The Nature of Science

Showing posts with label microbiology. Show all posts

Tricky Little Buggers

Biology concepts – immune defense, antibiotic resistance

Naim Süleymanoğlu is better known as Pocket

Hercules (4' 10"). He was born in Bulgaria, but is

of Turkish descent. He competed and retired

several times, and won gold medals from 1983

to 1998. He is one of the first competitors to

lift more than 2.5x his own body weight.

Therewas a small Turkish weightlifter a few years back whose nickname was “Pocket Hercules.” He won gold medals in three separate Olympics and was the one the best examples of big things in little packages. Last week we talked about the immune systems of vertebrates, invertebrates and plants, now let’s talk about the defenses of the smallest organisms – bacteria are the Pocket Hercules of biology.

Do bacteria have defense mechanisms? You bet – they get attacked all the time. For bacteria that stray into or purposefully target animal or plant hosts, the perils are many and varied. Antimicrobial peptides try to burst them, antibodies try to bind them up and point them out to killer cells. Macrophages and other phagocytic cells try to eat them or wall them off from the other host cells. Organisms will even sacrifice their own cells just to make sure they kill the bacteria. It’s a jungle out there.

We don’t have the time nor the room to go into the thousands of ways that bacteria protect themselves from plant, invertebrate, and vertebrate immune attack, but we can give a few examples, like deception. Mimicry is when a bacterial antigen looks much like one of our molecules, so that the body is either fooled into not attacking, or tempers its attack.

Other bacteria change their clothes to remain hidden. Just when an immune system sees it and starts the attack, Neisseria gonorrhoeae changes its surface molecules and becomes invisible again. On the other hand, Yersinia pestis remains invisible by living inside macrophages.

Some bacteria stunt our antibody response. The best way to keep from being attacked is to not allow the host to recognize and identify you. The bacteria that cause TB inhibit our immune system from producing specific antibodies.

Some bacteria vary the antigens they show on

their surface in order to evade the immune system.

In this bacterium, the dark areas are stained for

one particular surface antigen. You can see that

some of the cells have none of that protein, some

have only that surface protein, and some have

discrete areas where that protein is expressed.

The defense is a good offense, so some bacteria attack. Pseudomonas strains kill the phagocytic cells that would try to eat them by releasing chemicals called aggressins. Staphylococcus aureus just confuses the phagocytes, producing toxins that stop their movement or make them move erratically.

These are but a few of the many bacterial defenses against our immune system. But they have evolved defenses against other threats as well, like our attempts to kill them with antibiotics.

We talked earlier about multidrug efflux pumps in bacteria that pump out the antibiotics with which we try to kill them. This is related to the stories in the media about antibiotic resistance in bacterial pathogens, but classic antibiotic resistance genes are often plasmid based defenses,as we have discussed. Recently, an additional defense against antibiotics has been recognized.

It seems most bacteria produce hydrogen sulfide (H₂S, smells like rotten eggs), which was previously thought to be only a metabolic byproduct. A late 2011 studyshows that H₂S is part of an integrated defense system used by almost all bacteria. The gas works to prevent oxidative damage. This is not unheard of since a few bacteria produce nitric oxide to do the same thing, but it is being recognized now that oxidative stress induction is a big part of how many antibiotics work. When the H₂S system was turned off in several pathogens, they became much more sensitive to antibiotics. Maybe this a lesson we can exploit in the future.

In addition to our attempts to kill them, the universe itself is a tough place to survive if you are a bacterium. They may end up in bright sunlight for long periods of time, or hurtling through space on a rocket or meteor. Bacteria have ways to protect themselves here as well. Ultraviolet radiation from the sun is a mutagen (causes mutations in DNA), but it also can break down cellular molecules to release oxygen radicals, like hydrogen peroxide or superoxide.

It has been known since the 1950’s that pyruvate and catalase, as well as the newly discovered H₂S discussed above, do some work in protecting the cell against oxidative damage, but a 2009 study described a whole new mechanism. It seems that E. coli has two proteins that seek out, identify, and repair oxygen radical-mediated damage to sulphur-containing cysteine amino acids within proteins.

Cysteine is the most reactive of the 20 common amino acids, which means that it are often located in the functional site of enzymes (where the enzyme reacts with the substrate). However, this reactivity also makes cysteine vulnerable to reaction with radicals, especially oxygen radicals, after which it becomes modified and non-functional.

Disulphide bonds are formed between adjacent cysteines on the

same peptide, far apart cysteines on the same peptides,

or between cysteines on different peptides. When

you (not me) get a permanent wave for your hair, the

disulphide bonds are broken or rearranged by a reducing agent.

