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71 Cards in this Set

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What are the 2 methods used to kill bacteria?
1)Physical methods:
-heat
-radiation
-filtration

2)Chemical methods:
-antiseptics/disinfectants
-antibiotics
How does heat kill bacteria?
-denatures proteins, DNA
-melts lipids
-moist heat is better than dry heat b/c of faster penetration and better at protein denaturation

*used because easy to perform*
What is pasteurization?
-mild heat used to reduce the number of bacter
-doesn't kill all bacyteria present and doesn't kill lspores
-delays spoilage because fewer bacteria in product
What is the safety margin used by canning industries?
-canning companies use heating conditions designed to kill 10E12 spores
-therefore all pathogenic organisms are killed
What to forms of radiation are commonly used in sterilization?
1)UV light: Cross links thymines in DNA, causes lethal mutations
-but has poor penetration props, good for surface only

2)Ionizing radiation(X and Gamma rays):
-dislodges electrons
-good penetration
-commercial uses only
What is Filter Sterilization?
-mechanical removal of bacteria (no kiling)
-used for heat sensitive liquids and gasses
-used in pharmaceuticals, growth media additives, surgical gasses, beverages
What is the purpose of chemical control methods?
-to reduce bacterial numbers to safe levels
-complete sterility may or may not be achieved
-use of germicides
-intended for use on surfaces
What are 2 types of germicides?
1)Antiseptics: for use on biological surfaces (eg: skin)

2)Disinfectants: for use on inanimate surfaces
What are some general features of germicides?
-more than 14000 different formulations from 300 diff chemicals
-act by denaturing proteins, nucleic acids or degrading lipids
What does the efficiency of germicides depend on?
-conc used
-time of exposure
-presence of organic material
Give 8 examples of disinfectants and antiseptics
1)Phenols: -denatures proteins, disrupts membranes
-disinfectant (eg: lysol)

2)Alcohols: -dissolve lipids
-anitseptic

3)Heavy Metals: -denatures proteins by binding -SH and -OH groups
-antiseptic (eg:dandruff shampoo)

4)Peroxides: -oxidizes lipids, proteins
-antiseptics (eg:anti acne cream)

5)Halogens: -denatures proteins & nucleic acids
-antiseptic (eg:iodine)
-disinfectant (eg:chlorine)

6)Quaternary ammonium compounds: -Cationic detergents based on NH4+, disrupts membranes
-antiseptic (eg:mouthwashes)

7)Gaseous agents: -denatures proteins and DNA by crosslinking organic groups
-disinfectant (eg:ethylene oxide, propylene oxide)

8)Chemicals as Preservatives: -used on food products to prevent microbial growth
-disinfectants (eg:organic acids, nitrates)
What are some sources to antibiotics? 3 of them.
-most are natural metabolic byproducts of soil microbes

-some are compounds synthesized in labs

-some are semisynthetic (chemically converted natural compounds to form a new antibiotic)
What are 3 general characteritics of antibiotics?
1)Selective Toxicity: -must kill bacteria without harming host
-expressed as therapeutic index (TI)

2)Cidal vs Static Effect: -Bacteriocidal=kills bacteria
-Bacteriostatic=inhibits growth

3)Spectrum of Activity:
-narrow vs broad spectrum
What is the therapeutic index(TI)?
Dose which is toxic to host/Dose required to kill bacteria
What are the 5 ways that antibiotics work?
1)Block DNA/RNA Synthesis
-eg rigamycin

2)Block protein synthesis
-eg erythromycin

3)Competitive metabolic inhibitors
-eg sulfonilamide

4)Disrupts cell membrane function
-eg polymyxin

5)Blocks peptidoglycan synthesis
-eg penicillin
What are the principles of combination antibiotics? 2 of them
-wants to avoid antagonism (one drug preventing the action of a second drug)

-wants to achieve synergism (enhanced effects vs either drug alone
What are some side effects to antibiotic use?
1)Toxic to host

2)Allergic reactions (eg: penicillin)

3)Disruption of normal flora (eg: messes up gut boys and causes diarrhea)
What is bacterial antibiotic resistance?
-when a normally senstive bacteria is no longer affected by antibiotic
How do we know if bacteria are resistant?
1)in vivo- patient is unresponsive to antibiotic therapy

2)in vitro- labs test for growth of bacteria in presence of the antibiotic
-determines: how resistant, correct antibiotic and proper dosage
What are 2 ways of measuring resistance?
1)Disk Diffusion Method:
-put disc of antibiotic on infected plate, measure growth of inhibition

