Microbiology

Question 1

Define ‘virulence’

Answer 1

Quality of being extremely poisonous, infectious or damaging OR the extent to which a disease or toxin possess this quality

Question 2

Briefly describe gram negative bacteria

Answer 2

On staining appear red/pink; have an outer layer followed by thin peptidoglycan layer in the cell wall

Question 3

Briefly describe gram positive bacteria

Answer 3

On staining appear violet/purple and have thick peptidoglycan cell wall

Question 4

What are cocci bacteria?

Answer 4

Spherical appearance

Question 5

What are bacilli bacteria?

Answer 5

Cylindrical rod appearance

Question 6

What are spirochaetes bacteria?

Answer 6

Curved/spiral appearance

Question 7

How can you distinguish between staphylococci and streptococci?

Answer 7

Staphylococci are catalase positive and streptococci are catalase negative

Question 8

What is a virus?

Answer 8

Single cell with no organelles, has either a DNA or RNA strand (not both) and a protein capsid which surrounds and protects the genome

Question 9

What are fungi?

Answer 9

Organism with mainly chitin cell wall, which have similar ultrastructure to eukaryotes but with 80S ribosomes

Question 10

What are protozoa?

Answer 10

Unicellular eukaryotes (parasites) with 80s ribosomes

Question 11

What are helminths?

Answer 11

Multicellular eukaryotes without a backbone or exoskeleton

Question 12

What is a parasite?

Answer 12

Any living form which is dependent on other living things for survival and causing some damage to the host

Question 13

Describe the structure of bacteria

Answer 13

Single circular chromosome is free in the cytoplasm (and sometimes plasmids), have 70s ribosomes, no mitochondria though or any membrane-based organelles

Question 14

What is peptidoglycan?

Answer 14

A cross-linked complex of polysaccharides and peptides

Question 15

What are pili?

Answer 15

Hair-like proteins which allow transfer of DNA between bacteria

Question 16

What are fimbriae?

Answer 16

Hair-like proteins which interacts with cell surface receptors to allow binding

Question 17

Describe the mechanisms by which bacteria adhere to the body

Answer 17

1) Stick to mucosa via Van der Waals at portal of entry
2) Proteins on microbe surface recognise host carbohydrates and bind OR pili/fimbriae attach
3) Surface molecules of microbe bind to complementary surface receptors on certain cells of the host tissue

Question 18

What is a biofilm?

Answer 18

Accumulation of bacteria on a cell surface due to van der waals forces (begins as slime and proliferation forms biofilm)

Question 19

What is viral antigenic shift?

Answer 19

Change in antigens on the surface of viruses to evade established immune responses

Question 20

How do viruses harm the host?

Answer 20

Induce histological cell changes in certain areas (cause giant cells), cause cells to enter apoptosis, incorporate nucleic acid into genome which can cause cancers

Question 21

What does catalase do?

Answer 21

Breaks down hydrogen peroxide to water and oxygen

Question 22

What are exotoxins?

Answer 22

Toxins produced by gram negative and positive bacteria to help bacterial spread, lyse cells and block protein synthesis and cell function

Question 23

What are endotoxins?

Answer 23

Toxins produced only by gram negative bacteria and cause an over-reaction of the immune response leading to host cell damage

Question 24

How do bacteria persist in the human body despite immunological defences?

Answer 24

Bind the host antibody the wrong way –> antibody neutralisation, disrupt complement binding and produce antiphagocytic enzymes, detoxifies harmful substances such as free radicals and hydrogen peroxide and produces heat shock proteins to prevent denaturation at increased temperatures

Question 25

Outline the course of viral infection

Answer 25

primary replication --> systemic spread --> secondary replication in susceptible organs following spread

Question 26

Describe the different modes of virus transmission

Answer 26

Direct (horizontal) - host to host contact Indirect (horizontal) - through food, water etc. Transplacental (vertical) Perinatal (vertical) Breast milk (vertical)

Question 27

Define incidence

Answer 27

Occurrence, rate or frequency of a disease

Question 28

Define prevalence

Answer 28

The proportion of a population with the condition

Question 29

What is meant by 'reproduction number (RO)'?

Answer 29

The number of transmissions per source of virus

Question 30

What is an antibiotic?

