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Block 1 - Fundamental Principles > Microbiology > Flashcards

Microbiology Flashcards

0
Q

What is a virion?

A

Complete infectious particle, assembly of proteins surrounding nucleic acid core

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1
Q

What two shapes can a capsid have?

A

Icosahedral or helical

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2
Q

What is a virus?

A

An obligate intracellular parasite

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3
Q

What is the range in sizes for clinically relevant viruses?

A

From 20-30 nm (picornaviruses) to 300 nm (poxviruses)

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4
Q

What are the different genomes a virus can have?

A 
Single stranded DNA
Double stranded linear DNA
Double stranded circular DNA
Single strand positive or negative RNA
Single stranded Segmented RNA
Double stranded segmented RNA
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5
Q

Why is RNA virus replication so error prone?

A

Viral RNA polymerase lacks proof reading function

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6
Q

What kind of DNA do most DNA viruses have? What about papovavirus? Parvovirus? Circovirus?

A

Linear dsDNA
Circular dsDNA
ss linear DNA
Circular ssDNA

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7
Q

What are classification schemes for animal viruses?

A 
Physical/chemical parameters 
Enveloped vs naked
Morphology
Capsid symmetry
Genomic nucleic acid - especially important
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8
Q

What is the current virus classification nomenclature?

A

Family/subfamily/genus/species/strain

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9
Q

What is the virus life cycle?

A
  1. Attachment to surface of target cell
  2. Penetration into cell
  3. Uncoating
  4. Replication
  5. Assembly of virion components
  6. Release of infectious progeny virus
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10
Q

Where do most RNA viruses and most DNA viruses carry out synthetic events and what is an exception to each?

A

RNA - cytoplasm - flu

DNA - nucleus - pox

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11
Q

What is virus entry into the host cell dependent on?

A

Prior high affinity interactions between the virus and cell that ultimately trigger internalization

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12
Q

What three possible mechanisms are responsible for virus penetration?

A
  1. Translocation of entire virion across pm
  2. Endocytosis of virus resulting in accumulation in cytoplasmic vacuoles
  3. Fusion of cell membrane with virion envelope
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13
Q

What does in coating mark the beginning of?

A

Eclipse phase when no infectious visions can be recovered

Not present in bacteria - can always get viable sample

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14
Q

How does replication of picornaviruses happen?

A

+strand RNA can be directly translated to enzymes needed for replication, then turned into -strand then turned into +strand progeny

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15
Q

How does replication of orthomyxoviruses and paramyxoviruses happen?

A

-strand segmented RNA, mature virion must carry a polymerase to produce +strand RNA

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16
Q

How does replication of reoviruses occur?

A

Double stranded RNA, virion must carry polymerase, partial assembly takes place earlier because dsRNA is a huge danger signal and must be hidden

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17
Q

How does replication of herpes occur?

A

dsDNA, DNA viruses can use host cell RNA polymerase

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18
Q

How are naked viruses released from cells?

A

During cell lysis after accumulation

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19
Q

What is tissue tropism and what is it dependent on?

A

Cell or tissue type that supports replication of a given virus, dependent on:
Cell receptors for virus
Proper cell transcription factors and replication co factors
Ability of cells to support viral protein synthesis
Presence or absence of local temp, ph, o2 tension, nonspecific factors in body secretions, digestive enzymes and bile

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20
Q

What is the sequence of virus spread?

A
  1. Implantation at portal of entry
  2. Local replication and local spread
  3. Dissemination from portal of entry
  4. Multiplication in target organs
  5. Shedding of virus
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21
Q

How do viruses disseminate from portal of entry?

A

Viremia through circulation - multiply in endothelial cells or fixed macrophages, diffuse through gaps, and are carried by migrating leukocytes
Neural via nerves

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22
Q

What is the incubation period?

A

Time between exposure to virus and onset of disease

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23
Q

What are the three determinants of viral pathogenesis?

