MICROBIOLOGY

Question 1

what is histology?

Answer 1

• the study of tissues and organs using microscopy

Question 2

describe the process of tissue preparation for microscopy

Answer 2

• preserve the tissue using formalin
• tissue processing which removes water from the tissue by adding ethanol (to replace the water) and then adding xylene (which removes ethanol)
• embed in paraffin wax (removes xylene and solidifies into a paraffin block)

Question 3

describe the process of light microscopy once the tissue has been prepared

Answer 3

• paraffin slice mounted on glass slide
• stained, easier to see under microscope
• most common stain is H\ematoxylin and Eosin (H&E)

Question 4

what is the most commonly used type of light microscopy?

Answer 4

• bright field microscopy

Question 5

when would we use frozen sections of tissue and why?

Answer 5

• during surgery
• for urgent analysis (less accurate results however)

Question 6

what is used to culture bacteria and fungi?

Answer 6

• solid nutrient media (agar-based)

Question 7

why do we use PCR?

Answer 7

• to amplify a specific sequence of DNA from the genome of an organism
• eg. can be used to amplify known section of chlamydia genome from a swab or urine sample

Question 8

explain the steps of PCR?

Answer 8

• denaturation: heat to 95ᵒϹ breaks hydrogen bonds between the two strands of DNA
• annealing: cool to 55ᵒϹ, allows primers to bind to their complementary sequences on the DNA
• extension: heat up to 70ᵒϹ and TAQ polymerase binds to primers and uses free nucleotides to assemble new strands of DNA

Question 9

how does reverse-transcriptase PCR differ from normal PCR?

Answer 9

• uses RNA instead of DNA (Uracil instead of Thymine)
• uses reverse transcriptase to make a complementary DNA strand from the RNA, then normal PCR is carried out on the c-DNA strand

Question 10

describe the gram stain and how it works

Answer 10

• the gram stain is used to study bacteria
• crystal violet dye and iodine bind to cell wall
• gram positive bacteria retain the stain when acetone is added and remain purple
• gram negative bacteria lose the purple stain when acetone is added and appear colourless until stained with a pink counterstain (safranin)
• this is due to gram positive bacteria having a thicker peptidoglycan cell wall so retains the stain

Question 11

describe acid-fast stain and why it is used

Answer 11

• used for organisms that do not readily take up the gram stain (eg. mycobacteria ( TB ), have waxy cell walls)
• acid and alcohol are added to the cells after they have been stained through another method
• if the cells withstand decolourisation from the acid and alcohol then they are known as acid and alcohol fast

Question 12

what bacteria is commonly found on decaying meat?

Answer 12

• Staphylococcus saprophyticus

Question 13

is Staph. saprophyticus gram positive or negative

Answer 13

• gram positive

Question 14

how can infectious agents be transmitted? (4 types)

Answer 14

• human to human spread (horizontal, and vertical transmission mother to foetus )
• animal to human
• environment to human (airborne, water, fomites)
• healthcare-acquired

Question 15

what is meant by the term virulence?

Answer 15

• virulence is a measure of the pathogenicity of a microorganism
• an organism is considered highly virulent if a small number of microorganisms can cause disease

Question 16

what are viruses and how do they work?

Answer 16

• viruses are intracellular parasites which depend on host proteins for replication
• they enter a cell, replicate, generate viral proteins, assemble the viruses, evade the host’s defence, and disperse to continue in the environment

Question 17

how are viruses classified?

Answer 17

• by the genome:
• single stranded RNA or double-stranded RNA
• single stranded DNA or double-stranded DNA

Question 18

what is chicken pox caused by?

Answer 18

• the Varicella Zoster virus

Question 19

how does shingles occur?

Answer 19

• the chicken pox virus (Varicella Zoster virus) causes shingles by becoming reactivated after being dormant in the nervous system for so long
• it can be triggered by a weakened immune system, stress, or by old age

Question 20

what is the virus responsible for causing flu?

Answer 20

• influenza

Question 21

what are some other common viruses?

Answer 21

• measles
• hepatitis
• human papilloma virus
• mumps
• ebola
• herpes

Question 22

what are the key features of a virus?

