Microorganisms for Study
BS = Bacillus subtilis
EC = E. coli ( Optional)
SM= Serratia maracescens
ML= Micrococcus luteus
Note - Bacteria divide rapidly. When a plate is inoculated with bacteria, the visible sign of this rapid growth is the formation of colonies on the surface.
http://www.austin.cc.tx.us/microbugz/03morphology.html - Pictures of bacterial growth on agar
In the broth evidence of growth is turbidity or cloudiness
On the slant growth underneath the surface is indicative of anaerobic organisms. Growth on the surface is indicative of aerobic.
Key- Organisms for study - Class Two
Bacillus subtilis - white(cream)colonies - Incubation temperature - 30oC
These gram positive, sporeforming rods produce colonies which are dry, flat, and irregular, with lobate margins
Micrococcus luteus - yellow colonies - Incubation temperature - 30oC
Circular, pinhead colonies which are convex with entire margins. This gram
positive coccus produces a bright yellow, non-diffusable pigment.
Serratia maracescens - pink to red colonies - Incubation temperature - 25oC
Some strains of S. marcescens produce the red pigment prodigiosin in response to incubation at 30o C, but do not do so at 37o C. This is an example of temperature-regulated phenotypic expression
Escherichia coli - white( cream) colonies - Incubation temperature - 37oC
This gram negative rod (coccobacillus) forms shiny, mucoid colonies which have entire margins and are slightly raised. Older colonies often have a darker center
Experiment 1. Additional practice with technique. Make the following tubes; Lab Partners
(3)4 slants - 1 for each bacterium
(3)4 Broths - for each bacterium
(3)4 Plates - Dilution streaks
8. Experiment 2A. Make a dilution streak of mixtures of bacteria to demonstrate the isolation of organisms.
Mixture 1 - SM and BS
Mixture 2- ML and SM
9. Experiment 4. Review Microscopy - Practice the oil immersion technique. Review the parts of the microscope.
How to use oil immersion - Oil immersion directions
10. Use the oil immersion procedure to look at slides of different shapes of bacteria. Coccus and bacillus.
Review of bacterial morphology. See supplement for cellular morphology