bacteriology (done) Flashcards
what are bacteria?
(1 mark)
single cell microbe with simple cell structure
info of bacteria?
(6 marks)
- most bacteria are vital for animal life (commensal) with few being parasites / pathogens that cause disease
- cell contains no nucleus, allowing cells to reproduce rapidly by binary fission
- DNA replicated within the cell, which seperates into 2 daughter cells
- cocci, bacilli / spirochete shape commonly
- can be oxygen obligate aerobe / anaerobe / facultative (can do both)
- produce endo + exotoxin which cause damage to host cell
bacteria general requirements for life?
(4 marks)
- water
- essential nutrients - vary according to species (usually carbon + nitrogen)
- correct pH - most mammalian pathogens require pH of 7.4
- correct temp - optimum temp for most pathogens is body temp e.g. 37-40 degrees C.
danger of bacteria that can form endospores?
(2 marks)
- the endospores are often dormant + resistant to hostile environmental conditions e.g. heat, cold, radiation, disinfectants
- these bacteria commonly cause serious infectous disease that are toxic to many organisms e.g. Anthrax
structure of bacteria?
(11 marks)
- ribosome - protein building, repair damage
- cytoplasmic membrane surrounded by peptidoglycan cell wall gives structure
- gel like matrix ‘cytoplasm’ made up of water, nutrients, gases + waste. contains the cell structures (ribosomes, chromosomes, DNA loops + plasmids)
- various external structures - e.g. flagellae for locomotion
- pilli - enable bacterium to attach to host. also involved with conjunction.
the 3 groups of bacteria based on their response to gaseous exchange?
(3 marks)
- obligate aerobes
- obligate anaerobes
- faculative anaerobes (both O2 + none)
how is bacteria classified?
(4 marks)
- size
- shape
- arrangements
- structure
shapes of bacteria?
(4 marks)
- cocci
- bacillus
- vibro
- spirochette
why might the vet decide to conduct a bacterial culture?
(6 marks)
- disease diagnosis
- treatment management
- antimicrobial selection
- prevent antimicrobial resistance
- environmental surveillance
- post mortem
what does bacterial culture allow?
(4 marks)
- cultivation of bacteria from sample
- identification of cause of infection +/ antibiotic sensitivity test
- ensuring most appropriate antibiotic selected for treatment
- reduces risk of antibiotic resistance
what are the common sampling sites?
(16 marks)
- fluids - blood, urine, CSF. synovial fluid, exudates, semen, sputum
- swabs - ear, skin, wounds, abscess, mucosa
- other - infection control surveillance
how to collect specimen?
(5 marks)
- ensure appropriate PPE available - zoonotic risk
- obtain sample as soon as possible following onset of clinical signs
- obtain the sample prior to administration of medication / 7-10 days post medication if possible
- asepsis should be maintained during sampling process to prevent contamination
- swab samples obtained pre- and post-cleaning and debridement can be useful
swab collection considerations?
(4 marks)
- remove crusts to expose exudate of scabbed lesions
- obtain sample from the edges of the lesions where infection is most active
- sterile saline can be used to moisten swab + improve harvest of cells
- use appropriate transport media, for sample being collected
transport media preservation + storage aims?
(3 marks)
- maintain viability (keep alive)
- prevent reproduction (doesnt look worse than is)
- must contaim essential nutrients
oxygen requirements?
(3 marks)
- obligate aerobes - oxygen for growth
- obligate anaerobes - grow in abscence of oxygen
- facultative anaerobes - grow aerobically when oxygen present, also function in abscence of oxygen
swab preservation and storage?
(5 marks)
- correct use of transport media - depends on sample obtained
- aimies media with charcoal common for aerobic bacteria
- aimies without charcoal
- virus transport media for viral sample
- anaerobic transport media - specific container with vacuum to ensure abscence of oxygen
other sample storage and preservation techniques?
(10 marks)
- urine - boric acid preservative, refigerated
- blood - blood culture broth
- faeces - sterile tube, refridgerated
- CSF - EDTA (DO NOT refridgerate)
- synovial fluid - EDTA
speciment collection considerations?
(7 marks)
- keep specimen cool to avoid bacteria growth
- label container appropriately including potential zoonosis
- deliver quickly to external lab
- follow specific guidelines set by external lab to ensure valid resuts
- full clinical history + patient signalment should be provided to the lab
- ensure containers aterile to prevent erroneous results
- anaerobic bacterial samples should not be exposed to oxygen
bacterial culture aims?
(4 marks)
- maintain viability
- encourage reproduction
- inhibit growth of unwanted microflora
- isolate individual bacterial colonies for species identification
2 types of culture media?
(and what they are used for)
(4 marks(
- liquid nutrient broths - used for bacteria that grow within liquid e.g. blood
- solid (jelly) nutrient solutions - agar based media prepared in a flat petri dish
use of solid media?
(1 mark)
isolation of individual species can only be achieved on solid media
media types?
