Monthly Archives: April 2019

Previously we focused on the microbiology and the pathogenesis of Bacillus anthracis, but today we will focus on the epidemiology of the bacteria.

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Classification of Anthrax in humans can be classified by the spore entry into the host. Anthrax acquired via break in the skin is termed as cutaneous, eating contaminated meat is termed as gastrointestinal and inhaling spores causes inhalation anthrax. (Cendrowski, S. et al, 2004)

Cutaneous anthrax develops a day to 7 days after exposure, it is relatively less dangerous and prevalent. Gastrointestinal anthrax has an incubation period of 1-7 days and is rare in the United States. Inhalation anthrax is the deadliest types with an incubation period of 7-28 days. (CDC, 2014)

Fig 1-Transmission of anthrax.https://www.brainkart.com/article/Epidemiology—Bacillus-anthracis_18070/

The chance of transmitting Anthrax from one person acting as an intermediate fomites to another person is rare and might result in cutaneous form of anthrax. B. anthracis spores maintain their viability in calcium rich soil with at high pH hence highly infectious to their host. Alkaline soil at a temperature of 15.5 °C with high level of moisture and organic matter promotes the vegetative form of the bacteria, which subsequently increase the production of spores. These conditions can affect outbreak of infection. (Dragon & Rennie, 1995)

B. anthracis is found in the soil hence herbivores are vulnerable to anthrax. Anthrax is enzootic in the southern states of India and 1612 outbreaks were reported between 1991 to 1996.Other enzootic cases of anthrax were reported in China, Nepal, Australia, Namibia and South Africa. The zoonotic nature of Anthrax also makes farmers and people handling animal products susceptible to the infection.In 1957, a Plant that processes goat hair in Manchester in the US was hit with an anthrax outbreak which resulted in 9 cases and 4 fatalities. (Hinton, 1999)

B. anthracis can be used as a biological weapon by the deliberate release of anthrax spores. Anthrax spores are targeted for bioterrorism because, the spores are ubiquitous, tasteless, microscopic and are dispersed without detection. In 2001, mailed letter were contaminated with B. anthracis, 22 people were infected, lead to 5 fatalities. (CDC, 2014) The Infectious dose(ID50) of anthrax in humans ranges from 1000-10,000. B. anthracis have monomorphic strains have identical phenotype and genotype ,based on their location of their habitat.Hence the source of the anthrax used for an attack can be determined. (WHO, 2008)

Anthrax can be prevented with antibiotics, Ciprofloxacinand doxycycline or Anthrax Vaccine Adsorbed (AVA). Infections can also be treated antibiotics and antitoxins. (CDC, 2014)

It has been a remarkable journey, hope you enjoyed yourself as much I did. Thanks for indulging me.

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Reference

1. Centers for Disease Control and Prevention,(2014) National Center for Emerging and Zoonotic Infectious Diseases (NCEZID)
2. Dragon, D. C., & Rennie, R. P. (1995). The ecology of anthrax spores: tough but not invincible. The Canadian veterinary journal = La revue veterinaire canadienne, 36(5), 295–301.https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1686874/
3. Hinton MH (1999) Infections and intoxications associated with animal feed and forage which may present a hazard to human health. Vet J. 2000; 159:124–138. [Google Scholar]
4. World Health Organization (2008)Anthrax in humans and animals – 4th ed. All rights reserved. Publications of the World health organization. Who Press, World health organization, 20 Avenue Appia, 1211 Geneva 27, Switzerland

Bacillus anthracis are gram-positive, non-mobile spores extracellular and inside their host, they exist as vegetative state.It has a single circular chromosome  with base pairs of 5,227,293 per DNA molecule with circular double-stranded DNA plasmids, pXO1 and pXO2. (Read,2003)

Video 1-https://www.youtube.com/watchv=7LRGT098lxc#action=share

The trophic level for B. anthracis is heterotrophic and since it is facultative anaerobe, it can be cultured in media with sources of amino acid, carbon, nitrogen and supplementary methionine and thiamine. A defined medium for B. anthracis culture will include glucose, adenine, guanine, thiamine, uracil, calcium and other amino acid sources. (Koehler, 2009)

The bacteria target the hemoglobin since it bound to iron and it is needed for metabolic processes such as growth and reproduction. B. anthracis utilizes hemophores, siderophores and transporter proteins for iron extraction.

Pathogenic mechanism such as inhibiting the normal function of the immune system ,Cytoloysis etc. of B.anthracis. courtesy of https://jamanetwork.com/journals/jama/article-abstract/194886

Inside a host cell, B. anthracis release lysosomal enzymes that lysed the host’s red blood cells, releasing its content, hence the bacterial hemophore takes up the iron released and transfer to their cytosol. Outside of a cell, at low iron levels, B. anthracis produce bacillibactin and petrobactin(siderophores) that have high affinity to iron. The minimal iron available readily binds to the siderophores and are transported via transporter proteins.(Eremenko, 2017; Koppisch et al, 2005; Cendrowski, S. et al, 2004)

B. anthracis thrives best at a temperature of 37°C and at temperatures above 43°C, bacterial growth is halted. At optimum temperature of 37°C, the Cell doubling times range from 30 minutes to 60 minutes in a complex media. (Charlton et al., 2007)

B. anthracis is the causative agent of anthrax, and the type of anthrax is determined by the spore entry into the host. The classification of Anthrax includes cutaneous, gastrointestinal and pulmonary and injection anthrax. (Cendrowski, S. et al,2004) (video 1) When conditions are not favorable, the infectious endospores of B. anthracis are produced .The dormant spores are ideal for bioterrorism since they can withstand any harsh conditions and are easily dispersed without trace.

