121 Flashcards
pros of microbes on food
food materials may require microbiologival activity such as yogurt
cons of microbes in food
food spoilage
food borne disease
why dont we know the true diversity of sample by culture
as we cannot culture all bacteria from a sample
3 domains of life
euksryotes
archea
bacteria
eukaryote
include fungi,animals,plants
an organism that consists of one or more cells each of which has a nucleus and other well developed compartments
bacteria
constitute a large domain of prokarytotic microorganisms
range from spheres to rods and sprirals
archaea
similar to bacteria in size
intermediate between bacteria and eukaryotes
archea characteristics
presence of tRNA and ribosomal RNAs
peptidoglycan cell walls
linked lipids built from phytanyl chains
occur in unusual habitats
virus size
0.01-0.2 um
bacteria size
0.2-5 um
eukaryotes size
5-100um
yeast size
5-10um
protists size
50-1000um
algae size
10-100um
cell volume importance
high SA:V of smaller cells leads to fast nutrient exchange
smaller cells = faster growth
lots of cells=mutation risk
barrier function
separation of cell from its environment
selectively permeable barrier
controls movements of molecules in or out a cells (transport proteins)
functions of bacterial cell membrane
barrier function
selectively permable membrane
site of respiration/photosynthesis
energy conservation(proton motive force)
diplococci
2 cells in line
streptococci
chain of cells
clump of cocci
clumps of cells
gram stain
stain with crystal violet
add iodine forms a complex
wash with ethanol
counterstain with safranin
why does lysozyme lyse and penicillin kill archaea
lack peptidoglycan , have variety of cell walls including ppseudo-peptidoglycan
gram + cell wall
almost 90% peptidoglycan - thick layer- with a cytoplasmic membrane layer as well on the inside. many have teichoic acids embedded. negatively charged so surface is negative so can bind to divalanet cations like mg and ca
gram- cell wall
thin layer of peptidoglycan surrounded by an outer membrane composed of lipids, proteins and lipopolysaccharides and porins . only 10% peptidoglycan
peptidoglycan structure
only found in bacteria
rigid layer glycan strands linked by glycosidic bonds. crosslinked strands by peptides.
lysozymes break G-M bonds bursting the cell
fimbriae
short, thin, hair like, proteinaceous appendages ( up to 1000/cell)
recognition and attachment to surfacs
pili
similar to fimbriae except onger thicker and less numerous (1/10), required for mating
polar flagellum
flagellum at end of cell
monotricheous
1 flagellum
amphitrichous
1 flagellum at each on of cell
lophotrichous
cluster of flagella at 1 or both ends
peritrichous
flagellum spread over entire surface of cell x
bacterial cytoplasm
contains ribosomes and nucleoid, cellular inclusions sometimes, macromolecules( rna, proteins), organic materials eg carbs + lipids
inorganic ions
the nucleoid in bacteria
irregularly shaped region, is location of singular chromosome or sometimes 2
plasmids
usually small closed circular dna molecules
exist and replicate independently of chromosome
not required for growth and reproduction
may carry genes that confer selective advantage eg drug resistance
cellular inclusions
granules of organic or inorganic material that are reserved for future use
may contain:
glycogen
poly-b-hydroxybutyrate (PHB)
polyphosphate granules
sulpher granules
cellular inclusions magnetism
specialist bacteria with magnetosomes
contain iron in form of magnetite
use is to orient cells in magnetic fields
gas vesicles- cellular inclusions
used for buoyancy in some aquatic bacteria
advantages of endospores
survive 100-1000 years- produced under unfavourable conditions
highly resistible to heat, drying. radiation and chemicals very low water content
contain calcium dipicolinate
special proteins protect dna
calcium dipicolinate
binds free water and helps dehydrate cell
halophillic bacteria
250 million year old crystal salt
culture media definition
nutrient solution that provide all the elements required for growth
chemically defined media
the exact chemical composition is known
complex media
exact chemical composition not known made of digests fo complex material such as milk protein beef yeast etc
binary fission
how bacterial cell divides into 2
dna replication
cell elongation
septum formation
doubling time/generation time
time needed for a population to double
exponential growth
batch culture
culture that is grown in a closed system, no additional nutrients are added and no waste products removed during culture period
lag phase in bacterial population
time interval between inoculation and maximal division rate ( cells adjusting to new environment )
log phase in bacterial growth
bacteria growing exponentially , constant doubling, maximum growth rate
stationary phase in bacteria growth curve
bacteria no longer reproduces but are still alive , no nutrients left…
viable but nonculturable bacteria
bacteria in a very low metabolic activity state where they dont divide but are alive and have the ability to become culturable once resuscitated
(or they just cant grow on conventionalble media )
total count
non specific dye that stains all bacteria , in most cases dead cells too
viable count
uses fluorescent activity dyes which counts all cells with activity
culturable count
count cells that can form colonies on solid media or increase turbidity in liquid media
advantages of total cell count
easy and fast
disadvantages of total cell count
uses special microscope counting slide
does not differentiate between live and dead bacteria
heterotrophs
require organic molecules made by other organisms
autotrophs
co2 is principal carbon source
phototrophs
use light as energy sourve to produce atp
chemotrophs
oxidise organic or inorganic compounds
where do obligate aerobes grow
need o2 for growth so grow close to top of test tube
abligate anaerobes
cannot grow in presence of o2 so grow at bottom of a test tueb
facultative anaerobes
can grow with and without o2
aerotolerant anaerobes
do not need o2 but can tolerate it
