Bacteria

Question 1

What is a commensal

Answer 1

acquired soon after birth, are able to adhere to body surfaces.
They form stable polymicrobial communities that are present throughout life as ‘ normal microflora ’ on the skin and in the hollow organs whose surfaces and cavities are open to the environment

Question 2

How does a microbe become a pathogen

Answer 2

it must find an appropriate niche within a host,
must compete with the normal microflora to gain a foothold in that niche
must evade or overcome normal host defences
it must express the genes that encode the factors that cause disease.

Question 3

What is pathogenicity

Answer 3

The ability of a microbe to damage a host

Question 4

What is Virulence

Answer 4

the relative capacity of a pathogen to damage a host

Question 5

What are virulence factors

Answer 5

The bacterial traits that confer pathogenicity; these include adhesins, toxins and capsules

Question 6

When are clinical consequences of bacterial infection apparent

Answer 6

when pathogenicity exceeds defence

Question 7

3 causes of tissue damage in a bacterial infection

Answer 7

Bacterial toxins- local/systemic
Inflammatory Response
Immune Response

Question 8

3 possible types of clinical disease due to an infection

Answer 8

Shedding of agent determined by severity of disease, type of pathogen and tissues affected
Acute
Subacute
Chronic

Question 9

2 possible outcomes of a subclinical infection

Answer 9

carrier state-> intermittent shedding of agent
Latent infection-> ashedding of agent if disease reactivated

Question 10

Examples of clinical changes in bacterial infection

Answer 10

Pathognomonic clinical presentations

Pyrexia
Depressed demeanour
Purulent discharge
Changes to white blood cell / neutrophil count
Acute phase proteins

Inflammatory response
Systemic e.g. Pyrexia (HR, RR)
Local e.g., pain, heat, swelling, erythema
Pus – neutrophils – acute
Granulomas – macrophages – chronic

Cardiovascular consequences
Congested mucous membranes (“brick” or dark red)
Toxic line (purple line in gums near teeth – horses)

Question 11

Neutrophils and inflammation

Answer 11

All inflammatory processes may be understood as a balance between marrow delivery and inflammatory-site consumption.
When marrow delivery exceeds consumption, blood neutorphilia develops
When tissue consumption exceeds

Question 11

Neutrophils and inflammation

Answer 11

All inflammatory processes may be understood as a balance between marrow delivery and inflammatory-site consumption.
When marrow delivery exceeds consumption, blood neutorphilia develops
When tissue consumption exceeds

Question 12

What is greasy pig disease

Answer 12

has a very typical presentation of skin lesions in piglets
Antibiotics that are susceptible to Staphylococcus Hyicus should be selected based on susceptibility test results.

Question 13

What is strangles

Answer 13

Strangles Strep equi equi but usually don’t treat with antimicrobials

Horse is dull, depressed, purulent nasal discharge, open wounds under jaw
Don’t usually treat with antibiotics
Most important thing is to get abscesses to drain
It is very infectious- main thing is isolating horse and monitoring in contact animals

Question 14

How long does culture and sensitivity take

Answer 14

48h culture
72hr+ sensitivity

Question 15

How does a gram stain work

Answer 15

1. Fixation
2. Crystal Violet
   The primary stain (crystal violet) binds to peptidoglycan, coloring cells purple.
   Both gram-positive and gram-negative cells have peptidoglycan in their cell walls, so initially, all bacteria stain violet.
3. Iodine
   Gram’s iodine (iodine and potassium iodide) is applied as a mordant or fixative.
   Gram-positive cells form a crystal violet-iodine complex.
4. Decolorisation
   Alcohol or acetone is used to decolorize the cells.
   Gram-negative bacteria have much less peptidoglycan in their cell walls, so this step essentially renders them colorless, while only some of the color is removed from gram-positive cells, which have more peptidoglycan (60-90% of the cell wall). The thick cell wall of gram-positive cells is dehydrated by the decolorizing step, causing them to shrink and trapping the stain-iodine complex inside.
5. Counterstain- safranin
   After the decolorizing step, a counterstain is applied (usually safranin, but sometimes fuchsine) to color the bacteria pink. Both gram-positive and gram-negative bacteria pick up the pink stain, but it is not visible over the darker purple of the gram-positive bacteria. If the staining procedure is performed correctly, gram-positive bacteria will be purple, while gram-negative bacteria will be pink.

Question 16

What is the golden time before a wound becomes infected

Answer 16

6 hours
before this is contaminated but not infected