bacteria
host interactions
symbiosis
commensalism
mutualism
parasitism
normal microbiota and hosts are usually mutually beneficial (rely on healthy microbiota)
normal microbiota often prevent colonization by pathogens
bacterial products are beneficial to the host
symbiosis
living together
commensalism
one benefits, the other is not affected
mutualism
both organisms benefit
parasitism
one benefits, the other is harmed - usually a microbe is affecting a much larger organism
infection
a pathogen grows and multiplies within or on another organism
infection doesn't always cause disease
most infections removed by immune system
infectious disease
due to the presence and multiplication of pathogens, part or all of the host is not capable of performing its normal function - normal function is comprimised
steps of bacterial infections
attach and invade host tissue
suppress host defenses
acquire nutrients from the host
propagate in the hosts
transmit to a new host
host-pathogen interaction
pathogensis
parasite
pathogen
pathogens and parasites enter and infect their animal and plant hosts in different ways
some microbes enter into a latent state during infection
pathogenicity
infection
entry of pathogen or parasite
infection doesn't always cause disease
most infections removed by immune system
primary pathogens
have ability to penetrate host (health) defenses
opportunistic pathogens
cause disease only in compromised hosts
immune system defective
break in tissue allows organisms access to new site
loss of other microflora allows organism to bloom
some microbes enter into a latent state during infection
organism can't be found by culturing
may remain dormant for years, then suddenly emerge to cause disease (ex: herpes virus)
they're there but don't come out
pathogenicity
ability to be a pathogen
the ability of an organism to cause disease
defined in terms of infectivity and virulence - infectivity - virulence
you either are a pathogen or you're not
infectivity
how easily an organism causes disease
virulence
measure of how severe the disease is - ebola virus: highly virulent: fatal (70%) - rhinovirus: highly infective but low virulence: not fatal - all pathogens but varies in degree of virulence (low or high) - usually additive
virulence of organism
we are quanitfying this
measure of the degree or severity of disease - determined by genetic makeup of organism - infectious does = ID50 - rate of lethal infections - lethal dose
infectious dose = ID50
- determine number of microbes required to cause symptoms in half of an experimental group of hosts
lethal dose = LD50
different because asks the amount needed to kill the plant instead of just infecting it - number of organisms to kill 50% of hosts
microbe with low LD50
few microbes needed to kill organisms - highly virulent --> more virulent than high LD50
microbe with high LD50
more microbes needed to kill organism - need more microbes to kill
infection cycle
for disease to spread, pathogen must pass from one animal (organism) to another
route an organism takes to spread disease is known as the infection cycle - must go from one host to anotherin
infect spread via
direct transmission
indirect contact
indirect contact
contact with formites
horizontal
contact with formites
inanimate object through which pathogens can be relayed to host
ex) spraying groceries during covid - "left behind" bacteria/germs
horizontal transmission via vectors
carried by others
mosquitoes- yellow fever, malaria
reservoir for disease organisms - may not show disease symptoms - ie. animal, bird, insect that harbors the pathogen - rats were harboring bacteria --> bubonic plague
pathogens portals of entry
pathogens use portals of entry best suited to their mechanism
mode of entry depends on pathogen - food-borne pathogens - airborne pathogens - mucosal surfaces - wounds (skin) - parenteral route
food-borne pathogens
ingested through mouth --> colonize intestine
airborne organisms
infect through the respiratory tract
mucosal surfaces
mouth or other mucosal area
parenteral route
needle use / dwelling IV
injected into the organism bloodstream
virulence factors
individual characteristics (genes) of a pathogen that allow the pathogen to invade hosts and cause disease
all virulence factors enhance the disease-producing ability of the pathogen
pathogens can be distinguished from avirulent organism by the presence of virulence factors - help establish the organism in the host and alter host functions to cause disease
encoded by virulence genes - include toxins, attachment protein, capsules, other factors (avoid host innate & adaptive immune systems)
virulence factors enhance the disease-producing ability of pathogen
facilitate bacterial attachment and invasion
