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I am Jailson Santos student at Saint Michael's College (Colchester - Vermont). This blog is an assignment from my class BI315 Microbiology - Fall 2014. For this assignment, every student will be responsible for learning about a specific bacterium and a specific virus, and the students should demonstrate knowledge of their organisms’ structure/function, lifecycle, relationship to human health and disease, metabolism, and epidemiology. I chose to write about the Propionibacterium acnes, and the Rabies virus.

I hope you enjoy learning about these two organisms, as well as learning more about the fantastic microbiology world.

Propionibacterium acnes

Acne is a disease related to the skin that affects almost 80 percent of adolescents and young adults. Propionibacterium acnes are bacterium known as the responsible for the development of acne. This bacterium is usually found in the pilosebaceous follicle (Figure 1). However, there is an obstacle to confirm that in fact P. acne is the responsible for cause acne. There is a difficulty in applying Koch’s postulates to the disease. In order word, it is an issue to isolating in pure culture these bacteria. For example, P. acne can be isolated from both acne and normal skin, which makes harder to identify and determine the role of this pathogen.

Figure 1. Normal pilosebaceous follicle. Notice the presence of the sebum which is secreted by the sebaceous gland. Source: http://www.niams.nih.gov

Characteristics of P. acne

These microorganisms are tolerant, anaerobic, gram-positive, commensal and nonmotile bacteria found in skin sites with high numbers of follicles secretors of sebum, including face, chest, and thorax. Considering the fact that our skin is constantly exposed to extreme conditions such as solar radiation, fluctuation of temperature, and deficit of water, the gram-positive cell wall (Figure 2) is an important advanced for these microorganisms. The cell wall provides them high structural stability and protection against the physical factors of the skin, which are responsible for the control of the bacteria colonization. The control of the growth of bacterium in the skin is due physical factors such as number and functions of follicles and glands, secretions, pH, and equilibrium of substance concentrations. For example, a secretion by the sweat glands, dermicidin, is active against gran-positive and negative bacterium. Another characteristic of these bacterial is that they are chemoorganotrophs, which means that their energy production is basically realized by the oxidation of organic nutrients found in the skin environment. Finally, these bacteria can performed fermentation metabolism. 

Figure 2. The gram positive cell envelope. Notice the dense layer of peptidoglycan and teichoic acids. Source: http://deltabiology.com

Epidemiology

Even if the uncertainty about the relationship between P. acne and acne disease, it is known that the presence of these microorganisms initiates the process of inflammation, which is one of the main symptoms of acne. In addition, the development of the other symptoms such as chronic inflammation (Figure 3), ductal hypercornification, and excessive sebum production are also known as a result of microbial action. Finally, the successful treatment of acne by using antibiotics such as erythromycin and clindamycin is another support to the hypothesis that microorganisms are involved in the development of acne.

Figure 3. Chronic inflammation of the skin of a teenager. Source: http://dermnetnz.org

These huge nodules are resulted first from small lesions called microcomedo, which are result from the increase in the secretion of sebum and the uncontrolled proliferation of keratinocytes. After, the continuous accumulation of sebum and keratinocytes, as well as the increase of the follicle cause the formation of comedones. Finally, the presence of colonies of P. acnes in the normal skin leads to an immune response which results in the process of inflammation of the comedones to a nodule (Figure 4).

Figure 4. Cycle of acne lesion. Note the pathway of the immune response that result in the process of inflammation. Diagram created by the student Jailson Santos, 2014.

Curiosity

Propionibacterium has an economic importance which is resulted from the participation of this bacterium in the industry of cheese. In other words, Propionibacterium is involved in the production of the Swiss cheese whose flavor derives from propionate, a product of fermentation which is a metabolism pathway performed by the bacterium.

References

Bojar, R. A., Holland, K. T. (2004). Acne and Propionibacterium Acnes. Elsevier, Clinics in Dermatology, 22:375–379.

Levy, P., Fenollar, F., Stein, A., Borrione, F., Cohen, E., Lebail, B., & Raoult, D. (2008). Propionibacterium acnes Postoperative Shoulder Arthritis: An Emerging Clinical Entity. Clinical Infectious Diseases, (12). 1884.

