Microbiology Week 1

Module 03 Homework Assignment

Use the information presented in this module along with additional outside research to answer the questions:

1. Describe the different stages of bacterial growth.

There are several different phases to bacterial growth the first of which is the lag phase. During lag phase bacteria acclimate themselves to their new surroundings, grow and get ready to divide. During this phase RNA, enzymes, and other molecules are synthesized. The following the phase is the log phase. During log phase the cells start to divide, growing exponentially until all available resources for growth are used up. Directly following log phase is the stationary phase. During the stationary phase growth stops due to the depletion of nutrients, and the cells maintain their numbers as only new cells are formed when the old ones die off, maintaining a stationary number. The last phase is that of decline, where the population decreases as the cells begin to die off.

2. Discuss four methods of measuring bacterial growth.

There are two main ways to measure bacterial growth: Direct and Indirect.

With the direct measuring you have: Plate count in which your measurement is taken from the visible cells on a plate.

Filtration is used to measure small quantities of bacteria from a large sample. The sample is filtered to retain bacteria and then transferred to a petri dish, where the colonies are counted after incubation.

Most probable number is used to measure bacteria that will not grow on a solid medium, this is only a statistical method that will determine with 95% probability that a bacteria will fall in a certain range.

Direct microscopic count, is when a bacteria is counted by hand using a microscope and a slide with a grid, the cells counted are then multiplied by a factor to get a rough concentration number.

With indirect measuring there are a few different way too: Turbidity where a bacteria is allowed to multiply until it become turbid. Then...