A
  1. Accessibility of virus to tissue
  2. Virus susceptibility to host defenses
  3. Cell susceptibility to viral multiplication
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24
What does pathogenesis of a virus result from?
Viral disruption of normal cellular processes
25
What is the host shut-off phenomenon?
Viruses induce a shutoff of cellular protein synthesis towards a complete shift to viral protein synthesis, culminates in cell lysis and tissue destruction
26
What are four factors contributing to viral diversity?
1. Mutation - subtle genetic change 2. Recombination/reassortment - major genetic change 3. Replication rate and number of progeny 4. Selective pressure in host
27
What is a quasi species?
A dynamic distribution of related genomes - some alive, some dead, some drug resistant, some not, etc
28
What are three types of viral recombination?
1. Independent reassortment = antigenic shift - in viruses with segmented genomes 2. Homologous recombination - template switching during RNA replication, common in RNA viruses and retroviruses (HIV) 3. Breakage/rejoining - prevalent in DNA viruses and large RNA viruses (SARS)
29
What are characteristic of orthomyxoviruses and what is one example?
``` Influenza Single -strand RNA Segmented genome allows reassortment Hemagglutinin and neuraminidase spikes RNA dependent RNA polymerase ```
30
What are two mechanisms that allow flu to alter its antigenic constitution?
Antigenic drift | Antigenic shift
31
What are basic characteristics of paramyxoviruses and what are some examples?
``` Linear ssRNA, -sense Genetically stable, narrow host ranges Parainfluenza Mumps and measles Respiratory syncytial virus ```
32
What are basics of picornaviruses and what are some examples?
No enveloped, +ssRNA Enteroviruses Hepatovirus Rhinoviruses
33
What are the basics of togaviruses and what are some examples?
Arthropod borne viruses Alphaviruses Rubivirus: rubella
34
What are the basics of flaviviruses and what are some examples?
Enveloped, +ssRNA | Yellow fever and dengue
35
What kind of virus is hepatitis c and what are the basic features?
Hepacivirus | +ssRNA, enveloped
36
What are the basics of bunyaviruses?
Enveloped, triple segmented -ssRNA | Four genera: bunyaviruses, phlebovirus, nairovirus, hantavirus
37
What are the basics of arenaviruses?
Enveloped, segmented circular -ssRNA Unique to tropical America Contracted by contact with rodents
38
What are caliciviruses and what are two examples?
+ssRNA, no envelope | Norwalk virus and hepatitis e
39
What are the basics of filoviruses and what is an important clinical example?
Enveloped, linear -ssRNA | Ebola
40
What are the basics of reoviruses and what do they include?
``` Medium sized nonenveloped, icosahedral Linear segmented dsRNA Include rotavirus (causes gastroenteritis) and Colorado tick fever (coltivirus) ```
41
What are the basics of coronaviruses and what is an example?
Large, +ssRNA Enveloped, contain surface spikes SARS
42
What capsid do DNA viruses have and what is the exception?
Icosahedral capsids | Pox virus - complex capsids
43
Which DNA viruses have a lipid envelope?
Pox Herpes Hepadna
44
Which two families doe the papovavirus combine?
Papilloma | Polyoma
45
How do DNA viruses maximize their genome?
Multiple promoters Alternative splicing Code from both strands (papilloma from one strand)
46
What are the phases of DNA virus replication and what happens in each?
Immediate early phase - genes expressed in absence of new protein synthesis, viral proteins that induce expression of others Early gene expression - regulatory proteins that participate in viral genome replication Late phase - structural components, not til after viral DNA synthesis starts, repression of early genes
47
Which viruses use host DNA polymerase mediated viral DNA synthesis and what does it require? What might it cause?
Papilloma and parvo Requires host cell in s phase Might cause a transforming infection
48
Which viruses use viral polymerase mediated DNA synthesis?
Adeno, herpes, pox
49
What are four mechanisms of viral DNA replication and what is an example of each?
1. Self priming (parvoviruses) 2. Bi-directional (papovaviruses) 3. Strand displacement (adenovirus) 4. Rolling circle (herpes)
50
What is the relative speed of cellular changes following hcmv infection compared to other viruses?
Slower than lots of others
51
What are the types of infection by DNA viruses?
Acute infection | Persistent infection - includes chronic, latent, and slow
52
What is the difference between the different types of persistent infection by DNA viruses?
Chronic - continuous production of low/moderate levels of virus Latent - little or no viral gene expression, no virus produced Slow - long incubation with low or undetectable levels of virus
53
What is a transforming infection?
Viral gene products can alter growth regulation of infected cells, can lead to oncogenesis and malignant progression Two stages - immortalization and other changes for malignancy
54
Parvoviruses
Small linear single stranded DNA No envelope Require helper to replicate Dependovirus - no disease in humans, requires coinfector
55
Papovaviruses
