B2.052 The Microbial World Flashcards
what are Koch’s postulates?
- the organism is regularly found in the lesion of the disease
- the organism can be isolated in pure culture on artificial media
- inoculation of this pure culture produces a similar disease in experimental animals
- organisms can be recovered from the lesions in the animals
what did threat of ID decline in the 1900s?
sanitation and hygiene chlorination of water antibiotics vaccination animal and pest control
why can diseases re-emerge?
evolution of microorganisms
intensive misuse of antibiotics (selection for the proliferation of resistant organisms)
increased globalization
decline in public health in some regions
increase in people with decreased immune function
what are the classes of infectious agents?
priors (infectious proteins) viruses (acellular) bacteria (prok) fungi (euk) parasites (euk) -protozoans (unicellular) -helminths (multicellular)
rank microorganisms by size
viruses
what is the requirement in bacteria to be classified as the same species?
> 97% identity in 16s rRNA
high degree of DNA sequence identity
more arbitrary than eukaryotes
bacillus
oval
coccus
circle
diplococcus
streptococcus
staphylococcus
2 cocci
chain of cocci
collection of cocci
funky shaped bacteria
coccobacillus: halfway between coccus and bacillus
curved rod
club shaped
spirochete
what is unique about the spirochete shape?
very thin
predestined to penetrate tissues
what is a spore?
formed under stress conditions
can survive in suboptimal circumstances better than the bacteria themselves
allow colonies to survive
what is the function of a capsule?
antiphagocytic
more chronic infection
gram positive
thick peptidoglycan cell wall
gram negative
thin PG layer with a second membrane
lipopolysaccharides acyl chain linkages with second membrane
spirochetes
have lipoproteins expressed on membrane
thing PG layer
flagella in between membranes
acid-fast
cant be stained by gram staining waxy surface -mycolic acids -porins -arabinogalactan
commensal
microorganism in symbiotic relationship with host
virulence
degree of pathogenicity
etiology
cause of disease
epidemiology
factors of disease spread sporadic- small isolated cases endemic- continually prevailing in a region epidemic- outbreak pandemic- worldwide outbreak
stages of infection disease
incubation period
prodrome
specific illness (localized or systemic)
convalescence
what is prodrome
nonspecific symptoms
what is convalescense
after resolution of symptoms to complete recover there can be complications
- chronic carriers
- latent infections
- permanent tissue damage
how do you measure virulence
ID50
LD50
microbiome of skin
gram+
microbiome of respiratory tract
nares- staphylococci
microbiome of GI
anaerobes
microbiome of GU
anterior urethra- lactobacilli
vagina- lactobacilli, others
what parts of the body are generally sterile
upper GU
lower respiratory tract
what is an example of a beneficial intestinal bacteria
E.coli producing vitamin K and B
what are types of gut flora restoration therapy and when are they necessary?
fecal transplants
probiotics
need in C.difficile treatment
what are 5 common transmission patterns
oral/aerosol fecal-oral venereal vector-borne (Lyme disease) zoonotic
what are portals of entry for a pathogen
skin, soft tissue (trauma) skin, bloodstream (bite) respiratory (inhalation) GI (ingestion) GU (sexual transmission) transplacental
what are primary pathogens?
if present, they have a high probability of causing disease
immunizations common
what are opportunistic pathogens?
some commensals
cause disease under certain conditions only
what are nonpathogens?
rarely cause disease
what are the stages of bacterial pathogenesis
transmission adhesion colonization spread damages to host (direct or indirect by immune response) evasion of immunity transmission
what are virulence factors?
help bacteria to invade the host, cause disease, and evade host defense
some are targeted by vaccines or detected by specific diagnostic tests
what are some virulence factor examples?
motility adhesins invasins exotoxins endotoxin (LPS) degradative enzymes capsules siderophores resistance to antibiotics
what are adhesins?
surface virulence factors that confer ability to adhere to host surfaces
what are examples of adhesins
pilli -type 1: adhere to mannose receptors -p pilli: adhere to Gal-Gal receptors protein adhesins biofilms: bacterial polysaccharides allow bacteria to stick to each other and attach to a surface
what are the 2 types of intracellular bacterial growth?
obligative- always require host cell
facultative- can also grow extracellularly
what are some mechanisms of systemic disease?
destruction of tissue barrier by tissue damaging enzymes
penetration of cell membrane
what are the 3 mechanisms of invasion of intracellular pathogens?
passive uptake: bacteria opsonized by complement are taken up by phagocytic cells
active invasion: invasins on bacterial cell surface induce uptake by non-phagocytes
transcytosis: intracellular motility by actin polymerization
what are exotoxins?
bacteria mediated pathogenesis
what are endotoxins?
host mediated pathogenesis
released when cells dies
LPS, gram negative and nonspecific immunity
what makes up the syringe complex in “syringe” secretion systems?
T3SS
what are examples of exotoxins?
enzymes (act on ECM, collagenase)
A-B type toxins (2 subunits)
membrane damaging toxins (phospholipases, pore forming toxins)
superantigens
depict A-B toxins
B portion binds to cell surface receptor
A portion is enzymatically active and is transported into cell interior
give examples of A-B toxins
- ADP ribosylating toxins
- diphtheria toxin inactivated elongation factor
- cholera/pertussis toxins activate adenylate cyclase (increase cAMP) - others
- shiga EHEC cleaves rRNA
- tetanus blocks release of neurotransmitter
describe host mediated pathogenesis
inflammation is mediated by microbial products (LPS, cell wall, some toxins), antibody and complement, and cell-mediated immunity
enhances microbial killing at the expense of the host tissue
autoimmunity in some chronic diseases
what are superantigens?
lock antigen presenting cell and lymphocytes together
results in continuous stimulation of the immune system
what is the mechanism of the endotoxin LPS?
released by cell lysis (not secreted)
toxic due to lipid A component
causes septic shock
binds to LPS binding proteins and interacts w host receptor CD14
what are 3 ways pathogens evade host immune responses?
defense (capsules, serum resistance due to LPS modifications)
offensive (toxins degrade immune components, killing of phagocytes)
stealth (antigenic variation)
how do bacteria obtain iron for growth?
siderophores
where are virulence factors encoded?
chromosome: stable
pathogenicity island: region of DNA
plasmid: extrachromosomal smaller DNA replicon, can be transferred, dispensable for growth
bacteriophage: bacterial viruses, can transfer DNA between bacteria
transposons: highly mobile DNA element
