Microbiology - Outcome 1 Flashcards
what are bacteria?
prokaryotes
what are prokaryotes?
unicellular (single celled) organisms that lack a defined nucleus or other organelles
what are the 2 categories of bacteria?
eubacteria and ancient bacteria
what are eubacteria?
true bacteria
what are ancient bacteria?
they inhabit extreme environments and carry out unusual metabolic reactions
what is the morphology of a bacterial cell?
its shape and size
what are the three main groups that bacteria morphology can be divided in to?
- cocci
- bacilli
- vibrio and spirillum
what is the shape of a bacterium if it has a cocci shape?
spherical or oval
if a bacteria name has the prefix diplo- what would its arrangement look like?
it would be in pairs
if a bacteria has the prefix strepto- what would its arrangement look like?
it would be in an arrangement of chains
if a bacteria has the prefix staphylo- what would its arrangement be?
it would be in an arrangement of clusters
what is the shape of a bacterium if it is rod shaped?
bacilli
what is the shape of a bacterium if it is curved or has comma-shaped rods?
vibrio
what is the shape of a bacterium if it has thick rigid spirals (in wave shapes)?
spirillum
what are the common structural components that all bacteria have?
- a genome (DNA)
- ribosomes
- cell membrane
- cell wall
what is a bacterial cell wall composed of?
peptidoglycan
what are the two groups bacteria are divided into based on their reaction to the Gram Stain?
gram positive and gram negative
describe a gram positive cell wall
- are thick (20-80 nm)
- contain several layers of peptidoglycan
- contain teichoic acids
describe a gram negative cell wall
- are thinner (1-3 cm)
- contain less peptidoglycan
- have an outer membrane which surrounds peptidoglycan layer of gram negative cell walls
- outer membrane contains a unique component called lipopolysaccharide (LPS)
- LPS is known as an endotoxin - plays a role in infection
- lipid A is the toxic component of endotoxin
- the space between the outer membrane and the cell membrane is called the periplasmic space
describe what happens to a gram positive cell wall when it undergoes the gram stain
retain purple colour of grams crystal violet dye and so appear purple when viewed under microscope
describe what happens to a gram negative cell wall when it undergoes the gram stain
they do not contain crystal violet dye and instead stain the pink colour of the counterstain safranin
what is peptidoglycan and what is its structure?
- a large polymer
- it has a backbone of alternating sugar molecules known as NAG and NAM
- it has some short lengths of protein used as cross linkers
what does the cross-linking of proteins in peptidoglycan result in?
- very large peptidoglycan sac whose units are interconnected
- the sacs are very strong yet also elastic
- also porous - allows molecules to pass through sturcture
what can peptidoglycan be attacked by?
antibiotics and enzymes
how does penicillin attack peptidoglycan?
inhibits formation of protein cross linkers, so cell walls are weaker and easily damaged
how does the enzyme lysozyme attack peptidoglycan?
cuts sugar backbone of peptidoglycan molecule, so it damages cell wall and lyses bacterial cells (ie kills them)
what cell wall type is more susceptible to damage from enzymes and antibiotics and why?
a gram positive cell wall is more susceptible to damage because it contains more peptidoglycan than a gram negative cell wall does
the structure of peptidoglycan in a gram positive wall is similar to that of a gram negative cell wall except what?
there is a greater variety of peptide arrangements and cross-linking
what is the function of the cell wall?
- gives bacterial cell shape and provides protection from osmotic lysis
- pathogenic bacteria have components which contribute to their ability to cause disease ie. pathogenicity
what is the function of teichoic acids?
- gives gram positive cells a negative charge and contributes to they ability to cause the production of antibodies (antigenicity)
- also aids in attachment of bacterial cells to tissues
what is the function of LPS (endotoxin?)
- confers toxicity
-determines virulence ie ability to infect body
what us the function of an outer membrane?
- presents outer surface with strong negative charge which helps bacterial cell evade phagocytosis
- needs to allow passage of nutrients through porins (special protein channels)
what do bacterial cell membranes consist of?
mainly of lipids with saturated fatty acids and do not normally contain sterols such as cholesterol
what does the bacterial cell membrane do due to the cell not containing any organelles?
