1. Faculty of Animal Science and Aquaculture; Agricultural Univ. of Athens; 75 Iera Odos St. 11855 Athens Greece
2. Laboratory of Biology; School of Medicine; Dept. of Basic Medical Sciences; Univ. of Athens; 11527 Athens Greece
3. Hellenic Army Biological Research Center; 6-8 Tax Velliou 15236 P. Penteli Greece
4. Laboratory of Microbiology and Infectious Diseases; Faculty of Veterinary Medicine; Aristotle Univ. of Thessaloniki; 541 24 Thessaloniki Greece
5. Inst. of Sciences of Food Productions; Natl. Research Council of Italy; CNR-ISPA; Lecce Italy
6. Food and Environment Research Agency; Sand Hutton; York YO41 1LZ UK