To prevent this radical-mediated damage, cysteines often occur in pairs, where links between the sulphurs of the two cysteines help to prevent oxidation (called disulfide bonds, they also serve to link peptides together and give proteins their proper form). A 2008 study showed that this mechanism provides unusual oxidative stability to a cysteine-containing enzyme of the bacterium, Desulfovibrio africanus.

But there are exceptions; lone cysteines do occur, and these are the cysteines most vulnerable to oxidative damage. The DsbG and DsbC proteins of E. coli patrol the cytoplasm looking for oxidized cysteines to fix.

Here is how ingenious the system is – oxidizing a cysteine may or may not unfold the protein, so DSbG is charged and can interact with the still-folded proteins to correct the cysteine problem, but DsbC is uncharged, so it works better with proteins that have been unfolded. Amazing - and bacteria developed it all on their own – well, with the help of the evolutionary pressure of things trying to kill them.

I mentioned that radiation is also a DNA mutagen. The mutagenic properties of radiation affect bacteria just like they affect us; it is just that some bacteria can protect themselves better once their DNA is damaged. Follow me closely here - by using protein repair and protection systems, bacteria like E. coli, with its DsbG and C enzymes, can keep protein functions going when other organisms would break down and die. Some of these protein functions include DNA repair after mutagenesis. So - some bacteria don’t survive radiation because they protect their DNA better, they survive because they repair the damage better.

This is an overlap of different types of images of a

radiodurans bacterium. The circles of blue green and

pink show high concentrations of manganese, while

red is iron. The manganese is clustered around the

DNA and works to repair it after radiation damage.

Other bacteria have a different mechanism to maintain protein function. According to a 2010 study, a shield of manganese metal atoms and phosphates was found in D. radiodurans. It had been long known that manganese was present in very high levels in bacteria that are most resistant to radiation, but its function was unknown.

The recent study shows that these manganese complexes work together to protect proteins from radiation damage, but not DNA. The key for this system is to keep proteins functioning, which can then repair any radiation damage to the DNA. This mechanism allows D. radiodurans to withstand prolonged radiation that is 1000x stronger than that which would kill a human.

So, bacteria have defenses against immune and environmental attacks. Does anything else attack bacteria? How about other bacteria - it’s dog eat dog out there, competition for resources is brutal. Many bacteria have poisons (bacteriocins) that inhibit or kill bacteria that are distantly related (because related types of bacteria are likely to be in the same places looking for the same food).

One type of bacteriocin are the lantibiotics. These protein toxins contain a nonstandard amino acid, called lanthionine. We mentioned above that cysteines are very reactive; lanthionine is a modified circular (polycylic) cysteine that gives the toxin its reactivity. And because it is cyclic, it is much less vulnerable to oxidative damage itself – funny how bacteria seem to cover their bases so well.

This is so cool. Bacteria that are engineered to produce

light were injected into rats. The rat in the middle was

also given a bacterium producing a bacteriocin to the

light producing bacteria. The whole rat bodies were

imaged while they were still alive to see if the bacteria

were alive and reproducing. Live animal imaging is a

great tool that is becoming more popular. Image by S.

C. Corr and P. G. Casey.

Lantibioticscome in two types, they either form pores in Gram⁺ bacterial cell walls or inhibit the cell wall formation. Because they attack only specific types of bacteria, lantibiotics are useful in cheese-making; they allow some bacteria to grow and ripen the cheese, while killing those that would cause the cheese to spoil. One type B lantibiotic just came through its phase I clinical trial in July 2012 with flying colors (phase I trials are meant only to test safety, not effectiveness).

A recent discovery illustrates just how bacteriocins are delivered to the target organism. It seems that bacteria can build a spike and a spike launching system anywhere on their cell membrane. The spike is spring loaded in a tube just 80 atoms long, and is fired at the target cell. Then the bacteriocin is released at the end of the spike to do its damage.

The release of toxin was already known, called a type IV secretion system, but the CalTech study that identified the spring-loaded spike as the delivery system is very new. Once fired, the whole system is broken down, ready to be rebuilt somewhere else in the cell. Amazing. (click for video)

Of course, for every punch there is an evolutionary counterpunch, so there are bacteriocin resistance mechanisms as well. Nisin, a bacteriocin active against strains of listeria, is approved as a food preservative. But listeria can spontaneously develop resistance to nisin. It appears that some strains change their membrane chemistry in order to render nisin ineffective. Therefore resistance could be a problem if we pursue the use of bacteriocins as antibiotics; we might end up back in the same situation that we're in now.

