microbioLAB #7: Effects of Chem Agents on Bacteria: Antimicrobial Agents and Disinfectants

Antimicrobial agents include what terms:

• antibiotics

• antiseptics

• disinfectants

• sterilization

antibiotics

1. are what?

2. function?

3. Describe the diff ways of administering them for antibiotic treatment

1. are antimicrobial agents used for fighting bacterial infections within the body.

2. They may either kill or inhibit the growth of bacteria.

3. There are different routes of administration for antibiotic treatment.

   • Antibiotics are usually taken by mouth

   • in more severe cases, particularly deep-seated systemic infections, antibiotics can be given intravenously or by injection.

   • Where the site of infection is easily accessed, antibiotics may be given topically in the form of eye drops or skin creams.

Antiseptics

1. are what?

2. can be used on what?

• are antimicrobial agents that applied to living tissues or body surfaces to destroy or inhibit vegetative pathogens.

• They can be used on human or animal body, skin, mucoses, wounds

disinfectants

1. are applied to what?

2. are they capable of killing all microorganisms?

3. What is sterilization and are disinfectants more effective than sterilization?

4. how do disinfectants work?

• are antimicrobial agents that are applied to the surface of non-living objects to destroy microorganisms that are living on the objects.

• Disinfection does not necessarily kill all microorganisms, especially resistant bacterial spores;

• it is less effective than sterilization, which is an extreme physical and/or chemical process that kills all types of life.

• Disinfectants work by destroying the cell wall of microbes or interfering with their metabolism.

Sterilization

• is the complete removal or destruction of all viable microorganisms. This technique is used on inanimate objects

Kirby-Bauer Method

1. what is it?

2. method was named after who in what year?

3. describe the process

4. how are the results interpreted?

5. what does a smaller diameter mean?

1. The method that is used to determine antibiotic susceptibility is the sensitivity disk method of Kirby-Bauer.

2. The method is named after W. Kirby and A.W. Bauer in 1966.

3. How it works:

   • The antibiotics are impregnated onto paper disks then placed on agar plates.

   • Muller-Hinton II agar (MH) plates are used in the Kirby-Bauer method.

   • The Plates are incubated for 16-18 hours.

   • During incubation, the antibiotic diffuses into the agar. If the antibiotic inhibits bacterial growth, a clear circular area—called the zone of inhibition—will form around the disk.

4. The diameter of the zone of inhibition around the disk is measured to the nearest millimeter.

4. A zone of certain size indicates susceptibility Or resistance of bacteria to antibiotics.

5. The smaller diameter or no zone = bacteria is resistant to the antibiotic tested.

Kirby-Bauer Method

1. MIC (Minimum inhibitory Concentr)

2. Antibiograms

1. MIC (Minimum Inhibitory Concentration): is the lowest concentration of an antibiotic that inhibits a visible growth of a microorganism after overnight incubation

2. Antibiograms: These are organized patterns of antibiotic susceptibility compiled from laboratory test results. They show how effective various drugs are against specific bacterial strains.

   • susceptibility determined by comparing zone diameter and size

E-test

1. does what?

2. useful for what kind of pathogens(aerobic/anaerobic)?

3. how does it work?

4. ea strip represents what?

5. zone of inhibition appears how many hours post incubation?

6. e-test allows for determination of what? what point?

• Determines level of antimicrobial activity.

• Useful for anaerobic pathogens.

• Bacteria is streaked to the plate and E-Test strips are placed on the surface that extend out.

• Each strip represents a different antibiotic.

• Zone of inhibition appears 24-48 hours post incubation.

• E-Test allow determination of MIC (minimal inhibitory concentration) from the point of intersection between the inhibition zone and the strip’s printed scale of MIC values.

Microbiostatic

These agents inhibit (stop) microbial growth rather than killing the microbes outright. The efficiency of a chemical agent here is determined by its ability to prevent population growth.

microbiocidal

how is their efficiency measured?

kill microorganisms; microbiocidal efficiency of a chemical is

determined with respect to phenol,

thus termed Phenol Coefficient (PC)

• Ex 1:10 (highest concentration at which lysol was effective) compare to 1:100 and 1:1000

antibiotics’ mode of axns:

• inhibition of cell wall synthesis

  • penicilin

  • cephalosporin

  • bacitracin

  • vancomycin

• inhibition of protein synthesis

  • chloramphenicol

  • erythromycin

  • tetracyclines

  • streptomycin

• inhibition of nucleic acid replication and transcription

  • quinolones

  • rifampin

• inhibition of plasma membrane

  • polymyxin B

• inhibition of synthesis of essential metabolites

  • Sulfanilamide

  • trimethoprim