Lab Quiz 8: Control of Microbe Growth

Antimicrobial

A chemical compound, regardless of its source (natural or synthetic), that is capable of killing or inhibiting microorganisms is referred to as: an Antimicrobial.

Zone of Inhibition Size

A large zone of inhibition around a disinfectant disk indicates that the bacteria being tested is Susceptible to the antibiotic.

Comparing Susceptibility of microbes to Chemical Disinfection

Bacteria's susceptibility to chemical disinfectants from least to most: 1. Bacterial Endospores (least sus) 2. Acid-fast bacteria 3. Gram-negative bacteria 4. Gram-positive bacteria (most sus)

Microbial structures Resistant to UV damage

Endospores and Protozoan cysts are less susceptible to UV damage.

Inoculating for Disk diffusion

How are agar plates inoculated for disk diffusion testing of antiseptics and disinfectants? A swab is used to inoculate the entire surface of the plate, producing a lawn of growth.

interpreting antimicrobic susceptibility testing result

Interpreting antimicrobial susceptibility testing results: Using the given table, label each test result as sensitive, intermediate, or resistant in regards to the organisms' susceptibility to each antibiotic. - Streptococcus pyogenes with 22mm zone around e-rythro disc: Sensitive - Staphylococcus aureus with 16mm zone around e-vrytho disc: Intermediate - Acinetobacter with 11mm zone around gentamicin disc: Resistant

Effect on agar thickness on Kirby-bauer results:

Mueller-Hinton agar plates are poured to a uniform thickness of 4mm. If a plate had been poured 7 mm thick, it would affect the the zones of inhibition; Making them smaller.

Least Resistant to UV

Prions are least likely to be damaged by the exposure of UV Radiation. UV damages DNA, Prions do not have DNA.

Antimicrobic Sensitivity Purpose

Sensitivity testing is done to determine what antimicrobials would be most effective for treating an infection.

Testing the effectiveness of Antiseptics and Disinfectants

Steps for testing the effectiveness of disinfectants and antiseptics using a disk diffusion: 1. Using a swab, inoculate a suspension of the bacteria onto an agar plate, spreading the inoculum over the entire surface. 2. Saturate sterile filter paper disks with the test chemical and place onto the inoculated agar plate. Repeat with each chemical being tested. 3. Incubate inoculated agar plates overnight to promote bacterial growth. 4. Observe plates to determine the presence of a zone of inhibition around each antiseptic or disinfectant disk.

Kirby Bauer Method Steps

Steps of the Kirby Bauer method sensitivity testing: 1. Label a sterile Mueller-Hinton agar plate with organisms name and your name. 2. Obtain a dilute suspension of the organism in nutrient broth to use as the inoculum. 3. Using a swab, inoculate the agar plate uniformly by swabbing in three directions. 4. Dispense antibiotic disks onto the inoculated surface using sterile forceps or an automatic dispenser. 5. Tap down disks with sterile forceps. 6. Incubate for 18-24 hours at 35oC. 7. Measure diameters of zones of inhibition and compare zone diameters to interpretive charts and determine if S, I, or R.

Disk Diffusion Method (KB)

The Kirby-Bauer method of antimicrobial sensitivity testing can be described as the Disk diffusion test.

zone of inhibition

The clear area devoid of bacterial growth around an antiseptic or disinfectant disk is referred to as the Zone of Inhibition.

Difference between Antiseptic and Disinfectant

The difference between an antiseptic from a disinfectant is: An Antiseptic is used to remove or kill microorganisms on tissue, whereas a Disinfectant is used to remove or kill microorganisms on inanimate objects.

Susceptibility of DNA sequences to UV Radiation:

The following DNA sequences CTTGAATT would be the most likely to be damaged by UV radiation because: Its the only sequence that includes adjacent Thymines is the CTTGAATT. The other sequences do not include adjacent thymines, so would not form thymine dimers upon exposure to UV radiation.

Factors affecting the Size of a zone if Inhibition

The following would affect the size of a zone of inhibition around an antiseptic or disinfectant disk: - The susceptibility of the microorganism to the chemical. - The concentration of chemical in the disk. - How quickly the chemical diffuses through the agar. - The depth of the agar

Limitations of UV Radiation

The limitations of using UV Radiation for disinfection is: - UV radiation does not penetrate through paper, plastics, or liquids. - UV radiation can damage the skin and eyes.

Kirby-Baur Test Method

The method of antimicrobial susceptibility testing that involves measuring zones of inhibition around antibiotic disks placed on a culture of bacteria prior to incubation: Kirby-Baur test.

Sterilizing with UV Radiation

The stainless steel surface of a biological safety cabinet used for media preparation can be appropriately sterilized using UV radiation.

Increases the effectiveness of a Disinfectant

The two factors that would increase the effectiveness of a disinfectant on a microorganisms is: - Concentration of disinfectant. - Time of exposure.

Wavelengths of UV light

UV light has shorter wavelengths than visible light waves, and its peak energy is at a wavelength of 254nm.

Effect of UV Radiation on DNA

When two adjacent thymine molecules are joined by a covalent bond as a result of exposure to UV light, this structure is referred to as a: Thymine Dimer.