MODULE 3 - Water Microbiology and Public Health Flashcards
water environments are generally oligotrophic. What does this mean?
very low in nutrients
what does mesotrophic mean?
medium amount of nutrients
what does eutrophic mean?
high amount of nutrients
why are most microbes found in surface levels of water?
in water environments the number of nutrients conc. decreases with depth so most found at surface
what are allochthonous microbes?
microbes not usually found in that habitat i.e. microbes in freshwater washed in from soil around it
what are autochthonous microbes?
microbes where water is their natural habitat. These microbes usually motile, aerobic and gram-neg rods
why are most water microbes gram-neg?
because the water body supports the bacteria so they don’t need thick cell wall which could also inhibit them from moving through the environment
how are aquifers formed?
if water is able to form on an impermeable substance e.g. starts as rain, travels down through soil layer and settles on bed rock
soil layer acts as filter and takes out a lot of impurities and nutrients
different aquifer environments form depending on what the rock is made up of so environment forms a selection pressure on the microbes that inhabit it naturally
once aquifers are contaminated…
they are very hard to purify again
what kind of freshwater environment are rivers?
classified as oligotrophic but vary
if good nutrient supply, microbes similar to those in soil enviro will inhabit it
highly oxygenated
river microbes adhere to surfaces so they aren’t washed away
what are seven variables regional councils look at when grading waters?
turbidity
dissolved oxygen
total phosphorous
total nitrogen
nitrate/nitrite ratio
dissolved phosphorous
E. coli levels
what are the four main sources of river pollution?
natural
agricultural
industrial
urban
when are lakes in temperate zones stratified and why?
during summer cause top layer warmed up making it less dense
summer winds usually light so top layer not disrupted
in autumn surface layer cools i.e. more dense i.e. mixes with lower layers i.e. no stratification
what are the three factors required for lake stratification?
temperate zone
summer
lake deeper than 10m
what are the different layers of a stratified lake?
warm surface layer called epilimnion
cold bottom layer called hypolimnion
between these layers is a zone of transmission called the metalimnion
different microbes inhabit each layer
what kind of energy production occurs in the epilimnion (top layer)?
here u get primary production by oxygenic photosynthesis
oxygen limited solubility in water so very quickly as u move down through water u get area with no oxygen available for microbes to carry out oxygenic photsynth
what kind of energy production occurs just below the metalimnion/thermocline?
anoxygenic photosynthesis which is an anaerobic process and only occurs in summer as only then does angle of sunlight allow sun to reach this layer
so there is sunlight but no oxygen
what kind of production occurs in the mud sediment below the stratified layers of the lake?
bacteria similar to soil environments live here
anaerobic fermentation, sulfate reduction (releases H2S) and methanogenesis (produces methane)
these all prod gas and methane isn’t soluble in water so disappears as bubbles well H2S doesnt
in the metalimnion, what two parameters decrease rapidly?
oxygen concentration and temperature
so it is a zone of transition of rapid change for two of our parameters
what is the third parameter in a stratified lake and where is it concentrated the highest?
hydrogen sulfide
generated in sediment so high conc. in lower areas of lake and we lose a lot of it and it never reaches the metalimnion hence why metalimnion only a zone of transmission for two of our parameters
what is leibig’s law of the minimum?
the population of organisms in an ecosystem is determined not by total quantity of nutrients present but by the nutrients present in lowest amount relative to the organisms requirement
i.e. a microbe will grow until a nutritional requirement becomes limiting
what is shelfords law of tolerance?
regardless of nutrient supply there are limits to environmental factors below and above which a microbe cannot survive /grow
e.g. if u put microbe in enviro with lots of nutrients but it is outside optimal temp./pH/oxygen conc. it still cannot grow
what two laws govern how/if a microbe can grow in an ecosystem?
leibig’s law of the minimum
shelfords law of tolerance
what is eutrophication?
when lots of nutrients present. high organic material (high in N and P) means we get increased oxidation by decomposing microbes which uses up oxygen = anoxic conditions and proliferation and production of toxic products by anaerobes
can be temporary or permanent
what is the general process (incl successions) of eutrophication?
large input of nutrients e.g. sewage
O2 drops
bacterial numbers spike
ammonium spikes and then oxidised to nitrate (two-step process)
nitrogen products spikes
as everything returns back to normal except algae and cyanobacteria begin to proliferate
why are lakes more difficult to reverse eutrophication than rivers?
they aren’t moving bodies of water
lakes shallower than 10m vulnerable cause less capacity to absorb organic materials (why deep lakes are generally more pristine)
what can we do to help reverse eutrophication of lakes in the first place?
