Week 1

Question 1

Organisms that make up the scope of medical microbiology

Answer 1

Viruses, bacteria, fungi and parasites

Question 2

Different morphologies that are characteristic of bacteria

Answer 2

Spherical- coccus rod- bacilli, spiral- spirochetes
Bacteria may be seen as individual cells in pairs or as chains of connected cells
All bacteria have a diameter of roughly 1 to 2 micrometers

Question 3

Bacterial cell walls/envelopes

Answer 3

Cell envelope= cytoplasmic membrane and cell wall
Cytoplasmic membrane- no sterols, integral and peripheral membrane proteins
Bacterial cell wall- composed of peptidoglycan n-acetylmuramic acid+ N-acetylglucosamine

Question 4

Gram positive vs gram negative

Answer 4

Gram positive- thick cell wall, retention of crystal violet, cell wall contains teichoic acids attached to either the cell membrane or the cell wall
Gram negative- thin cell wall, extraction of crystal violet, consists of outer and inner membrane, periplasm contains peptidoglycan layer

Question 5

Outer leaflet of outer membrane (GRAM -)

Answer 5

LPS: lipid A (embedded in the outer membrane), core polysaccharide, and O antigen to provide serum resistance and antibody recognition
LPS (lipid A)- endotoxin that at low doses causes fever, complement mediated lysis, B cells, macrophages, and acute phase response, at high doses causes septic shock, hypotension, and circulatory collapse

Question 6

Peptidoglycan

Answer 6

Cross linkages of N-acetylglucosamine, and N-acetylmuramic acid
The third amino acid of some tetrapeptide is crosslinked to the terminal amino acids of other tetrapeptide
Penicillin binding protein- responsible for synthesis of side chains
Vancomycin- binds the side chain preventing crosslinking

Question 7

Virus

Answer 7

Not cells, metabolically inert

Extracellular form- composed of set of genes protected by a protein containing coat

Question 8

HIV life cycle

Answer 8

DNA copy of the retroviral genome is made and inserted into the genome of infected cells, proviral DNA is transmitted to all daughter cells, and in some cases is translated. Viral antigens attempt to remove the protein products but offer no response to latent infection

Question 9

AIDS developement

Answer 9

HIV is actively replicating in lymphoid tissues. CD4 T cells are turning over at an accelerated rate due to immune response during period of clinical latency. AIDS onset is marked by the inability of the immune system to eliminate the virus thus leading to opportunistic infection

Question 10

Zoonosis

Answer 10

A disease communicable to humans by other animals
Evidence- geographic coincidence, phylogenetic relatedness, prevalence in the natural host, plausible routes of transmission
Ex. HIV, SARS, West Nile Virus

Question 11

Arbovirus

Answer 11

Insect vector that transmits disease to a single species and feeds off a second host
West Nile Virus and Japenese Encephalitis virus (flavivirus), Eastern equine encephalitis virus (flavivirus)

Question 12

SARS transmission

Answer 12

coronavirus zoonotic transmission from civets, contagious and sometimes fatal respiratory illness, propagated via superinfectors

Question 13

Viral replicative strategies

Answer 13

Double stranded DNA virus: Immediate Early Proteins, Early Proteins, Late Proteins
Single strand positive sense RNA viruses: replicated antisense mRNA plus protein cleavage
Single strand negative sense RNA viruses: Virus proteins and sense RNA
Retrovirus: RT to ds DNA transcribed into mRNA, translated and replicated

Question 14

Types of viral infection

Answer 14

Productive infection- full viral replicative cycle and viral progeny are produced
Abortive infection- viral genes are expressed but infectious progeny do not result, cell dies
Latent infection- viral genome is established inside the cell, some genes may be expressed, cell remains viable

Question 15

Requirements of productive replicative cycle

Answer 15

Attachment, Penetration, Disassembly/release of genome, Eclipse or Replication, Assembly, Release from cell

Question 16

Properties of Virus

Answer 16

Virion Size
Virion shape and symmetry (icosahedral, helical, complex)
Numbers and sites of morphological units in the capsid
Presence or absence of a lipid protein envelope

Question 17

Similarities and differences between enteric and respiratory viruses

Answer 17

Route of entry: mouth/intestinal tract versus respiratory
Trigger mechanism: acid independent versus acid dependent
Primary disease: gasteroenteritis, poliovirus, neuroinvasive versus common cold, respiratory tract infection, encephalitis, mumps, rubella
enteroviruses are naked icosahedral rna’s

