Flashcards in Bacteriology Deck (35)
Single cell microbe with a simple cell structure.
Most bacteria are vital for...
human life (commensal) with very few being parasites or pathogens that cause disease
Describe bacteria cells
The cell contains no nucleus, allowing the cell to reproduce, very rapidly, by binary fission. Cytokinesis
Require a suitable environment to live and reproduce
Some bacteria can form...
endospores that are dormant and very resistant to hostile environmental conditions e.g. heat, cold, radiation, disinfectants.
What can endospore producing bacteria cause?
seriously debilitating infectious disease e.g. bacillus anthracis (anthrax)
What are the three categories of bacteria?
Name four classifications of bacteria
Why might a vet choose to conduct a bacteria culture?
Joint pain/chronic lameness
Non healing wound
Chronic or aggressive gastroenteritis
Surgical wound breakdown
Give examples of fluid samples
Give examples of swab samples
Give examples of tissue samples
Describe patient prep for bacteria samples
Obtain sample prior to administration of antimicrobial medication.
Dermatology samples should not be clipped or aseptically prepared prior to sampling
Describe facultative anaerobes
Grow aerobically when oxygen is present but can also function in the absence of oxygen e.g.
Describe preservation and storage of bacterial samples
Clean, sterile and leak proof container.
Correct use of transport media. This will depend upon the sample obtained.
Aimies media with charcoal added is commonly used for aerobic bacteria. – useful for fastitious bacteria
Aimies without charcoal
Virus transport medium
Anaerobic transport medium
Can be refrigerated in not testing immediately
Do not freeze samples
Describe solid media
Agar alone provides no nutrition for bacterial growth.
Specific nutrients and growth factors are impregnated in to the agar base. These are designed to encourage growth of particular organisms.
Isolation of individual species can only be achieved on solid media.
Un-innoculated Media plates should be stored with in the refrigerator and NOT frozen
Name 4 types of media types
Selective / differential media.
Describe simple (basal) media
Provides basic nutrition for growth of nutritionally undemanding species e.g. E Coli
Nutrient broth, nutrient agar
Describe enrichment media
Specific nutrients are added to basal media for growth of fastidious bacteria (complex nutritional requirements) e.g.
Blood agar - used to detect haemolytic bacteria strains.
chocolate agar – contains haemoglobin, for detection of respiratory bacteria
Describe selective/differential media
Designed to inhibit growth of certain bacteria while not affecting growth of others.
Deoxycholatecitrate used for growth of salmonella spp.
McConkey’s bile lactose agar contains bile salts which encourage the growth of enteric species e.g. E coli
Sabouraud’s media used for the growth of ringworm.
Describe transport media
Used to transport or store samples e.g. Swabs
Not used to support or encourage growth but to ensure survival of organisms until analysis can be carried out.
Describe how to grow bacteria
Once inoculated replace the lid and put in an incubator with agar side upper most, to avoid condensation droplets spoiling the bacteria growth.
Incubate at 37 ̊C for 18-24hrs.
If no growth after 18-24hrs incubate for further 24hrs.
What results will be seen when growing bacteria?
Colonies of bacteria will appear as round raised lumps along the streak lines.
Colonies of different species may show different characteristics helpful for identification e.g. colour.
What techniques may be used to help identify bacterial colonies?
Zeihl Neelson – acid fast
How can you identify bacteria?
Staining with a suitable stain e.g. Gram stain allows cell morphology to be observed.
Bacteria can be classified by the thickness or composition of the cell wall structure.
Describe Simple stains (methylene blue)
Colours cells allowing shape, size and arrangement to be observed.
Describe Differential stains (Gram’s stain, Ziehl-Neelsen)
This is a combination of 2 dyes, a primary and a counter stain, that allows differentiation of cell types.
Describe Structural stains
This stains certain parts of the cell e.g. Flagella, microspore and capsule also aiding in identification of the bacterium.
Describe gram stains
This is the most frequently used stain in microbiology that provides the first step in identifying bacteria.
Bacteria are categorised by the colour that they stain
Gram’s positive – blue / purple
Gram’s negative – red / pink
Describe gram positive bacteria
Gram positive have a thick, porous petidoglycan layer (outer layer of the cell) which absorbs the purple crystal violet stain.
e.g. a number of staphylococcal and streptococcal spp.
Absorbent layer also will absorb toxic substances so much easier to destroy.