install buffer zones around farms and surface water
reduce livestock density
reduce fertiliser applications
plant more native trees in wetland areas
what are six adaptations that microbes have made to aquatic environments?
smalls cells (ultramicrobacteria); helps increase s to v ratio to deal with oligotrophic conditions
sheathed bacteria; provides protective function and helps them attach to objects
pigment production; protects from UV
motility (two methods); flagella or gas vacuoles: helps bacteria move to nutrients or away from hazards
magnetotactic bacteria; magnetosomes are membrane vesicles containing chains of iron oxide particles so bug can respond to geomagnetic fields of earth
utilisation of nutrients in low conc; increased uptake/high affinity enzymes, stalk (anchors bacteria to solids and increases SA)
what are gas vacuoles?
one of two methods of motility in aquatic microbes - gas vacuole made up of many gas vesicles arranged in randomly orientated bundles
what is the biological purpose of magnetosomes?
bacteria in N hemisphere swim northward and downward
bacteria in S hemisphere swim southward and downward
allows microbes to move towards sediments and towards areas of optimal oxygen conc.
how are magnetosomes arranged and what could they be used for in medicine?
orientated in parallel lines
generally 35-125nm
could be used as contrast in MRI scans or as biological probes
what are the seven factors which effect microbes in a marine environment?
O2 conc. (generally low in marine enviro)
salt content (ocean salty so marine microbes mild halophiles)
hydrostatic pressure (increases as you go deeper)
sunlight penetration (depends on season, latitude and turbidity)
temp. (decreases w depth)
pH
nutrients (marine is oligotrophic)
what are the three environmental extremes marine microbes are faced with?
high salt
high pressure
low nutrients
what are halotolerant microbes?
microbes that can withstand significant changes in salinity
what are halophilic microbes?
microbes that have an absolute need for high salt concentrations (often require sodium top maintain intracellular K+ conc.)
what is a saltwater wedge?
where both fresh and salt water (salt underneath cause more dense)
generally occur in estuaries and change w tide
due to change microbes living here highly adaptable i.e. mostly halotolerant
what are piezotolerant microbes?
tolerating pressure
what are piezophilic microbes?
dependent on pressure
most microbes deeper than 3000 metres are
pressure affects cellular physiology, deep sea microbes enzymes fold in different ways and sometimes outer membrane different to help cope
what type of gradient can be found around hydrothermal vents?
temperature gradient
they are also dark, pressurised and not much carbon
how do tubeworms survive in/around hydrothermal vents when there’s no organic material and they have no digestive system?
they have trophosome which is loaded with sulfur granules and bacteria
O2 and CO2 from seawater and H2S from vent absorbed in gill plume and then passed down to worm capillaries which then gets it to the bacteria living in trophosome
bacteria in trophosome are chemolithotrophic meaning they use reduce inorganic compounds as source of energy and electrons
what are the two reactions occurring inside tube worm?
sulfide oxidation (sulfide to sulfate); key part of this reaction is energy (ATP and NADH) produced which is used for second reaction
fixing carbon dioxide into organic carbon which is the food source for the worm and microbes inside
this means the chemolithotrophic bacteria are primary producers in thermal vent enviro
why is H2S a problem usually and how does the tube worm deal with it?
H2S blocks respiration by blocking O2 binding sites on haemoglobin (hb) and by poisoning cytochrome c
tube worm has modified free hb with high carrying capacity for O2, hb can also bind H2S, modified cytochrome c which H2S doesn’t inhibit
what are the advantages for the tube worm and the advantages for the bacteria in their mutualistic relationship?
tubeworm receives nourishment from reduced carbon
bacteria gets raw materials (O2, CO2 and H2S) and a safe environment
what is chemosynthesis?
passing energy up to higher organisms (I think usually through TCA cycle)
e.g. sulfide-oxidising bacteria to tube worm
what is photobacterium?
a chemolithotrophic luminescent bacterium which has mutualistic relationship with angler fish
what are the three substrates involved in the light-emitting reaction in luminescent bacteria?
long chain aldehyde compound (RCHO)
flavin mononucleotide (FMNH2) derivative
oxygen
explain the light-emitting reaction displayed by luminescent bacteria?
