microbio Control of Microbial Growth

Bacteria are classified by their

Optimal growth temperatures

Pyschrophiles

Grow best at temperatures below 15 degrees C

Mesophiles

Grow best at temperatures between 15 and 45 degrees C

Thermophiles

Grow best at temperatures above 45 degrees C

Heat controls growth by

Denaturing enzymes and melting lipids

Thermal Death Time

Shortest exposure time to heat that results in no growth

UV light kills bacteria and causes

Pyrimidine (thymine) dimers in DNA and leads to mutation

Plasmolysis

In a hypertonic environment, water leaves the cell, causing the protoplasm to shrink and cell dies

High pH———-, while low pH———-

can break DNA strands, can break hydrogen bonds in proteins

Antiseptics

Chemicals safe for use on living tissue

Disinfectants

Chemicals used on inanimate objects

Kirby-Bauer Method

A disk diffusion test where antibiotic disks are placed on agar

A clear zone of no growth( ZOI) indicates a ineffective chemical

Why is an autoclave more effective that sterilizing in a dry oven?

Moist heat penetrates microbial cells more effectively to denature proteins

Examples of physical agents that control microbial growth in lab

Change in incubation temperature, exposure to UV, and heat