No envelope Icosahedral Double stranded circular DNA Only infects human cells Papilloma virus - maintenance in differentiating cells, productive viral replication in differentiated cells Polyoma viruses - BK(causes renal disease and hemorrhagic cysts), JC(can cause PML), MCV
56
Which types of hpv cause cancer? Which does the vaccine protect against?
16, 18, 31 | 6, 11, 16, 18
57
Adenovirus
No envelope Linear double stranded DNA Respiratory disease, pink eye, hemorrhagic cystitis
58
Herpesviruses
Envelope Linear double strand DNA Icosahedral
59
Herpes disease associations
``` HSV 1 & 2 - cold sore, genital HHV 3 - varicella zoster HHV 4 - Epstein Barr - mono, burkitts lymphoma HHV 5 - CMV - birth defects, retinitis HHV 6 - fever and rash HHV 8 - kaposi's sarcoma ```
60
Acyclovir
Anti herpesviral drug Only infected cells convert to pro form by phosphorylation Guanine nucleotide analog that terminates DNA synthesis
61
Hepadnavirus
``` Hep b Mixed single and double stranded DNA Reverse transcription step Restricted to liver cells Infection can be cleared or persistent Effective vaccine ```
62
Pox virus
Variola virus - causes small pox
63
What is contained in the nucleocapsid of a retrovirus?
Two copies of genome Reverse transcriptase Integrase
64
What are the coding regions of a retrovirus?
Gag gene - core proteins Pol gene - for reverse transcriptase, integrase, protease Env gene - surface glycoproteins
65
What kind of virus is a human T cell leukemia virus? HIV?
Delta retrovirus | Lentivirus
66
Endogenous retroviruses
Not capable of replication | Indicated in autoimmune diseases
67
HTLV1
Four additional regulatory genes Infection through infected lymphocytes not free virus Three major mechanisms of transmission: blood transfusion, sex, transplacental or breast milk Infect cd4 cell Causes adult T cell leukemia and HTLV1 associated myelopathy (HAM) Less than 1% infected individuals will develop disease
68
What is the predominant HIV Clade in the US?
HIV-1 M Clade B
69
What is the retrovirus life cycle?
``` Absorption Entry Reverse transcription Integration Transcription Translation Assembly Budding ```
70
What is the virion structure of HIV/retroviruses?
Envelope has gp41 and gp120 from cleavage of gp161 on env gene 7 additional proteins encoded that act as gene regulators
71
How does HIV enter the cell?
Gp120/gp41 requires binding to at least 2 coreceptors Major receptor is CD4 (binds gp120) Coreceptors are CCR5 (m tropic viruses - bind preferentially to macrophages, don't form syncytia) and CXCR4 (t tropic, preferentially bind T cells, form syncytia) - gp120 binds first and exposes fusion domain on gp41, then ph dependent conformational change leads to fusion
72
What are targets of antiretroviral drugs?
``` Reverse transcriptase (NRTIs and NNRTIs) Protease Integrase CCR5 coreceptors Fusion inhibitors ```
73
What are some inappropriate uses of anti microbial drugs?
Use in animal feed | Over prescribed
74
What is the difference between and antibiotic and an anti microbial drug?
Antibiotic from microorganisms that kills or inhibits growth of other microorganisms Anti microbials comprise true antibiotics and synthetic drugs
75
What is the difference between narrow spectrum, extended, and broad spectrum antibiotics?
Narrow - kills gram + but not gram - Broad spectrum treats both - can lead to superinfection Extended spectrum is extra broad
76
What is the difference between empiric and definitive therapy?
Empiric - don't fully know what the patient has, use broad spectrum drugs
77
What are the differences in structure of gram + and gram - bacteria?
Gram+ has no outer membrane Gram+ has much thicker cell wall of peptidoglycan Gram+ have no periplasm - resistance enzymes can diffuse out
78
What are sites of drug action in a bacterium?
``` Cell wall Inner membrane Transfer of C1 units to make bases, amino acids DNA synthesis Transcription Translation ```
79
What are three causes of natural selectivity of bugs?
Drug accessibility Target sites Metabolism
80
What are mechanisms by which bacteria acquire resistance?
Mutation Transduction - single gene transfer, common among gram+ Conjugation - through pilus, mainly gram- but cross species can occur Transformation - bacteria can release DNA that is absorbed into recipient cells
81
What are the results of drug resistance?
Lower drug accessibility Drug inactivation Altered target Increase in concentration of competing substrate
82
What must you expose the bug to for effectiveness? In an immunocompromised patient?
Minimal inhibitory concentration | Minimal bacteriocidal concentration
83
What are two examples of sanctuaries?
Heart valve | Synthetic prostheses
84
What aspects of the micro environment affect antibiotic action?
Ph Pus, hemoglobin Oxygen
85
What are situations in which prophylaxis with antibiotics is effective?
Prevention of specific infection Dirty surgery - GI tract or head and neck Cardiac surgery Implantations of prostheses or surgery in patients who have them Dental work on patients with rheumatic fever or valve lesions Young children with sickle cell disease
86
What are typical side effects of antibiotics?
Allergies | Renal toxicity and ototoxicity

Block 1 - Fundamental Principles (6 decks)

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