Overview of Waterborne Pathogens - Waterborne Pathogens: Detection Methods and Applications - page 9

Microbiology Definitions—cont'd
Genera: A taxonomic category ranking used in biological classification that
is below a family and above a species level, and includes group(s) of species
that are structurally similar or phylogenetically related. In binomial nomencla-
ture, the genus is used as the first word of a scientific name. The genus name is
always capitalized and italicized, e.g. Cryptosporidium . In order for a genus to
be descriptively useful, it must have monophyly, reasonable compactness, and
distinctness.
Species: A taxonomic category subordinate to a genus (or subgenus) and
superior to a subspecies or variety, e.g. Cryptosporidium parvum . An exact defini-
tion is difficult but could be thought of as populations of organisms with a high
degree of genetic similarity. In terms of sexually reproducing organisms, a spe-
cies could be thought of as a group of organisms that could potentially inter-
breed and produce fertile offspring.
Strains: A simple definition is that a strain is a genetic variant or subtype of
a microorganism. According to the first edition of Bergey's Manual of Systemic
Bacteriology, “A strain is made up of the descendants of a single isolation in pure
culture and usually is made up of a succession of cultures ultimately derived from
a single colony.” For a more detailed discussion, see Ref. 5 .
Spores: A dormant, reproductive cell formed by certain organisms. It is
thick-walled and highly resistant, enabling it to survive under unfavorable con-
ditions so that when conditions revert to being suitable they give rise to a new
individual.
Cysts/oocysts: A resting or dormant stage of a microorganism/the encysted
zygotic stage in the life cycle of some sporozoans. Encystment helps the microbe
to disperse easily, from one host to another or to a more favorable environment.
When the encysted microbe reaches an environment favorable to its growth and
survival, the cyst wall breaks down by a process known as excystation .
Prokaryotic: This cell type is a simple structure and is confined to the bacteria.
They are typically less than 5 µm long and 1 µm wide and have little structural
organization within the cell. The single DNA molecule is in direct contact with the
cytoplasm. Prokaryotes reproduce asexually by division.
Eukaryotic: This cell type is more complex than the prokaryote, contain-
ing several distinct intracellular compartments. These structures are known
as organelles, e.g. a nucleus, and are surrounded by membranes, enabling the
maintenance of chemical conditions within the organelles, which is different
from cytoplasm. There is no such thing as a typical eukaryotic cell as they exhibit
considerable diversity. Eukaryotes can reproduce sexually or asexually.
Culture: With regard to microorganisms, this term refers to in vitro culti-
vation of cells. Culturing of microorganisms requires specific culture media