Category Archives: Lecture

Mechanisms of infectious disease

Giardia cell, SEM.

Giardia cell, SEM. (Photo credit: Wikipedia)

The fiction blog io9.com has a very accessible summary of the mechanisms by which an infectious agent (virus, bacterium, fungus, protozoan) can cause disease once it gets into the human body. Instead of reprinting the article, I will call out a set of bullet points from it, and point everyone to the original article. I urge all BIO230 students to go read this summary, as this covers a lot of the material in our upcoming exam. The author, Joseph Bennington-Castro outlines 4 basic mechanisms which allows a microorganism to cause disease once it is in the human body. Several of these have been discussed in BIO230 lecture:

  • Exotoxins. These are proteins that are made by and secreted by many different kinds of microorganisms, which when released by the pathogen directly cause damage to the host. There are many, many different microorganisms that can make exotoxins.
  • Endotoxins. These are lipid components of the Gram negative outer membrane, which when released into the blood stream (either by the bacterium being killed by phagocytosis, or by an antibiotic) cause a variety of disease conditions throughout the body. These symptoms include fever, inflammation, shock, and disseminated intravascular coagulation.
  • Immune response. The presence of some pathogens can trigger an inappropriate immune response that itself can cause damage to the human body. Rhinoviruses for instance trigger localized inflammation in the upper respiratory tract during infection, with very little cellular damage. Symptoms of disease are therefore caused by the immune response.
  • Tissue burden. The picture to the right is a Giardia lamblia cell, a protozoan parasite of the mammalian intestine. In an acute Giardia infection, the walls of the intestine are coated by the organism as it attaches using the suction cup seen in the picture. Since the intestine is coated with these cells, nutrient adsorption by the host is significantly impaired, resulting in diarrhea.

End of Course Material, Fall 2012

The final exam for Prof. Singleton’s sections of BIO230 is scheduled for the following times, and will be held in the computer lab in PAC185:

  • MWF  11 AM section:  Monday, Dec 17th, 10:15-12:15 PM
  • MWF 1PM section: Monday, Dec 17th, 12:45-2:45 PM

New material following the 3rd exam will include:

  • Gram positive bacteria: Chapter 19
  • Gram negative bacteria: Chapter 20
  • Viruses: Chapter 13
  • Specific viruses: Chapters 24 and 25
  • Additionally, the chapter on Introduction to Genetics (Chapter 7) will be VERY helpful to understand viruses

The above schedule is ambitious, and I do not expect that we will get through it all. We will cover the material on viruses by the last lecture.

The final exam for this course is cumulative. A significant portion of the final (approximately 40%) will draw on the final series of lectures dealing with our discussion of the above listing of pathogenic microorganisms. However, there are a number of topics that I consider of critical importance for which we will be responsible from the first 3 exams. Material that you should be familiar with will include:

  • Chapter 3 Cell Structure; pp 56-66,72-76,80-85
  • Chapter 4 Microscopy; pp 97-105,108-112
  • Chapter 6 Nutrition; pp 166-172, 176-179, 185-189
  • Chapter 9 Control; pp 258-261, 263-270, 277
  • Chapter 10 Antibiotics; pp 285-299 (understand the mechanisms of drug killing, not specific examples of antibiotics)
  • Chapter 14 Infection; pp 402-416, 418-420, 423
  • Chapter 15, Innate Immunity; pp 436-440, 444-448,451-453
  • Chapter 16, Adaptive Immunity, pp 460, 463-464, 466-471, 482-485
  • Chapter 17, Immunization, pp 491-497
  • Chapter 18, Immune Disorders, pp 512-522

Can AZT be taken by pregnant women with AIDS?

Picture courtesy of UNAIDS

Emily Nix (11 AM Micro) found our discussion on selective toxicity and antibiotics very interesting, and wanted to know more about the prophylactic use of antivirals such as AZT when given by HIV+ women to prevent vertical transmission of the virus to their unborn babies. Here is Emily’s summary of what she found out about this critical topic:

After posting a question on our discussion board about pregnant women and AZT treatments, I noticed that there were a lot of “google posts” online about pregnant AIDS patients taking AZT’s.  Because of our discussions in class about AZT affecting DNA synthesis, I began to wonder how a pregnant woman could take AZT without it negatively affecting her baby.  Adults can take AZT because most of our cells are not synthesizing DNA, unlike those of bacteria.  But, a baby would have a much higher DNA synthesis rate than an adult, so couldn’t a fetus therefore be adversely affected?  Since a mother’s blood doesn’t mix with her fetus’s during pregnancy does that mean her baby is safe from negative side effects?   Because I am very interested in doing humanitarian work, especially in Africa where the AIDS rate is high, I decided to do some research on AIDS patients and AZT’s.

The first website I discovered was a drug site that offered information about Zidovudine, a drug which contains AZT.  Zidovudine is given to mothers with HIV so they do not give the virus to their child during the birthing process (Zidovudine, Retrovir, 2010).  I also noticed that the drug information for Zidovudine included dosage amounts for infants and young children too.  I thought this was really interesting, especially since a fetus and a small child would certainly have more developing DNA than an adult, and would therefore be assumed to have more negative side affects from the drug.  Even if a fetus is protected by the fact that his or her mother’s blood does not mix while in utero, a young child would certainly be receiving the “full effects” of drug when taking it “out of utero.”