RCHO + FMNH2 + O2 —> FMN + RCOOH + H2O + light
catalysed by luciferase and energy requiring (2NADH and 1ATP)
because energy requiring bacteria control this reaction under auto induction system
what is the auto induction system used by bacteria for the light-emitting reaction?
bacteria prod substance called autoinducer and reaction proceeds when this builds up to certain conc.
i.e. once substance reaches critical level we get induction of luciferase enzyme and reaction proceeds
what are the advantages for the fish and what are the advantages for the luminescent bacteria?
fish gets light which it can use to repel enemies and attract food
bacteria gets safe habitat with constant environment and protection
how can we use bioluminescence as a biomarker?
can tag bacteria with luciferase enzyme to indicate toxin conc. solution
i.e. as toxin conc. increase luminescence decreases cause bacteria being killed by toxin
how do shipworms survive living off wood when they need nitrogen and wood only got C, H and O, also why is this relationship mutualistic?
has bacteria in gland which is obligatory marine bacteria and can degrade cellulose (with cellulase) and can fix nitrogen in dissolved sea water (with nitrogenase)
shipworm gets cellulose broken down and fixed nitrogen (two nutritional requirements)
bacteria gets safe and secure enviro
what causes algal blooms?
eutrophic conditions can lead to algal blooms which involves rapid increases of aquatic microbes leading to toxin production by these microbes which can be harmful
harmful algal blooms can impact on all layers of the food web
what is Alexandrium minitum?
protozoa involved in many NZ algal blooms
produces neurotoxin called saxitoxin which blocks sodium channels in nerve cell wall preventing normal nerve impulse
so sodium ions cannot be transported meaning decreased or no impulse propagation causing paralytic selfish poisoning
selfish beds have to be closed –> economic loss
how do we know what the fuck was happening thousands of years ago just by looking at a sediment core from the bottom of a fucking lake?
also what the fuck does this tell us about algal blooms?
can analyse eDNA from core to see which microbes lived in that environment
we can see from this that post European settlement is when we see bloom forming from cyanobacteria appearing in eDNA
prob means white people polluting
what is the waterborne disease infection cycle?
starts with infected person –> pathogens in faeces –> contaminated water source –> consumption of non-potable water –> susceptible person –> infected person
what is an example of a waterborne pathogen that is a bacteria?
campylobacter
causes gastroenteritis
source of contamination is human/animal faeces
what is an example of a waterborne pathogen that is a protozoa?
giardia intestinalis
cryptosporidium parvum
both cause gastroenteritis and source of contamination is human faeces
what are some examples of waterborne pathogens that are viruses?
Rotavirus
Norovirus
both cause gastroenteritis and source of contamination is human faeces
what is campylobacter?
gram negative, microaerophile, spiral rods, motile (flagella), optimum temp. 42 degs
C. jejuni most common bacteria cause of gastroenteritis in NZ
low infectious does, symptoms 2-5 days after infection and last 7-10
bloody (sometimes) diarrhoea, fever, abdominal pain
how can campylobacter lead to Guillain-Barre syndrome?
possibly by molecular mimicry i.e. structure of campylobacter LPS resembles components on human nerve cell
what is it about campylobacter that makes it such a good pathogen?
low infectious dose
cell shape and motility (helical shape, flagella) which help it get through intestinal mucus and into ep cells
adherence (adhesion proteins)
invasion mechanisms (penetrates intestinal mucous layer)
toxin prod (cytolethal distending toxin)
what is the key difference between the protozoa giardia intestinalis and cryptosporidium parvum?
giardia intestinalis is the flagellate subgroup (motile)
cryptosporidium parvum is the sporozoan subgroup (non-motile)
what are the key similarities between the protozoa giardia intestinalis and cryptosporidium parvum?
animal reservoirs - GI tract
widespread in enviro
cause frothy, watery diarrhoea, abdominal cramps
infection self limiting (in healthy adults)
polymorphic (takes on diff forms)
cysts resistant to chlorine at drinking water levels
cysts should be removed by modern water treatment plants
low infectious dose
antibiotic treatment available
describe the giardia lifecycle?
thick wall structure of cysts protect it from stomach acid
once in small intestine giardia comes out of cyst which results in two trophozoites
trophozoites adhere to epithelial cells in small intestine
form cysts again as they move down colon (poss due to cholesterol starvation) and then fuck off into enviro
how does giardia cause malabsorption?
villus blunting
describe the cryptosporidium lifecycle?
lifecycle involves both asexual and sexual repro
cysts are called oocysts and thick cell wall protects from stomach acid
once in small intestine they come out of cysts resulting in 4 sporozoites
these enter epithelial mucosal cells and undergo binary fission into 8 merozoites
merozoites start sexual reproduction resulting in oocyst formation
oocyst released back into enviro with thicker cell walls cause of sexual repro
top 7 differences between giardia and cryptosporidium?
