microbiology Flashcards
Which five agents cause infection?
- viruses
- bacteria
- fungi
- parasites
- prions (mis-folded proteins)
Which three factors allow an infection to occur?
- barriers to infection
- environment
- growth factors
What are viruses?
- small, metabolically inert structures which need living host cells to replicate inside
- infect animals, plants and bacteria
- different shapes
What are the three major components of a virus?
- genetic material (DNA/RNA)
- protein coat (capsid)
- lipid envelope derived from the host cell (some viruses)
Describe a T4 bacteriophage.
- genetic material but no organelles (rely on host’s organelles to reproduce)
- use surface protein(s) to bind to cell + insert genetic material into it
- formation of biologicalvirusesduring the infection process in target host cells
What are bacteria?
- unicellular, cell membrane, cell wall
- genetic material is free DNA (asexually reproduce)
- some move using flagella and attach via fimbriae
How can bacteria be classified?
- shape → coccus, spirillum, bacillus
- ability of cell wall to take up stain; G+VE/G-VE (determines structural strength → survival in environment)
- name → Genus species (italics/underlined)
What are the four stages of gram-staining and the results that we should receive for a Gm+VE and Gm+VE cell?
• Stage 1: primary dye
- reagent: crystal violet
- colour (G+VE): purple
- colour (G-VE): purple
• Stage 2: trapping agent
- reagent: iodine
- colour (G+VE): purple
- colour (G-VE): purple
• Stage 3: decolouriser
- reagent: alcohol/acetone
- colour (G+VE): purple
- colour (G-VE): colourless
• Stage 4: counter-stain
- reagent: safranin/carbol fuchsin
- colour (G+VE): purple → thick peptidoglycan cell wall retains primary stain
- colour (G-VE): pink → thin peptidoglycan cell wall does not retain primary stain and is protected by lipophilic outer cell membrane
Describe fungi.
- own eukaryotic kingdom → cell membrane, cell wall, nucleus and cytoplasmic structures
- reproduce sexually + asexually
- can be yeasts (Candida albicans) or molds (Aspergillus fumigatus) or diamorphic (switch between both forms)
What are the three types of parasite? Give an example of each.
- ectoparasites → live outside host body i.e. fleas, ticks (type of spider)
- endoparasites → live inside host body i.e. worms
- epiparasites → parasite which lives on another related parasite i.e. malaria
What are the two general classes of human parasite?
- unicellular organisms (protozoa)
- parasitic worms (helminths)
What type of life cycles do parasites have and what are many human infections classed as?
- often complex life cycles which involves other animal(s)
- “accidental”
Describe prions.
- smallest infective agent → proteinaceous infectious particles which lack nucleic acid (non-living)
- proteins fold abnormally and accumulate, mainly in neural tissue → very difficult to destroy
- concerns over cleaning surgical instruments
How do different viruses infect host cells for different lengths of time and what does this mean?
- some stay dormant in host with symptoms re-appearing months/years later
- others immediately leave host cells and symptoms rapidly appear
Give examples of viruses.
Hint - liver one with the alphabet
- chickenpox virus/varicella → can lay dormant for decades, emerging to cause shingles
- rhinovirus → infects hosts for days, causing a cold
- hepatitis C → chronic liver infection over years
- severe → ebola, SARS coronavirus (severe acute respiratory syndrome)
- variable → flu (different viral influenza strains)
- mild → rhinovirus (causes the common cold), herpes simplex (STI that causes cold sore/genital sores)
Give examples of bacterial diseases.
Hint - ‘m’ for blood, ‘b’ for heart, ‘c’ for skin and ‘s’ for throat
- meningococcal sepsis → bacteria enter blood and multiply, damaging walls of blood vessels causing bleeding into skin and organs
- bacterial endocarditis → infection of inner lining of heart
- cellulitis → common, serious bacterial skin infection
- streptococcal throat infection → at the back of the throat
Give examples of mild and severe fungal infections in immunocompromised patients.
(Hint - mild → TAR - THG person, talcum powder and the circles on potatoes, severe → IC)
• mild - thrush - athletes foot - ringworm • severe (in immunocompromised): - cryptococcal meningitis → HIV patients - invasive candida (infection caused by yeast) → ICU
What is parasitic disease giardia?
- bloody diarrhoea, caught from drinking infected water, may be seen in stool under a LM
- cyst formed aids survival + spread
- reproduces by binary/multiple fission or sexually (or both)
- individual protozoon is hermaphroditic (an organism which produces gametes normally associated with M and F sexes)
What is the parasitic disease malaria?
- one of the biggest killers worldwide
- complex life cycle
- reproduces in female anopheles’ mosquito and infects human RBCs
What are the four types of malarial parasite and which problem has arisen from different strains in different areas?
(Hint - P. FVOM)
- Plasmodium falciparum (most common)
- P. vivax
- P. ovale
- P. malariae
- different types occur in different geographical areas w/ some overlap; resistance to treatment now problem
What are the different types of helminths (parasitic worms)?
