Fun 2: 11:00 - 12:00 Scribe: Molly Clark

Fun 2: 11:00 - 12:00 Scribe: Molly Clark

Thursday, October 29, 2009 Proof: Karla Thomason

Dr. Benjamin Mycobacteriology Page 1 of 10

I.  Mycobacteriology [S1]:

a.  Ok so now we’re going to talk about mycobacteria. So this is what TB looks like when it grows in the lab. You get these huge numbers of bacteria. This is a really low powered picture sort of micrograph, and these are individual bacteria here. But it grows in all these nice forms. And that’s real rare; most mycobacteria don’t grow that way. I think it looks like a Chinese dragon, so this is a mascot.

II.  Mycobacteria sp. [S2]

a.  Ok so what are mycobacteria? They’re really defined by the acid-fast things. So we have a specific stain we’ll talk about, and if something is acid fast positive, then it’s probably a mycobacteria. Although there are some exceptions.

b.  It’s because they have mycolic acid. So they have acids that have 78 to 91 carbons in these mycolic acids. So they’re very long chains, and this really prevents the normal stains from being taken up by these organisms. And it also prevents it from decolorizing. Alcohol decolorizes essentially everything, but these aren’t decolorized because of the mycolic acids.

c.  They also have some waxes.

d.  They’re all obligate aerobes, so they have to have oxygen to grow, which is kind of rare.

e.  And they’re also slow growing, so it takes days to weeks to form colonies. So before you get a colony of tuberculosis growing, it takes about 3 weeks on media. So you send the specimen in, and then wait 3 weeks before you get a diagnosis, which is really kind of a problem. It takes a long time for them to divide.

III.  Identification of Acid Fast Bacilli [S3]

a.  Identification. First the acid fast stains as I mentioned.

b.  Mycobacteria predate animal life, so there’s many different species of mycobacteria.

i.  There are 140, but they keep dividing. There’s probably several more than that now.

ii.  They live in soil and water and all over. And we don’t get infected with those very often at all.

iii.  More recently we’ve seen about 40 different species that have infected patients, especially immunosuppressed patients. A lot of these are AIDS patients. We had some that we knew about before infecting patients, but now they’re very common. The most common one we see, actually, is not tuberculosis; it’s mycobacterium maybe. It really is found largely in HIV positive patients.

IV.  The Bacterial Cell Wall [S4]

a.  These are the bacterial cell walls. These are the things you’ve been hearing about since the gram-positive organisms. This is a peptidoglycan layer. So this is what retains the gram stain. This is the cytoplasmic membrane. All of them have the cytoplasmic membrane.

b.  This is a gram-negative organism, which I’ll be talking about Monday. It has the same cytoplasmic membrane, plus a very thin peptidoglycan layer, so the gram stain doesn’t get trapped in the layer of peptidoglycan. Then the gram-negative organisms have an outer membrane. So this is where the endotoxin, the LPS, survives. Then they have other proteins through that.

c.  This is a mycobacterium. You can see that the peptidoglycan layer. It turns out they’re really gram-positive organisms genetically, but they don’t stain and we don’t look at them as gram positives really. They have arabinogalactan layer. Then these are all the mycolate acids, and they have porins through it. So they have a real complex cell outer membrane on mycobacteria.

V.  Obligate Pathogenic Mycobacteria [S5]

a.  So there’s only two that are obligate pathogens. The rest of them live in soil and environmental conditions and occasionally will affect people, especially immunosuppressed people.

b.  Obligate mycobacteria tuberculosis is not found in nature. It is normally not found in any other animals. A lot of zoo animals can be infected, and nonhuman primates can be infected. All the nonhuman primates on campus are tested routinely with the skin test. People that work around them have to be tested and monitored to make sure we aren’t giving all of our monkeys tuberculosis.

c.  There was a lawsuit where an elephant and its handler both had TB, and both of them were suing trying to figure out which one infected the other one. I don’t know if they ever figured out who was the culprit.

d.  TB was actually the first organism shown to cause disease using Koch’s postulates. So the organism was isolated from disease, put back in an animal, caused the same disease, and was reisolated. Those are Koch’s postulates, and tuberculosis, which is a harder organism to grow, was the first one.

e.  Mycobacterium leprae causes leprosy, which is more important here than you would think. And Hansen is who it was named after, and he actually was disbarred because he tried to transmit leprosy from a daughter to her mother. So he implanted leprosy in the mother’s eye, and he didn’t go through IRB process. And even then they didn’t like that, and he remained a researcher the rest of his life and was not able to work with patients anymore.

VI.  No Title – Epidemiology Graph [S6]

a.  This is the epidemiology of tuberculosis. See this starts a long time ago in 1860 in Britain and Whales. Even before we knew what the organism was, the damage was decreasing. So the number of deaths per hundred thousand was three hundred, which is extremely high, but it was already decreasing. And a lot of this is due to social changes like getting people less crowded, etc.

b.  And then Koch developed the TB skin test actually. He though it was a treatment. It turned out not to be. And it didn’t change the rate of decline of the organism.

c.  Here you can see WWI, and here you can see WWII (two spikes in the graph).

d.  BCG vaccination, which we’ll discuss a little bit, really doesn’t change the epidemiology of the organism. It might protect people from developing disease immediately, but it doesn’t protect them from being infected and having a latent infection and reactivating later, which is what most TB is.

i.  The most infectious TB is someone that’s been infected, had a latent period, and then reactivated. Those are the ones that are infectious.

e.  Chemotherapy may have had some effect, but it’s not clear, especially early because they became resistant very quickly.

