Microbes in health and disease Flashcards
microbes have good and ugly sides, the side that shows depends on
host factors, microbe factores and interactions with & in their shared environments
ex: probiotics are beneficial bc stimulate immunity and anti-inflammatory responses but also have ben linked to some cancers, chronic and fatal infections
what is a pathogen? what is a parasite?
Pathogen (virus, bacteria, fungi) = microbial agent of disease (causative agent - etiological agent)
Parasite: normally used to denote worms, protozoa
*ectoparasite lives on surface of host, endoparasite lives inside hosts body
what in an infection
infection = present of pathogen
- occurs when a pathogen or parasite colonizes and begins to grow on or in a host
- infection does not necessarily mean disease
what are primary pathogens and examples
- cause disease in healthy hosts
- Shigella flexneri - cause of bacillary dysentery
- Mycobacterium tuberculosis, E.coli
what is an opportunistic pathogen and examples
- cause disease only in immunocompromised patients
- ex Pneumocystis jirovecii causes life threatening infections in AIDS patients
ex: Pseudomonas aerginosa in cystic fibrosis lungs
What is pathogenicity - what is it defined by
- pathogenicity is organisms abiltiy to cause disease
- defined in terms of how easily it causes disease (infectivity) and how severe that disease is (virulence)
what is virulence and how is it measured?
- virulence is a measure of the degree of severity of a disease
- emasured via infectious dose ID50 and/or the lethal dose (ID50)
what are the 4 levels of containment
BSL 1/risk group 1 microbes: normal sterile techniques
BSL II/RG2: limited access lab, biosafety cabinets - agents with little risk of aerosol transission
BSL III (RG3); labs with negative air pressure - agents are virulent and transmitted by inhalation
BSL IV: complete isolation - agents are highly virulent, requires positive pressue lab suits ex: ebola,
routes of infection cycle
- can be direct or indirect
horizontal transmission
- occurs from one member of a species to another via
- food/water (oral), contact (body fluids/secretions), aerosols, formites (contaminated inanimate objects), vectors (animals like mosquitoes and ticks)
Vertical Transmittion
- from parent to child
Accidental Transmission
- host not part of normal infectious cycle unintentionally encounters that cycle
what is a reservoir?
animal, bird or insect that normally harbors a pathogen
- use portals of entry best suited to their mechanisms of pathogenesis
*since bird have higher body temp then humans can carry pathogen without getting the disease
- reservoirs are critically important for survival of a pathogen as a source of infectino
ex: cattle are reservoir fro STEC (shiga toxin producing E.coli)
portals of entry for pathogens
mouth: water and food borne pathogens
pesiratory tracts: airborne pathogens
parenteral route: agents transmitted by vectors
wounds and needle punctures
what is a Zonotic disease?
- diseases of animals that when transmitted to huamns can cause disease
ex: swine and bird flu, salmonella, ebola, rabies
what are unintended consequences of technology and process on pathogens
- human progress has opened new avenues of infection - travel by jet, blood banks, suburban sprawl
ex: Mad cow disease and modern farming practices, lyme disease and suburban development, Hepatitis C and transfusions and transplants, influenza and live poultry markets in asia, E.coli and meat processing plants, SARS CoV
influences of climate change on emerging diseases
- has effected epidemiology of infectious disease and emergence of new pathogens
- ex: rising air temps can extend the habitat of mosquito and teck vectors to hgiher mountain elevations and wider latitudes - vector life cycle shortens
- extending a pathogens range can bring it into contact with novel groups of hosts
- increased rain and flooding promote the breeding of mosquito vectors that transmit disease
what is immunopathogenesis
- aplies when the immune response to a pathogen is a contributing cause of pathology and disease
- often :friendly fire” by our immune system reacting to a pathogen that causes major tissue and organ damage
ex: Rhuematic fever & group A streptococcus (agent of strep throat)
Guillian Barre syndrome (nerve damage, trigered by various bacterial and viral pathogens)
what is epidemiology
examines the distributions and determinants of disease frequenc in human populations
whats an endemic
disease always present at low frequency in a population
ex: cold, cancer
what is an epidemic
sudden rise in disease frequency over short time
Sars amd mers
what is a pandemic
- eidemi that occurs over a wide geographic area
COVID, HIV
to cause a disease all pathogens must
- gain access to the host
- find thier unique niche and colonise
- evade, subvert and overcome host defences - Intracellular pathogens enter and replicate within host cells
- Obtain or steal nutrients from host usually damaging the host and multiply
- have an EXIT strategy for transmission to a new host
how can pathogens be distinguished from avirulent counterparts
- by presence of virulence factors to help accomplish goals
if pathogen were thief the virulence factors are the tools of the trade
*factors can be cell associated or secreted into the surroundings
describe Koch’s postulates
- criteria for establishing a causative link between in infectious agent and a disease
*proved mycobacterium tuberculosis caused tuberculosis
*note issues may be if microbe is present in two animals but only one shoes disease
describe modfied molecular Kochs postulates
- suspected virulence gene can eb confirmed as having a role in virulence or pathogenicity only if it fulfils a set of “molecular koch postulates”
1. The phenotype under study should be associated with pathogenic strains of a species
2. Specific inactivation of the suspected virulence genes should lead to a measurable loss in virulence or pathogenicity - the gene(s) should be isolated by molecular methods
3. Reversion or replacement (complementation) of he mutated gene should restore pathogenicity
where are virulence genes found
- on pathogenicity islands in chromosome, on plasmids or even phage genomes
- has clusters of virulence genes with specific function related to virulence and pathogenicity
* can knock out whole siland or a specific gene on it
- originally inherited trhough horizontal transmittion from a diff species
- PI have GC content different from the rest of the genome - foten flanked by phage or plasmid genes
what is the frist step towards infection
attachment
- human bod has many ways to exclude/remove pathogens
- express adhesions - general term for any microbial factor that promotes atachment or adhesion
- abcteria have a variety of strategies to bind to specific host cell recpeotrs
ex: type 1 pili/fimbriae , outer membrane and call wall proteins, lipoteichoic acids
what are biofilms, what type of infection dot hey paly an important role in?
- biofilm is when bacteria attach to surface in bulk
- play important role in chronic infections bc enables persistent adherence and resistance to host defenses (ex phagocytosis, complement medited lysis) and limit accessibilty of antimicrobial peptides and agents
what do bacterial toxins do and what are the two major types
- bacterial toxins subvert the host cell/tissue functions
- can be divided into:
Exotoxins: secreted to the bacterial surroundings
- proteins produced by various types of bacteria
- Kill host cels and unlock their nutrients
Endotoxins: are cell associated
- Lipid A of lipopolysaccharide of gram negative bacteria is a component of the outer membrane - can hyperactivate immune systems to harmful level
how are bacterial toxins classified? what are the categories?
(9)
- classified based on mechanism of action
- Plasma membrane disruption (phospholipases, pore forming toxins)
- Disrupt cell cytoskeleton (formation of actin filaments and budding disrupted)
- Protein synthesis distruption (toxin attacks ribosome)
- Cell cycle disruption
- Signal transduction disruption
- Disrupt cell-cell adherence, connective tissues etc
- disrupt vescile traffic within host cells
- interefere with exocytosis
- superantigens (binds receptors together)
describethe two subunits of AB toxins
B subunit: binds to host cell, delivers A subunit to cytoplasm, often 5 B subunits form a pore for A entry
A subunit: has toxic activity (ADP-risosyltransferase)
ex: Diphtheria toxin (inhibits host cell protien synthesis), cholera toxin (increases fluid secretion and electrolyte loss)