(4 marks)
- simple media
- enrinchment media
- selective / differential media
- transport media
use of simple basal media?
(and examples)
(2 marks)
provides basic nutrition for growth of nutritionally undemanding species
example: nutrient broth, nutrient agar
use of enrinchment media?
(2 marks)
nutrient agar base with added ingredients to encourage growth of fastidious bacteria e.g. blood, egg
use of selective / differntial media?
(and example)
(2 marks)
basic nutrient agar with added ingredients to inhibit the growth of some bacteria strains, while not effecting other e.g. sabourauds for fungal culture
labelling of the agar plate inoculation?
(3 marks)
- patient name
- date + time of inoculation
- VS initals
what temperature should the plate be inoculated at?
(2 marks)
incubate at 37 degrees C for 18-24h
if no growth after this, incubate for further 24h
how do colonies of bacteria appear?
(2 marks)
- round raised lumps along streak lines
- colonies of diff species may show diff characteristics (e,g, colour) help for identification
what techniques may be used to help identify bacterial strains?
(3 marks)
- microscopic evaluation
- gram staining
- Zeihl Neelson - acid fast
use of staining bacteria?
(1 mark)
allows cell morphology to be observed, easier classification / identification
how does gram staining classify the bacteria?
(2 marks)
categorised by the colour they stain:
* gram +/ve is purple
* gram -/ve is pink
alternative bacterial stains?
(what they are and how they are differnt)
(6 marks)
- simple / structural stains (methylene blue) - allows shape, size + arrangement observation
- differential stains (gram stain, Ziehl-Neelsen) - combination of fixative + 2 dyes, primary and counter stain that allows differentiation cell types
- structural stains - stains certain parts of the cell (e.g. flagella, microspore and capsule
info of gram positive bacteria?
(2 marks)
- thick, porous peptidoglycan layer which absorbs both stains, but purple crystal violet stain is most visable
- absorbent layer will absorb toxic substances so much easier to destroy
info of gram negative bacteria?
(3 marks)
- thin peptidoglycan layer which is protected by a further impenetrable outer membrane
- thin peptidogylcan layer doesn’t retain crystal violet stain but absorbs pink safranin stain
- outer membrane + ‘slime layer’ repel the stain and disinfectant - much more difficult to destroy
How to gram stain?
(8 marks)
- introduce slide to crystal violet - primary stain
- iodine - makes dye less soluble so it adheres to cell wall
- alcohol - decolouriser washes stain from gram-negative cell wall
- safranin - counterstain allows dye adherence to gram-negative cells
example of gram-negative and postitive bacteria?
(2 marks)
- positive - staphylococcus
- negative - pseudomonas
info of acid fast bacteria?
(5 marks)
- rarely diagnosed in veterianry
- have waxy (mycolic acid) outer layer
- highly resistant to staining and treatmnet
- Zieh Neelsen stain required (appears red, all other organisms stain blue).
- zoonotic
examples of acid fast bacteria?
(2 marks)
mycoplasma
myobacterium tuberculosis
how to Ziehl-Neelsen stain?
(4 marks)
- apply carbolfuschin (primary stain) for 30 secs
- heat fix cells
- decolourise with acid alcohol for 15-20 secs
- apply methylene blue (counterstain) for 30 secs
- rinse excess stain
what is the purpose of sensitivity testing?
(3 marks)
- allows selection of the most appropriate antimicrobial
- allows patient to be treated quickly and effectively
- reduces the risks associated with antimicrobial restistances
how does antibiotic resistance in bacteria occur?
(4 marks)
- in a popuation of bacteria, one bacterium mutates and becomes antibiotic resistant
- antibiotic kills of all bacteria except for the antibiotic resistant bacterium
- antibiotic resistant bactrium multiples, forming a population of antibiotic resistant bacteria
- antibiotic resistant bacteria can transfer their mutation to other bacteria
what is the disc agar infusion method?
(how it works)
(2 marks)
- most used method, determines the susceptibility of a microorganism to a specific antimicrobial agent
- antimicrobial agent diffuses into the solid medium from the filter paper resulting in the inhibition of reproduction of the microorganisms on its surface
- a zone of inhibition forms around the disc, beyond this zone an unaffected area of normal microbial growth is present.
how is the disc agar method carried out?
(5 marks)
- bacterial colony from loop / swab spread over agar plate
- manufactered disc containing range of antibiotics is applied to plate surface
- incubate for 18-24hrs at 37 degrees C
- resistance zone cut off is specific to each antibiotic
- accurate measurement of the zone diameter and comparison to an interpretation chart is necessary to properly interpret the test
disposal of bacteriological sample equipment?
(3 marks)
- place all equipment in suitable disinfectant, following use, during the procedure
- seal all equipment in autoclave bag and autoclave prior to disposal or re-use
- once autoclaved, equipment to be disposed of should be placed in infectious waste
