Lecture 20 General Microbiology Flashcards
What is pathogenicity?
- Ability to produce pathological change or disease
- Pathogen: any disease-producing microorganism.
What are gnotobiotic animals?
- All microbial species present are known.
- Germ-free
- Used to study interactions of aimals and specific microogranisms
- Only certain known strains of bacteria and other microorganisms are present.
How do you establish gnotobiotic animal colonies in mammals?
- Free of microbes in utero
- Established by caesarean-section delivery in germfree isolate
- Maintain in sterile environment
- Normal mating and delivery of gnotobiotic mammals maintains colony
How do you establish gnotobiotic animal colonies in BIRDS?
- Germicide treatment of fertile eggs
- Hatch eggs in sterile isolators
What are the characteristics of gnotobiotic animals?
- More susceptible to pathogens, except those cause by protozoa that use gut bacteria as food source
- Does not carry any pathogen load
What is normal microbiota? What is ectosymbiosis? What is endosymbiosis?
Normal microbiota: microbes regularly found at a site
Ectosymbiosis: one organism remains outside of the other
Endosymbiosis: one organism is present within the other
Why is it important to study normal huma microbiota?
- To gain insight into possible infections resulting from injury
- To understand causes and consequences of overgrowth of microbes normally absent from a body site
- To increase awareness of role played by indigenous microbe in stimulating immune response
What makes our skin so awesome?
- Has both resident microbiota and transient microbiota
- Mechanically strong barrier
- Keratin intractable to micriobial attack
- Most areas subject to periodic drying
- Slightly acidic
- Salty
- Inhibitory substances (e.g., lysozymes)
Describe what leads up to acne vulgaris.
- Causes in part by activities of Propionibacterium acnes.
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Sebum: fluid secreted by oil glands.
- Accumulates, providig hospitable environment for P. acnes
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Comedo: plug of sebum and keratin in duct of oil gland
- Results from inflammatory response to sebum accumulation.
How are the microbes in the respiratory tract?
- No normal microbiota
- Microbes moved by:
- Continuous stream of mucous generated by ciliated epithelial cells
- Phagocytic action of alveolar macrophages
- Lysozyme in mucus
How are the microbes in the mouth??
- Contains organisms that survive mechanical removal by adhering to gums and teeth
- Contribute to formation of dental plaque, dental caries, gingivitis, and periodontal disease.
How are the microbes found in the stomach and small intestine???
- Most microbes killed by acidic conditions
- Some survive if passed through stomach very quickly.
- Some can survive if ingested in food particles
How are the microbes in the large intestine (colon)?
- Largest microbial population of body
- Eliminated from body by peristalsis, desquamation, and movement of mucus.
- Replaced rapdily because of their high reproductive rate.
What is the microbiota like in the Genitourinary tract?
- Kidneys, ureter, and bladder
- Normally free of microbes
- Distal portions of urethra
- Few microbes found
- Female genital tract
- Complex microbiota in a state of flux due to menstrual cycle
- Acid-tolerant lactobacilli predominate
Describe the various relationship normal microbiota and the host can experience.
- Usually mutually beneficial
- Normal microbiota often prevent colonization by pathogens
- Opportunistic pathogens: members of normal microbiota that produce disease under certain circumstances
- Compromised host: debilitated host with lowered resistance to infection.
Describe the overview of what is involved in host resistance to a pathogen.
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Immune system: recognizes foreign substances or microbes and acts to neutralize or destroy them.
- Composed of widely distributed cells, tissues, and organs.
- Immunity: ability of host to resist a particular disease or infection
- Immunology: science concerned with immune responses.
What are the two types of immune responses?
- Nonspecific immune response: offers resistance to any microbe or foreign material
- AKA nonspecific resistance, innate immunity, and natural immunity
- Natural immune response: resistace to a particular foreign agent
- AKA acquired immunity, adaptive immunity and specific immunity
- Improves on repeated exposure to agent
What is a parasitic organism? What is parasitism? What is a parasite?
Parasitic organism: a symbiont that harms or lives at the expense of its host
Parasitism: relationship between a parasite and its host
Parasite: by convention, when used without qualification, refers specifically to protozoan or helminthic organism
What are the two types of parasites?
Ectoparasite: lives on surface of host
Endoparasite: lives within host
What are the four different types of hosts?
Final host: host on (or in) which parasite either gains sexual maturity or reproduces
Intermediate host: serves as temporary but essential environment for some stage of parasite’s development
Transfer host: is not necessary for development but serves as vehicle for reahing final host
Reservoir host: nonhuman organism infected with a parasite that can also infect human
Define infection.
Infection: growth and multiplication of parsite on or within host
Define pathogen:
Pathogen: any parasitic organism that causes infecious disease
Primary (frank) pathogen: causes disease by direct interaction with host
Opportunistic pathogen: causes disease only under certain circumstances
What are the factors impacting outcome of host-parasite relationships?
- Number of organisms present
- Virulence of pathogen
- Virulence factors: products or structural components that contribute to virulence or pathogenicity
- Host’s defenses or degree of resistance
What is virulence?
- Degree or intensity of pathogenicity
- Determined by three characteristics of the pathogen
- Invasiveness: ability to spread to adjacent tissues
- Infectivity: ability to establish focal point of infection
- Pathogenic potential: degree to which pathogen can cause damage to host.
What are the 7 mechanisms of pathogenesis of bacterial diseases?
