NRSG 205L Lab 7 - Bacterial Isolation

Salmonella

Genus of rod-shaped, gram-negative bacteria typically found in the digestive tract of animals

Salmonella is one of the most common causes of what condition?

Food poisoning (causes a condition called salmonellosis)

What family does Salmonella belong to?

The same family as the genus Escherichia

2 characteristics shared by both Escherichia and Salmonella

1. Have optimal growth temperature of 37ºC

2. Grow in the gut of the host

What happens to Salmonella at 4ºC?

Bacterial growth is halted, but the bacteria are not killed off

2 ways to prevent Salmonella contamination

• Store food in the refrigerator

• Before consumption, heat food to 75ºC for at least 10 minutes to kill off any traces of Salmonella that may be present

Biosafety level ___ should be followed in the lab when working with Salmonella

2

2 ways to maintain biosfaety in the lab when working with Salmonella

1. All instruments that come in contact with Salmonella must be sterilized

2. All work with the bacteria should be conducted in a designated workspace

Salmonellosis

 infection that is one of the leading causes of food poisoning

What have some strains of Salmonella developed resistance to? What is the implication of this?

Some strains of Salmonella have developed resistance to acidity, allowing them to multiply in the small intestine

How does Salmonella harm the host?

Upon cell death, these bacteria release endotoxins that result in inflammation

4 symptoms of salmonellosis

1. Diarrhea

2. Vomiting

3. Cramps

4. Fever

Duration of infection of salmonellosis

4-7 days

Treatment/recovery of salmonellosis

Most individuals recover without intervention, but some cases must be treated with fluid replacement and hospitalization

Critical cases of Salmonellosis

Salmonella can enter the bloodstream, cause sepsis, and potentially be fata

Around _____ million Salmonellosis cases are estimated

93.8

When did a surge of salmonellosis cases occur? Likely due to what phenomenon?

A surge of cases occurred in the 1980s, likely due to reduced genetic diversity due to modern poultry farming practices, a growing concern public health

Salmonella Shigella Agar (SSA) medium

Restricts certain gram-positive strains while permitting the growth of specific gram-negative strains

3 main components of SSA medium

1. Peptone

2. Lactose

3. Essential micronutrients

2 selective agents of SSA medium

1. Bile salts

2. Neutral red

What happens to the pH indicator in an SSA medium?

pH indicator, neutral red, turns red when pH drops below 6.8 due to lactose fermentation by E. Coli

Carbon source of salmonella

Salmonella uses peptone as a carbon source and does not ferment sugar

2 reducible sulfur sources in SSA medium

1. Ferric acid

2. Sodium thiosulfur

Salmonella color in SSA medium

Most Salmonella strains produce hydrogen sulfide, turning the medium black

Shingella color in SSA medium

Shigella lacks the enzymes for sulfur reduction, maintaining its original color

What must occur to identify a species in the lab?

To identity a species, individual strains have to be grown separately, starting from a single cell

Streaking

most commonly used method to isolate strain originating from a single cell

Principle of streaking methods

spreading a large number of cells over an agar plate in a sequential manner until they are well separated

How are streaks organized on an agar plate?

Each streak is numbered and colored to indicate the order of application

What occurs after streaking?

The plate is incubated and cells start dividing, forming colonies

Colonies consist of ____________________________

genetically identical clones originating from single cells

Isolated colonies

Tend to grow larger than those in close proximity and have less competition for nutrients

Purpose of isolated colonies

offer an opportunity to establish a pure culture, a genetically identical bacterial population, suitable for further in-depth study in either liquid or solid media

2 other qualities that can provide useful information for identification

1. Morphology

2. Motility

Function of sterile technique

ensure a clean lab environment and ensure the reliability of experimental results

6 steps used to keep lab work sterile

1. Lab doors and windows are closed

2. Wire loop and glass spreader are sterilized before and after use with a Bunsen burner

3. Lids from bottles and tubes are held when removed, and not placed on the bench during material transfer from one bottle or tube to another

4. Neck of a bottle or tube is immediately heated using the Bunsen burner

5. Bottle or tube is opened for the minimum time possible, and while open, all work is performed close to the Bunsen burner flame

6. Media and equipment are sterilized

Logarithmic scale

nonlinear scale that is used when measurements differ by several orders of magnitude

5 common uses of the logarithmic scale

1. Earthquake strength

2. Sound loudness

3. Light intensity

4. Growth curves

5. pH of solution