promote bacteria growth
promote disease symptoms
evade host defense mechanisms - allows better survival for bacteria
virulence genes
encode factors allowing pathogen to invade host
include toxins, attachment protein, capsules, other factors (avoid host innate & adaptive immune systems) - virulence factors
pathogenicity islands
section of genome - contain multiple virulence genes - often encode related function - eg. protein secretion system, toxin production
transferred as a block from other organisms (HGT) - often flanked by phage or plasmid genes - a lot of these are moved around by viruses - often have GC content different from rest of genome
microbial attachment
human body expels invaders - flush out invaders before they effect - mucosa, dead skin constantly expelled - liquid expelled from bladder - coughing, cilia in lungs - expulsion of intestinal contents
bacteria must adhere to host tissue - pili (fimbriae) - adhesins - capsules -biofilm
pili (fimbriae)
hollow fibrils with tips to bind host cells
hairlike surface appendages
protein at the tip binding to host receptor
adhesins
surface proteins bind host cells - any microbial factor that promotes attachment - anything that helps bacteria attach
afimbriate adhesins
bacteria surface proteins that promote attachment, but are not pili (bacterial hemaggulutinnin)
types of pili
both involved in attachment - different pili from different bacterial species have been classified based on phenotypes - type I pili - type IV pili
type i pili
adhere to mannose residues on host cell surfaces (static) - doesn't extend/retract - made of repeats of the pilA subunits (focus)
type iv pili
assemble on cell surface, dynamic (continuously assemble and disassemble)
motor allows bacteria motility
Pilin PilA is made as a preprotein and inserted into inner membrane
PilD is a peptidase that removes a leader sequence from a PilA preproteins prior to pilus assembly
PilT and PilF are NTP-binding proteins that provide energy for retraction and assembly
The secretin PilQ is required for the type IV pils to cross the outer membrane
type IV pili and motility
involved in gliding or twitching motility
spider man motility - bacteria make type IV pilus --> depolymerize --> pulls it back in through the cell - pilus has become shorter - bacteria has moved through the cell
twitching motility
other bacteria use non-pilus adhesins that mediate binding to host tissue: - streptococcus pyogenes: M protein - bordetella pertussis: pertactin
biofilms and infection
bacteria can attach to surfaces, forming a biofilm - make it more difficult to expel
biofilms play important roles in chronic infections (cystic fibrosis, dental plaque, chronic otitis media, osteomyelitis, chronic wound infections)
biofilms are often resistant to antibiotics - incomparsion to their platonic bacteria
toxins
exotoxins
endotoxins
cause damage to host cell
goal: release nutrients so they can consume
exotoxins
secreted out the cell --> impacts another cell (host cell)
kills host cells --> releasing nutrients
many microbes secrete exotoxins after attachment
bacteria secrete exotoxins (cytotoxin) - cytotoxin kills host's cells
endotoxins
only found in and made by gram- bacteria
non-protein toxic compound
hyper-activate host immune systems to harmful levels - cause endotoxic shock
present in gram neg. bacteria - part of LPS; released when gram neg. bacterial cell is broken down
dead gram- bacteria release endotoxin (lipid A) which includes effects such as fever, inflammation, diarrhea, shock, and blood coagulation
present in lippolysaccharide of outermembrane - lipid A released as bacteria die - causes massive release of cytokine from host cells - triggers fever, shock, and death
bacterial toxins
following attachment, many bacteria can secrete protein toxins called exotoxins
exotoxins fall into five broad categories
toxins subvert host function
5 categories of protein exotoxins 1) cell membrane disruption - cause host cell membrane leakage - bacterium pokes hole in membrane --> leakage - hemotoxin 2) block protein synthesis - target eukaryotic ribosomes --> not prokaryotic 3) block 2nd messenger pathways 4) superantigens over-activate the immune system 5) proteases cleave host proteins
cell membrane disruption
alpha toxin, cap and rim, stem
inhibit protein synthesis
shiga toxin, receptor mediated endocytosis via Gb3, mRNA, ribosome, NH3
activate second messenger pathways
stable toxin, Gtp --> cGMP, Na+, Cl-, H2O
alpha toxin
hemolysin
category 1 of toxin
the hemolytic alpha toxin is produced by straphylococcus aureus - forms transmembrane, seven-member pore in target cell membranes - can determine if patient has strain through blood plating