VII.  Mycobacterium tuberculosis [S7]

a.  So Mycobacterium in the world today. Humans are the only natural host.

b.  A third of the population is infected. So a third of the population has organisms in them that are alive and can cause disease if they become immunosuppressed. But most of them don’t, as we’ll discuss later. About 5% of the population in the United States have TB in them, and so that means the rest of the world is pretty much 100%. These organisms can reactivate at any time.

c.  So this is about 2 billion people infected, and 9.2 million of those have tuberculosis disease every year. So it’s still a high number in the world. And we’ll go over what it’s like in Alabama and the United States.

d.  So 1.7 million deaths are caused by tuberculosis a year, so that’s 10% or so of people dying of tuberculosis disease.

VIII. Tuberculosis in the United States [S8]

a.  This is what’s happening in the United States post what I’ve just showed you. From 1980s to 1992 it was going down, but then it leveled off.

i.  And this is where people thought that TB was controlled. We had 30,000 cases a year, and it was going down every year. So people quit going through all the trouble of the TB control.

ii.  HIV was taking hold at this time. We put all the HIV patients together. TB and HIV are very synergistic, so TB causes CD4 cells to go crazy. HIV grows in CD4 cells, and so they are very synergistic. If you decrease the immune response, TB grows better also.

b.  And so the prevalence went up, and at this point they decided they should do something. So they increased the TB control and quit putting all of the HIV patients together without watching for TB very closely, and the rate started to go back down again.

c.  And we’ve continued down an anchor below 13,000, but not much. It’s kind of leveling off. We’re getting kind of where it’s harder to clear the rest of them.

d.  One of the problems was in New York City is where they put all these HIV patients together. They were treating a lot of them, and they developed very bad drug resistance. And so there was one strain that only infected HIV patients. The organism was so sick from being resistant to a lot of antibiotics that it really couldn’t infect an immunocompetent person, but when they started treating the HIV patients better and not allowing them to infect each other, it really went away pretty quickly.

e.  So you can see here there’s only about 5% mortality in the United States. We’ve had 2 deaths at UAB in the last year from TB. I think both of them were HIV patients. AT least one of them was.

IX.  U.S. Tuberculosis Cases [S9]

a.  This is what’s happened with tuberculosis cases in the United States. So you can see in 19991 there were 20,000 cases. We’ve continued to go down, and we find now that the US born is less than the foreign born. So these are people that were infected in other countries, and we’re 80 or 90% percent that people who are skin test positive have latent infections. They can develop disease.

b.  And so you can see that the rate per 100,000 of the US born is 2.1. And foreign born is 20.7 per 100,000. And so it’s very different, and the rate of foreign born is very constant. So there are not increasing in numbers, but not decreasing either.

c.  And interestingly, if you look at the fingerprints and look at these organisms, very rarely is TB transmitted from foreign born to native born.

i.  So that’s because you have to be really close to someone to be infected by transmit tuberculosis.

ii.  An elevator or a classroom even, often aren’t infected. But you have to be in an enclosed space for several hours usually. And so people segregate into their own people really, and so outbreaks, kinds of disease really follow social lines amazingly so.

iii.  So try not to be afraid of foreign born because they might have TB because it’s really not transmitted much to someone that’s not very close to them.

X.  Alabama Tuberculosis Cases [S10]

a.  This is what happens in Alabama. You can see that this is 1985. There were very nice decrease, and we’re down below 200 cases here right at the national average. When we started we were quite a bit above the national average, but Alabama does a very good job of controlling tuberculosis.

i.  If someone is diagnosed with tuberculosis, the county health department or state health department will treat him or her.

ii.  And if they don’t want the treatment and can’t be found, they will put them in prison so they can finish the treatment. And they’re good at getting people to complete their treatment so they don’t transmit and develop drug resistance.

XI.  Examples of high prevalence countries [S11]

a.  This is an example of some other countries. These are places that I’ve work with tuberculosis.

b.  So here is Namibia. Here there are 1.8 million people and 16,000 cases of tuberculosis. It’s difficult to know how they count because they don’t diagnose very well. The tuberculosis rate per 100,000 is 822. The death rate is 61.

c.  Zambia is here. They have 11.5 million people and 78,000 cases. They have a rate of 680.

d.  And this is the US from 2006 probably. We had 300 million people and 13,000 cases. The rate is 4.2 (much lower). A lot of people have tuberculosis in other parts of the world. This is just one example of what there are.

XII.  Transmission of Tuberculosis [S12]

a.  So transmission. Transmission is by infectious droplets. And surgical masks don’t help. So if someone’s wearing a suit and a surgical mask, it doesn’t help. It works for influenza but not for tuberculosis. You have to wear an N95 mask that excludes 95% of the particles the size of a bacterium to really help.

b.  The droplets that are really infectious are very small. So they hold only a few organisms. It’s only 1-5 microns, so only a few organisms can fit in that.

i.  The reason is that they have to get down into the alveoli. If they lodge in the upper respiratory tract, you will cough them up or swallow them, and they’re not very infectious.

ii.  But if they get down into the alveoli they can infect alveolar macrophages and set up an infection.

c.  Droplets settle 9mm per minute in still air. So if someone has contaminated your air, it takes 90 minutes in still air for these to settle out of your breathing area.

d.  There was a case in Gadsden. There was a convenience store that had a bathroom where people smoked crack, and somebody who had TB would cough in the bathroom. And the next person to go in got transmitted. Usually you can track people by knowing who you know and who you get it from, but in this case they didn’t know who they were getting it from. And there were 78 cases of one fingerprint of TB in Gadsden from this one store. The health department was able to close the store down. It was just too convenient, and this solved the problem.