Ecology and risk assessment of E. coli O157:H7 and Salmonella Typhimurium in the primary production chain of lettuce : proefschrift / Eelco Franz . Wageningen :  Wageningen University , 2007 . 216 s . Doktorandská dizertačná práca (PhD.). - Wageningen University . ISBN 978-90-8504-728-5 . [1, of that borrowed 0]