Microorganisms for Study

BS = Bacillus subtilis

EC = E. coli ( Optional)

SM= Serratia maracescens

ML= Micrococcus luteus

Growth characteristics.

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. 

Excellent Streak 1


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



Micrococcus luteus.  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

Colony terminology




 Experiment 1.  Additional practice with technique. Make the following tubes; Lab Partners

(3)4 slants - 1 for each bacterium

(3)4 Deeps

(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