Bacteriology Flashcards by Amy Carter

Define bacteria

Single cell microbe with a simple cell structure.

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Most bacteria are vital for…

human life (commensal) with very few being parasites or pathogens that cause disease

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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

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Some bacteria can form…

endospores that are dormant and very resistant to hostile environmental conditions e.g. heat, cold, radiation, disinfectants.

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What can endospore producing bacteria cause?

seriously debilitating infectious disease e.g. bacillus anthracis (anthrax)

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What are the three categories of bacteria?

Obligate aerobes

Obligate anaerobes

Facultative anaerobe

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Name four classifications of bacteria

Size

Shape

Arrangement

Structure

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Why might a vet choose to conduct a bacteria culture?

Joint pain/chronic lameness

Dermatitis

Otitis

Non healing wound

Chronic or aggressive gastroenteritis

Surgical wound breakdown

Pyoderma

Cystitis

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Give examples of fluid samples

Blood

Urine

CSF

Synovial fluid

Exudates

Semen

Sputum

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Give examples of swab samples

Eye

Ear

Skin

Wounds

Abscesses

Penis

Vagina

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Give examples of tissue samples

Liver

Lung

Kidney

Spleen

Cardiac

Lymph node

Skin

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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

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Describe facultative anaerobes

Grow aerobically when oxygen is present but can also function in the absence of oxygen e.g.

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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

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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

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Name 4 types of media types

Simple media.

Enrichment media.

Selective / differential media.

Transport 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?

Microscopic evaluation

Grams staining

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.

Gram’s positive

Gram’s negative

Acid fast

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.

Describe gram negative bacteria

Gram’s negative bacteria have a thin peptidoglycan layer which is protected by a further outer membrane. Small holes ‘porins’ are contained within the outer membrane The thin peptidoglycan layer does not retain the crystal violet stain but absorbs the pink safranin stain. e.g. pseudomonus aeruginosa

Describe acid fast bacteria

Rarely diagnosed in vet practice. Have a waxy (mycolic acid) outer layer. Highly resistant to staining and treatment. Gram positive bacteria. Ziehl neelsen stain required ( red on blue background.) All other organisms stain blue. e.g. mycoplasma, mycobacterium tuberculosis, m leprae, nocardia Can be zoonotic

What is sensitivity training?

Indicates which antimicrobial is most appropriate to eliminate infection Allows the patient to be treated quickly and effectively Reduces the risks associated with antimicrobial resistances

Describe disc agar infusion

Most commonly used method to determine the susceptibility of a microorganism to a specific antimicrobial agent (efficiency, cost and convenience) Antimicrobial agent diffuses into the solid medium from the filter paper resulting in the inhibition of reproduction of the microorganism on its surface. A zone of inhibition forms around the disc, beyond this zone an unaffected area of normal microbial growth is present

What is the method for disc agar infusion?

A bacterial colony from loop or swab is spread over an agar plate A manufactured disc containing a range of antibiotics is applied to the plate surface. Incubate for 18-24hrs at 37 ̊C The 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 this test. Depending on these results the isolate will be classed as being susceptible, intermediate or resistant to that specific antimicrobial agent

How should you dispose of bacteriological sample equipment?

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 (orange bag).