Schaeverbeke, T., Lequen, L., Barbeyrac, B., Labbe, L., Bebear, C. M., Morrter, Y., Bannwarth, B., Bebear, C., Dehats, J. (1998). Propionibacterium Acnes Isolated from Synovial Tissue Fluid in a Patient with Oligoarthrttis Associated with Acne and Pulstulosis. Arthritis and Rheumatisms. Vol. 41, No. 10. Octohcr 1998. pp 1889-1893

TANGHETTI, E. A. (2013). The Role of Inflammation in the Pathology of Acne. Journal of Clinical & Aesthetic Dermatology, 6(9), 27-35.

Rabies virus

Rabies or “Hydrophobia” is a zoonotic viral infectious disease because it is transmitted from animals (dogs, bats, foxes, skunks, and raccoons) to humans (Figure 1). Rabies is a disease present in more than 150 countries, and is the cause of the death of almost 55,000 people every year.

The rabies virus attacks on the central nervous system (brain and spinal cord) of the animal and is excreted in its saliva by which can be transmitted to other animals. There are others ways beside bite by which a person can become infected by rabies such as non-bite exposure and human to human transmission. The initial symptoms of rabies are: flu, fever, headache, and infection that can progress quickly to hallucinations, paralysis, and eventually death.

Figure 1. Cycle of transmission of the virus. Notice that the virus is transmitted from an animal to humans and the virus affect the brain cells. Source: http://www.medindia.net/patients/patientinfo/rabies.htm

Characteristics of Rabies virus

Rabies virus (Figure) is a specie of the Lyssavirus genus of Rhabdoviridae family, which is grouped in the order Mononegavirales together with the Filoviridae (e.g., Ebola virus).

Figure 2. The virus structure. Notice the presence of the 5 proteins and the spikes that surround the virus. Source: http://www.infectionlandscapes.org/2013/05/rabies.html

Rabies virus is a rod- or bullet-shaped, enveloped virus that has a single stranded negative-sense RNA genome. The negative sense RNA means that the genome is complementary to mRNA and thus must be converted to positive-sense RNA, which is similar to mRNA and thus can be immediately translated by the host cell, by an RNA polymerase before translation. All rabies viruses have a rigid bullet shape with a flat base and a round tip. Their genomes are responsible to encode five genes that code for: nucleoprotein (N), phosphoprotein (P), matrix protein (M), glycoprotein (G), and a viral RNA polymerase (L). Another two major structural components complete the structural of the virus: helical ribonucleoprotein core (RNP) and surrounding envelops. Approximately 400 trimeric spikes, which are found on the surface of the virus, are formed by glycoprotein (G). Finally, the processes of replication and transcription are critically related to nucleoprotein (N).

An interesting characteristic of Rhabdoviruses is that they have the most diverse hosts. For example, they are widespread among a great diversity of organisms such as plants, insects, fishes, mammals, reptiles and crustaceans. The reasons for why they have these diverse host is because they have a large number of possible molecule receptors. For example, despite the fact that rabies virus can only infect cell lines of neural origin, RABV viruses have acquired the ability to use ubiquitous receptors of non-neural cell types. Many studies have shown different molecules as the ubiquitous receptors for RABV such as phospholipids, gangliosides, and three proteins: the nicotinic acetylcholine receptor (nAChR), the neural cell adhesion molecule (NCAM), and the low-affinity nerve-growth factor receptor, p75NTR.

Epidemiology

According to the WHO the number of people who die every year around the world due to rabies in developing countries is a large number. For example, in Asia 30,000 people die every year, and in Africa 24,000. In Europe, due the policy of animal vaccination, the human rabies has disappeared from many European countries, but the virus is still present and some cases of canine rabies (Figure 3) have been found.

Figure 3. Dog infected by rabies virus. Source: http://dermnetnz.org

http://www.affordableanimalremoval.com/rabies/

References

Albertini, A. V., Baquero, E., Ferlin, A., & Gaudin, Y. (2012). Molecular and Cellular Aspects of Rhabdovirus Entry. Viruses (1999-4915), 4(1), 117-139.

Yousaf, M. Z., Qasim, M., Zia, S., Khan, M. R., Ashfaq, U. A., & Khan, S. (2012). Rabies molecular virology, diagnosis, prevention and treatment. Virology Journal, 950.