MICROBIOLOGY Flashcards
what is histology?
- the study of tissues and organs using microscopy
describe the process of tissue preparation for microscopy
- 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)
describe the process of light microscopy once the tissue has been prepared
- paraffin slice mounted on glass slide
- stained, easier to see under microscope
- most common stain is H\ematoxylin and Eosin (H&E)
what is the most commonly used type of light microscopy?
- bright field microscopy
when would we use frozen sections of tissue and why?
- during surgery
- for urgent analysis (less accurate results however)
what is used to culture bacteria and fungi?
- solid nutrient media (agar-based)
why do we use PCR?
- 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
explain the steps of PCR?
- 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
how does reverse-transcriptase PCR differ from normal PCR?
- 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
describe the gram stain and how it works
- 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
describe acid-fast stain and why it is used
- 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
what bacteria is commonly found on decaying meat?
- Staphylococcus saprophyticus
is Staph. saprophyticus gram positive or negative
- gram positive
how can infectious agents be transmitted? (4 types)
- human to human spread (horizontal, and vertical transmission mother to foetus )
- animal to human
- environment to human (airborne, water, fomites)
- healthcare-acquired
what is meant by the term virulence?
- 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
what are viruses and how do they work?
- 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
how are viruses classified?
- by the genome:
- single stranded RNA or double-stranded RNA
- single stranded DNA or double-stranded DNA
what is chicken pox caused by?
- the Varicella Zoster virus
how does shingles occur?
- 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
what is the virus responsible for causing flu?
- influenza
what are some other common viruses?
- measles
- hepatitis
- human papilloma virus
- mumps
- ebola
- herpes
what are the key features of a virus?
- 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
what are prions, and what are the key features of a prion?
- infectious proteins
- no nucleic acids
- consist only of proteinacious infectious particles
what are Koch`s Postulates to establish pathogenicity of an organism ?
( four stages )
- 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
name 2 common gram positive bacteria
staphlococcus aureus
strep. pneumoniae
name 2 common gram negative bacteria
E. Coli
Klebsiella
Salmonella
Pseudomonas
name 3 factors in a host that may predispose to infection
extremes of age
diabetes
immune suppression eg steroids
broken skin ( wound, post surgery, iv cannula )
malnutririon
give 2 examples of hospital acquired infection
- UTI from catheter
- Clostridium difficile from excess antibiotic use
- MRSA post surgery or in central lines
describe basic infection prevention principles in healthcare
- hand hygiene
- appropriate PPE
- sterile technique eg for procedures ( ANTT )
- safe disposal of sharps
- isolating infected patients
what are the peri operative measures of safeguarding against infection ?
( name four )
- operating theatre air quality ( eg laminar flow for orthopaedic )
- sterile equipment
- sterile PPE
- antibiotic prophylaxis ( give before procedure )
- skin disinfection ( 5% chlorhexidine )
what organisms can be transmitted by needlestick injury ? name 3
- HIV
- Hepatitis B
- Hepatitis C
how do you manage a needlestick injury ?
- 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
name some mechanisms of action of antibiotics and an example for each
- 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
how does antimicrobial resistance affect management of infection (4 things) and how can it be tackled (3 ways)?
- can make treating infections difficult, longer hospital stays, higher costs, increased deaths
- tackle : antibiotic stewardship ( careful use ), monitor organisms, develop new treatments
name some notifiable diseases ( 3 )
COVID-19
Monkeypox
Malaria
food poisoning : salmonella, campylobacter
TB
( + anything we immunise against : tetanus, measles, diptheria…)
( list on www.gov.uk )
how do you report a notifiable disease ?
send form to the proper officer when disease is suspected
( don`t wait for laboratory confirmation )
notification forms on www.gov.uk
name a cause of an STI in 4 different pathogen classifications and how you would test for them
- 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 )
discuss consent framework for notifying STDs and legal requirements
- 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 )
what are the mechanisms for haematogenous spread of organisms and what infections can be caused ?
spread of organism to distant site eg osteomyelitis, can be vertebral or intervetebral
