Growth Patterns in Broth, Bacterial Growth,Atlas of Growth Patterns in Broth, A Photographic Atlas for the Microbiology Laboratory
Purpose
Bacterial genera—and frequently different species within a genus—demonstrate characteristic growth patterns in broth that provide useful information when attempting to identify an organism.
Principle
Microorganisms cultivated in broth display a variety of growth characteristics. Some organisms float on top of the medium and produce a type of surface membrane called a pellicle; others sink to the bottom as sediment. Some bacteria produce uniform fine turbidity while others appear to clump in what is called flocculent growth. Refer to Figures 3-35 and 3-36. Figure 3-37 shows an example of a pigmented species (Rhodospirillum rubrum) in broth.
3-35 GROWTH PATTERNS IN BROTH From left to right in pairs (by type of organism):
Enterobacter aerogenes and Citrobacter diversus—motile members of Enterobacteriaceae
(uniform fine turbidity), Enterococcus faecalis and Staphylococcus aureus—nonmotile Grampositive cocci (sediment), Mycobacterium phlei and Mycobacterium smegmatis (relatives of
Mycobacterium tuberculosis)—nonmotile with a waxy cell wall (pellicle).
3-36 FLOCCULENCE IN BROTH
This is a Streptococcus species from
a throat culture demonstrating
flocculence in Todd-Hewitt Broth.
3-37 PIGMENT IN BROTH
Rhodospirillum rubrum has a red color due
to carotenoid pigments. It
grows as a photoheterotroph in the presence of
light and the absence of
oxygen.
Suggested Reading
- Michael J. Leboffe & Burton E. Pierce. A Photographic Atlas for the Microbiology Laboratory 4th edition 2011
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