Lecture 11: Mechanisms of Microbial Infection

bacterial pathogenicity— can the organisms

1. colonize tissues/cells?: Requires adhesion, multiplication/colony growth, tissue invasion, and evading immune defense

2. produce toxins that damage cells and tissues?: induce cytolysis (cell disruption) or invasion, and evading immune defense

what are exotoxins

secreted (external) products, typically made by gram-positive bacteria

what are endotoxins

membrane (internal) compounds, typically from gram-negative bacteria

routes of entry

direct contact, penetration, ingestion, inhalation, ascending

regional and systemic spread

following local tissue invasion and colonization, microbes can spread systemically via lymphatic and blood vessels

what are the bacterial mechanisms to breach barriers

transcytosis, white blood cell trafficking, anoxal transport

what is transcytosis

when bacteria travels in vesicles through/across cells

what is white blood cell trafficking

when bacteria hitches a ride on immune cells

what is axonal transport

bacteria cells travel via nerve cell endings

what ways can intact lining barriers can be breached by

epithelial loss or disruption, weakened cell attachments, excessive moisture

what ways can initial colonization of bacteria occur

within mucus layer, attached to surface cilia or microvilli, within epithelial cells (via endocytosis, “taking up” organisms), after a barrier has been breached

what ways can initial colonization occur

• due to bacterial motility (moveability) through mucus and/or tissue via flagellum, whip-like extension, or due to unique shapes (spiral)

• due to attachments between the bacteria and cell surface receptors via fimbriae, finger-like “fringe” extensions

what are the bacterial targets in the body

• epithelial cells of all organ systems

• leukocytes and other immune cells

• cells of the CNS and PNS

how can bacteria evade immune detection

using immune cells (macrophages) to prevent detection by other immune cells (lymphocytes) → pyogranulomatous

what is a virulence factor

molecules and genes that enable microbes to replicate and cause disease

examples of the virulence factors

• colonize targets at portals of entry

• invade targets at portals of entry

• evade barrier systems and defense mechanisms

• suppress innate and adaptive immune responses

• acquire nutrition from target substances, cells, and tissues

what do virulence factors allow for

allow microorganisms to arrive, survive, and thrive by escaping detection and destruction