Answer 22

• have genetic material (DNA or RNA)
• no cell membranes, cytoplasm, or organelles
• cannot independently synthesise macromolecules (depends on host cell)
• genetic material packed in capsules

Question 23

what are prions, and what are the key features of a prion?

Answer 23

• infectious proteins
• no nucleic acids
• consist only of proteinacious infectious particles

Question 24

what are Koch`s Postulates to establish pathogenicity of an organism ?
( four stages )

Answer 24

• organism found in abundance in diseased host ( not healthy tissue )
• can be grown in pure culture
• this organism causes disease if introduced into healthy host
• can be re-isolated from the inoculated host and can identify the organism as identical to the original

Question 25

name 2 common gram positive bacteria

Answer 25

staphlococcus aureus
strep. pneumoniae

Question 26

name 2 common gram negative bacteria

Answer 26

E. Coli
Klebsiella
Salmonella
Pseudomonas

Question 27

name 3 factors in a host that may predispose to infection

Answer 27

extremes of age
diabetes
immune suppression eg steroids
broken skin ( wound, post surgery, iv cannula )
malnutririon

Question 28

give 2 examples of hospital acquired infection

Answer 28

• UTI from catheter
• Clostridium difficile from excess antibiotic use
• MRSA post surgery or in central lines

Question 29

describe basic infection prevention principles in healthcare

Answer 29

• hand hygiene
• appropriate PPE
• sterile technique eg for procedures ( ANTT )
• safe disposal of sharps
• isolating infected patients

Question 30

what are the peri operative measures of safeguarding against infection ?
( name four )

Answer 30

• operating theatre air quality ( eg laminar flow for orthopaedic )
• sterile equipment
• sterile PPE
• antibiotic prophylaxis ( give before procedure )
• skin disinfection ( 5% chlorhexidine )

Question 31

what organisms can be transmitted by needlestick injury ? name 3

Answer 31

• HIV
• Hepatitis B
• Hepatitis C

Question 32

how do you manage a needlestick injury ?

Answer 32

• wash site with soap and water
• puncture wound should be allowed to bleed
• check immunisation status eg hep B
• blood tests for exposure
• consider post exposure prophylaxis eg immunoglobulin

Question 33

name some mechanisms of action of antibiotics and an example for each

Answer 33

• inhibit cell wall synthesis : beta lactam eg penicillins, vancomycin
• inhibit protein synthesis : aminoglycosides (gentamicin), macrolides (erythromycin)
• inhibit DNA replication : quinolones
• inhibit folic acid metabolism : trimethoprim

Question 34

how does antimicrobial resistance affect management of infection (4 things) and how can it be tackled (3 ways)?

Answer 34

• can make treating infections difficult, longer hospital stays, higher costs, increased deaths
• tackle : antibiotic stewardship ( careful use ), monitor organisms, develop new treatments

Question 35

name some notifiable diseases ( 3 )

Answer 35

COVID-19
Monkeypox
Malaria
food poisoning : salmonella, campylobacter
TB
( + anything we immunise against : tetanus, measles, diptheria…)

( list on www.gov.uk )

Question 36

how do you report a notifiable disease ?

Answer 36

send form to the proper officer when disease is suspected
( don`t wait for laboratory confirmation )

notification forms on www.gov.uk

Question 37

name a cause of an STI in 4 different pathogen classifications and how you would test for them

Answer 37

• viral : herpes simplex 1 and 2 ( PCR ) , HIV ( serology ) , human papilloma virus
• bacterial : neisseiria gonnorhoea ( gm negative stain, culture ), syphilis / treponema pallidum ( serology )
• fungal : candida albicans ( culture )
• protozoa : trichromonas vaginilis ( microscopy, culture )

Question 38

discuss consent framework for notifying STDs and legal requirements

Answer 38

• legal duty to notify disease confidentially
• duty to inform partners of index case ( in public interest )
• should inform index case that going to do it, their consent not required
  ( GMC backs this , has guidance eg you may protect unborn baby )

Question 39

what are the mechanisms for haematogenous spread of organisms and what infections can be caused ?

Answer 39

spread of organism to distant site eg osteomyelitis, can be vertebral or intervetebral