motility (guardia trophozoites motile, crypto not)
attachment to mucosal cells (giardia adhere using sucking disc, crypto enter mucosal cell)
replication (guardia asexual, crypto both)
cysts vs oocysts (asexual gives rise to cysts, sexual to oocysts)
number of trophozoites (2)/sporozoites (4) after excystation
susceptible individuals (giardia can cause chronic infection, crypto can kill so is worse)
resistance of cysts to Cl- (crypto more resistant cause thicker layers in oocyst)
describe norovirus?
ss+ RNA
non-enveloped
caliciviridae
30nm
about 10 viral particles
common in closed communities e.g. cruise, hospo
all ages and no vaccine
describe rotavirus?
ds RNA
non-enveloped
reoviridae
75nm
about 100 viral particles
affects infants and children
vaccine available
slightly more dangerous than noro to kids cause has enterotoxin causing diarrhoea causing dehydration
what are the main similarities between norovirus and rotavirus?
both highly contagious, spread by contaminated food, water or contact, both cause vomiting and diarrhoea
why can norovirus be difficult to get rid of?
cause no lipid envelope making it less susceptible to alcohols and detergents (you have to use chlorine based detergent)
what are some sources of potable water?
surface waters - rivers, lakes, reservoirs
ground water - aquifers, spring water (via bores)
desalination of sea water
what is a catchment area (or watershed)?
area of land around a surface water source
what are the main types of natural pollution which cause contaminated water?
salts, minerals
animal or plant waste
dissolved gasses
run-off from peat bogs, silt
natural radioactivity, heavy metals
what are the main types of human pollution which cause contaminated water?
thermal (warmer water = more microbial growth)
pathogenic microbes (from human faeces)
organic matter from industries (can lead to O2 decrease)
toxic compounds (heavy metals accumulate)
eutrophication (leads to anoxic enviro)
detergents
radioactivity
water source quality is crucial to what?
quality of treated water
a good water source has absence of natural and human pollution (no agri, no industry, no landfills and no people)
what are the stages of water treatment systems?
protection of source water
sedimentation or screening (removes solid material) (raw water pH 6.4-6.7)
aeration (removes dissolved acid which improves odour and taste)
chemical flocculation with polyaluminium chloride (removes very fine particles e.g. microbes) (water pH decreases to 5.0-5.5 and after floc adjusted to 6.5 w lime)
filtration through sand
chlorination (pH decreased to 5.0-5.3 so this is more effective)
fluoridation
ultra violet light treatment (254nm) (after pH increased to 7.5 w lime for distribution)
explain the filtration through sand step to water treatment?
traps other particles and microbes that haven’t been trapped by previous processes
head indicators indicate pressure when filter gets clogged and so filter gets backwashed to clear it
membrane filtration more modern filtration to get rid of crypto oocysts better
why is chlorine great for treating water?
it available in many forms, cheap, easy to apply and leaves residual concentration
HOCl is the chemical mainly responsibly for killing microbes in chlorine (forms when Cl2 added to H2O)
what is the final residual conc. of chlorine in distribution systems?
0.2mg/L right through distribution system as this kills microbes and protects water
what is the conc. of fluoride in drinking water?
0.75mg/L
when could some problems occur for water treatment?
pollution of source water (can overload filters)
increased demand for treated water (increased vol going through systems that might not be able to handle)
out-of-date pipes and plant
biofilms in pipes
inefficient treatment programme
contamination after treatment
what is an example of an inefficient water treatment program?
heavy rain caused turbidity increase in Milwaukee so that treatment was ineffective leading to cryptosporidium outbreak
contamination occurred cause pathogen was present in untreated water source (cattle, abattoir, human sewerage), inadequate treatment process (recycling backwash water), spring rains and snow melt compounded problem, mechanical faults
what are NTUs?
nephelometric turbidity units (a unit for turbidity)
countries have regulations for maximal turbidity of drinking water e.g. <0.3 95% of time in NZ
US regulation was dropped from <0.5 95% of time to <0.3 95% of time after Milwaukee
what recommendations were made after campylobacter outbreak of Havelock north?
high standard of care must be embraced
protection of source water of paramount importance
maintain multiple barriers against contamination (this recognises more than one barrier between consumer and source reduces likelihood of contamination)
why do you want to take a water sample from the middle of a body of water?
since microbes grow near surface and sediment more commonly and you want your sample to be representative of a whole body of water
keep water cool and dark and test within six hours of sampling
what is biochemical oxygen demand (BOD)?
measures demand for O2 by bacteria during degradation of organic matter and indicates conc. of organic compounds in water
so when dissolved organic matter high, then biological oxygen demand is high (problematic as could deplete water O2 leading to anaerobic conditions)
why do you put a sample in 20 degrees in the dark and measure after 5 days when measuring biological oxygen demand (BOD)?