- the cell membrane takes on all the functions for which a double membrane is required in eukaryote cells
- eg site of respiration and in photosynthetic bacteria it is the site of photosynthesis
- site of biosynthesis of lipids and cell wall component eg peptidoglycan
- thought to be involved in coordination of DNA replication during cell division
what does selectively permeable barrier mean?
- regulates the passage of substances into and out of the cell
- allows free passage of water and small uncharged molecules
-larger molecules and charged molecules require transport systems
what receptors do bacterial cell membranes contain and what does this allow?
they contain receptors which allow the bacterial cell to respond to chemicals in the environment in chemotaxis
what are mesosomes and where are they observed and what is their role?
- in-foldings of the bacterial cell membrane
- observed in both gram positive and gram negative bacteria
- they are artefacts
what is the bacterial chromosome?
one large circular molecule of DNA which lies free in the cytoplasm in an area called the nucleoid
what are plasmids?
smaller, circular extra chromosomal pieces of DNA
what is the genome?
the total DNA content of the prokaryotic cell
what are inclusion bodies?
- distinct granules of organic or inorganic material contained in the cytoplasm
- usually reserve materials
what can some inclusion bodies be?
membrane bound vesicles in the cytoplasm containing photosynthetic pigments or enzymes
what are examples of cytoplasmic inclusion bodies and their functions?
glycogen granules
- reserve carbon and energy source
gas vesicles
- buoyancy in water
what group of bacteria notably form endospores?
gram positive bacteria
what are endospores?
highly resistant structures which enable bacteria to survive periods when the environment is hostile to growth eg exhaustion of an essential nutrient
they are NOT reproductive structures
what are flagella and what Is it composed of?
filamentous structures composed of the protein flagellin which are attached to the cell surface
what is the function of flagella?
to allow a swimming cell movement or motility
how do bacterial flagella move?
they rotate like a propeller
what are the 3 structures that a flagellum is composed of?
- the filament
- the hook
- the basal body
what is the function of the filament in a flagellum?
- largest part of flagellum
- extends from the cell surface to the tip of the flagellum
what is the function of the hook in a flagellum?
short curved segment linking the basal body to the filament
what is the function of the basal body in a flagellum?
anchors the flagellum and is composed of a system of rings
what are the two patterns of flagella distribution in bacteria and how is it determined?
- flagella distributed over the whole surface
- flagella arising from one or both poles of the cell
the pattern distribution is genetically determined and can be used to distinguish between bacteria
what are pili and what are they composed of?
- short, fine, hair like structures on the surface of bacterial cells
- shorter and more rigid than flagella
- composed of proteins called pilins
what are the two types of pili found?
- common pili
- f pilus
what is the function of common pili?
- involved in attachment - in nature usually surfaces as an animals teeth of ships hull
- determinants of bacterial virulence because they allow pathogenic bacteria to attach to the hosts cell and resist phagocytosis
what is the function of f plus?
- only produced in bacterial cells which contain a special plasmid called the f plasmid
- the f plasmic brings about genetic exchange (mating in bacteria) through a process called conjugation
what is a capsule?
- a polysaccharide
- a well organised layer outside the cell wall which is not easily washed off
what are the functions of capsules?
- aid in attachment of bacterial cells to surfaces
- aids in pathogenicity, protect bacterial cells from engulfment by protozoa and by phagocytosis
- protect bacterial cells against desiccation (dried)
how do bacteria reproduce?
- by an asexual process called binary fission
- results in the formation of two genetically identical cells from one original cell
- requires duplication of chromosome
- cell then elongates
- plasma membrane pinches inward at centre of cell
-when nuclear material been evenly distributed, cell wall thickens and grows inward to separate dividing cell.
what is the generation time?
the interval of time between one division and the next
what does binary fission as used by bacteria result in?
exponential growth and a growth curve forms
what are the phases of bacterial growth?
- lag phase
- log phase/exponential phase
- stationary phase
- death phase
describe the lag phase
- little growth occurs because cells re adapting to new environment
- shock of transfer may kill some organisms, but biochemical activity is intense as they store nutrients, synthesise enzymes and prepare for binary fission
describe the lag phase in cold temperatures
lag phase is longer due to proteins (enzymes) work more slowly
describe the log phase
- stage of active growth
- rate of growth accelerates until a constant rate of growth is reached and population is in ‘logarithmic’ or ‘exponential’ growth
- at some point growth will start to decline due to nutrients etc become depleted/ there is an increase of toxic materials
describe the log phase in cold temperatures?
