Preparations that might be seen in a laboratory include:

• IEP plates
• Ouchterlony plates
• Paper/starch chromatograms
• Test -tubes
• Culture plates - Fungal - Viral -
• Bacterial

Immunoelectrophoretic (IEP) plates and ouchterlony plates

These combine electrophoresis and double diffusion of separate areas of antigen and antibodies into a common medium. Where antigen and antibody meet and interact precipitation bands are formed.

Different proteins are distinguished by their electrophoretic mobility (ability to move under an electric current) and their antigenic characteristics or immune properties.

The supporting medium is usually agar gel or cellulose on acetate film or glass.

These are not stable preparations, some that have been dyed are more stable.

Clear medium slight haze with milky colour precipitate.

Darkground illumination is best for these plates.

The alternative to lights underneath the specimen is a light box which gives a more diffuse illumination. If there were no specimen the camera should see only black. Specimen photography - Laboratory preparations 1

Chromatograms

This is a method of chemical analysis in which the substances to be tested are spread by their ability or inability to be moved by a solvent e.g. alcohol.

The chemicals can be separated using a number of different media paper, starch columns, cellulose, silica or kaolin on glass plates or acetate. All of these are absorbent surfaces, is a surface action.

Visualizing and recording the bands can be difficult as they are often pale so contrast filtration may be needed. Some chemicals may fluoresce under ultraviolet with characteristic colours, naturally or artificially by the addition of another chemical. The compounds or chemicals may also be labelled with radioisotopes which can be seen using X-ray film. These can be copied in the same way as normal radiographs.

Flat lighting is best for those on an opaque substrate and translucent starch columns or gels using brightfield illumination as below.

It may be useful to use a contrast filter with these gels. A Wratten 12 or 15 yellow filter is good to increase contrast with blue coloured gels for black and white prints.

It may be necessary to use ultraviolet fluorescence for some chromatograms. The image opposite was taken for the dermatology department to show an extract of Tansy. The important chemical which caused a reaction is seen in the quenching of the fluorescence in the first sample.

Culture plates

Most commonly these are seen in the form of petri dishes also test-tubes and culture flasks or bottles.

In test-tubes and flasks the media is set at an angle to provide a larger surface area. The medium the culture is grown on or in can be translucent or opaque. The most likely media you will see is agar broth (derived from seaweed alginate), blood or meat broth. Made at 100°c it is a liquid, cools to 40°c when blood or other nutrients are added, sets when cold to form a gel. The blood cells are added after being Iysed, that is broken down with the cell walls disintegrated. Normal blood is opaque and darker if cooked. Haemolysis - breaking down of blood.

Close-up (x4) of Staphylococcus aureus on blood agar

Mycological plates 

As above usually on a plain agar plate.

Photographic problems - important with fungal plates to show colour, shape and contour of the culture. Directional lighting for shape and contour and brightfield transillumination to show some of the colours more clearly or a mixture of both lighting methods. It can also useful to use darkfield illumination. (See references below for more details)

Photography of the underside through the base can also be important for looking at the different composition. Also above the plate looking at the mycelium, the fruiting bodies of the fungus.

Bacterial and viral cultures

The medium will be inoculated with bacteria from a sample taken on a swab or using platinum wires from another culture. They are then incubated at 37° (body temperature). Looking for shape and distribution of the colonies, samples are taken once grown to look at under the microscope to identify. The culture plate is used to let the bacteria multiply sufficiently so that there is enough to be able to identify them.

It is important to demonstrate colour and shape of colonies. Darkfield is useful, with a small amount of cross-lighting where the medium is transparent.

Handling

Should handle them as little as possible as are working with infectious material so need to avoid the possibility of cross-infection between you and the culture. Ideally covers should be kept in place, but this can be difficult if labels are on the cover or they are scratched.

Organize to take the photographs first then remove the lids taking great care to put the right lid with the right plate after photography. Having a set up that is already calibrated helps. Might have to photograph with the lids on or in a laboratory if the culture is infectious or culture has to be used quickly after photography.

Handle fairly rapidly as material can deteriorate once outside an incubator and the agar gel can dry up or crack if left under hot lights too long. Fungal cultures can change, some grow rapidly, hot lights will speed up growth.

Cultures can be kept in a fridge before photography but not for too long and have to avoid condensation on the plates in a hot or humid studio.

Tip - If left in the fridge too long, like anything else, the plates can go mouldy!!