Lab 11 study guide

chemicals that may be applied safely to skin or other biological tissues

• chemicals that kill or inhibit the growth of vegetative cells on the surfaces of nonliving materials
• more toxic than antiseptics

• apply the chemical to a freshly inoculated plate
• incubate the culture
• look for the zone of inhibition (area of no growth)
• zone only shows if bacteria has been killed or slowed growth--can't tell which

slows growth of bacteria

actually kills bacteria

• antiseptics used on skin
• disinfectants used to kill bacteria on hard nonliving surfaces

alcohol

iodine

heavy metals

detergents

phenols (thymol)

oxidizing

The continued application of a single agent will select for microbial mutants that are resistant to that agent. That risk is minimized when you use higher concentrations and is almost eliminated when ytou use a combination of effective agents.

• bacteriostatic only slows the growth of organisms
• bactericidal kills organisms
• zone of inhibition does not discriminate between the two. don't know if the organism was killed or slowed.

The size of the zone depends not only on the effectiveness of the antiseptic or disinfectant but also on its ability to diffuse into the medium. Even a very effective chemical that does not readily diffuse out from its source will not produce a very large zone of inhibition.