- log phase is longer due to proteins (enzymes) work more slowly
- on growth curve, the log phase is shallower as rate of binary fission is slower
describe stationary phase
- growth rate here is zero (cell growth is balanced by cell death)
- most cells are resting
- microbial population at its maximum
describe death phase?
- number of cells dying is greater than the number of new cells being formed
- resources have decreased so much the population cannot be retained
what are psychrophiles?
- cold-loving bacteria
- cause food spoilage in fridge
what are mesophiles?
- live around room temperature and human body temperature
what are thermophiles?
- heat-loving
- contaminants of dairy produce, can withstand pasteurisation
how have psychrophiles adapted?
- accumulate a high concentration of solutes in their cytoplasm to prevent freezing
- requite proteins that can work more efficiently at low temperatures
how have thermophiles adapted?
- have thermostable proteins (do not denature when temperature rises)
- able to maintain structure of their membrane ie can’t be allowed to become too fluid
- need to prevent H-bonds holding DNA helix together from destabilising
how have acidophiles adapted?
- accumulate H+ ions as H+ ions diffuse into cell from acidic environment
- H+ ions are actively pumped out to maintain an approx. neutral internal pH
how have alkalophiles adapted?
- H+ ions tend to diffuse out of cell (moving down conc. gradient)
- have to be actively pumped into the cell to maintain an approx. neutral internal pH
what would happen if the adaptions to different pHs failed?
pH would affect charges on amino acids used to build proteins, can’t form chemical bonds needed to maintain
protein structure and the proteins would denature
what are macronutrients and what are they used for?
- major essential nutrients that are required in significant quantities
- P H S N O C
- used to synthesise carbohydrates, lipids, proteins and nucleic acids
- they repair cells and produce new cells
what are micronutrients?
other trace elements needed in very small amounts
- Mn Co Zn Ni Mb
can usually be obtained in sufficient amounts as contaminants of water
what are autotrophs?
- photosynthetic bacteria that typically use CO2 as sole source of cellular carbon
- CO2 is reduced to form organic cell constituents and energy is required to do this
what are heterotrophs?
bacteria that obtain carbon largely from organic nutrients ( eg sugars) which enter an energy-yielding metabolic pathway, usually resulting in production of CO2
what is glucoses dual role ?
- source of energy
- source of carbon for the assembly of other molecules
what are the 4 groups that micro-organisms can be categorised into depending on oxygen requirements?
- obligate aerobes
- facultative anaerobes
- obligate anaerobes
- microaerophiles
describe obligate aerobes
- require oxygen for respiration as oxygen is used as terminal electron chain in ETS
- without CO2 aerobic respiration can’t occur
describe facultative anaerobes
- aerobic bacteria that can respire in absence of oxygen by using alternative terminal electron acceptors such as nitrate or sulphur
describe obligate anaerobes
- need an oxygen-free environment
- find oxygen toxic because they lack enzymes needed to overcome the toxicity problem of ‘free radicals’
describe microaerophiles
- grow at optimally low oxygen concentrations
- use oxygen as the terminal electron acceptor in respiration but find high concentrations of oxygen toxic
what are antibacterials?
chemicals that are used to inhibit growth of bacteria
what does bacteriostatic mean and what are some examples ?
prevents the growth of a bacterium
- antibiotics (tetracycline)limit their growth by interfering with cellular processes such as protein synthesis, DNA replication, or other aspects of bacterial cellular metabolism
- chemicals include preservatives such as nitrites/nitrates and also lactic acid, used to prevent microbes in food from reproducing and causing food spoilage.
what does bacteriocidal mean and what are some examples?
kills bacteria
- chlorine-based disinfectants kill off original population of bacteria
- antibiotics (penicillin) inhibit cell wall synthesis
what must the environment provide for a bacterium to survive?
- essential nutrients
- optimal physical conditions
- absent of any bacterial agents
which parts of the body are populated by various microbial species and which parts ARE NOT?
- surface tissues eg skin and mucous membranes are populated
- internal tissues (organs, blood, muscle etc..) are free of micro-organisms
what is normal flora?
a population of micro-organisms that infect the body without necessarily causing disease.
what is microbial antagonism and how does it work?
