Biomedical Engineering Reference
In-Depth Information
Clostridiaceae
*Clostridium
*Peptostreptococcus
Veillonellaceae
*Veillonella
Chlamydiae (Chapter 13)
Actinobacteria (Chapter 14)
Class Bacilli and Class Clostridia constitute a group of bacteria that, together, are
sometimes called Class Firmicutes. In this topic, the class name “Firmicutes” is
abandoned because it has been used, at various times, to include Class Mollicutes
(Chapter 11). Still, Class Bacilli and Class Clostridia are sister classes and share a
number of important phylogenetic properties and are best discussed together.
Class Clostridia and Class Bacilli are characterized by Gram-positive
species that have a low G
C ratio (a feature that distinguishes this group
from Class Actinobacteria, Chapter 14, whose members are Gram-positive,
with a high G
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C ratio). Bacteria in Class Clostridia and Class Bacilli have a
propensity for synthesizing biologically active chemicals, accounting for sev-
eral of the most potent toxins in biology (e.g., botulinum toxin, tetanospas-
min). Members of Class Bacilli and Class Clostridia tend to be short rods
(bacilli) or round (cocci), anaerobic, and capable of forming endospores.
Endospore formation, though not present in all members of Class Bacilli and
Class Clostridia, is never seen outside these classes.
Bacterial endospores, often referred to by the shortened form, “spores,” are
fundamentally different from the spores produced by members of Class
Protoctista (i.e., endospores are not the equivalent of the germinative cell of a
multi-stage life cycle). Bacterial endospores are simplified forms of the bacteria,
consisting of the DNA genome, some small amount of cytoplasm, and a special-
ized coating that confers resistance to heat, radiation, and other harsh external
conditions. Endospores are virtually immortal, and can be re-activated, under
favorable growth conditions, after lying dormant for hundreds or perhaps mil-
lions of years [53]. Due to their ability to grow under anaerobic conditions, and
to lay dormant for long periods, it can be nearly impossible to prevent infections
caused by pathogenic species of Class Bacilli and Class Clostridia.
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Bacilli
Bacillales (catalase positive)
Listeriaceae
*Listeria
Staphylococcaceae
*Staphylococcus
Bacillaceae
*Bacillus
Lactobacillales (catalase negative)
Enterococcaceae