disrupts cells (red blood cells) by forming pores in the membranes
shiga toxin
disable ribosome
fits into category 2. of exotoxin
produced by shigella flexneri and e. coli O157:H7 (jack in the box microbe) - O157:H7 gastrotestional disease that was found in jack in the box
disrupt protein synthesis by destroying 28S rRNA found in ribosomes - disables ribosomes from translating proteinsA
AB toxin
b subunit
a subunitb
B subunit
binds to host cell - looks the same outside but can contain whatever - delivers A subunit to cytoplsm - delivery module (not toxic) - often 5 B subunits form a pore for A entry
A subunit
has toxic activity - ADP-ribosyltransferase - toxin to eukaryotic cells
ADP-ribosylating toxins
diphtheria toxin - category 2
cholera toxin - category 3
the 5B:1A toxin complex binds the ganglioside GM1 on host membrane lipid rafts
toxin is endocytosed
the phagosome containing CT is taken to the ER
the A1 subunit is removed from the B subunits and exported into the cytoplasm
the A1peptide attaches an ADP ribose to an amino acid within the host G protein that regulates adenlate cyclase
cyclic AMP levels rise and activate ion transport systems causing an electrolyte imablance
water from the cell follows the ions, causing diarrhea
diphtheria toxin - category 2
disrupts protein synthesis
made by corynebacterium diphtheriae
ribosylates elongation factor 2
blocks ribosome function; cell dies
forms pseudomembrane over trachea
chlorea toxin - category 3
get it from dirty, unfiltered water
made by vibrio cholerae - quorum sensing system
ribosylates to overactivate adenylate cyclase - adds a ribose
cAMP activates ion transport; water follows - water goes into gut
uncontrollable diarrhea - very water --> dehydration
anthrax toxin
made by Baccilus anthracis - good spore formers - has tried to be used as bioweapon
two active toxins - edema factor - lethal factor
edema factor
raises cAMP levels - cause fluid secretion and tissue swelling
lethal factor
cleaves protein kinase
blocks immune system from attacking
bacillus nathracis and anthrax toxin
protective antigen subunit PA is made as a single peptide
PA binds to host cell surface where a human protease cleaves off the orange part showing in part B
seven PA fragments autoassemble in the membrane to form a pore
the other two components of anthrax toxin- EF and LF- bind to the ring and are carried into the cell by endocytosis
EF and LF are expelled through the PA pore into the cytoplasm
Endotoxin - LPS
lipopolysaccharide LPS - only made by gram- bacteria - has LPS on outer layer - component of outer membrane - LPS contains endotoxing - activates inflammatory response - imefmune system recognizes it as foreign - can cause toxic shock (endotoxic) - barrier of outside and inside
effect of neisseria meningitidis endotoxin
some antibiotics lower bacteria # but this causes large release of LPS - little pools of blood under skin
protein secretion pathways
many pathogens use specific protein secretion pathways to deliver toxins - close to host cell or in host cell
proteins may not kill cell but redirect host signaling pathways in ways that benefit microbe
many secretory systems have structural resemblance to other innocuous systems
type 1, 2, ,3, and 4
type 1 secretion pathway (sec)
general secretion pathway
one step process of secretion
consists of 3 protions - ATP binding cassette protein - periplasmic protein: membrane fusion protein - outer membrane channel protein
hemolysin (alpha toxin) secreted through type 1 secretion system
type 2 secretion system
use pilus like extraction/retraction mechanism to push proteins out of cell (similar to type 4 pili)
modified for secreting proteins
can extend and retract
type 3 secretion system T3SS
injects proteins directly into host cell - hypodermic needle - one step injection (similar aspects to flagella motor)
injected proteins (type 3 effectors)
essential for gram- pathogens - e. coli, salmonella, yersinia pestis, pseudomonas aeruginosa and syringae
type 4 secretion system
type 4 similar to conjugation pilus
secrete both DNA and proteins
can extend and retract - motility - transport proteins or DNA either: - outside of cell or into target cell
type 3 effectors T3SE
salmonella injects over 13 toxins - induce tight attachment to host - cause host to engulf bacteria - induces actin rearrangement in cell - suppress host immunity - causes diarrhea in host - if we disable it would allow for many diseases to be controlled
crown gall
plant cancer
uncontrolled cell growth implemented by bacteria
T4SS - T-DNA
crown gall disease: creates a home for bacteria that they can only live in and has food production
T-DNA: T region - oncogenic genes - opine synthesis (specialized amino acids)
