Exercise 13: Control of Microorganisms

What are chemicals that can kill or inhibit the growth of microorganisms?

antibacterial agents

Agents that end in -cide/-cidal will:

kill the microbes that are used to treat

Bactericidal=

will kill microbe

Agents that end in -static will:

inhibit growth of microbes

Bacteriostatic=

inhibits growth; will not kill

What are the three major types of antimicrobials?

-Disinfectants

-Antiseptics

-Antibiotics

A disinfectant is:

a strong chemical agent used on inanimate surfaces

Disinfectants are as effective as sterilization, T or F?

false; not as effective; may not kill resistant spores.

Examples of disinfectants are:

-bleach

-lysol

Antiseptics are:

chemical agents that may be safely applied to living tissue

Antiseptics are only able to inhibit growth since it is an agent that can be used on living tissue, T or F?

false; can kill OR inhibit microbes

Antiseptics can prevent infection, T or F?

true

Antibiotics are:

compounds that may be administered for systemic circulation (via pills, injections, or other methods) for the purpose of killing bacteria or inhibiting their growth

Most antibiotics used today are true antibiotics, T or F?

false; most are synthetic analogs of naturally occurring compounds

What test is used as a antibiotic sensitivity testing method?

Kirby-Bauer Test

What type of streak must you do when starting a Kirby-Baier test?

a lawn inoculation

What is placed on the lawn of bacteria prior to incubation for a Kirby-Bauer Test?

antibiotic impregnated paper discs

Clearing around the antibiotics discs is called:

the zone of inhibition

What is the zone of inhibition used for?

zone is measured to determine if a organisms is susceptible, resistant, or intermediate to a certain antibiotic

What medium is used for a Kirby-Bauer Test?

Mueller-Hinton Agar (MH)

MH=

Mueller-Hinton Agar

MH agar is used for this test because the pH of the agar is ____. Why?

neutral (7.2-7.4); b/c anything outside this range can affect the stability and function of the antimicrobials

What is the depth of the MH agar plate? Why?

4mm; depth can affect lateral diffusion rate of antibiotics

What happens if the initial concentration of the bacteria inoculated is too low?

overestimation of bacterial sensitivity

What happens if the initial concentration of the bacteria inoculated is too high?

"swamps" the antimicrobial, or quickly deplete nutrients, which can affect the growth of the bacteria

An assessment with too low or too high of initial bacteria inoculation is fine, as the antibiotic will do its job regardless, T or F?

false; not a proper assessment

Kirby-Bauer test is only done when?

under extraordinary circumstances: infectious agent unknown, antibiotic resistance, or immediate life-threatening condition such as meningitis or endocarditis

How is susceptibility determined on a Kirby-Bauer Test?

by measuring the diameter of the zone of inhibition around the antimicrobial disk

The diameters that differentiate a bacteria from being resistant, intermediate, or susceptible are all the same, T or F?

false; each antibiotic have different measurements according to what bacteria they are working against.

When the antimicrobial disk is placed on the medium that is inoculated with bacteria, what does it start doing?

diffuses into the agar; will leach and spread throughout medium over time

Over time, the diameter of what area will increase?

diffusion area

What is established in the medium, with the highest concentration closest to the disk and lower concentrations farther from the disk?

concentration gradient

Highest concentration of antimicrobial will be closet or farther from the disk?

closest

Lower concentration of antimicrobial will be closet or farther from the disk?

farther

How does one do a lawn inoculation on agar?

streaking heavily in one direction, the rotate plate and streak at 90 degrees