2)Tube Dilution Method
-if growth occurs at high antibiotic concentration, then bacteria is resistant
-can find Minimal Inhibitory Conc (prevent growth)
-can find Minimal Bactericidal Conc (kills bacteria)
What are 3 mechanisms used to become resistant to antibiotic?
1)Direct inactivation of antibiotic
-bacteria produces enzymes which break down antibiotic

2)Prevent uptake or promote excretion of anitbiotic

3)Alteration of antibiotic target:
a)overproduction of target overwhemls antibiotic
b)mutated target no longer recognized by antibiotic
How is resistance acquired by bacteria? 2 of them
1)Spontaneous mutation in DNA (gives an altered target)
-low freq

2)Acquire new resistance gene (gene for inactivating enzyme)
-plasmids may carry multiple resistance genes, passed on from bac. to bac.
What factors lead to the spread of resistance? 3 of them
1)Clinical overuse of antibiotics

2)Lack of patient compliance (ie:failure to take drug as prescribed). Therefore not all bac. killed and survivors develop reistance.

3)Widespread nontherapeutic use of antibiotics:
-gut basteria constantly exposed to antibiotics
-develops reservoir of resistant bacteria

**Key Points:
-if antibiotics are continously in enviro, then bacteria is constantly exposed, therefor continual selective pressure for resistant strains**
What would you do to limit the developement of resistance? 5 of them
-promote responsible clinical use of antibiotics
-restrict use of some antibiotics in human and animal health
-rotate use of different types of antibiotics
-use combo antibiotics to slow devel of resistance
-better public education in responsible antibiotic use
What are some new sources of antibiotics?
1)New soil, water bacteria and fungi continuously being screend to find undiscovered antibiotic

2)Rejuvenate existing antibiotics: may be lethal to bac again

3)Novel nonmicrobial sources of antibiotics

4)Rational drug design
-pick specific bacteria and target it
-make a chem which kills it
-takes about 10 years to do
What is a virus?
-a non cellular infectious agent
-nucleic acid usually surrounded by a protein coat
-metabolically inert
-reproduce only within a living host cell
What are some key ways in which viruses differ from liveing cells? 5 of them
-much smaller in size
-simple (non-cellular) structure and organization
-contains either DNA or RNA, but never both
-not capable of independent reproduction
-2 distinct phases in life cycle (depends on whether inside or outside of the cell)
What is host range?
-range of organism used by virus as host
-viruses have host specificity
-host specificity determined by receptors on host cell and presence of suitable metabolic machinery in host cell
What is the structure of viruses?
a)has many types of nucleic acid
-ds DNA
-ss DNA
-ds RNA
-ss RNA ('plus' orientation = mRNA)
-ss RNA ('minus' orientation = anit mRNA)

***nucelic acid can be circular or linear
virus will ONLY HAVE ONE TYPE of nucleic acid***

b)Has 3 types of protein coats:
1-Helical
2-Icosahedral
3-Complex

c)Presence or absence of envelope
What is a capsomer?
What is a capsid?
-indiviual protein subunits which comince to make a complete shell for viruses
What are the 3 basic shapes of protein coats for viruses?
1)Helical: capsomeres coiled in rod shaped spiral form

2)Icosahedral: capsomers in a geometric conficuration of 12 corners and 20 faces ("geodesic dome")

3)Complex: helical 'tail' attached to icosahedral head (eg: bacteriophage)
What's the difference between a naked and and enveloped virus?
Naked virus:
-NA core enclosed only by capsid
-capsid may contain spikes (helps bind to receptors)

Enveloped virus:
-core + capsid + outer lipid envelope
-spikes associated with envelope
-parts of envelope are teaken from host cell plasma membrane as virus exits from host cell
What 3 factors are taken into account when classifying viruses?
1)Type of nucleic acid

2)Type of protein coat

3)Presence or absence of envelope
Go over the life cycle of viruses.
1)Adsorption: virion attaches to host cell

2)Penetration: intact virion (or it's NA) enters the cell

3)Uncoating: release of viral NA from capsid (skipped if NA alone penetrates)

4)Gene Expression: viral genes expressed to produce more viral NA and viral proteins

5)Assembly: new intact viruses assemble inside host cell

6)Release: virus particles exit host cell
What is a virion?
-a virus outside of the host cell
What is Lytic infection?
-lysis of bacterial host cell and release of new virion
What is lysogenic infection?
After attachment and penetration:
-vireus genome recombines into bacterial chromosome (prophage)
-phage genome replicates as part of chromosome
-all bacterial daughter cells carry virus in prophage state

**prophage may bust out of chromosome and enter lytic pathway**
What are the 2 possible outcomes of bacteriophage infection?
1)Lytic infection