(Hint - C(T), T(F), N(R) and last example rhymes with colitis and made of elephants)
• cestodes (tapeworms) → segmented, flat - fish, pork, beef tapeworms: can cause malabsorption or in variety of chronic diseases
• trematodes (flukes) → unsegmented, flat, oval worms
- lung flukes, liver flukes, pancreatic flukes, intestinal flukes, blood flukes (i.e. schistosoma)
• nematode (round worm) → biggest family which is cylindrical, with digestive tract, lips, teeth and anus
- (diarrhoea/malabsorption) e.g. elephantiasis caused by filarial worms asymptomatic or syndrome elephantiasis (severe swelling of limbs)
What is the helminth (blood fluke) schistosoma, how does it travel and what are its symptoms?
- clinical disease commonly found in children who play in water → socioeconomically devastating
- goes from: fresh water snails → flukes penetrate skin → adult worms migrate to veins → worms live + lay eggs for rest of host’s life → eggs penetrate vascular endothelium, enter bladder/gut + excreted in urine/stool to freshwater
- symptoms → diarrhoea, fever, abdominal pain, hepatosplenomegaly/cystitis, urethritis, eventually bladder cancer
What are examples of diseases caused by prions (misfolded proteins)?
(a CV is BS …K? where only 1 + 2 haven’t gone paagal and ‘S’ for in sheep)
- CJD (Creutzfeldt-Jakob disease) – fatal, degenerative neurological disease - transmitted via contaminated hGH, surgical instruments and corneal grafts
- variant CJD - typically occurs in young adults
- BSE - another form of ‘mad cow disease’ that occurs in cattle
- scrapie – virus that occurs in sheep
- kuru- similar to vCJD (‘mad cow disease’) thought to be spread by cannibalism
Why do pathogens need nutrients and how can microbes inhabit so many possible environments?
- to meet energy needs and provide necessary elements (CHON) to synthesise building blocks
- successful in obtaining nutrients from variety of sources
Why does growth and reproduction of microbes require energy?
- synthesis of new molecules, main building blocks (protein, DNA, RNA) and precursors (i.e. FAs, AAs, nucleic acids, carbohydrates)
Define metabolism.
all biochemical reactions that take place inside the cell to maintain its viability, growth and reproduction
What is a catabolic pathway and an anabolic pathway?
- catabolic: break down molecules to produce energy (larger substrates, smaller products)
- anabolic: use energy to combine small molecules into macromolecules (energy + source of elements - C)
What is the organism’s:
a) energy source if the name includes ‘photo?’
b) energy source if the name includes ‘chemo?’
c) carbon source if the name includes ‘auto?’
d) carbon source if the name includes ‘hetero?’
e) electron donor source if the name includes ‘organo?’
f) electron donor source if the name includes ‘lito?’
a) light
b) chemical compounds
c) CO₂
d) organic compounds
e) organic compounds
f) inorganic molecules
If an organism lacks ability to produce essential compound in body then how must it be obtained?
consumed in diet
What are E. Coli mostly composed of and which compounds act as catalysts in synthesis processes?
- water
- other compounds e.g. vitamins
What is passive diffusion compared to active transport?
- passive diffusion: no energy needed, driven by conc. gradient.
- active transport: requires energy, requires receptors and work even against conc. gradient
What is group translocation?
less energy, involved phosphorylation of molecule
What are the physical requirements of microbial growth?
Hint - TOWPLP
• temperature → affects protein structure + fluidity of cytoplasm and cytoplasmic membrane, requirements can differ (i.e. thermophiles) • water → all bacteria require ‘wet’ habitat as drying kills them - pH - osmolarity • oxygen • pressure • light • physical space availability
What is optimum growth temperature?
temp at which metabolic activity is at its peak and thus growth rate highest
What is ‘water activity’ (Aw) and how does it affect bacterial growth?
• vapour pressureof a sample divided by that of pure water at sametemp
- low Aw → high solutes conc. (hypertonic solution)
- bacterial growth correlates to Aw more accurately than absolute water content
- usually required at least 0.8
How does pH affect microbe growth?
- high/low pH inhibit microbial growth
- acidic conditions of some body parts are defence mechanism (e.g. stomach and vagina)
- acidophiles can tolerate acidic conditions and alkalinophile lives in alkaline media (i.e. soil and alkaline water like Vibrio cholera)
- interacellular pH usually near normal
What is an:
a) obligate aerobe? (Hint – oxygen is obligatory)
b) anaerobe? (Hint – an-aerobes)
c) facultative anaerobes? (Hint – facultative means optional)
d) microaerophiles? (Hint – micro means a very small amount of tolerance)
e) aerotolerant microbe? (Hint – aerotolerant can survive without oxygen and can tolerate it too using enzymes)
a) requires O₂ for energy-production (respiration)
b) do not use O₂ for energy-production
c) can survive with or without O₂
d) can tolerate oxygen levels from 2-10% (limited ability to detoxify hydrogen peroxide and superoxide radicals)
e) anaerobes but have some enzymes that detoxify oxygen’s poisonous forms
What are the defence mechanisms of the body?
Hint - SMS-BIC
- skin
- mucus membranes
- stomach acid
- commensal microflora
- immune system → innate or learnt
- behaviour (e.g. good hygiene practices)