Question 18

Virus entry mechanisms/triggers

Answer 18

Norovirus- naked, cell-surface recptors
Rotavirus- no acidic trigger, relies on proteolysis for trigger, cell surface receptors have not been identified
Poliovirus- CD155 receptor, receptor binding triggers conformational change in capsid shell that forms pore

Question 19

Virus evasion of innate immune response

Answer 19

Rotavirus- has dsRNA, transcription and processing of +ssRNA occurs while they are extruded through channels of the double layered- particle thus avoiding dsRNA
Poliovirus- dephosphorylation of cab binding protein, stops translation accumulates vesicles and disrupts Golgi, virus maintains translation via IRE’s (cap-inpendent).

Question 20

Viral gene expression strategies

Answer 20

Rotavirus- viral rna have high affinity with ribosome and translation initation factors
Poliovirus- polyprotein with autocatalytic activity, cap-independent translation, inhibts PKR and TATA binding protein

Question 21

Structural components of virion (HSV)

Answer 21

Core- viral DNA (double stranded linear), tighly packaged
Capsid- 125 nm diameter icosahedron
Tegument- Viral proteins located between capsid surface and envelope, gets injected into cell, subverts normal cellular function
VHS- virion host shutoff
VP16- transcription factor promotes viral gene expression
Envelope- Lipid bilayer composed of membrane proteins and glycoproteins

Question 22

Latency

Answer 22

Virion latent within neurons (HSV) or B lymphocytes (EBV), exists as an autonomous episome, reactivation occurs post-stress

Question 23

Acyclovir

Answer 23

Treatment for herpes infection (used more for life-threatening HSV, severe cases of varicella)
Mechanism- Thymidine kinase (viral in origin) phosphorylates acycloguanosine, cellular polymerases phosphorylates twice more, terminates herpes DNA polymerase, only works for nonlatent cells

Question 24

Primary versus Secondary Hosts

Answer 24

Primary- Species that maintains virus in nature. Typically experiences relatively benign recurrent infections resulting from successful establishment of latency.
Secondary- Virus causes a typically fatal encephalitis

Question 25

Shingles vs Zoster

Answer 25

Zoster
Mode of transmission- respiratory droplets, person-to person contact, transfer of secretions
Replication of virus in the spleen and liver infecting leukocytes, virus is carried to capillary endothelial cells to epithelium leading to lesions on skin and mucosa
Shingles- seeding of virus in peripheral sensory ganglia (DRG) leads to pain in the dermatome corresponding to the spinal level of the infected ganglia

Question 26

HPV

Answer 26

Transmission: direct contact with infected tissues or secretions
Proliferation of cells in basal layer of skin and mucosa
Basal layers do not produce viral progeny
As infected cells differentiate and move to surface, malginant transformation occurs as viral progeny is created and released
Viral genome integration is a requirement for malignancy ie. E6 and E7

Question 27

EBV

Answer 27

Structure: large linear DNA, uses both cell and virus encoded polymerase
Two important genes: LMP1- virus transforming protein, and LMP-2- blocks B cell differentiation
Transmission: saliva, infects oropharynx epithelia
B cells are infected and induced to proliferate, some are latently infected so T cell response is not completely effective
Mechanism of gene disruption- c-myc translocation
Disease caused- Burkitt’s lymphoma, non Hodgkin’s lymphoma, nasopharyngeal carcinoma

Question 28

HBV cancers

HCV cancers

Answer 28

hepatocellular carcinoma caused by immune response

hepatocellular carcinoma and cirrhosis

Question 29

Merkel Cell Carcinomas (an agressive skin cancer seen in elderly or immunosuppressed)

Answer 29

80% of MCC tumors express Merkel Cell Virus
Virus- circular episome
Clonal integration of the genome into T antigen leads to a mutagenic event that induces MCC

Question 30

PKR mechanism

Answer 30

PKR binds viral RNA–> Activates–> Phosphorylates EIF2–> Inhibits translation iniation
This mechanism is inhibited by poliovirus

Question 31

Common cold

Answer 31

Adenovirus, Picornavirus, Coronavirus, Respiratory syncitial virus (does not produce durable immunity NOT due to antigenic variation)