3 Chemical Control of Microbial Growth

Objectives: In this lab you will:

1. Learn about disinfectants and the various factors that need to be considered when choosing a disinfectant.
2. Set up an experiment to determine the effectiveness of five different common disinfectants

Introduction

The use of chemicals to control microbial growth dates back at least as far as the 1800’s. Tincture of iodine was used as antiseptic during the Civil War, and Joseph Lister established the practice of aseptic surgery using a disinfectant known as carbolic acid (phenol) in the 1860’s. Since that time, many types of disinfectants (agents that are used to eliminate or kill vegetative cells on surfaces) and antiseptics (agents that are used to eliminate or reduce vegetative cells on living tissue) have been used. Although disinfectants and antiseptics may be effective at killing vegetative cells, they do not usually achieve sterilization.

Various factors need to be considered when choosing a disinfectant or antiseptic. It is very important to know which microbes are present to determine what type of disinfectant would work best. It is also important to realize that the effectiveness of a particular disinfectant may be affected by pH, temperature, concentration, and exposure time. Ideal disinfectants should be effective against the particular contaminants present, usable at a low concentration, require a relatively short exposure time, and have a long shelf life. It should also be water soluble, non-toxic to humans and animals, and cost-effective.

Method:

1. Divide your plate into 10 sections as shown.
2. With a gloved hand, rub all 5 fingers on a dirty surface such as the floor, toilet, the floor, a cell phone.
3. Gently touch each finger to each of the 5 spaces to the left on the plate.
4. One by one, wash each finger with a different chemical and imprint again on the right side of the place. Inlude your name, finger number, date, and chemical used.
5. Bacterial growth will be observed next lab period.