Regardless of this possible downside, scientists have found a way to bring bacteriocins into the battle against antibiotic resistance. An E. coli has been engineered to contain the gene for pyocin, a bacteriocin that kills strains of Pseudomonas bacteria. E.coliand Pseudomonas are not closely related, so E. coli would not naturally possess this toxin, scientists added the gene to the E. coli.

This is schematic of the engineered bacteria to kill Pseudomonas.

P. aeruginosa make chemicals when their numbers reach a

certain density. These trigger pyocin production in the E. coli,

but also triggers the production of the protein that lyses the

E. coli. When lysed, the pyocin attacks the P. aeruginosa.

When the engineered bacteria encounters Pseudomonas, it does two things; it produces the pyocin toxin to kill the target cell, and the engineered E. coli commits suicide. No release system has been engineered into the E. coli, so the only way they get the pyocin to the target is to have the E. coli produce a lysin that destroys its own cell membrane.

This suicide accomplishes two things, it releases the pyocin to kill the target, and it prevents the engineered E. coli from hanging around forever, possibly trading genes with other bacteria or causing havoc in some unforeseen way.

So it looks like bacteria have it made. They can resist immune system attacks, some can resist environmental onslaughts, they even have ways to protect themselves against competition and threats from other bacteria. No wonder they have always been the predominate life form on Earth. But bacteria do have foes of considerable power – veritable “Micro-Hercules” – we will meet them after Thanksgiving.

Let’s take a couple weeks to talk about the biology of turkeys and the so-called “tryptophan nap.”

Basler, M., Pilhofer, M., Henderson, G., Jensen, G., & Mekalanos, J. (2012). Type VI secretion requires a dynamic contractile phage tail-like structure Nature, 483 (7388), 182-186 DOI: 10.1038/nature10846

Saeidi, N., Wong, C., Lo, T., Nguyen, H., Ling, H., Leong, S., Poh, C., & Chang, M. (2011). Engineering microbes to sense and eradicate Pseudomonas aeruginosa, a human pathogen Molecular Systems Biology, 7 DOI: 10.1038/msb.2011.55

For more information or classroom activities, see:

Bacterial defenses–

http://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&ved=0CB8QFjAA&url=http%3A%2F%2Fwww.pct.edu%2Fdegreesthatwork%2Fdocs%2Fword%2F1_2-Science_Teacher_Series-Nanotechnology.doc&ei=kOFlUKW8OcjnyAHv8ICgAg&usg=AFQjCNFIooLBtpkA1vko0-lRwai7x7v1Zw

http://www.smallerquestions.org/blog/2012/5/21/from-soil-to-human-evolution-of-bacterial-immune-evasion-mec.html

http://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=3&ved=0CC4QFjAC&url=http%3A%2F%2Fwww.educationscotland.gov.uk%2FImages%2FInfectiousDiseasesandImmunityTeachersNotes_tcm4-669755.doc&ei=o99lUJN5woXLAdeYgHg&usg=AFQjCNH-uSO824WJUdpVkxUg4xhP1C_fZA

http://crohn.ie/archive/primer/imunevad.htm

http://textbookofbacteriology.net/antiphago.html

http://textbookofbacteriology.net/antiimmuno.html

http://www.sciencedaily.com/releases/2010/04/100425151159.htm

http://faculty.ccbcmd.edu/courses/bio141/lecguide/unit2/bacpath/evade.html

http://www.ncbi.nlm.nih.gov/pubmed/15231256

http://www.sciencedaily.com/releases/2011/11/111117144009.htm

http://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=2&ved=0CCoQFjAB&url=http%3A%2F%2Fassets.cambridge.org%2F97805218%2F01737%2Fsample%2F9780521801737ws.pdf&ei=_N5lUPu4D8-GyQGEy4GAAQ&usg=AFQjCNEKYTv8woZ0L40EEdezU3UKyIXmCA

http://phys.org/news193846665.html

Bacteriocins –

http://www.foodsafetynews.com/2011/09/a-lantibiotic-steps-up-to-kill-harmful-bacteria/#.UGXgahhf13I

http://www.sciencedirect.com/science/article/pii/S2211546312000034

see Pubmed (http://www.ncbi.nlm.nih.gov/pubmed) for more information on these defenses.

Ironing Out The Black Death

Biology concepts – iron, genetic disease, infectious disease, immune evasion

It is strange to think of people as rusting, but there are

days when I get up and swear that my joints have

frozen – my age makes me assume it is rust.

In truth the molecules of rust are very much like

some molecules in your body; too many of these in

the wrong places, and maybe you are rusting.

Believeit or not, someone you know is rusting - and it probably saved his/her ancestor’s life.

Animals require iron to survive; normal adult humans carry about 3.5-4 grams of iron in their bodies. It’s vital for every cell. Red blood cells use iron as part of the hemoglobin molecule that carries oxygen, But all other cells use iron in part of electron transport chain that makes ATP, and in the synthesis of DNA.