- involves competition between micro-organisms
- they benefit the host by preventing the overgrowth of harmful organisms
- normal flora use all available space and nutrients, which stop more dangerous pathogenic microbes from becoming established
what happens if the balance of normal flora becomes unbalanced and what is an example of this and what causes it?
- disease can occur
- in human vagina - normal flora of bacteria (Lactobacilli)
- Lactobacilli maintains a pH of 3.5-4.5 and inhibits growth of yeast Candida albicans (cannot grow in acidic conditions)
- antibiotics kill off ‘friendly’ bacteria causing pH to become neutral, causes increase in C. albicans and causes thrush
what is symbiosis?
the relationship between the body and its normal flora
what is mutualism?
the symbiosis is beneficial to both the body and the micro-organisms (+/+)
what is an example of mutualism?
lactobacillus living in human vagina
- derives nutrients from environment
- produces acid to prevent overgrowth of other organisms
what is commensalism?
the symbiosis is only beneficial to the micro-organisms and the body gains no effect (+/0)
what is an example of commensalism?
aerobic bacteria Staphylococcus epidermis
- lives on conjunctiva of eye
- no benefit to humans as well as no harm
describe the bacterial populations on the skin
- Staphylococcus and Propionibacterium acnes ( P. acnes)
- skin is not favourable environment due to lack of moisture, salt from sweat and acidic pH of skin
- moister areas of skin tend to have largest microbial populations
describe the bacterial populations on the oral cavity
- Streptococci (capsule) species of bacteria found here
- availability of moisture, nutrients, suitable pH and temperature ideal for colonisation.
- microbes found in mouth will be aerobes and facultative aerobes within hours of birth
- once teeth emerge, anaerobes become established due to nature of gingival groove
- as teeth grow - various streptococci species attach to enamel using their capsules and adherence factors.
- this contributes to formation of plaque, tooth decay and gum disease
describe the bacterial populations of the large intestine (colon)
- colon has largest microbial population in the body
- majority of microbes recorded here are anaerobic
- main component is gram negative, such as E. coli
plants can form close symbiotic associations with microbes to what?
fix nitrogen
what is an example of plants forming symbiotic association with microbes?
- Rhizobium can establish a symbiotic relationship with legumes (peas, clover etc..)
- fix atmospheric nitrogen for use by the plant
- bacterium encodes large plasmid that is not used when it grows as a free-living organism in soil
- vital for infection of susceptible host plant
- bacterium infects root hairs and causes ‘nodules’ to form
- nodules reduce nitrogen gas to ammonia and other nitrogen-containing compounds
what is the equation for nitrogen fixation?
N2(g) –> NH3 / NH4+
what are bacteria and fungi principal decomposers of and what are they responsible for?
- decomposers of plant liter and animal carcasses
- responsible for nutrient recycling within soil - contribute to soil fertility
how do autotrophs (including photosynthetic cyanobacteria) fix and corporate CO2 into organic matter?
by using energy from sunlight
what happens to organic compounds (CO2) of autotrophs when they are eaten by larger microbes and then they in turn are eaten by other animals?
the organic compounds are digested and resynthesised
what form of nitrogen do higher plants utilise?
NO3- (nitrates) and NH4+ (ammonium)
how do microorganisms obtain sources of nitrogen?
vary their nitrogen source
- NO2- (nitrite)
- NO3-
- NH4+
- N2
- organic nitrogen
what determines the microbial population in a natural body of water?
by the physical and chemical conditions which are present
what conditions impair the microbial life in water?
- temperature
- salt levels
- light levels
- oxygen concentrations
what is the biggest population of bacteria found in water?
psychrophiles - some include photosynthetic cyanobacteria like anabaena species
what are some examples of pathogenic microbes that can be found in water?
- vibrio cholerae
- salmonella thyphi
how do UK domestic water supplies prevent water contamination?
by physically separating water supplies from the sewage supplies and the water is filtered and chlorinated to removed any pathogens
what is a transient population?
where bacteria will be added and removed from the original location
what bacterial species is directly beneficial to humans and what are the benefits of it?
E. coli in the human gut
- gains nutrients moisture and warmth
- produces vitamin K needed for blood clotting
(mutualism)
what are some bacterial species that is beneficial to humans outside of the body and how do they work?
