Schematic outline of the proposed defense of breaches of the bacterial outer membrane. Host systems (whether antimicrobial peptides, antibody and/or complement) have opened the outer membrane, allowing lysozyme and host proteases to attack periplasmic components, leading to a further breach of the peptidoglycan. Host attack is hampered by protease trapping (bacterial α2-macroglobulin) and lysozyme inhibition (Ivy), giving PBP1C a chance to repair the glycan chains. The fate of the colonizing bacterial cell will now depend on whether the bacterial defenses are exhausted or the host attacking components are too limited to achieve cell lysis. Elements of the scheme are not drawn to scale.