Factors Facilitating Microbial Invasion By Larry M Bush, MD, FACP, Charles E Schmidt College of Medicine, Florida Atlantic University Reviewed / Revised Aug 2022 | Modified Sep 2022 View Patient Education Virulence Factors Microbial Adherence Antimicrobial Resistance Defects in Host Defense Mechanisms Microbial invasion can be facilitated by the following: Virulence factors Microbial adherence Antimicrobial resistance Defects in host defense mechanisms Virulence Factors Virulence factors assist pathogens in invasion and resistance of host defenses; these factors include Capsule Enzymes Toxins Capsule Some organisms (eg, certain strains of pneumococci, meningococci, Haemophilus influenzae type b) have a capsule that blocks phagocytosis, making these organisms more virulent than nonencapsulated strains.