Ti plasmid - opine catabolism - virulence region: T4SS
beneficial uses of A. tumefaciens T-DNA integration
basis of how to make transgenic plants
agro-mediated plant transformation - efficient way of getting transformed plants
agro-mediated transformation is used for many different species including plants and fungi
disarmed Ti plasmids are used to introduce genes of interest into plant host chromosome
helper ti plasmid
need functions of helpers to help clone into smaller plasmid
divides plasmid into 2 because its really big
other virulence factors
siderophores, hormones, and ice nucleation
siderophores
bacteria produced iron catchers
steals iron from host
ice nucleation
certain infected crops fell more to frost damage
economic loss
plant pathogenic bacteria can catalyze ice formation by serving as biological ice nuclei
water remains in supercooled state to temps as low as -40c in absence of ice nuclei - need for ice to form around
presence of certain bacteria, freezing can occur at much higher temps like -2 to 10c
applications of ice nucleation
snowmax - freeze dried formulation that serves as source of ice nuclei for snow making (ski resorts)
frost ban - ice- p. syringae mutant thats sprayed on frost sensitive plants to out compete ice+ strains - niche displacement prevents damage
antibiotics
infections considered minor now killed most patients 60 years ago - importance of treating disease using antibiotics was recognized early 1940
what are they and where do they come from? - compounds produced by one species of microbe can inhibit growth or kill other microbes - soil dwellers and other bacterias in soil biome
discovery of antibiotics
usefullness of molds known to ancients
fleming found penicillin in 1929 - drug forgotten --> thought to be unstable
penicillin: bread mold paste - put paste on patients
howard florey rediscovered penicillin 1940 - purified penicillium
gerhard domagk - sulfa drugs (antibiotic discovery)
drug taken (prontosil) doesn't affect bacteria
drug metabolized by body into sulfanilamide
sulfanilamide is an analog of para-aminobenzoic acid (PABA)
drug stops bacterial growth by inhibiting the conversion of PABA --> folic acid
prontosil
screened for on agar plate didn't affect bacteria
found to be successful in animal trials
sulfanilamide
infects with synthesis
some antimicrobial agents are initially inactive until converted by the body to an active agent
PABA --> folic acid
paba is precursor to folic acid
folic acid not synthesized by humans, dietary supplement
bacteria don't transport folic acid - need to make from precursor - if they can't make it, they can't grow it
normal folic acid formation
P, PABA, G components go into enzyme --> synthesis --> folic acid
folic acid formation blocked
P, SFA, G components go into enzyme --> P doesn't fit properly --> no synthesis --> components go back out
selective toxicity of antibiotics
must affect target organisms - shouldnt affect humans or other animals
many have side effects at high concentration
drug should affect microbial physiology
side effects at high concentration
chloramphenicol interferes with ribosomes - high levels interferes with red blood cell making
can cause allergic response - antibiotics foreign substances in our bodies
drug affects microbial physiology
doesn't exist or is greatly modified in humans - peptidoglycan - differences in ribosome structure - prokaryotes vs eukaryotes - biochemical pathway missing in humans/animals
spectrum of activity
broad spectrum
narrow spectrum
source of antibiotics
broad spectrum
effective against many species - can affect your native bacteria - doctor doesn't need to know specific bacteria
narrow spectrum
effective against few or a single species - need to know what patients infected with (time cost)
source of antibiotics
most discovered as natural product
some modified by artificial means - increase efficacy, decrease toxicity to humans - synthetic chemotherapeutic agents - clinically useful but chemically synthesized
types of bacterial compounds
bactericidal
bacteriostatic antibiotics
batericidal
antibiotics kill target organism
bacteriostatic antibiotics
prevent growth of organism - cant kill organism - immune system removes infection
many drugs only affect growing cells - inhibitors of cell wall synthesis - only effective if organism is building new cell wall (penicillin) - have to take antibiotic until all cells leave stationary phase
minimal inhibitory concentration
lowest concentration that prevents growth -varies for diff bacterial species - test by diluting antibiotics
lowest concentration wit no growht - may have some living but non-growing organisms - plate liquid without antibiotic - no colonices = minimal lethal concentration