In plants, iron is used in chlororphyll production, in nitrogen fixation, and in regulation of transpiration (moving water and nutrients up to the leaves). Plants are a decent source of dietary iron, but heme iron (from meat) is much more easily absorbed.

In both plants and animals, the amount of iron is highly regulated. Iron is most often bound to proteins; one type in cells, another in the blood, and they lock it up tight. When you need more, your gut cells (enterocytes) release some of their stored iron and then take in more from the food you eat.

People who absorb too little iron (from poor diet or absorption defects) have a hard time carrying oxygen to their tissues because they don’t have enough hemoglobin. They are fatigued, dizzy, lose their hair, and less able to fight off infections. Weirdly, they may demonstrate pagophagia; a compulsion to eat ice! The reason for this is open for discussion, but one hypothesis says there is an ancient crunching desire, related to chewing on bones to get at the iron-rich marrow.

Pagophagia (eating ice) is one type of pica. In pica, a

person craves to eat something that is not a food source.

Some people with pica will eat hair (trichophagia)

or dirt (geophagy). I guess if you have to have pica,

ice craving isn’t so bad. And yes, some people crave

plastic, like parts of your keyboard.

Too little iron keeps you sick - and apparently always refilling the ice tray. But too much iron is just as bad; both ends of the scale can kill you.

Hereditary hemochromatosis (HH) is an autosomal recessive (need two mutated copies) disease of iron storage and transport. Patients with this disease may have as much as 20-40 grams of iron in their bodies; they can even set off metal detectors at airports!

All this iron causes medical problems too. People with HH will accumulate iron in their liver, heart, skin and other tissues. Excess iron plus fats can produce free radicals and oxygen radicals. The radicals can react with many molecules, including those you need in order to keep your cells functioning properly.

Radicals can break down enzymes, destroy mitochondria, and even react with the iron itself to produce iron oxide – rust; biological rust being called hemosiderin. Could HH patients be like the frozen Tin Man that Dorothy finds in the Wizard of Oz? Of course not, tin doesn’t rust – it’s a good thing L. Frank Baum was a writer and not a metallurgist!

The brown color is hemosiderin pigment that has been

deposited in the tissues. Most times, your body will

resorb this colored material, like when a bruise goes

away over time. In hemochromatosis, there is too

much hemosiderin to be completely removed.

Over time, the damage from free radicals and from hemosiderin buildup causes systems to shut down. Without treatment HH is lethal - so it is important to know how all that iron gets there.

We said above that enterocytes are the storage area for iron absorbed from your diet. In HH, the export signal is broken and they keep dumping their stored iron into the bloodstream. Even worse, the enterocytes lose the ability to sense if the body needs more iron. As a result of HH, gut cells keep absorbing more iron and releasing it into the bloodstream.

It’s a bad thing to inherit hemochromatosis…..EXCEPT if Yersinia pestis is lurking in the environment. Y. pestis is the bacterium that causes the plague. The organism can be passed from person to person, but also from fleas to people, and from fleas to animals to people.

You can read about how Y. pestis ensures it is transmitted to a new host from the flea’s midgut, but for reasons of decorum, I won’t go into it here. And I suggest you don’t eat before you read about it.

Y. pestis plague comes in three flavors; septicemic(travels through the blood), bubonic(causing swellings), and pneumonic(some organisms go to the lungs). In the case of pneumonic plague, coughing promotes transmission from person to person and is more lethal. But bubonic plague is more painful.

The plague has been a killer throughout human history, but Y. pestis’ relationship to the flea is evolutionary rather new. About 20,000 years ago, Yersinia killed the flea as well. According to new research, it took relatively few genetic changes to allow plague bacteria to keep the flea alive and to survive in its midgut. It was at this point that humans' trouble really began. It is estimated that a third of the population of Europe was lost to plague in 14^th century. The infection still occurs today, but is highly treatable with antibiotics. Your immune system has problems getting rid of Y. pestis on its own.

Normally, your immune system recognizes foreign organisms and eliminates them, through either innate or adaptive mechanisms. However, Y. pestis has several tricks up it sleeve to avoid recognition and destruction by your immune system.

The lymphatic system is comprised of vessels, and

is considered part of your circulatory system. It

helps in eliminating wastes from the blood and

tissues, aids in absorbing fats and fat soluble

vitamins, and regulates fluid levels. A main function

is to move fluid and cells through the checkpoints,

the lymph nodes. Here, the fluid is checked for

foreign molecules and antigen presentation to the

immune cells in the nodes.

