[Recent bacterial risks in foods]

Knowledge about bacterial foodborne diseases has broadened over the last 15 years. To this development have contributed improved isolation and identification methods but also the application of systematic epidemiological studies. In principle, no "new" bacteria have been discovered but their occurrence in foods was not known (e.g. Campylobacter jejuni/coli) or their detection in foods could not be firmly linked with disease in man (e.g. Listeria monocytogenes, E. coli O157:H7). For campylobacteriosis, listeriosis and yersiniosis foods are considered to be the main source of infection. Many of these "new" agents cannot only be detected in diseased, but also in healthy man and the environment. Frequently importance of foods as source of infection can only be proved by epidemiological studies. Traditional isolation and identification procedures are not sufficient to differentiate between virulent and avirulent strains. Molecular genetic methods as applied for e.g. enterotoxigenic E. coli allow the detection of virulence factors, however, in many instances relationship is lacking between the frequency of detection of a certain strain in food and clinical manifestation of disease. In particular, the recent listeriosis problems reveal the importance of individual host defence mechanisms and infectious doses for the evaluation. These aspects challenge the ideal complete absence (i.e., zero tolerance) of a certain microorganism in a specific food.)