2)Lysogenic infection
T/F Some viruses can act as antibiotics.
T
-viruses attack bacteria
-problem is controlling the virus afterwards
What steps are involved in adsorption?
-requires receptors on eucaryotic cell membrane
-receptors are recognized by viral spikes (proteins)
-spike+receptor interaction determines virus host rand and tissue specifictiy
-blocking receptor+spike interaction may prevent infection (eg: antibodies)
What 3 mechanisms are involved in Penetration?
1)Direct penetration through host membrane by naked viruses

2)Fusion of virion envelope with host cell, parts of viral envelope left behind by enveloped viruses

3)Endocytosis: uses existing phagocytic mech of cell (enveloped viruses)
What steps are involved in uncoating?
-exposes virus nucleic acid to hosts biochemical machinery
-can occur during penetration or after penetration
-usually due to host hydrolytic enzymes which degrade capsid
What steps are involved in gene expression?
-viral nucleic acid is transcribed, translated, replicated
-usually completely dependent on host cell enzymes
-can be very complex, depending on type of NA in virion
What is the difference between 'early' and 'late' genes of the viral genome?
-Early genes-> transcribed immediately after entry into cell

-Late genes-> transcribed only after new viral RNA polymer is made
What steps are involved in assembly?
-building of new intact virus from component parts
-process varies depending on type of virus
>some spontaneous self assembly of capsid proteins
>sometimes requires enzymes from virus and/or host
>may occur in cytoplasm or nucleus
-poorly understood process for animal viruses
What steps are involved in release?
A)For Naked Viruses:
-virus particles assembled and accumulate in cytoplasm
-host cells biosynthesis stops
-host cells die and lyses
-virions are released

B)For Enveloped Viruses:
-virus glycoproteins are inserted into the inside of host cell membrane
-assembled virus capsid begins to bud out through the membrane
-envelope aquired while budding
*Budding may or may not kill the cell
*if host cell survives, may continue to shed virus
*some viral protinds may be left behind on cell surface, cell is killed by immune system
What are 4 possible outcomes of viral infections?
1)Lytic Infection:
-host cell is killed as virions are released

2)Peresistent (Chronic) Infection:
-host cell survives
-virus shed for a long period of time
-infectious virions constantly present in patient

3)Latent Infection:
-host cell survives
-viral genome replicates as part of host chromosome
-very limited ecpression of viral genes
-no mature infectious virus released
-viral gene expression may be triggered at future time

4)Host Cell Transformation:
-formation of cancerous host cells by tumor viruses
What are 5 problems with antiviral agents?
1) Side effect & toxicity to host cells: -viral life cycle is closely linked to that of the host cell
-it is hard to affect one without affecting the other
-many viruses still cannot be treated with anti-viral agents

2)Latent viruses may not be susceptible

3)Many viruses have long incubation periods

4)Resistance to some antivirals are developing

5)Developement of new agents is difficult
What are prions?
-infectious agents consisting only of protein
-an abnormally folded variant of a natural protein found in neurons
-causes slow diseases (ie: mad cow)
Whats the difference between PrP(C) and PrP(SC)?
-PrP(C) is a good prion (protease sensitive, does not aggregate)
-PrP(SC) is a bad prion (protease resistant, readily aggregates). Becomes spongy masses and clogs neurological system (causes mad cow)

-PrP(SC) can convert PrP(C) to PrP(SC) if they come in direct contact with eachother
What are some problems faced when diagnosing viral infections?
-symptoms of some viral disease mimic other microgbial diseases
-different types of viruses may produce similar symptoms
-diagnostic methods based on growth are more difficult for viruses than bac.
What is serology?
-looks for antibodies produced against viruses in patients blood
-used to diagnose viral infection

-can't tell diff b/w past and current infections
-might take long for antibodies to be made
What 3 methods are used to diagnose viral infections?
1)Serology

2)Look for virus infected cells in host. Done adding antibodies tagged with fluorescent dye

3)Try to grow and identify virus directly from host.
-Requires use of Tissue Culture Cells (TCC)
-Add virus to TCC and allow infection
-look microscopically for ctyopathic effect on cells
-virus will cause change in morphology
>cell lysis
>rounding, fusing of cells
>inclusions inside cells

*slow process*
How do viruses cause symptoms of disease? 4 of them.
1)Virus replication leads to host cell lysis

2)Virus infection alters host cell metabolism

3)Viral glycoproteins (spikes) insert into host cell membrane

4)Production of 'virokines' during virus infection
T/F Viruses often stay at the site of first contact with the host.
F
-Viruses spread via blood or lymphatic system
-may infect cells at other sites as long as suitable cell receptors are present
T/F Viruses can infect almost every body organ
T
-these bastards are versitile
What viruses are responsible for causing diarrhea?
-Enteric viruses (eg: Rotavirus, Norwalk virus, Adenovirus, Astrovirus)

