revealed full-length, high-mannose glycosylated NSP4. The lack of Golgi network-specific processing of the caveolar NSP4 glycans supports studies showing that NSP4 bypasses the Golgi apparatus. Confocal imaging showed the colocalization of NSP4 with caveolin-1 early and late in infection, elucidating the temporal and spatial NSP4-caveolin-1 association during infection. These data were extended with fluorescent resonance energy transfer analyses that confirmed the NSP4 and caveolin-1 interaction in that the specific fluorescently tagged antibodies were within 10 nm of each other during infection. Cells transfected with NSP4 showed patterns of staining and colocalization with caveolin-1 similar to those of infected cells. This study presents an endoplasmic reticulum contaminant-free caveola isolation protocol; describes the presence of full-length, endoglycosidase H-sensitive NSP4 in plasma membrane caveolae; provides confirmation of the NSP4-caveolin interaction in the presence and absence of other viral proteins; and provides a final plasma membrane destination for Golgi network-bypassing NSP4 transport.

Negative-staining electron microscopy of the urine for the detection of polyomavirus infections

Negative-staining electron microscopy (EM) has played a pivotal role in diagnostic virology. It is a rapid technique for viral detection in the urine and can provide an easy means for monitoring viral activity and productive infections. EM of urine for the detection of polyomaviruses has hitherto not been systematically evaluated as a screening tool for renal transplant patients at risk for BK polyomavirus nephropathy (BKN). Here, the authors discuss technical aspects of negative-staining EM of urine (n = 76 samples) and present a simple and rapid protocol for the semiquantitative evaluation of patient samples. In two patient populations (either with (n = 15 samples) or without (n = 15 samples) an established diagnosis of BKN), EM results were compared with two previously established techniques for monitoring polyomavirus activation: (1) cytology for the quantitation of decoy cells, and (2) quantitative PCR assays for the detection of BK virus DNA load levels. In both patient groups, the dynamics of decoy cell shedding by urine cytology closely paralleled free viral particle shedding by EM, and viral load levels as measured by PCR. A trend toward higher readings was observed in patients with BKN (median values, control versus BKN groups: decoy cells 21 versus 50/slide; free virions by EM: 32 versus 66 viral particles/10 high-power fields; PCR: 3.5 x 10(8) versus 5.4 x 10(8) BK virus copies/ml; all differences not statistically significant). The authors conclude that negative-staining EM and the semiquantitative assessment of free viral particles in the urine can be a useful clinical method to identify patients at increased risk for BKN. EM can be used alone or in combination with urine cytology or PCR assays.

A Goose-Sourced Paramyxovirus Isolated from Southern China

We report the isolation and characterization of a paramyxovirus from geese in South China during 1997. The isolate, designated as goose paramyxovirus/QingYuan 1997-1 (GPMV/QY97-1), showed pathogenicity to geese and could agglutinate chicken erythrocytes. Its hemagglutinating activity was inhibited by antiavian paramyxovirus serotype 1 (APMV-1) serum. The F gene of isolate was amplified by reverse transcription polymerase chain reaction, and sequence analysis proved that its sequence conformed to that reported in the literature, encoding an F0 protein of 553 amino acids with 13 cysteine residues and 6 potential glycosylation sites. It also contained multiple basic amino acids at the deduced cleavage site of the fusion protein, which is a typical feature of highly virulent APMV-1 strains. Sequences analysis of the F gene of GPMV/QY97-1 revealed a homology with other APMV-1 isolates, with its identity ranging from 84.1% to 99.9% on a nudeotide basis and from 88.8% to 99.6% on an amino acid basis. Phylogenetic analysis of the APMV-1 isolates showed that this isolate most closely resembled the reference APMV-1 strain GD/1/98/Go, which was originally isolated from geese in 1998.

Detection of human polyomaviruses in urine from bone marrow transplant patients: comparison of electron microscopy with PCR

BACKGROUND

We studied electron microscopy (EM) as an appropriate test system for the detection of polyomavirus in urine samples from bone marrow transplant patients.

METHODS

We evaluated direct EM, ultracentrifugation (UC) before EM, and solid-phase immuno-EM (SPIEM). The diagnostic accuracy of EM was studied by comparison with a real-time PCR assay on 531 clinical samples.

RESULTS

The detection rate of EM was increased by UC and SPIEM. On 531 clinical urine samples, the diagnostic sensitivity of EM was 47% (70 of 149) with a specificity of 100%. We observed a linear relationship between viral genome concentration and the proportion of urine samples positive by EM, with a 50% probability for a positive EM result for urine samples with a polyomavirus concentration of 10(6) genome-equivalents (GE)/mL; the probability of a positive EM result was 0% for urine samples with <10(3) GE/mL and 100% for urine samples containing 10(9) GE/mL.

