Identification of atypical Aeromonas salmonicida: inter-laboratory evaluation and harmonization of methods.

The atypical isolates of Aeromonas salmonicida are becoming increasingly important as the frequency of isolation of bacteria belonging to this group continues to rise. The primary object of this study was to compare and evaluate the results obtained in various laboratories concerning the biochemical identification of atypical Aer. salmonicida before and after standardization of media and methods. Five laboratories examined 25 isolates of Aer. salmonicida from diverse fish species and geographical locations including the reference strains of Aer. salmonicida subsp. salmonicida (NCMB 1102) and Aer. salmonicida subsp. achromogenes (NCMB 1110). Without standardization of the methods, 100% agreement was obtained only for two tests: motility and ornithine decarboxylase. The main reason for the discrepancies found was the variation of the incubation time prior to reading the biochemical reactions. After standardization, improvement was obtained with the identification; however, disagreement was still observed between the different laboratories. These findings demonstrate the difficulties involved in a proper identification of atypical Aer. salmonicida and also that data presented in the literature on various strains of Aer. salmonicida are not readily comparable. This paper seems to be the first on standardization of microbiological tests for identification of fish pathogens and the results obtained show the need for standardization of methods both within and between laboratories.

Changes in plasma vitellogenin, sex steroids, calcitonin, and thyroid hormones related to sexual maturation in female brown trout (Salmo trutta).

Female brown trout (Salmo trutta) from a wild strain (Baltic sea trout) and a cultured strain were sampled individually for blood plasma at regular intervals during the period around final sexual maturation. The plasma samples were analyzed for vitellogenin (VTG), estradiol-17 beta, testosterone, 17 alpha, 20 beta-dihydroxy-4-pregnen-3-one (17,20 beta-P), calcitonin, tri-iodothyronine (T3), thyroxine (T4), and total and free plasma calcium. In the wild fish, VTG, estradiol-17 beta, and testosterone peaked 30 days before ovulation, while 17,20 beta-P had a sharp peak at ovulation. Both T3 and T4 declined at the beginning of the sampling period, reached minimal levels 30 days before ovulation, and rose sharply at the time of ovulation. Calcitonin levels were elevated during final maturation. Total plasma calcium correlated with plasma VTG levels. In the cultured strain, sampling was started 2 weeks before ovulation. The levels of VTG, estradiol-17 beta, and testosterone decreased throughout the sampling period. 17,20 beta-P and calcitonin concentrations were high during the period close to ovulation. Plasma thyroxine remained at basal levels in cultured trout. The discrepancies observed between wild and cultured females may be due to differences in stress susceptibility, environmental conditions, life cycles, or to genetic divergence between the strains.

Measurement of the temperature inside the rotor of the Airfuge and its operation at low temperature.

A method based on the slow hydrolysis of saccharose allows the temperature inside the revolving centrifuge tubes to be measured with precision. Equipment that enables the instrument to be operated at low temperature is also described.