Immune cells can circulate in your blood, move in and out of your tissues, or may be located in your lymphatic system. In the lymph nodes, they gather to exchange information, like workers gossiping around the water cooler. If an antigen processing immune cell (APC) has encountered a foreign antigen, the APC will break it down and place pieces of the antigen on its surface, so the antigen can stimulate other immune cells.

The processed antigen is presented to the many types of immune cells in and moving through the lymph nodes, including B cells that make antibodies, and T cells that direct immune responses or directly kill organisms. This quickly increases an immune response; one cell encounters the invader, but by going to a central location (lymph node), thousands of cells can be stimulated.

Amazingly, Y. pestisactually lives and reproduces in your lymph nodes! The painful swellings in bubonic plague are the inflamed lymph nodes where the organism is reproducing. Each swollen node is called a buboe, hence the name of the plague. Buboes occur most commonly in the armpit (axilla), on the neck, or in the groin area – not a pleasant way to spend a weekend - maybe your last weekend.

The lymph nodes are the headquarters for stimulating immune responses, yet the Y. pestis lives here very happily. It manages this through several evasion mechanisms:

1) antiphagocytic proteins – Y. pestis can inject proteins into phagocytic cells that makes them poor at eating and killing. These proteins also makes immune cells unable to signal other immune cells that Y. pestis is there.

2) invasion proteins – plague bacteria can avoid immune detection by living insideseveral different host cell types; the macrophage is the major example.

3) survival proteins – Y. pestis can live inside the macrophages that are supposed to destroy them by turning off macrophage killing mechanisms.

4) heme stealing proteins – Y. pestis can steal iron from the host. And here is where HH comes in.

Here is a buboe on a plague patient’s neck. It is not unlike the parotid

salivary gland swelling that takes place during the mumps, just

bigger, more painful, and more lethal. I chose to show one from the

neck precisely because I didn’t want to show you one from the groin.

Hereis an organism that is perfectly happy living inside and in the company of the cells that are supposed to kill it - we’re doomed. Yet having a disease like hemochromatosis can save us. How can that be? Well, microorganisms need iron too. For much the same reasons as animals and plants, bacteria and other microorganisms must have a supply of iron. They may get it from their diet, or, as is the case with Y. pestis, they steal it from their host.

I can hear what you're saying - this doesn’t seem to make sense since HH results in lots of iron in cells. True, but there is an exception. HH leaves two cell types starved for iron - the enterocyte, which we already know about, and the macrophage. The reason for iron-poor macrophages during hemochromatosis is not completely understood, but one possibility is that the HH mutation affects macrophages the same way it affects enterocytes.

One important function of macrophages is to eat and destroy old host cells, including erythrocytes. The iron of the hemoglobin from all those degraded RBC’s is stored and recycled; this is an important mechanism that the body uses to reuse the iron it already has. But in HH, the macrophages may be pumping out the iron they take up from old RBCs, just as the enterocytes keep pumping out the iron they take up from the gut contents.

The iron-poor macrophage essentially starves the intracellular plague bacteria by not providing them with iron. This is a happy accident for us, but it isn’t as if the macrophage doesn’t already know this trick. Iron can be an important immune weapon. In mycobacterial infections (that cause pneumonia), macrophages actually raise the iron concentration in the ingested bacteria and kill them that way. In other infections, macrophages sequester their iron and starve the organisms.

Bloodletting is an old time treatment for nearly every

disease. They thought that disease was caused by too

much blood. Strange, but bleeding (phlebotomy) is now

the accepted treatment for hemochromatosis. Leeches

are now used as anti-clotting mechanisms, and fly

maggots are used to clean out dead tissue – all are

gross, and all are effective!

Macrophageiron manipulation is not a natural immune response to Y. pestis, but HH helps to bring about the same effect, and this makes HH valuable. It is believed that many survivors of the plague in the 12^ththrough 15^th centuries had hemochromatosis. What is more, the gene is present in as many as 1/3 of living people of European descent, meaning that HH is probably massively underdiagnosed. It is likely that you know someone with HH, whether they not it or not.

Natural selection kept this mutation in the gene pool because it presented a reproductive advantage in times of plague. With antibiotics, we probably do not need this mutation any longer, but it is here and will take quite a while to be bred out of the population, especially since HH treatments (like bleeding, see the picture at right) help people live with the disease long enough to pass on their genes.

There are more examples of bad genes saving us from disease, like chemokine receptor mutations preventing HIV infection and aldehyde dehydrogenase mutations discouraging alcoholism. But next week we will focus on immune systems run amok and how parasites can reel them in.