Next, I decided to pursue a study done on the effects of Zidovudine in pregnancy published by the New England Journal of Medicine.  In this study, it was concluded that while Zidovudine resulted in very adverse effects in mice embryos, overall it did not harm human fetuses (Sperling, et. al, 1992).  Despite this result, it was also taken into consideration that many of the mothers and children treated with Zidovudine during pregnancy were HIV positive, and as a result had many other factors which could affect their baby-both before and after birth.  Additionally, since Zidovudine has not been in use very long, many of its later effects may not be known (Sperling, et. al., 1992).

After learning that in most cases Zidovudine did not negatively affect a fetus, I decided to investigate the logistics of why.  Unfortunately, I could not find any “exact answer” to my question, but I did find some answers as to how exactly Zidovudine works which helped me to form a hypothesis myself about why it does not seem to harm fetuses.

Similar to the AZT facts we discussed in class concerning bacteria, Zidovudine works to limit the ability DNA synthesis to occur (Monson and Schoenstadt, 2010).  Just like bacteria, and any other living thing, viruses need DNA to survive.  However, the HIV virus is different in the fact that it must first change its RNA to DNA to replicate.  This process is done by using the protein reverse transcriptase enzyme.  Zidovudine works in the body to “trick” reverse transcriptase into thinking it is a building block used to make DNA.  When the reverse transcriptase attempts to use the Zidovudine to make DNA, it does not work (Monson and Schoenstadt, 2010).  Based off of this information, I hypothesize that because the Zidovudine is “selectively toxic” to the HIV virus it does not (or has not been proven to) disrupt a human’s DNA synthesis enough to cause drastic side affects-in mother or child.

The health-promoting effects of alcohol

The common fruit fly (a sobering observation!)

The BIO230 class is currently discussing the control of microorganisms in the environment, and one chemical method that we pay close attention to in class is the use of ethanol.  Ethanol is powerful disinfectant, and is commonly used to reduce or eliminate microorganisms on inanimate surfaces. Its mode of action is to denature nucleic acids in microbes, and when used appropriately it is an effective bacteriocidal compound. A similar compound, isopropanol, is also frequently used as a topical antiseptic and wound cleanser, and has a similar mode of action.

My long-standing interest in alcohol prompted my immediate attraction to this report in the biomedical literature (with the intriguing title Alcohol Consumption as Self-Medication against Blood-Borne Parasites in the Fruit Fly), which I came across via the science blog io9.com. Researchers at Emory University in Atlanta, Georgia, started from an interesting premise: the fruit fly Drosophila melanogaster, which of course feeds on fruit, also ingests yeasts on rotting fruits, which can then ferment the sugars in the fruit to produce ethanol. The flies consequently have developed a high tolerance to the biological effects of ethanol. The researchers then wanted to see whether ethanol then might offer the fly some matter of protection against invading organisms. Read the rest of this entry

End of Course Material, Fall 2011

The final exam for BIO230 is scheduled for the following times:

  • MWF  11 AM section:  Monday, Dec 19th, 10:15-12:15 PM
  • MWF 1PM section: Monday, Dec 19th, 12:45-2:45 PM
  • MW 5 PM section: Friday, Dec 17th, 5:00-7:00 PM

New material following the 3rd exam will include:

  • Gram positive bacteria: Chapter 19
  • Gram negative bacteria: Chapter 20
  • Viruses: Chapter 13
  • Specific viruses: Chapters 24 and 25
  • Additionally, the chapter on Introduction to Genetics (Chapter 7) will be VERY helpful to understand viruses

The above schedule is ambitious, and I do not expect that we will get through it all. We will cover the material on viruses by the last lecture.

The final exam for this course is cumulative. A significant portion of the final (approximately 40%) will draw on the final series of lectures dealing with our discussion of the above listing of pathogenic microorganisms. However, there are a number of topics that I consider of critical importance for which we will be responsible from the first 3 exams. Material that you should be familiar with will include:

  • Chapter 3 Cell Structure; pp 56-66,72-76,80-85
  • Chapter 4 Microscopy; pp 97-105,108-112
  • Chapter 6 Nutrition; pp 166-172, 176-179, 185-189
  • Chapter 9 Control; pp 258-261, 263-270, 277
  • Chapter 10 Antibiotics; pp 285-299 (understand the mechanisms of drug killing, not specific examples of antibiotics)
  • Chapter 14 Infection; pp 402-416, 418-420, 423
  • Chapter 15, Innate Immunity; pp 436-440, 444-448,451-453
  • Chapter 16, Adaptive Immunity, pp 460, 463-464, 466-471, 482-485
  • Chapter 17, Immunization, pp 491-497
  • Chapter 18, Immune Disorders, pp 512-522

A new way to prepare for Micro Exams

This photomicrograph reveals Mycobacterium tub...

Eat more Bacteria! Image via Wikipedia

Nick Altland (got a 4 in BIO230, Spring 2010, so you know he knows what he’s talking about) has suggested a double-blind, case control study that he thinks might be helpful for YCP Nursing students in Microbiology. He came across an article via phys.org about a study presented at the annual meeting for the American Society of Microbiology, and posted the link for me to find on my wall on Facebook. He has suggested that breathing dirt might be an effective study strategy. I of course wanted to find out more!

In this article, with the provacative title “Can Bacteria Make You Smarter?” researchers at the Sage Colleges in New York examined the effects of a common soil bacterium Mycobacterium vaccae, which is likely inhaled fairly commonly by all of us. My quick search of Pubmed indicates that  M. vaccae does not cause any significant human disease, but has had a fair amount of interest due to its ability to intensify an immune response when used as an adjuvant. Adjuvants are compounds that are added to vaccines that increase the ability of the vaccine components to promote  effective, long-lasting protection. Read the rest of this entry

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