in dark cause no photosynthesis can occur and oxygen conc. remains constant or decreases, measure every day and compare with 5th day
what are some advantages of measuring biological oxygen demand (BOD)?
its been historically used so if we use this test we can compare to historical data
only measuring the biodegradable portion of organic compounds (only bit we interested it)
what are some disadvantages of measuring biological oxygen demand (BOD)?
five days is too long (this why they developed COD)
what is chemical oxidation demand (COD)?
potassium dichromate used to oxidise organic material to CO2 and H2O
amount of dichromate used up is proportional to the amount of organic material in that water sample
what is the advantage of chemical oxidation demand (COD)?
quicker than BOD
what is the disadvantage of chemical oxidation demand (COD)?
cannot determine between biodegradable and non-biodegradable so is an overestimation
why does BOD slightly underestimate biodegradable portion of water and why is this not really a problem?
cause reaction not complete in 5 days but all cause main thing is showing trends (comparing to previous data)
why cant we just look for pathogens with culturing when looking for faecal pollution in water?
many genera
special culture conditions required
some cannot be cultured e.g. norovirus
present in low numbers
once you find them its prob too late
what is the solution since we can’t look for pathogens when looking for faecal contamination in drinking water?
use an indicator organism to test for faecal contamination
if water contains indicator organism, there is faecal contamination and thus probably some waterborne pathogens
what is the ideal indicator organism?
bacterial inhabitant of only large intestine
non-pathogen (so must be of normal gut microflora)
easy to culture and identify
present in large numbers (more than the pathogen)
survives longer in water than pathogens but doesn’t reproduce in water
no indicator organism meets all 5 ideal requirements, but which family of microbes is close af?
coliforms - family enterobacteriaceae
aerobes and facultative anaerobes, gram-negative, conspire forming, rod shaped, ferment lactose within 48 hours at 35 degrees
all coliform except Escherichia coli can be isolated from soil meaning they would give false positive indicating soil and not just faecal matter
E. coli is a faecal coliform which ferments lactose at 44.5 digs and is our best indicator org
what are some disadvantages of using indicator bacteria?
could fail to detect disease-causing viruses
doesn’t detect risk from toxic algae
E. coli may have rapid die-off rates in certain waters (quicker than pathogen cause used to warm intestinal enviro not cold water, this main thing meaning it doesnt meet all 5 reqs)
viable but non-culturable (VBNC) indicator bacteria could lead to erroneous conclusions
what might cause indicator bacteria to go into viable but non-culturable state (VBNC) and why is this a problem?
injury to bacteria from chlorine, pH, nutrient shortage could cause it to go into VBNC
this is a problem as it might not make pathogens go into this state as well
why is clustering of microorganisms an issue for water treatment?
bacteria naturally aggregate together in water and so aren’t evenly distributed meaning sampling can be iffy
biofilm formation in distribution pipes and sleuthing of these can cause clustering
what are the main aspects of E. coli which make it a good faecal indicator in drinking water?
present in high numbers in faeces of all mammals
doesn’t multiply in environment outside host
detection methods inexpensive
simple, sensitive and specific
it survives long enough* under a broad range of drinking water conditions
*only bit that’s not perfect
what are the two main ways we can test for indicator bacteria?
filter (can catch large amounts of bacteria in a water sample, outdated method)
enzyme substrate coliform test (ONPG-MUG) (preferred method)
explain the the enzyme coliform test (ONPG-MUG)?
coliforms produce beta-galactosidase which acts on ONPG substrate and turns it yellow
E. coli produce beta-glucuronidase which acts on MUG substrate and turns it fluorescent blue (under UV light)
so if you see yellow, you know there are coliforms in the sample and if you see fluorescent blue you know the water sample has indicator (E. coli) meaning faecal contamination
clear = neg control
what are the acceptable levels of E. coli for drinking water?
<1 E. coli per 100ml
what are the acceptable levels of (oo)cyst for drinking water?
<1 (oo)cyst per 100L
with the ONPG-MUG, what does it mean if treated water has coliforms present and faecal coliforms absent?
means its probably just from a bit of soil so not disease causing but maybe some treatment issues
with the ONPG-MUG, what does it mean if treated water has faecal coliforms present?
drinking water not safe to drink as faecal contamination
what does it mean if treated water has non-pathogenic bacteria in water?
maybe water has a weird smell and turbidity and will be investigated but still safe to drink as it is faecal coliforms you need to worry about
