Fruits and vegetables are ecological niches for a diverse and changing microflora, which usually does not include types pathogenic to humans. Intact fruits and vegetables are safe to eat partly because the surface peel is an effective physical and chemical barrier to most microorganisms. In addition, if the peel is damaged, the acidity of the pulp prevents the growth of organisms, other than the acidtolerant fungi and bacteria that are the spoilage organisms usually associated with decay. On vegetables, the microflora is dominated by soil organisms. The normal spoilage flora, including the bacteria Erwinia and Pseudomonas, usually have a competitive advantage over other organisms that could potentially be harmful to humans.