Chouikha I, Hinnebusch BJ. (2012). Yersinia-flea interactions and the evolution of the arthropod-borne transmission route of plague. Curr Opin Microbiol. DOI: 10.1016/j.mib.2012.02.003

For more information or classroom activities, see Survival of the Sickest, by Dr. Sharon Moalem, or the following sites:

Iron in biochemistry –

http://www.webelements.com/iron/biology.html

http://www.ncbi.nlm.nih.gov/pubmed/11160590

http://bloodjournal.hematologylibrary.org/content/112/2/219...

http://www.chemistry.wustl.edu/~edudev/LabTutorials/Ferritin/Ferritin.html

http://astrobiology.nasa.gov/articles/finding-iron-s-role-in-life-on-early-earth/

http://nautilus.fis.uc.pt/st2.5//scenes-e/elem/e02640.html

http://serc.carleton.edu/sp/mnstep/activities/36016.html

http://healthymeals.nal.usda.gov/hsmrs/Illinois.../Classroom_Activities.pdf

http://kidshealth.org/parent/medical/heart/ida.html

http://www.doctoroz.com/vp-videos/iron-absorption-animation

http://www.youtube.com/watch?v=g97zy_G_mYk

Hereditary hemochromatosis –

https://koshland-science-museum.org/sites/all/exhibits/exhibitdna/inh05text.jsp

http://www.youtube.com/watch?v=UeRr-S2aWrY&feature=related

http://www.authorstream.com/Presentation/MKDah-923675-hereditary-hemochromatosis/

http://kidshealth.org/parent/general/aches/hh.html

http://thisisnotaperfectworld.blogspot.com/

http://www.jbcc.harvard.edu/programs/manville/Sci_genetic%20sym.html

Y. pestis plague –

http://medievaleurope.mrdonn.org/lessonplans/plague.html

www.michrenfest.com/the_black_plague_classroom_simulation.pdf

http://www.mademan.com/mm/bubonic-plague-facts.html

http://theweek.com/article/index/233008/the-7-year-old-who-caught-the-bubonic-plague

http://www.themiddleages.net/plague.html

http://rarediseases.about.com/cs/bubonicplague/a/111602.htm

http://plague.emedtv.com/yersinia-pestis/yersinia-pestis.html

http://www.who.int/mediacentre/factsheets/fs267/en/

http://web.uconn.edu/mcbstaff/graf/Student%20presentations/Y.%20pestis/Yersinia%20pestis.html

http://www.atsu.edu/faculty/chamberlain/Website/lectures/lecture/plague.htm

http://www.youtube.com/watch?v=7l4gLPzE-B4

Immune evasion strategies –

http://crohn.ie/archive/primer/imunevad.htm

http://www.ncbi.nlm.nih.gov/books/NBK27176/

http://textbookofbacteriology.net/antiimmuno.html

http://www.nature.com/news/2011/110921/full/news.2011.550.html

http://www.science20.com/catarina_amorim/how_friendly_bacteria_avoid_immune_attack_to_live_happily_in_the_gut

http://www.wellcome.ac.uk/news/2009/news/wtx053411.htm

http://www.thepigsite.com/pigjournal/articles/1284/porcine-immunology-the-battle-between-the-immune-system-and-pathogens

http://f1000.com/reports/b/3/1/

http://www.sciencedaily.com/releases/2010/05/100523205818.htm

http://www.genengnews.com/gen-news-highlights/researchers-discover-how-some-pathogens-evade-the-immune-system/81243811/

Feelin' Hot Hot Hot!

Biology concepts – fever, infectious disease, sexually transmitted disease, innate immune system

Would you be willing to be a human guinea pig, to

see if one disease might stop another? The term

“human guinea pig” refers to the fact that from the 1890’s

to the 1920’s guinea pigs were a major model for medical

research. Later replaced by rats and mice that could be

bred faster, guinea pigs were used to develop the first

diphtheria antitoxins, which subsequently saved

millions of lives.

Wouldyou be willing to let a doctor give you a disease? What if that might save you from another disease? You suppose this might be O.K., if the disease you were being given on purpose wasn’t too nasty.

What if the disease you're to be given as treatment is a form of the infection that kills a million people each year, the second most of any infection? Now you're thinking the disease you already have must be pretty horrible if this is the best idea for a cure. Let’s investigate and see if it might be worth it to save you from.... neurosyphilis.

Syphilis is a sexually transmitted disease that has distinct stages. The primary infection is marked by a lesion on those parts of your body that are most at play in the contracting of a sexually transmitted disease. It is amazing that some scientists believe that sexually transmitted diseases such as syphilis, in their primary stages, actually make sexual relations feel better. The organism (Treponema pallidum) benefits from this because the infected individuals might be more likely to have sex more often and this is an opportunity for the organism to be transmitted to additional hosts. Called “host manipulation” this is an evolutionary process that is just now gaining more attention, and will be something we will talk a lot more about in this blog in the near future.