- Streptococcus lactis and lactobacillus are used in cheese manufacture
- lactobacillus bulgaricus is used in yoghurt manufacture
- bacteria convert the sugar (lactose) in milk into lactic acid, causes milk proteins to denature and milk to curdle and thicken
what are examples of bacteria being genetically engineered to produce valuable chemicals?
- E. coli and lactobacillus have been engineered to produce large quantities of phenylalanine which is used in diet drinks
- microbes have been genetically engineered to produce human insulin and human growth hormone (hGH)
- insulin - E. coli given copy of human insulin gene, makes human insulin hormone - process carried out in yeast (fungi)
- hGH- previous source was cadavers, now fungi is used
how does tetanus affect the body?
- C. tetani spores excreted in faeces to soil
- when spores enter wound they revert back to vegetative bacilli that produce several toxins - tetanospasmin
- this toxin acts at synapses inhibiting the removal of acetylcholine (Act) by interfering with cholinesterase, enzyme which normally breaks down Ach
- with Ach left over in the synapse, synaptic impulses arise causing muscles to contract
- toxin provides sustained and uncontrolled muscle contractions of muscles and spasms throughout body
what is tetanus caused by?
Clostridium tetani - gram positive, anaerobic spore-former found in intestines of many animals
what is anthrax caused by?
bacillus anthracis - gram negative, spore-forming rod
- spores germinate rapidly on contact with human tissues and the bacterial cells produce toxins which account for most of the damage done by this bacterium
what are the three ways humans acquire anthrax?
- working with animal hides, leads to inhalation of spores and pulmonary anthrax
- consumption of contaminated meat, intestinal anthrax
- contact with spores from soil, anthrax of skin ie cutaneous anthrax
how does pulmonary anthrax affect the body?
involves haemorrhaging and severe blood infection and is usually fatal
how does intestinal anthrax affect the body?
- involves acute inflammation of intestinal tract
- initial signs of nausea, loss of appetite, vomiting, fever followed by abdominal pain vomiting blood and diarrhoea
how does cutaneous anthrax affect the body?
- begins as a raised itchy bump that resembles insect bite, develops into painless ulcer
- lymph glands in adjacent area may also swell
what causes typhoid fever?
salmonella typhi - gram negative rod which is highly resistant to environmental conditions outside body
- acid resistant - can survive low pH of stomach
how does typhoid fever affect the body?
- invades tissues of small intestine causing deep ulcers and bloody stools
- enters bloodstream an patient displays symptoms of increasing fever, lethargy and delirium
- appearance of rose spots on abdomen indicates that blood is haemorrhaging in skin
- bowel perforation and gall bladder infection may also occur
how can typhoid fever be treated but what may happen to some individuals who do recover?
use of antibiotics - chloramphenicol
however some patients who recover continue to harbour and shed organisms for years and such individuals are termed carriers
what is cholera caused by?
vibrio cholerae - gram negative bacterium
how does cholera affect the body?
- the bacteria enters intestinal tract in contaminated water or food
- susceptible to stomach acid, if ingested in sufficient numbers, enough will remain and colonise intestine
- secrete enterotoxin that stimulates a massive loss of fluid
what are symptoms of cholera?
- colourless watery stools
- wrinkling of skin
- sunken eyes
- muscular cramps
- thickening of blood
- urine production ceases
- shock and coma
how can cholera be treated?
- antibiotics - tetracycline - only kills bacteria
- replenishing of body fluids must be replaced by IV injection of salt solutions, consumption of glucose and salts or consumption of an oral rehydration solution (ORS)
what are opportunistic pathogens?
bacteria that do not usually cause disease in their normal habitat in a healthy person but which become pathogenic when they enter other habitats through broken skin, mucuous membrane
what is meant by an indirect detrimental effect of bacteria on humans and what is an example of this?
- indirect effects would be plant and animal diseases caused by bacteria that are not only a concern in terms of their possible impact on food safety but also on their economic impact if animals and crops have to be destroyed
- and example of this is Agrobacterium tumefaciens - causes crown gall tumours in plants.
- no direct effect to humans as not transmissible to humans yet commercial tree growers couldn’t sell trees with infection due to unattractive appearance