microaerophillic
need o2 but tolerate it at a low concentration
mesophile
grow best between 20-40 degrees
most bacteria in our body are these
thermophiles
grow bet between 45-80 degrees
live in hot springs compost heaps etc
hyperthermophiles
grow best above 80 degrees
live in hot springs
facultative aerobe
not required but grows better with oxygen
a useful enzyme produced by thermophilic bacteria
taq polymerase from thermus aquaticus used for pcr
histology
study of animal and plant tissues
cytology
study of cells under microscope
light microscope mag res ect
x1000 magnification
200 nm resolution
brightfield
phase-contrast
fluorescent
electron microscope
1 x 10^6
resolution down to 0.2nm
scanning EM
transmission EM
resolution
separation distance at which 2 objects in an image can be apart and still distinguished as separate
whats a host
organisms that supports growth of viruses, bacteria and parasites
pathogen
organism that causes disease, by impairing or interfering with the normal physiological activities of the host
pathogenicity
the ability to cause disease
virulence
the degree or intensity of pathogenicity (determined by toxicity and invasiveness)
infection
bacteria persist in host without necassarily causing tissue damage
disease
overt damage to the host, parts of body cannot fulfill their normal function
why did miasma theory sometime works
it was based on theory of bad smells causing disease so lots of cleaning and diverting of sewage was done and it prevented cholera. Dr. William Farr was convinced by this theory and that cholera was transmitted by air
robert koch
1843-1910
established germ theory
tried to prove specific microorganisms caused disease (kochs postulates)
developed simple methods for obtaining disease in pure culture
kochs postulates
infecting mice or collecting microorganisms from dead animals
led to discovery of causes for anthrax, TB and cholera
opportunistic pathogens
only cause serious disease when host defences are impaired
e.g. pseudomonas aeruginosa
often exist in envrionment
primary pathogens (obligate)
capable of causign diseae in absence of immune defects
e.g. syphilis- treponema pallidum
need to cause disease to survive
human-human and animal-human transmission
reservoirs
bacterial pathogens need at least 1 reservoir
such as other humans, animals and environment
reservoir examples for anthrax
agent= bacillus anthracis
reservoir in livestock and soil
reservoirs examples for legionnaires disease
agent= legionella pneumophila
reservoir in high moisture environments like air con
direct host-host transmission
airborne= aerosols like coughing
body contact like kissing and touching
indirect host-host transmission
vector-borne- living organisms like arthropods(insects,tics), vertebrates (rats,dogs)
non living- food, water, soil, fork, bedding, surgery instruments
colonisation
establishment of a stable population of bacteria in the host
body naturaly has this- microflora
pathogen must be able to compete for nutrients/surface attachment sites
why do bacteria adhere to tings
to overcome flushing mechanisms
e.g. streptococci to tooth surface and staphylococci to plastic catheters
how do bacteria adhere to things
association- involves non-specific forces like charges/ hydrophobicity
then adhesion- specfic host receptors. can form biofilm from aggregation which can disperse and spread
adhesions
fimbriae and pili
capsules and slime layer
flagella
(lipo) teichoic acids (gram+)
host receptors for adhesion include
blood group antigens
extracellular matric proteins e.g. fibronectin, collagen
invasion of bacteria
some bacteria penetrate through/between cells
some invade epithelial and some invade phagocytic cells
invasion of bacteria using lytic compounds
often accomplished by lytic compounds that attack the host tissue
e.g. collagenase
also determined by evasion of host defences
invasins
virulence factors
resisting phagocytosis
bacteri produce structures preventing effective contact. capsules, special surface proteins
bacteria surviving inside phagocytic cells
often very pathogenic bacteria
antibody avoidence
capsules
antigenic variation- switch between different types of surface structure
sometime degradation of antibodies
avoidance of complement
capsules can prevent complement activation
lipopolysaccharides (gram - ) sometimes hinder pore formation
how does tissue damage occur
irone acquisition
direct effect of bacterial toxins
indirect effects of bacterial toxins
induction of autoimmune response
nutrient acquisition- iron uptake
essential element for bacteria growth
bacteria express high affinity iron uptake systems to get the iron as iron levels too low in tissues
siderophores- bind iron with high affinity
direct binding of iron transport proteins like transferrin
exotoxin
act on specific targets e.g. protein synthesis
made by gram + and -
protein
secreted by living bacteria
heat labile
highly immunogenic
potential lethal
endotoxins
(LPS) bound to cell
action is indirect- activates many host systems that cause damage
made by gram-
lipopolysaccharide
part of cell membrane
heat stable
weakly immunogenic
lethal at high concs
human exposure to exotoxins
ingestion of preformed exotosin e.g. food poisoning
colonisation of mucosal surface or tissue like cholera
colonisation of wound- e.g. clostridium perfringens grows in wounds or abscess causing tissue degradation
whys is called endotoxin
as they are bound to cells and released when bacterium lyses or during cell growth
activates host systems leading to fever, shock, blood coagulation, inflammation
prokaryotes in summary
circular chromosome with plasmids
fimbria adhesion
capsule adhesion/evasion
no nucleus
no membrane enclosed organelles
rapid reproduction
binary fission
benefit or harm- mutualist, commensal, pathogen
3 domains of protists
prokaryotes- bacteria and archaea
eukaryotes- eukarya
4 eukaryote supergroups
excavata
SAR
archaeplastida
unikonta
ER simple
protein glycosylation
membrane factory
lipid synthesis
photoautotrophic
‘plastids’
green plastid= chloroplast
photosynthesis
algae- some have a cell wall