-infected due to ingestion of infected food and water
What is Rotavirus?
-naked, dsRNA, double layered capsid (acid resistant)
-infects villi
-leads to lysis which causes fever, vominting, diarrhea
-up to 10E9 virion/ml of feces released
-symptoms last approx 1wk
-affects young kids, 90% of adults have antibodies against rotavirus
What is Hepatits C Virus (HCV)?
-a blood borne virus
-inflames the liver
-causes: weight loss, fever, jaundice, fatigue, muscle and joint pain, loss of lever function, death

-Enveloped, ssRNA
-fast replication
-infected by blood or body fluids only!!!
-20% of acute patients eliminate virus w/o further probs with treatment
-80% acute of patients enter chronic state (infection persists for >6mths)
What is Herpes Simplex Virus (HSV)?
-large, enveloped, dsDNA virus
-a nervous system virus
-has a huge host range
-infection begins at breaks in mucosal surfaces or skin (ie: needs contact with infected animal)
-HSV enters epithelial cells (causing fluid filled blisters)
-HSV may spread to neurons causing Latent infections:
>analogous to 'prophage' state
>little viral gene expression
>no damage to host cell
What are the 5 types of Herpes infections?
1)Oral herpes (cold sores) - HSV-1

2)Herpes keratitis - infects eyes

3)Herpes whitlow - fingers

4)Genital Herpes - (HSV-2)
-point of entry is dink or vagi
>vesicular lesions occur (itch, pain, discharge)
>first infection, get flu like symptoms
>virus becomes latent, can be reactivated whenever

5)Herpes encephalitis - migration of HSV to brain. F's up behavior, seizure, fever, nausea
How do you control Herpes Simplex Virus (HSV)?
-acyclovir: not a cure, shortens duration of active leions

-avoid contact with active lesions

-can kill with a good soap wash. Kills lipid envelope
What is West Nile Virus(WNV)?
-a virus of the nervous system
-enveloped, ssRNA
-transmitted by mosquitoes, breast milk, organ transplants, blood transfusion
-may cause fever, headache, rash, swollen glands
-lasts 3 to 4 days, no long term effects

-patients >50yrs are at risk of developing encephalitis
>inflames brain
>headache, high fever, disorientation, stiff neck, muscle aches, paralysis, convulsions
>symptoms last for weeks then subside

*no real vaccine
What is the influenze virus?
-a respiratory tract virus
-enveloped, ssRNA, segmented RNA(8 pieces)

2 types of spike proteins on envelope
1)Neuraminidase(N):
-degrades mucus that lines epithelial cells or resp. tract
-required for release of mature virion from host cell
2)Hemagglutinin(H):
-for attachment
Go over the life cycle of the influenza virus.
-attaches to epithelial cell receptos
-virion envelope fuses with host membrane
-releases ssRNA into cytoplasm and migrates to the nucleus
-assembly of mature virion in cytoplasm
-released by budding

**transmitted by aerosols or hand to nose contact**
**damages host cells and kills them**
What are the 3 types of influenza virus?
Type A:
-most common
-broad host range (humans, birds, pigs)
-can cause pandemics(world wide spread)

Type B,C:
-infect only humans
-don't cause pandemics(small outbreaks)
-usually milder symptoms
How do different flu strains arise? 2 mechanisms.
1)Antigenic Drift:
-spontaneous mutations in H or N genes which give rise to minor changes in H or N proteins

2)Antigenic Shift:
-completely new H and/or N protein acquired from another flu virus
-possible becusae of segmented genome
What is the ebola virus?
-only found naturally on African continent
-Enveloped; 1 ssRNA with 12 genes
-broad host range
-causes viral hemorrhagic fever
-virion enters directly into blood or inhaled
-tend to hang out in blood, lungs, and nasal secretion

*2 days of infection: high fever, headache, fatigue, bloody diarrhea
*7-10 days of infection: mucosal bleeding, circ system collapse, shock, blindness, death
What do we know about Ebola's transmission? 3 of them
1)Zoonotic disease:
-animal to human transmission

2)Human to human transmission:
-via physical contact with secretions, blood of patients
-airborne spread possible but rare

3)International outbreaks are possible (ie: beyond Africa)
What hypothesis were made regarding the genesis of viruses? 3 of them.
1)Retrograde evolution:
-cells which have continually lost funstion so as to become completely dependent on another host

2)Cellular origin
-combos of cellula macromolecules (protein, NA) that gained ability to self assemble and replicate

3)Parallel evolution of cells and viruses when life first began

**No strong evidence for any of the above**
Why are viruses important from a scientific viewpoint? 3 reasons
-models for gene organization and expression

-used as vectors for introducing new genes into animal cells

-used as possible agents of human gene evolution