3.1. Using a haemocytometer to estimate the concentration of cells, spores or sperms

In fields of quantitative experimental research e.g. cell culture and microbiology (including bee pathology), it is important to determine the exact concentration or number of bacteria, cells, or spores and even small organisms (hereafter referred to as particles) to guarantee accuracy and reproducibility of experiments (Hefner et al., 2010). The quickest reliable method is direct microscopic or total cell counts of a culture or a suspension through the use of a counting chamber or haemocytometer (Cantwell, 1970; Paul, 1975; Strober, 1997). This method takes into account all cells or spores, cultivable or not, as long as they have a recognizable shape or trait and are not confused with other material in the sample. Further methods can be used to detect culturable (i.e. viable) particles. The plate count method allows for the counting of clonal unicellulars that form colonies and can be cultivated on an appropriate medium (see the European foulbrood paper of the BEEBOOK (Forsgren et al., 2013)). It is also possible to use spore germination test (see BEEBOOK paper on fungi (Jensen et al., 2013)) or fluorescence staining, Fenoy et al. (2009) for this purpose.