Bacteria in the body
List host molecules that can act as receptors for becterial adhesins
(slide 16)
What are abscesses?
A painful collection of pus comprising dead tissue, white blood cells, and bacteria.
Which mechanism does bacteria use to establish infection?
After entry, a bacterial pathogen must find a way to stay in the host if it is to establish the focus of the infection. Adhesion of bacteria to a host is of paramount importance as it is a prerequisite for colonisation and infection.
What are biofilms?
Biofilms are aggregations of multiple microorganisms that secrete extracellular polymeric substances to form a protective matrix that adheres to biotic and abiotic surfaces. Detachment of cells or biofilm aggregates may result in bloodstream or urinary tract infections. Cells in biofilms have dramatically reduced susceptibility to antimicrobial agents. Biofilms are resistant to host immune system clearance.
What types of surfaces can bacteria adhere to in the human body?
Continuously shedding surfaces: -Cellular surfaces (host cells or receptors on host cells) -Acellular surfaces (mucous, extracellular matrix components) Static surfaces: (e.g. medical devices, bones, teeth)
List the characteristics of biofilms important in infections disease processes.
Detachment of cells or biofilm aggregates may result in bloodstream or urinary tract infections Cells in biofilms have dramatically reduced susceptibility to antimicrobial agents. Biofilms are resistant to host immune system clearance.
What is a portal of entry? What are the 3 main portals of entry?
Entry of pathogens is a primary requirement for exogenous disease. Any point at which pathogens can enter body is called a point of entry. Normal flora can sometimes cause endogenous infections/disease because they are already present in the body. 3 main portals of entry: 1. Mucous membranes (e.g. Diarrhoea) 2. Skin (e.g. Gas gangrene) 3. Parenteral (e.g. Bubonic plague)
What is extracellular bacteria?
Extracellular bacteria do not invade cells and proliferate instead in extracellular environment.
Learning objectives
Following this lecture,students will have the knowledge and skills to be able to: • Describe in detail, the mechanisms by which bacteria gain entry to, interact with, replicate and disseminate within, and cause damage to their host • Describe the various types of virulence factors that enable bacteria to cause disease • Explain what exotoxins are and their specific mechanisms • Describe the various bacterial forms and their importance in the context of medical microbiology
What is intracellular bacteria?
Intracellular bacteria invade cells and proliferate inside them because: The can't survive outside host cell (obligate) Provides them with a selective advantage (facultative)
What are endospores?
Metabolically inactive, tough, and non-reproductive structures produced by certain bacteria.
Define the following terms: Pathogen Pathogenicity Virulence
Pathogen: A harmful microbe that causes infection and disease. (Infection occurs when a microbe enters your body and reproduces. Disease occurs when the host sustains sufficient damage to perturb homeostasis.) Pathogenicity: The capacity of a microbe to cause damage in a host. (Damage can result from direct microbial action or the host immune response, or both). Virulence: The degree of damage caused by a microbe.
What are the consequences of biofilms on indwelling medical devices?
Several indwelling medical devices have been shown to harbour biofilms, resulting in measurable rates of device associated infections.
What is required for "lock and key" adherance of bacteria to biotic surfaces?
Specific( 'lockRandRkey'( adherence( of( bacteria( to( bioQc( surfaces( requires( the( parQcipaQon( of( two( complementary( factors: - Adhesin:(( o A(surface(structure(that(binds(a(bacterium(to(a(specific(surface - Receptor:(( o A( complementary( binding( site( on( the( surface( of( the( host( that( bind(specific(adhesins
Virulence is mediated by virulence factors. List and define the 5 virulence factors.
Virulence factors are components of a pathogen that damages the host. - Adhesins: Coordinate binding of microbe to host cell. - Invasins: Enable microbe to invade a host cell. - Impedins: Enable microbe to avoid hosts defence mechanisms. - Aggressins: Cause direct damage to the host - Modulins: Cause indirect damage to the host
List the bacterial factors involved in adhesion.
• Gram+(cell(wall:( - LTAs/WTAs( - PepQdoglycan( • Gram−(cell(wall:( - LPS( - Outer(membrane(proteins( - Type( I( fimbriae( in( Enterobacteriaceae:( Bind( specifically( to( mannose( terminated( glycoproteins( on( eucaryoQc( cell( surfaces • Gram+/−(cell(wall:( - Capsule( - Type(V(pili:(Thought( to(play(a( role(in(adherence(and(biofilm( formaQon( - SRlayer:( Proteinacious( outermost( cell( envelope( component( allowing(adherence - Flagella:( Macromolecular,( mulQRcomponent( structures( primary(funcQon(in(moQlity,(but(also(adhesion(
List mechanisms that bacteria use to enter the host.
• Respiratory tract: Breathing • Gastrointestinal tract: Ingestion of food and liquids • Genitourinary tract: Abrasions or tiny tears in surrounding tissues and bodily secretions. • Skin: Openings such as hair follicles, perspiration ducts or breaks in skin. • Parenteral: Insect bites, injections, surgical procedures
