Environmental Engineering Reference
In-Depth Information
the flow, waiting for their opportunity to meet up with their unsuspect-
ing host or hosts. To some degree, when the pathogenic microorganism
finds a host, it is finally home and may have found its final resting place.
Bacteria*
Of all the microorganisms studied in this text, bacteria are the most widely
distributed, the smallest in size, the simplest in morphology (structure), and
the most difficult to identify and classify. Because of considerable diversity,
even providing a descriptive definition of a bacterial organism is difficult.
About the only generalization that can be made is that bacteria are single-
celled plants, are procaryotic (the nucleus lacks a limiting membrane), are
seldom photosynthetic, and reproduce by binary fission.
Bacteria are found everywhere in our environment—they are present in
the soil, in the air, and in the water. Bacteria are also present in and on the
bodies of all living creatures, including humans. Most bacteria do not cause
disease; not all of them are pathogenic. Many bacteria perform useful and
necessary functions related to the life of larger organisms.
When we think about bacteria in general terms, we usually think of the
damage they cause; in fact, “the form of water pollution that poses the most
direct menace to human health is bacteriological contamination” (Black-
Covilli, 1992, p. 23). This is partly the reason why bacteria are of great
importance to water specialists. For water treatment personnel tasked with
providing the public with safe, portable water, controlling and eliminating
disease-causing bacteria pose a constant challenge (see
Table 6.3
).
Attempts to eliminate disease have placed bacteria high on the list of
microorganisms of great interest to the scientific community. This interest
has spawned much work geared toward enhancing our understanding of
bacteria; however, we still have a great deal to learn about bacteria. “We are
still principally engaged in making observations and collecting facts, trying
wherever possible to relate one set of facts to another but still lacking much
of a basis for grand unifying theories” (Thomas, 1983, p. 71).
One of the important aspects of bacteria for which we still lack complete
understanding is the infecting dose. Determining, for example, the num-
ber of viable pathogenic cells necessary to produce infections is difficult.
The National Academy of Sciences (1977, 1982), for example, reported values
varying from 10
3
to 10
9
pathogenic cells per person, with subjects infected
representing from 1 to 95% of the total subjects tested.
* This section was adapted from Spellman, F.R.,
Microbiology for Water/Wastewater Operators
,
Technomic, Lancaster, PA, 1997, pp. 19-80.
