It might not be too dramatic to state that bacteria, viruses, fungi, and specs represent a unique, insidious, and dangerous class of contaminants: unique in that under the right conditions the contamionant population can multiply over; insidious in that these organisms can penetrate into small openings and crevices that can persist for long periods of time; and dangerous in that they can affect human health, so these contaminants must be destroyed and/or removed to achieve the desired cleanliness and aspetic condition. That's the role of disnfectants