Bacteroid fragilis: Microbiology Assignment Report - HS 120

This report provides a comprehensive overview of Bacteroid fragilis, a gram-negative, anaerobic bacterium. It begins with the clinical manifestations of infections caused by Bacteroid fragilis, including abdominal infections and diarrhea. The report then details the bacterium's structure, classification, and natural habitats, primarily the gastrointestinal tract. The pathogenesis section explains the virulence factors, such as fimbriae and toxins, that contribute to its pathogenicity. Host defense mechanisms and epidemiological data, including its prevalence and antibiotic resistance, are also discussed. The report then covers diagnostic methods, treatment options involving specific drug combinations, and preventive measures, including hygiene and probiotics. Finally, it addresses dental considerations and relevant research findings related to this bacterium, supported by multiple references.

Bacteroid fragilis

Microbiology Assignment
Instructor:
Name: Date: June
29, 2018
Microorganism: Bacteroid fragilis
Clinical Manifestations: Bacteroid fragilis is a gram negative
bacteria that comprises of about 0.5% of the natural intestinal
flora in human beings (Boleij et al.,2014). It is known to cause
abdominal infections and perpetual diarrhoea. The
microorganism is mainly isolated from the stool sample of human
beings. The Bacteroid fragilis is responsible for causing
inflectional abscesses in various animal models employed to
carry out research studies such as the most common mammalian
model of Rattus species.
Structure: Bacteroid fragilis are classified under the group of
gram negative, pleuromorphic, anaerobic and rod shaped
bacterias. This group of bacteria does not form spores and
manifests the pathogenicity through the production of
enterotoxins. The genetic constitution of the microbes depict a
rich Guanine and Cytosine content up to almost 43.19% in
certain strains of the microbe (Boleij et al.,2014). The genetic
regulation of the microorganism is controlled by the vital sigma
factors that act in accordance with the responsiveness to
environmental stress.

Classification: With respect to the system of classifying and
placing microorganisms under the higher order taxonomy, the
bacteriod is placed under the following order:
Bacteria; Chlorobi; Bacteriodetes; Bacteriodes; Bacteriodales;
Bacteriodaceae; Bacteriods. (Ishikawa et al.,2013)
Some of the common strains would include, Bacteroides
vulgatus, Bacteriodes distadonis, Bacteriode eggerthii,
Bacteroide ovatus and Bacteroid fragilis (Eitel et al.,2013).
Natural Habitats: Bacteroid fibrosis are mainly found in the
gastrointestinal tract, especially around the colonic region of the
large intestine. This group of microorganism has been identified
as a potential opportunistic pathogen that is generally not
harmful. The occurrence of the microbe is also found in the
nasopharyngeal region, the internal surface of the mouth, the
skin and the vaginal tract.
Pathogenesis: Bacteroid fibrosis is identified as a potential
human opportunistic pathogen and it manifests the pathogenicity
through the five most important virulence factors which includes
the fimbriae, the structure that helps in the attachment of the
microbe to a specific substrate, the capsule that helps in
phagocytosis through lysis, presence of enzymes that resist the
toxic property of oxygen, presence of short chain fatty acids that
serve as a protection tool from the killing of the pathogen
intracellularly and finally the release of endotoxins that renders
weaker defence mechanism of the host organism.
Host Defense: Bacteroid fragilis comprises of a polysaccharide
capsule that acts as an immunological modulator and is capable
of generating a number of immune responses. The pathogenic
component of the bacteria produces a ‘metalloprotease’
component known as the fragilysin toxin that leads to an

increased influx of the mannitol due to the induced drop in the
dosage compensation of the HT-29 and MDCK cells (Virology,
BIMP,2013). Fragilysin or the Bacteroid fragilis toxin is also
responsible for altering the tight junctions and inhibiting the
adherence junctions of the MDCK cells (Smith et al.,2013). The
toxic property of fragilysin is responsible for the degradation of
the E-cadherin component in the HT-29 cells.
Epidemiology: The Bacteroid fragilis has been reported to be
the most common strain that forms a major part of the intestinal
flora. Studies reveal that more than 40% of the bacteroid group
is dominated by the strain of Bacteroid fragilis (Boleij et
al.,2014). The microbe is pleuromorphic, with an average size of
about 1.5 μm and 2 μm wide (Boleij et al.,2014). This strain is
penicillin resistant due to strong B-lactamase activity.
Diagnosis: The diagnosis of the infection caused by the
bacteroid includes a wide range of molecular biology tools and
biochemical tests. Some of the biochemical tests include,
Thioglycolate test in combination with bile, bile test that
measures an optimum percentage of 20% resistance action of
bile, PCR technique and the traditional method of screening the
pathogen with the help of analysing dark colonies formed in the
bacteroides bile esculin agar medium (Smith et al.,2013).
Treatment: A combination of drugs with the composition of
‘Metronidazole’, ‘Chloramphenicol’ and ‘Cephalosporin’ is
generally prescribed by the physicians to treat patients with the
infections caused due to the pathogenicity of the bacteroid
(Smith et al.,2013). Pencilin is not prescribed to patients affected
with an infection caused by this microbe because it is inactive
against this strain due to the ability to exhibit Beta-Lactamase
activity.

Prevention: Preventive measures include maintaining
cleanliness in health and hygiene practices. Infections in the
gastrointestinal tract can be avoided by the intake of mild doses
of probiotics, maintaining a balanced diet in the right proportion
and infections in the vaginal tract can be avoided by the use of
different mild antiseptics that would help in the correct
regulation of the pH balance and strictly check the degree of
pathogenicity.
Dental Considerations: Research studies reveal that most of
the patients affected with dental problems face issues related to
infection in the mandibular region and Clindomycin is strongly
recommended to cure the problem. In addition, maintenance of
proper oral hygiene with respect to regular mouth washing and
brushing at least twice a day can help in lowering the possibility
of a dental infection caused by the bacteroid.
References:
Boleij, A., Hechenbleikner, E. M., Goodwin, A. C., Badani, R.,
Stein, E. M., Lazarev, M. G., ... & Platz, E. A. (2014). The
Bacteroides fragilis toxin gene is prevalent in the colon
mucosa of colorectal cancer patients. Clinical Infectious
Diseases, 60(2), 208-215.
Eitel, Z., Sˇki, J., Urbßn, E., & Nagy, E. (2013). The prevalence of
antibiotic resistance genes in Bacteroides fragilis group

strains isolated in different European countries. Anaerobe,
21, 43-49.
Ishikawa, E., Matsuki, T., Kubota, H., Makino, H., Sakai, T.,
Oishi, K., ... & Tanaka, R. (2013). Ethnic diversity of gut
microbiota: species characterization of Bacteroides fragilis
group and genus Bifidobacterium in healthy Belgian adults,
and comparison with data from Japanese subjects. Journal
of bioscience and bioengineering, 116(2), 265-270.
Smith, P. M., Howitt, M. R., Panikov, N., Michaud, M., Gallini, C.
A., Bohlooly-y, M., ... & Garrett, W. S. (2013). The microbial
metabolites, short-chain fatty acids, regulate colonic Treg
cell homeostasis. Science, 1237242.
VIROLOGY, B. I. M. P. (2013). Multidrug-resistant Bacteroides
fragilis—Seattle, Washington, 2013. Morbidity and
Mortality Weekly Report (MMWR), 62(34), 694-696.