NOVELTY - In preventing or reducing the adverse effects of pathogens in animal or human digestive tract, microorganism biomass (B1) comprising non-living microorganism biomass, obtainable by cultivating microorganisms on a cultivation medium comprising lignocellulosic material, is used.    USE - For preventing or reducing the adverse effects of pathogens e.g. Salmonella (preferably Salmonella enterica) genera and Escherichia coli, in animal or human digestive tract including stomach, small intestine and/or colon; as a food or feed topping, food or feed extender or feed or food supplement in feed or food composition which is a ruminant or monogastric animal feed composition, or nutritional product for human use; for preparing feed or food additive; for inactivating pathogen in contaminated feed or food products; and for preparing feed or food products for feeding animals such as ruminant, monogastric, aquaculture, preferably livestock selected from pigs, horses, poultry, cattle, goats and sheep, especially chicken and pig (all claimed).    ADVANTAGE - The method improves the well-being and increases the productivity of animal.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are included for the following:    (1) feed or food composition (C1) comprising the microorganism biomass (B1);    (2) preparing (M1) a feed additive involving: a) cultivating at least one microorganism in cultivation medium comprising lignocellulosic material; b) subjecting the microorganism to a step of cell disruption to obtain non-living biomass of the microorganism; c) isolating a solid phase containing the microbial biomass and residues of lignocellulose of step (b); and d) optionally, drying the microbial biomass obtained from step (c);    (3) feed or food additive (a1) obtainable from the method (M1);    (4) inactivating (M2) a pathogen in a contaminated feed or food product involving providing feed or food product contaminated with a pathogen; providing feed or food additive (a1); mixing the feed or food product with the feed or food additive; and    (5) preparing (M3) feed or food product involving providing feed or food substance; providing feed or food additive (a1); and mixing the feed or food substance with the feed or food additive.