The gumma lesions (left side) of secondary syphilis are not

meant for polite society. It's no wonder the Elizabethans

opted for the ruff collar (right side).

Thesecond stage of syphilis is marked by lesions, called gumma, on many parts of your body. You know those huge collars that the Elizabethans wore in 1500-1600 England? (see picture) As the story goes, the collars actually came into fashion as an attempt to keep syphilitic gummas out of sight. Syphilis ran roughshod through the English royal families at the time. Whatever the royals did everyone else wanted to do, so the collars became a fashion hit.

The tertiary (3^rd) stage of syphilis is much more likely to be fatal. Appearing anywhere from 3-15 years after the primary lesion, tertiary syphilis attacks the brain, heart, liver, or bone tissues of the victim. Neurosyphilis can bring dementia, hallucinations, psychosis, as well as unsteady gait and movements (ataxia or paresis). While only a quarter of the patients reach this stage, it is a nasty way to go.

Do you agree that being purposefully infected with one disease to avoid the ravages of neurosyphilis might be worth considering? Even if the doctors were going to give you....... malaria?

This is the spirochete bacterium Treponema pallidum,

the causative organism of syphilis. Recent evidence

suggests that the bacterium is flatter and less like a

corkscrew than previously thought. They don’t look like

they have a flagella to move around, but they do. It is

located INSIDE the cell, which makes the whole cell

whip back and forth, not just the tail.

In the modern day, the treatment for syphilis is antibiotics; penicillin G can easily kill T. pallidum in the primary and secondary stages. However, antibiotics do not cross the blood brain barrier very easily (this barrier is made by very tight junctions between the cells and reduced movement of molecules through the cells, in order to protect your brain from toxins and infectious agents). Very high doses of drugs must be used to treat neurosyphilis. They may not work at all and might bring side effects.

But in the days before antibiotics, other treatments had to be sought. In the state of Indiana, USA, just as in all states and countries at the turn of the 20^th century, syphilis was rampant in mental hospitals. This was both the cause and effect for some of the incarcerations, and was a source of constant battle in the institutions.

For better or worse, these patients were a stable population for the testing of different therapies for neurosyphilis, and Walter Bruetsch at the Central State Hospital in Indiana was a leading American researcher on the use of malaria to combat neurosyphilis.

Originally developed by Professor Julius Wagner-Jauregg of Vienna, Austria, the “malaria cure” was used to originally to treat paresis (very unsteady) and general paralysis patients; he suggested that fevers were helpful in paresis and tertiary syphilis.

Wagner-Jauregg had noted as early as 1887 that in the tropics, both malaria and syphilis were common, but those with syphilis rarely progressed to the tertiary stage, with the paresis that if often brought. In 1917, he treated nine paretic patients with good results, so other institutions expanded the study of this treatment. In Indiana, several decades of work were summarized in a series of papers in the 1940’s, making Indiana the prime American spot for “malaria cure work.”

The female Anopheles mosquito can take in quite a bit

of blood in just a short time. Take too long and they

could get squished.....but take hot blood in too fast

and they roast. That drop of fluid at the end of their

abdomen evaporates and helps cool their body as they

suck up the 37˚C blood, according to a 2011 study.

So how might malaria help in the treatment of syphilis? To discuss this, we have to know a few things about malaria. It is an infectious disease caused by an apicomplexan parasite called Plasmodium falciparum, although early hypotheses implicated bad air in the disease – hence the name; mal= bad, and airia = air. This organism has a complex life cycle, part of which occurs in the gut and salivary glands of the Anopheles mosquito and part of which occurs in human liver and then red blood cells (erythrocytes, RBCs).

There are five species of malaria parasites; P. falciparum is the one that causes the most severe disease. Other species include P. vivax and P. malariae, which are dangerous but do not cause as many deaths. They are also the prevalent species outside of Africa.

The merozoite (meros= portion, and zoo = animal, so like half an animal) stage of the organism invades the RBC’s and reproduces asexually. Periodically the merozoites burst out of the depleted erythrocytes and look for new blood cells to infect. These periodic bursts are timed differently in the different species, from every 48 hours for P. falciparum, or every 36 hours for P. vivax. When they break the RBCs and escape into the bloodstream, an immune reaction is stimulated by the broken cells, including a very high fever, from 103-110˚F!

The fever itself may be lethal, but there other factors, such as the fact that infected cells have parasite proteins on their surface that makes them sticky. The infected RBC's don't pass through the entire circulation and can block circulation in the brain or spleen and cause other problems. So which part of the infection was helpful in tertiary syphilis?

