Affiliation: | (1) Mikrobiologisches Institut, Eidgenössische Technische Hochschule, ETH-Zentrum, CH-8092 Zürich, Switzerland;(2) Present address: PLIVA Research Institute, YU-4100 Zagreb, Yugoslavia;(3) Present address: Centre de Recherche Nestlé, BP 353, CH-1800 Vevey, Switzerland |