Laboratory Methods for Detecting Viral Infections

The first methods for detection of bacterial infections were available around 1880. After staining, bacterial pathogens were recognized in the light microscope because of their size and could be cultivated in culture media. Viruses evaded this approach, as they are significantly smaller, and as obligate parasites are not able to multiply in cell culture media. Although some viral infections could be associated with specific cellular changes and certain depositions in the infected tissue around the turn of the century, e.g. Negri inclusion bodies in nerve cells during rabies, a specific diagnosis was only possible through the development of cell culture methods and modern molecular biology. Today, viral infections can be detected directly by determining the agents, individual viral proteins, or their genetic information, or other materials in the blood of infected people or animals by using appropriate methods. Direct detection of viruses is possible, with the exception of latent or persistent infection forms, only during the acute phase of the disease. In some cases, the pathogens are present in the infected organism only before the symptomatic phase, so the direct detection of the virus is frequently not successful. Therefore, infections or contact with pathogens is usually demonstrated in virus diagnostics indirectly by characterization of the developing specific immune response.

Rapid algal toxicity assay using variable chlorophyll fluorescence for Chlorella kessleri (chlorophyta)

Three methods of algal assays--the standard assay, microassay, and the proposed fluorescence assay--are compared from the point of view of reliability of EC50 detection, the minimum required time for the detection, sensitivity of individual measurement, i.e. at which cell density the particular assay can be used for EC50 estimation, and the time stability of the EC50 values. The assays were performed with green alga Chlorella kessleri strain LARG/1 growing in potassium dichromate solution in Z-medium ranging from 0.01 to 100 mg Cr L⁻¹. The inoculation cell density was set according to the standards to 10⁴ cells mL⁻¹ and according to spectrophotometer/plate reader detection limit. The average EC50 ranged from 0.096 to 0.649 mg Cr L⁻¹ and there were no significant differences in EC50 between the assay type and the inoculation methods with the exception of the significant difference between EC(c)50₇₂ (EC50 established from biomass measured as chlorophyll a concentration after 72 h of cultivation) in the standard assay and EC(r)50 (EC50 derived from growth rate) in the microassay in the standard inoculation experiment due to low variability of their values. The EC(f)50 (EC50 derived from variable fluorescence measurement) values correspond to EC50 values derived from the growth rates. Fluorescence measurement revealed the toxic effect of the chromium after 24 h of exposure at cell density of 5 x 10⁴ cells mL⁻¹, less by half than other used assay methods. The positive correlation of EC(f)50 and time was found in the standard inoculation experiment but opposite effect was observed at the spectrophotometric one.

Highly stable first-generation biosensor for glucose utilizing latex particles as the enzyme-immobilizing matrix

The ability of polystyrene latex beads to immobilize glucose oxidase was applied to construct a stable biosensor for glucose. This biosensor measures glucose by detecting the hydrogen peroxide produced by the enzyme. The biosensor performance was studied by amperometry. Glucose concentrations ranging from 1 to 50mM can be measured with this sensor. The sensor is active over a broad range of pH and is very stable, which makes it suitable for a number of possible applications.