kms

Catalase Test (+ vs -)

- Positive: Catalase utilized, BUBBLES FORMED

- Negative: No catalase utilized, NO BUBBLES

Bacteriostatic

Inhibits growth

Bactericidal

Prevents growth by killing microorganisms

MIC

- Minimum Inhibitory Concentration

- Lowest concentration of antibiotic needed to inhibit growth

MBC

- Minimum Bactericidal Concentration

- Lowest concentration that prevents growth and induces cell death

Analyzing MIC and MBC

- If MBC is close to MIC, agent is bactericidal

- If MBC>>>MIC, agent is bacteriostatic

Calculate MIC ***

1) Identify correct tube

2) Calculate dilution factor (df=transfered/total)

3) Calculate antibiotic concentration

Disc Diffusion (Kirby Bauer Method)

- Shows if the bacteria is sensitive or resistant to chosen antibiotics.

What standard does Kirby Bauer use?

MHA and McFarland standards

Kirby Bauer Method: Diameter meaning

- The bigger the diameter of the clearing (zone of inhibition), the more effective the drug at killing the bacteria.

Kirby Bauer Method: Limitations

- Cannot use this test to decipher between bacteriostatic or bactericidal drugs

- Can only determine efficacy of antibiotic for that given bacteria

Zone of Inhibition

Diameter of the clearing

Disc Diffusion Standardization Factors

1) Sensitivity of the organisms

2) Antimicrobial molecule size and concentration

3) Density of culture

4) Diffusion rate of agent

5) Incubation time and temp

6) Size of inoculum

7) Interactions

Biofilm

- Sticky material made up of polysaccharides, proteins, lipids, and DNA that contains bacteria

Where is biofilm found

- In moist environments where excess nutrients are available

Planktonic Cells

Floating cells

Sessile Cells

Cells attached to a surface