CONCLUSIONS

UC/EM is rapid and highly specific for polyomavirus in urine. Unlike real-time PCR, EM has low sensitivity and cannot quantify the viral load.

Laboratory diagnosis of norovirus: which method is the best?

Noroviruses (NV) are transmitted by fecally contaminated food, vomit, and person-to-person contact. They are one of the main causes of non-bacterial acute gastroenteritis in nursing, old people and children's homes. NV outbreaks are characterized by a short incubation period (12-48 h), nausea, vomiting and diarrhea, and high secondary attack rates. The illness is generally mild and self-limiting. The aim of diagnostic procedures in viral gastroenteritis is to avoid nosocomial infections on the one hand and unnecessary antibiotic treatment on the other. Diagnostic procedures for NV are based on the detection of virus in stool samples by (immune) transmission electron microscopy (TEM), antigen ELISA, or polymerase chain reaction (PCR). In our study, a total of 244 stool samples obtained from 227 patients between March and May 2002 were tested by TEM, antigen ELISA and in-house PCR. Our data showed that PCR has the highest sensitivity (94.1%), followed by TEM (58.3%), and ELISA (31.3%), while specificity was highest for TEM (98.0%), followed by ELISA (94.9%), and PCR (92.4%). All three methods tested (TEM, ELISA and PCR) are useful for epidemiological investigations in gastroenteritis outbreaks; however, to maximize diagnostic validity for individual cases, at least two of the methods should be combined.

Electron microscopy for rapid diagnosis of infectious agents in emergent situations

Diagnostic electron microscopy has two advantages over enzyme-linked immunosorbent assay and nucleic acid amplification tests. After a simple and fast negative stain preparation, the undirected, "open view" of electron microscopy allows rapid morphologic identification and differential diagnosis of different agents contained in the specimen. Details for efficient sample collection, preparation, and particle enrichment are given. Applications of diagnostic electron microscopy in clinically or epidemiologically critical situations as well as in bioterrorist events are discussed. Electron microscopy can be applied to many body samples and can also hasten routine cell culture diagnosis. To exploit the potential of diagnostic electron microscopy fully, it should be quality controlled, applied as a frontline method, and be coordinated and run in parallel with other diagnostic techniques.

Avian paramyxovirus serotype 1 isolates from the spinal cord of parrots display a very low virulence

The spinal cord of 32 psittacines suffering from proventricular dilatation disease (PDD) was investigated. In six cases, a virus was isolated which upon electron microscopic examination revealed morphological details typical of members of the Paramyxoviridae. All isolates were subsequently characterized as avian paramyxovirus serotype 1 (APMV-1) by type-specific polyclonal antisera. According to their reactivity with APMV-1 specific monoclonal antibodies, the six isolates shared epitopes within the haemagglutinin-neuraminidase spike protein, distinct from pigeon-type paramyxoviruses and the LaSota vaccine strain. This grouping was further corroborated by properties of the haemagglutinin: all isolates showed a very thermosensitive haemagglutination activity and were rapid eluters. Virulence of the APMV-1 isolates in 1-day-old specific pathogen free (spf) chicken was very low, with intracerebral pathogenicity indices between 0 and 0.1. In embryonated spf chicken eggs, psittacine isolates replicated to high titres (10(8.6)-10(10.7) EID50/ml). However, they exhibited a reduced lethality over an observation time of 7 days (10(6.1)-10(8.3) ELD50/ml). In a haemagglutination inhibition test with parrot sera from birds with no history of APMV-1 vaccination, sera reacted preferentially with two isolates compared with APMV-1 vaccine strains LaSota and B1. The other four isolates exhibited a differentiated reaction pattern with the parrot sera, indicating an antigenic inhomogeneity. This is the first report of isolating very low virulent APMV-1 from neuronal tissue of parrots and implications for a possible role in slow progressing disease will be discussed.

Diagnostic electron microscopy is still a timely and rewarding method

BACKGROUND

Parallel to its technical development starting in the 1930s, electron microscopy (EM) became an important tool in basic and clinical virology. First utilized in the rapid diagnosis of smallpox, it developed to a diagnostic routine in the early 1960s using the negative staining technique. EM was applied to infected cell-cultures and also to 'dirty' specimens including urine, feces, vesicle fluid, liquor. With the implementation of molecular biological and genetic techniques, the use of diagnostic EM decreased.

OBJECTIVES

(1) To give a perspective on future indications and possible uses by discussing the past and the present of diagnostic EM, (2) To describe the system of External Quality Assessment on EM virus diagnosis (EQA-EMV) established in 1994 by our laboratory and its achievements.