Answer 30

A natural antimicrobial substance produced by a microorganism

Question 31

What is an antimicrobial?

Answer 31

A type of antibiotic that is synthesised chemically, or modified from natural resources

Question 32

What are some bacterial targets for drugs?

Answer 32

Cell wall synthesis, bacterial protein synthesis, nucleic acid metabolism and bacterial cell membrane

Question 33

Describe and name two antimicrobials that affect the bacterial cell wall

Answer 33

Beta lactams - inhibit cell wall synthesis by binding to transpeptidases which cross-like in the cell wall,, leading to an unsupported cell --> cell ruptures --> bacterial death Glycopeptides - inhibit cell wall synthesis in gram positive bacteria by binding to cell wall precursors

Question 34

Describe and name three antimicrobials that inhibit protein synthesis

Answer 34

Aminoglycerides - bind to 30s subunit of ribosome --> disrupts structure --> prevents translation initiation Tetracyclines - bind 30s subunit (bacterial ribosome) --> prevents AA amino acid incorporation --> incomplete, non-functional proteins Macrolides - bind to 50s subunit --> prevent translocation of protein along the ribosome

Question 35

Describe and name two antimicrobials that inhibit nucleic synthesis

Answer 35

Quinolones - inhibit DNA synthesis | Rifampicin - inhibits RNA polymerase

Question 36

Outline the infectious cycle of a virus

Answer 36

attachment and particle entry --> decoding and uncoating of genome --> translation of viral mRNA by host ribosomes --> genome replication --> assembly and release of particles containing genome

Question 37

What is a viral capsid?

Answer 37

Protein shell of a virus

Question 38

What are capsomeres?

Answer 38

One of the individual protein units which make up the capsil (outer coat)

Question 39

Define 'genome'

Answer 39

Complete set of genes present in a cell or organism

Question 40

What is a nucleocapsid?

Answer 40

Capsid of a virus with the enclosed nucleic acid

Question 41

Describe the function of viron proteins

Answer 41

Assemble protective shell, bind to specific external receptors on host cells, transmit signals to induce genome uncoating, induces fusion with host cell membrane, transports genome to appropriate site within host cell

Question 42

What are RNA viruses?

Answer 42

Viruses containing RNA, if it has a positive polarity it can be transcribed immediately, if it has a negative polarity it has to be converted to positive before it can be translated

Question 43

What are antivirals?

Answer 43

Drugs which target viral proteins, predominantly viral enzymes

Question 44

Describe the influenza virus

Answer 44

Orthomyxocirus has an envelope, single stranded RNA, 8 segmented genes and surface spikes of haemagluttinin protein and neuraminidase

Question 45

What does antigenic shift and drift of the influenza A virus involve, and what can this cause?

Answer 45

Antigenic shift involves the shift in haemagluttinin and can lead to a pandemic Antigenic drift involves changes to the virus due to host to host transmission (evolution) and this leads to epidemics and involves haemagluttinin and neuraminidase proteins

Question 46

Describe how amanitidine and rimantidine work to treat flu

Answer 46

Inhibits the viral M2 protein which decreases viral H+ influx and this inhibits viral uncoating and inhibits the coating process as a new viron aims to leave (by binding to haemagluttinin)

Question 47

Describe how neuraminidase inhibitors work to treat flu

Answer 47

Stops neuraminidase from cleaving sialic acid from glycoconjugate and therefore stops viron release, aggregation of virons and also increases virus inactivation conducted by respiratory mucus

Question 48

Describe the HIV virus

Answer 48

Single stranded RNA present, reverse transcriptase, integrasem protease

Question 49

Describe the treatment of HIV

Answer 49

HAART (highly active anti-retroviral therapy) where drugs include inhibitors of reverse transcriptase, integrase, protease and fusion and entry modalities

Question 50

Describe the hepatitis C virus

Answer 50

An enveloped virus with a single-strand of RNA

Question 51

What is an emergent virus?

Answer 51

When a virus has adapted and emerged as a new disease/strain

Question 52

What is a resurgent virus?

Answer 52

When a virus increases in prevalence one more after a period of little activity or occurrence

Question 53

Define 'serotype'

Answer 53

The type of organism, determined by its constituent antigens