The consensus idea was that the malarial fever killed the T. pallidum of syphilis. Microorganisms like to live inside us because we provide them with something they need, and they have evolved to live best at our temperature. A fever is one way your body tries to make you a bad host for the organism. A high fever, induced by malaria, would make you a very inhospitable host for T. pallidum, and could be lethal to the organism.

Think about this the next time you want to take an Advil or Tylenol for that low grade fever. By medicating yourself, you are preventing your body from using one of its natural defenses against infectious agents. But high fevers cause damage on their own, so declining an anti-febrile (anti-fever) drug when your temperature is 100˚F is much different that counting on your body alone when the fever is 105˚F and you're having convulsions.

Here is a macrophage (false color image) ingesting

bacteria. The macrophage is part of the innate

immune system, it can phagocytose (eat) many

different foreign invaders. One macrophage can

take up and destroy hundreds of bacteria. They

stick to tissue culture plates not because they are

sticky, but because they're trying to eat the plate!

Work done by Dr. Walter Bruetsch at Central State Hospital during the 1940’s questioned whether it was the high temperature of the fever that stimulated T. pallidum destruction. Artificial fevers were not as effective as malarial fever in treating neurosyphilis; Bruetsch suggested that malarial fever and the RBC destruction it brought stimulated innate immune macrophage activity, while artificial fever stimulated only adaptive immune lymphocytes and resulted in lowered Ab concentrations (called titers) at the same time, making the adaptive response less effective. Bruetsch concluded that it was the activation of the innate system that produced results in treating general paralysis and neurosyphilitic paresis. The obvious answer isn't always the complete answer.

In later years, antibiotics took over as the major treatment for syphilis, and only rarely does the infection progress to the tertiary stage. However, proponents of fever therapy have, over the years, suggested that malaria as a treatment could be used for a variety of infections, from lyme disease to HIV.

The primary cheerleader for using malaria to treat HIV infection was none other that Henry Heimlich, inventor of the Heimlich maneuver. In the late 1990’s and early 2000’s Heimlich carried out a series of highly questionablestudies on malaria fever in HIV infection. It is not altogether clear whether proper informed consent was used, and the results of the studies have been universally discounted. But that is not where HIV and malaria part company.

A schematic cartoon shows how HIV replicates. It

first attaches and uncoats. The RNA is reverse transcribed

and then transcribed and translated into protein.

When the new virus assembles itself, the coat proteins

have to be chopped up into usable pieces. This is the

job of the HIV protease. Protease inhibitors stop this

and prevent virus maturation.

It turns out that protease inhibitors used to treat HIV infection may be potent inhibitors of P. falciparum as well. HIV takes over a cell and forces it to produce the proteins and RNA to form new HIV particles. Many of the proteins must have portions cut off to make them functional; this is the job of the protease (prote= protein, and ase = cut). Protease inhibitors prevent this cleavage and therefore stop the formation of new viral particles.

It turns out that malaria parasites use proteases very similar to those of HIV, and preliminary studies indicate that these drugs can prevent reproduction of the organisms. As hard as it has been to come up with useful malaria drugs, here’s hoping that human studies are successful.

Finally, there is some speculation that malaria and HIV are linked. The dangerous P. falciparum was not used to induce fevers in syphilis patients; doctors used less virulent Plasmodium species, such as P. malariae or P. vivax. Charles Gilks, in a 2001 paper in Philosophical Transactions of the Royal Society, suggests that some primate strains of malaria were also used, wherein infected monkey blood was injected directly into the syphilis patients. Gilks wonders if this is where a simian immunodeficiency virus made the jump to mankind. I think that is an extremely long leap.

Next week let’s work the other side of the street; do some diseases keep you from getting malaria? Yes, and there are more than you might have guessed.

C. Gilks (2001). Man, monkeys, and malaria Philos Trans R Soc Lond B Biol Sci DOI: 10.1098/rstb.2001.0880

For more information and classroom activities, see:

Syphilis –

http://www.metapathogen.com/syphilis/#biology

http://www.news-medical.net/health/Syphilis-History.aspx

http://microbewiki.kenyon.edu/index.php/Treponema_pallidum

http://www.microbiologybytes.com/video/Tpallidum.html

http://faculty.ccbcmd.edu/courses/bio141/lecguide/unit2/bacpath/contactcell_spiro.html

http://www.biomeds.eu/cms/show_article/30007.html

http://www.cdc.gov/osels/ph_surveillance/nndss/casedef/syphiliscurrent.htm

http://www.slideshare.net/shahparind/syphilis-and-neurosyphilis-101

Malariotherapy in syphilis and other infectious diseases –