A pathogen (disease-causing microorganism or virus) is likely to first encounter a neutrophil. The biological component could be an enzyme, cell, cell receptor or microorganism. Yeast is the microorganism that is responsible for fermentation in beer. A monovalent vaccine is designed to immunize against a single antigen or single microorganism. The modified microorganism is killed after fermentation. Smoking is used to preserve salmon against microorganism spoilage. An enterotoxin is a protein exotoxin released by a microorganism that targets the intestines. With the advent of modern microbiology, classification based upon the causative microorganism became possible. The degree of antimicrobial activity varies with the type of microorganism tested. Rapamycin is a macrolide, produced by the microorganism "Streptomyces hygroscopicus" and showed antifungal properties. Sucrose increases the liquid's osmotic pressure, which prevents microorganism growth. The company Evolva has developed a genetically modified microorganism which can produce vanillin. This microorganism, "A. cerati", has functional mitochondria that lack a genome. The colony morphology can be of great use in the identification of the microorganism present. Lupins is nodulated by the soil microorganism "Bradyrhizobium" sp.