STUDY DESIGN

EQA-EMV is run to evaluate, to confirm and to improve the quality of diagnostic EM. Two different types of specimen are sent out: (1) prepared grids to assess and train the diagnostic skills of the participants, (2) stabilized virus particle suspensions to assess preparation efficiency.

RESULTS

Diagnostic EM differs from other diagnostic tests in its rapidity and its undirected 'open view'. To emphasize these advantages, the indications for diagnostic EM are discussed, fundamental for a continuing future adaptation. Besides appropriate techniques, quality control measures are required to achieve and keep high diagnostic standards. The results from 6 years of EQA-EMV are presented.

CONCLUSIONS

In the history of diagnostic EM in virology, a change in use has been seen. Starting in the 1990s and coincident with the broad introduction of 'modern' diagnostic techniques, the number of EM diagnostic labs has decreased considerably--in spite of the obvious advantages of this technique. To guarantee the continuing performance of diagnostic EM in the future. EQA runs have to be performed as with other techniques in the diagnostic armament. The growing number of participants and participating countries indicates an interest in as well as a need for this program.

Bacteriophage diversity in the North Sea

In recent years interest in bacteriophages in aquatic environments has increased. Electron microscopy studies have revealed high numbers of phage particles (10(4) to 10(7) particles per ml) in the marine environment. However, the ecological role of these bacteriophages is still unknown, and the role of the phages in the control of bacterioplankton by lysis and the potential for gene transfer are disputed. Even the basic questions of the genetic relationships of the phages and the diversity of phage-host systems in aquatic environments have not been answered. We investigated the diversity of 22 phage-host systems after 85 phages were collected at one station near a German island, Helgoland, located in the North Sea. The relationships among the phages were determined by electron microscopy, DNA-DNA hybridization, and host range studies. On the basis of morphology, 11 phages were assigned to the virus family Myoviridae, 7 phages were assigned to the family Siphoviridae, and 4 phages were assigned to the family Podoviridae. DNA-DNA hybridization confirmed that there was no DNA homology between phages belonging to different families. We found that the 22 marine bacteriophages belonged to 13 different species. The host bacteria were differentiated by morphological and physiological tests and by 16S ribosomal DNA sequencing. All of the bacteria were gram negative, facultatively anaerobic, motile, and coccoid. The 16S rRNA sequences of the bacteria exhibited high levels of similarity (98 to 99%) with the sequences of organisms belonging to the genus Pseudoalteromonas, which belongs to the gamma subdivision of the class Proteobacteria.

In vitro expression of UL56 gene of herpes simplex virus type 1; detection of UL56 gene product in infected cells and in virions

In order to investigate the functional properties of the UL56 gene of herpes simplex virus type 1 (HSV-1), it was necessary to express the UL56 protein in vitro. The DNA sequences corresponding to the open reading frame of the UL56 gene of HSV-1 strain F were amplified from genomic viral DNA by PCR using primers corresponding to the translational start and termination regions of the UL56 ORF. The PCR product (705 bp) was inserted into the EcoRI/XbaI recognition sites of the bacterial expression vector pMal-c2. This procedure allowed the expression of the viral UL56 gene fused to the maltose-binding protein (MBP) of Escherichia coli, and subsequent cleavage of the fusion protein with the specific protease factor Xa. The induced fusion protein was purified by affinity chromatography using amylose columns. The apparent molecular weight of the fusion protein was about 70 kDa. Factor Xa cleaves the fusion protein into two subfragments of 42 kDa (MBP) and 30 kDa (UL56). Rabbit antisera induced against recombinant UL56 protein were used for detection of the UL56 gene product during the infection cycles of HSV-1. The presence of the UL56 protein was detected in infected cells and in HSV-1 virions by Western blot experiments and by immunofluorescence assays. A strong and increasing cytoplasmic fluorescence was observed in RC-37 cells infected with HSV-1 strain F between 6 and 16 h post-infection. In addition it was found that human HSV-1 IgM/IgG positive convalescent sera recognized the recombinant UL56 protein.

Epstein-Barr virus in lingual epithelium of liver transplant patients

Thirty-three liver transplant patients and 20 controls were examined for the presence of EBV in epithelium of the lateral border of the tongue by negative staining electron microscopy. Five of the specimens (15%) showed particles typical of the herpes virus family, while all controls were negative for EBV. In 3 of the 5 patients moderate oral hairy leukoplakia was observed clinically. Our results indicate that EBV may be expressed at the lateral border of the tongue of liver transplant patients, who in some cases show oral hairy leukoplakia clinically.