Influence of storage on monodispersed cells of Mycobacterium terrae used for quantitative carrier test prEN 14563.

The degree of cell clumping increased with time of storage (1% cell clumps immediately after homogenization and 3 and 6.5% after 48 and 96 h of storage, respectively), and the number of living single cells decreased. Quantitative carrier tests were carried out with these cells using ortho-phthaldialdehyde (OPA) and coco fatty aminoxethylate as biocides. In contrast to OPA, with coco fatty aminoxethylate the reductions obtained with freshly homogenized mycobacteria were significantly higher (P = 0.02) than those obtained with mycobacteria kept in the refrigerator for 4 days. Therefore, it is advisable to prepare the test suspension freshly for each test.