The sporulation process of Bacillus anthracis.
http://slideplayer.com/slide/5677854/18/images/73/Bacterial+cell+structure+Endospores+(spores)+–+Sporulation.jpg

Binary fission occurs when bacteria g the copied DNA into two and it finally closes off, by forming a cross-wall. The two-daughter cell separate, and they are identical to the mother cell. B. anthracis undergo gene transfer by close contact via conjugation. The virulence plasmids pXO12 and pXO1 can be transferred during conjugation, the bacterial cell with the plasmids become the donor. (Green et al,1989)

We could go, on and on about this amazing bacteria, but time and cyberspace wouldn’t allow.

Bye for now.

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Reference:

1. Cendrowski, S., MacArthur, W. and Hanna P. (2004), Bacillus anthracis requires siderophore biosynthesis for growth in macrophages and mouse virulence. Molecular Microbiology, 51: 407-417. doi:10.1046/j.1365-2958.2003.03861.x

2.Charlton, S. , Herbert, M. , McGlashan, J. , King, A. , Jones, P. , West, K. , Roberts, A. , Silman, N. , Marks, T. , Hudson, M. and Hallis, B. (2007), A study of the physiology of Bacillus anthracis Sterne during manufacture of the UK acellular anthrax vaccine. Journal of Applied Microbiology, 103: 1453-1460. doi:10.1111/j.1365-2672.2007.03391.x

3. Eremenko, E.I. (2017)A Bacillus anthracis system for acquisition of heme-bound iron. Microbiol. Virol. (2017) 32: 1. https://doi.org/10.3103/S0891416817010037

4. Koehler T. M. (2009). Bacillus anthracis physiology and genetics. Molecular aspects of medicine, 30(6), 386–396. doi:10.1016/j.mam.2009.07.004

5.Koppisch, A.T., Browder, C.C., Moe, A.L. et al. Biometals (2005) 18: 577. https://doi.org/10.1007/s10534-005-1782-6

6.Read, T. et al (2003) The genome sequence of Bacillus anthracis Ames and comparison to closely related bacteria .NATURE | VOL 423 | © 2003 Nature Publishing Group 81 | www.nature.com/nature. https://deepblue.lib.umich.edu/bitstream/handle/2027.42/62580/nature01586.pdf?sequence=1&isAllowed=y

https://www.cdc.gov/anthrax/news-multimedia/animations-and-videos.html

The origin of Anthrax is believed to be Egypt and Mesopotamia. It was present during the times of Moses as the fifth Egyptian plagues that affected oven, human, camel etc. (CDC,2017)

The causative agent for Anthrax isBacillus anthracis. Its name was derived from the Greek word for coal, describing the black dry scab observed on affected organisms. B. anthracis is a nonmotile, rod-shaped gram- positive obligate bacteria is an aerobic that ranges from 1–1.5 × 3–10 μm in size. The bacteria exist as oval dormant spore naturally existing in the soil until, introduced via inhalation by their host. They are activated into their vegetative forms triggered by the availability of resources.(Fig 1)

Fig 1.Two forms of B. anthracis in the spore and vegetative form. https://www.cdc.gov/anthrax/basics/index.html

B. anthracis has virulence plasmids pXO1 that has a three toxins lethal factor, edema factor and protective antigen and pXO2 is involved in the production of polyglutamyl capsule. Hence pXO1 is responsible for necrosis ,edema and  bleeding  and PXO2 capsule production prevents phagocytes from engulfing the B. anthracis in its vegetative form in the host.(Leppla ,1982).The toxin produced is an A-B toxin ,where the protective antigen toxin is the medium that delivers the edema and lethal toxin from the outside to inside  of the host cell.(Lacy & Collier, 2002)

The dehydrated spore is surrounded by a membrane and a specialized cortex that limits the exchange of water and solute to and from the spore. This is the protective outer layer that withstands chemical, enzymatic and desiccation. (Setlow, 2006).

B. anthracis cultured at 37°C in sheep blood agar has an off-white appearance, non-hemolytic, comma shaped slightly cover with irregular edges. (Fig 2) It is observed purple rod unicellular or chain or rods when stained with gram stain and observed under the microscope. (Fig 1)

Photo of Bacillus anthracis colonies in blood agar. Courtesy of CDC/Larry Stauffer.

Fig 3. Mucoid colonies of Bacillus anthracis due to production of polyglutamyl capsule. http://textbookofbacteriology.net/Anthrax_2.html

This is all for now about the infamous Anthrax bacteria..

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REFERENCE

1.CDC ( 2017): Centers for Disease Control and Prevention, National Center for Emerging and Zoonotic Infectious Diseases (NCEZID)

2. Leppla SH.(1982)Anthrax toxin edema factor; a bacterial adenylate cyclase that increases cyclic AMP concentrations of eukaryotic cells. Proc Natl Acad Sci U S A1982;79:3162–6. [PMC free article][PubMed] [Google Scholar]

3.Lacy D.B. & Collier R.J. (2002) Structure and Function of Anthrax Toxin. In: Koehler T.M.  Anthrax. Current Topics in Microbiology and Immunology, vol 271. Springer, Berlin, Heidelberg. https://link.springer.com/chapter/10.1007%2F978-3-662-05767-4_4#citeas

4.Setlow P.(2006) Spores of Bacillus subtilis: their resistance to and killing by radiation, heat and chemicals. J Appl Microbiol101, 514–525.

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