The phylum
Bacteroidetes is composed of three large groups of bacteria with the best-known category being
Bacteroidaceae. This family of gram-negative bacteria is found primarily in the intestinal tracts and mucous
membranes of warm-blooded animals and is sometimes considered pathogenic.
Comprising
Bacteroidaceae are the genus
Bacteroides and
Prevotella. The latter genus was originally
classified within the former (i.e.
Bacteroides), but since the 1990's it has been classified in a separate genus
because of new chemical and biochemical findings.
Bacteroides and
Prevotella are gram-negative, anaerobic,
rod-shaped bacteria that inhabitant of the oral, respiratory, intestinal, and urogenital cavities of humans,
animals, and insects. They are sometimes pathogenic.
Fecal
Bacteroidetes are considered for several reasons an interesting alternative to more traditional indicator
organisms such as
E. coli and
Enterococci. Since they are strict anaerobes, they are indicative of recent
fecal contamination when found in water systems. This is a particularly strong reference point when trying to
determine recent outbreaks in
fecal pollution. They are also more abundant in feces of warm-blooded animals
than
E. coli and
Enterococci. Furthermore, these latter two organisms are facultative anaerobes and as such
they can be problematic for monitoring purposes since it has been shown that they are able to proliferate in
soil, sand and sediments.
The
Pig Bacteroidetes ID™ service is designed around the principle that fecal
Bacteroidetes are found in large quantities in feces of warm-blooded animals. Furthermore, certain categories of
Bacteroidetes have been
shown to be predominately detected in swine. Within these
Bacteroidetes, certain strains of the
Bacteroides and
Prevoella tgenus have been found in swine. As such, these bacterial strains can be used as
indicators of swine
fecal contamination.
One of the advantages of the
Pig Bacteroidetes ID™ service is that the entire water is sampled and filtered for
fecal
Bacteroidetes. As such, this method avoids the randomness effect of culturing and selecting bacterial
isolates off a petri dish. This is a particular advantage for highly contaminated water systems with potential
multiple sources of
fecal contamination.
Accuracy of the results is possible because the method uses PCR DNA technology. PCR allows quantities of
DNA to be amplified into large number of small copies of DNA sequences. This is accomplished with small
pieces of DNA called primers that are complementary and specific to the genomes to be detected.
Through a heating process called thermal cycling, the double stranded DNA is denatured and inserted with
complementary primers to create exact copies of the DNA fragment desired. This process is repeated rapidly
many times ensuring an exponential progression in the number of copied DNA. If the primers are successful in finding a site on the DNA fragment that is specific to the genome to be studied, then billions of copies of the
DNA fragment will be available for detection by gel electrophoresis.
The gel electrophoresis apparatus uses an electrical field to distinguish different DNA fragments according to
their molecular weights. Lighter DNA fragments will move farther along the gel than their heavier counterparts.
At the end of the procedure different bands of accumulated DNA fragments will aggregate at different parts of
the gel. It is this accumulation of DNA fragments that creates a band on the gel. Researchers use these bands
to distinguish certain genomes such as the swine gene biomarker from the
Bacteroides and
Prevotella genus.
These banding patterns confirm or negate the presence of the fecal
Bacteroidetes swine gene biomarker. As
such, the banding patterns can be a good indicator of swine
fecal contamination. Nonetheless, in order to
strengthen the validity of the results, the
Pig Bacteroidetes ID™ service should be combined with other DNA
analytical services such as the
Pig E. coli ID™ and
Pig Fecal Virus ID™ services.
