APBI M2 - Lesson 1

Cocci

these are round and also referred to as spherical

Bacilli

rod-shaped

Successful pathogen

• attach

• enter

• evade host defences

• multiply

• exit to re-infect

Motility

virulence factor that gives bacteria advantage to being successful

• bacteria cells can move via flagella, cilia, gliding

Capsules

virulence factor that gives bacteria advantage to being successful

• thin external envelopes produced by some cells that help to protect them from host immune cells (like avoiding phagocytosis)

Spores

virulence factor that gives bacteria advantage to being successful

• bacterial stages resistant to destruction by heat or dehydration; allow org to survive through difficult environmental conditions

Glycocalyx

virulence factor that gives bacteria advantage to being successful

• surface attachment mechanism that assists some bacteria in clinging to fish membranes

Cell wall

virulence factor that gives bacteria advantage to being successful

• both Gram-+ and Gram-ve bacteria have cells but +ve bacteria is exposed and leads to staining characteristic

  • cell was = hydrophobic and helps bacteria to clump together and survive against attacks of host immune systems

Toxins

virulence factor that gives bacteria advantage to being successful

• produced by gram+ and gram- bacteria ; may produce rapid death of invaded host or can reduce effectiveness of host immune response in variety of ways

  • some gram +ve orgs produce exotoxins in cytoplasm that're released from dead / live bacteria

  • gram -ves may produce endotoxins that're cell membrane components and released only on death of cell

Oxygen requirements

virulence factor that gives bacteria advantage to being successful

• some bacterial species = anaerobic; can survive in tissues that've lost their blood supply

 

Systemic bacteria

• some bacteria only cause disease once inside organ / tissue

  • they might be fine external of the fish but if where they aren't supposed to be --> bad

  • once inside they can use bloodstream to travel to all organs and tissues

  • getting in: through gut / intestinal wall, skin, lesions or sores, natural openings like lateral line / sensory pores, and parasites

 

External bacteria

• cause skin + fin damage

  • not all are pathogenic; many bacteria existing normally on the skin will never cause disease

  • normal flora = protective and acts as competition for pathogenic bacteria

  • need to know what's normally present and which may be disease causing

 

Surface infections of fish

1. increase in numbers of bacteria in water where fish held

2. numbers increase, resulting increase in number of bacteria settling onto mucus layer

3. mucus defence eventually overwhelmed and can't adequately slough pathogens off

4. numbers build, bacteria through mucus and colonize skin

5. bacterial growth increase, skin damage starts → skin and gill damage results

 

Mechanisms of horizontal transmission

• direct contact

• through water

• passively via fomites

• actions of 3rd org like bird

Pathogenic bacteria

(bacteria) some specialized for invading living tissues

Saprophytes

bacteria that’re primarily environmental orgs

Gram’s stain

• cell wall staining characteristics that lets you classify bacteria as Gram positive or gram negative

• purple = gram-positive

• red = gram-negative

Gram positive

• stain purple because they have a dye called Gram's violet in their exposed peptidoglycan layer

• retains crystal violet-iodine complex during alcohol decolourization

Gram negative

• stain red cuz peptidoglycan layer hidden below outside layer and so they don't retain violet dye

• thin peptidoglycan between inner/outer membranes, alcohol disrupts outer membrane, crystal violet washes out → safranin counterstain taken up → red/pink

Enrichment media

adding certain special growth enhancing substances to a basic nutrient medium so it supports growth of certain fastidious microorgs

Selective media

• addition of specifical chemical substances that'll prevent growth of 1 group of bacteria without inhibiting others

  • ex. acids, antibiotics, dyes, etc.

Differential media

• adding certain chemicals / reagents that'll result in a kind of growth / change in medium; lets observer differntiate between types of bacteria

  • like adding substance which can be precipitated or used in the growth of the colony so there's a visible change in the medium

 

Streak plate isolation

• Most material obtained from fish contain mixed pop of microorgs

  • to make detailed study of characteristics of indiv species comprising mixture you have to isolate them in pure culture

• 4 diff kind of streaks

• plate now has mixed culture that you will now be able to remove individual and discrete colonies

  • each one represents one original bacterium

• you can re-streak them and obtain pure culture bacteria after another pass to run tests for full ID