A balanced technique for preparation of specimens from pathogenicity studies for scanning electron microscopy

This paper reports our experiences with preparing delicate biological specimens for scanning electron microscopy. Three different washing methods were evaluated: One method allowed the analysis of the location of the bacterium Mycoplasma mobile on piscine gill epithelium and the optimal evaluation of histopathologic changes caused by this microbe. These results were achieved when specimens were washed three times in a cacodylic acid buffer after completion of the in vitro infection experiment in gill explant cultures. We also found that of three different concentrations of glutaraldehyde, a fixation with a 1.5% solution was sufficient to achieve excellent structural preservation, even without using post fixation in osmium tetroxide. Furthermore, this study showed that the use of acetone-carbon dioxide in the critical point drying procedure resulted in well-preserved piscine gill epithelium and mycoplasmas. Finally, long-term storage of tissue specimens in 0.1 M cacodylic acid buffer is possible if the buffer is changed on a monthly basis to avoid growth of unwanted microorganisms, such as fungi.