Bacterial Growth Lab Report

Chapter 5

Bacterial Growth

Micro-organisms such as bacteria can be grown in the laboratory if essential components required for their survival are present. The cat of growing bacteria in the lab is referred to as culture and the environment on to which the bacteria is grown is called culture medium. The essential ingredients required for bacterial growth include: o Carbon source o Nitrogen o Metal irons o Presence or absence of Oxygen o Optimal temperature o Optima pH o Moisture

Forms of Media

There are different forms of media onto which bacteria is grown in the laboratory: o Solid o Semi-solid and o Fluid medium

Solid medium typically contains about 2% solidifying gel called Agar. It is used mainly in petri dishes and its main purpose

"Chemiosmotic hypothesis of oxidative phosphorylation". Nature. 213 (5072): 137–9. Bibcode:1967Natur.213..137M. doi:10.1038/213137a0. PMID 4291593; Berg JM, Tymoczko JL, Stryer L. Chapter 18 Oxidative Phosphorylation. Biochemistry. 5th edition, New York: W H Freeman; 2002). Many bacteria such as Enterobacteriaceae and Staphylococcus are facultative anaerobes.

Aerotolerant Aerobes

This group of bacteria get their energy from fermentation alone but unlike anaerobes they are not affected by the presence of oxygen. An examples of such as bacteria is Lactobacillus which is part of the normal flora of the gut and vaginal tract.

Microaerophiles

Microaerophilic bacteria require oxygen for growth and multiplication but at levels lower than found in the atmosphere. They are killed by high oxygen concentration and an example is Helicobacter pylori, a bacteria that can cause stomach

This generation time is however variable with more fastidious organisms such as Mycobacterium tuberculosis and Clostridium species taking longer time to grow. The growth of bacteria in a culture medium is described in a bacterial growth shown in the diagram below with four distinct growth phases (Zwietering MH, Jongenburger I, Rombouts FM, van 'T Riet K (1990). "Modeling of the Bacterial Growth Curve". Applied and Environmental Microbiology. 56 (6): 1875–1881).

Lag Phase: This is the period immediately after sub-culturing bacterial cells on culture medium. During this phase there is no apparent cell division as the bacteria are adjusting to the new environment, finding sources of food and synthesizing enzymes for metabolism

Log Phase: Bacterial cells divide by binary fission and the bacterial population grows exponentially (1, 2, 4, 16, 32 etc.)

Stationary Phase: Bacterial cell division cannot continue indefinitely as the cells begin to run out of food and space. During this phase the number of new cells equals the number of cells that are dying.

Death Phase: During this period the number of cells dying is greater than new cells being generated because of exhaustion of space and available nutrients. In addition there is accumulation of toxic metabolites which affects bacterial