- Maintain a reservoir: place to live before and after causing infection
- Be transported to host
- Adhere to, colonize, and/or invade host
- Multiply or complete life cycles on or in host
- Initially evade hose defenses
- Damage host
- Leave host and return to reservoir or enter new host
Elaborate on “maintaining a reservoir”, a mechanism of pathogenesis of diseases.
- For human pathogens, most common reservoirs are:
- Other humans
- Animals
- Environment
Elaborate on “transport of the pathogen to a host”, a mechanism of pathogenesis of diseases.
- Direct contact
- e.g. coughing, sneezing, body contact
- Indirect contact
- Vehicles (e.g. soil, water, food)
- Vectors: living organisms that transmit pathogen
- Foimtes: inanimate objects that harbor and transmit pathogens
Elaborate on “attachment and colonization”, a mechanism of pathogenesis of diseases.
- Adherence: mediated by special molecules or structues called adhesins
- Colonization: establishment of a site of microbial reproduction on or within host
Elaborate on “invasion of the bacterial pathogen”, a mechanism of pathogenesis of diseases.
- Can be active penetration of host’s mucous membranes or epithelium
- Can be passive penetration
- e.g., skin lesions, insect bites, wounds
- Once below mucous membrane, bacterium can spread to deeper tissues
- Involves productin of specific products and/or enzymes tat promote spreading
Elaborate on “growth and multiplication”, a mechanism of pathogenesis of diseases.
- Occurs when pathogen finds appropriate environment within host
- Some bacteria invade specific cells
- Some actively grow in blood plasma
- Bacteremia: presence of viable bacteria in blood.
- Septicemia: presence of bacteria or their toxins in bloodstream.
Elaborate on “leaving the host”, a mechanism of pathogenesis of diseases.
- Must occur if microbe is to be perpetuated
- Most bacteria leave by passive mechanisms
- E.g., feces, urine, droplets, saliva, or desquamated cells
How are bacterial virulence factors regulated?
- Often environmental factors control expression of virulence genes
- e.g., Corynbacterium diptheriae: gene for diphtheria toxin regulated by iron
- e.g. Bordetella pertussis: expression of virulence gees increased at body temperature
- Vibrio cholerae: gene for cholera toxin regulated b pH, temperature, and other factors
What are pathogenicity islands?
- Large segments of DNA that carry virulence genes
- Acquired during evolution of pathogen by horizontal gene transfer
- E.g. genes for type III secretion system
- enables gram-negative bacteria to secrete and inject virulence proteins into cytoplas of eukaryotic host
Define the following: intoxications, toxin, toxemia, and antitoxins.
Intoxications: diseases tht result from entry of a specific preformed toxin into host
Toxin: specific substance that damages host
Toxemia: condition caused by toxins in the blood of host
Antitoxins: neutralizing antibodies
Toxoid: inactivated toxin used to elicit immune response.
What are exotoxins?
- They typically can be AB exotoxins: composed of two subunits -
- A subunit - responsible for toxic effect
- B subunit - binds to target cell
- They can also be hemolytic reactions:
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Beta-hemolysis: complete lysis
- Observed as zone of clearing around colony on blood agar
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Alpha-hemolysis: partial lysis
- Observed as geenish zone around colony on blood agar
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Beta-hemolysis: complete lysis
- Can also employ phospho-lipases: exotoxin removes the charged polar head groups from the phospholipid part of the host cell membrane. This destablizies the membrane and causes the host cell to lyse.
What are the 3 roles of exotoxin in disease?
- Ingestion of preformed exotoxin (intoxications)
- Colonization of mucosal surface followed by exotoxin production
- Colonization of wound followe by local exotoxin production
What are endotoxins?
- Lipopolysaccharide complex on outer membrane; lipid A portion is toxic
- Usually capable of producing general systematic effects: fever, shock, blood coagulation, weakness, diarrhea, inflammation, intestinal hemorrhage, fibriolysis.
- Bring about these effects indirectly
- Endotoxin interacts with host molecules and cells, activating host systems
- e.g., interaction with macrophages -> release of endogenous pyrogen
- e.g., binding to LPS-binding protein -> release of cytokines
How do viruses evade the immue system?
- Mutations that change antigenic sites or alter expression of antigens
- Infection of immune system cell, diminishing their function
- Infection of tisues with few MHC molecules
- Production of proteins that inhibit MHC molecule function
- Production of free antigens that bind neutralizing antibodies
How do bacteria evade the immune system?
- Have mechanisms to resist complement system, phagocytosis, and specific immune responses
- Evading the complement system:
- Capsules
- Lengthened O-chains
- Serum resistance: modified lipooligosaccharides interfere with formation of membrane attack complex.
- Resisting phagocytosis involves:
- Capsules
- Production of specialized surface proteins that block adherence of phagocytes to bacterium
- Production of proteases that cleave complement factor C5a (phagocyte chemoattractant)
How do bacteria survive inside phagocytic cells?
- Escape from phagosome before fusion with lysosome
- Resistance to toxic products of phagolysosome
- Prevent fusion of phagosome and lysosome
How do bacteria evade specific immune responses?
- Evading specific immune response by:
- Capsules
- Genetic variation of surface antigens
- Production of IgA proteases
- Production of proteins that interfere with antibody-mediated opsonization
Opsonization: the process by which a pathogen is marked for ingestion and destruction by a phagocyte
