Anaerobic Bacteria pg. 8
Sara McGowan
1,2: Here are the relevant chapters in Murray. I strongly suggest you read these chapters, don’t just rely on the lecture because this is an overview and there is other information in the book.
3: Basic difference between anaerobic bacteria and others that you’ve studied, which are mostly facultative organisms that can grow with or without oxygen. There’s a whole spectrum and aerobic bacteria are obligate. They must have oxygen to grow, e.g. Pseudomonas. The Microaerophilic require oxygen in reduced quantities, e.g. Campylobacter that cause intestinal disease. They will not grow in atmospheric oxygen. Capnophilic means they require CO2 in the atmosphere, e.g. Neisseria gonorrhea, Hemphylius influenza; more fastidious organisms like Pneumococcus. The vast majority of bacteria in human infections are the facultative. We are going to talk today about the spectrum in anaerobic bacteria, the obligate anaerobes and aerotolerant. Keep in mind that there are varying conditions required, not just in temperature but also in atmospheric conditions.
4. They live in certain places and they live there because of certain conditions. You have to have reduced or no oxygen. The pH and oxidation-reduction potential are also important. The basis of either being able to grow in oxygen or not are these enzymes: cytochrome systems, superoxide dismutase and catalase are the fundamental mechanisms by which we, as well as bacteria, can detoxify the high-energy radicals that are produced from oxygen metabolism. If they lack those, they kill the cell. Facultative anaerobes have some of these, but not sufficient quantities to be totally able to grow in atmospheric oxygen.
5. This is a schematic showing the same thing. If you have anaerobic bacteria, it lacks this detoxifying pathway. You have high-energy radicals including hydrogen peroxide that are toxic to the cell. Down here, it’s all turned into water or atmospheric oxygen. Facultative organisms or organisms that grow in the presence of oxygen have those enzymes. They have those cytochrome systems; that’s how they survive. Anaerobic bacteria do not have these, but there is a spectrum. Aerotolerant organisms have some enzymes, but not the quantity that’s required.
6. Where do they live in people? We have a lot of anaerobes that we carry around everyday. The majority of the microbial flora in your colon are anaerobes (over 90%). We usually only think about pathogens or problems with that flora like with Shigella or Campylobacter. The facultative bacteria cause intestinal disease or often extra-intestinal disease, but they are a small portion of the population. Anaerobes live in a variety of places, based upon this condition (oxidation-reduction potential and anatomic site), e.g. periodontal pockets, dental plaque, colon. The extreme locations are H electrode and O electrode. They are not floating around in the body; they live in places like the colon, like the oral cavity, but not on the surface like Streptococcus mutans. They live in pockets so they are protected from oxygen and have these other conditions.
7. This is a way of putting them in different categories: gram-negative rods, gram-positive rods, gram-negative cocci and gram-positive cocci. There’s a commonality to a lot of them. The colon is mentioned in all categories, so there’s a very mixed flora in the colon. There are others that are focused in the oral cavity. Some are specific to the vagina or skin. Propionibacteria is an aerotolerant anaerobe whereas some of these others are strict anaerobes. The only ones found in soil are the Clostridium. Bacillus are the spore forming aerobic rods and Clostridium are the spore forming anaerobic rods. The spore allows them to exist in condition s that they would otherwise not grow in.
8. Where can there be problems with anaerobic bacteria? First, remember where they live. Areas adjacent to those places are often subject to infection. If there’s reason for dissemination e.g. infection from a human bite can be nasty, involving anaerobes. If someone has aspiration pneumonia and gets an abscess in the lung, could get in the bloodstream and to the brain. There’s a lot going on in the mouth. If you have surgical or other disruptions like appendicitis that ruptures, your peritoneal cavity can have abscess formation. If they get loose from the spot where they normally live as part of our normal flora, that’s when they can cause problems.
9. Some of the oral diseases like Vincent’s Angina is a good example s synergy. This is not caused by a single bacterium. It’s hard to see in the picture, but there are three morphological types. Scrape the mouth and do a gram stain; they are all gram negative. Treponema are very thin and corkscrew-like. Fusobacterium are long and fusiform. The short fat rods are probably Prevotella/Bacteroides. There is overgrowth of these organisms that are normally there, but because of poor oral hygiene have multiplied and cause damage.
10. Not quite as acute is Adult Periodontitis. The same process is going on, but it’s not as acute. Usually not caused by that same group of organisms. What you see is progressive receding of the gums because of all of the toxins being produced by the bacteria that are hiding in crypts. No matter how good the teeth are, eventually the gums are gone and they can’t hold their roots into the bone.
11. Much more serious are things like brain abscess. When you eat, if you have poor dentition and your teeth are loose or you get your teeth cleaned, with all of that activity you get showering of oral bacteria. That puts you at risk if, for example, you have a defective heart valve, you could get endocarditis. If it’s chronic, it may get to the brain and cause an abscess. In aspiration peneumonia, the classic example is an alcoholic who passes out and they regurgitate stomach acid and contents and they aspirate. They get oral flora and foreign body material from the stomach and acid. All of that destroys tissue and once you get destroyed tissue, anaerobes are happy because they have a place to hide from oxygen. They will cause abscesses and bacteremias as well.
Back to slide 10. This is a gram stain of an aspiration of an anaerobic abscess. These are neutrophils around the white cells. There are gram-positive cocci and rods and there are gram-negative rods. Like in Vincent’s Angina, this is characteristic of anaerobic infections: abscess formation and mixed flora. Often if you have a Staphylococcus infection of the arm it’s one organism, S. aureus. This is different, most of theses abscesses have multiple organisms in it and can include facultative organisms they don’t have to be strict anaerobes.
12. In people with poor peripheral circulation, like diabetics, just like other bacteria it can get into sores that do not heal well and then cause tissue damage. This is polymicrobic cellulitis. It’s not the most common cause of this sort of thing, but it can be involved. It depends on a number of things like personal hygiene.
13. We group them by gram stain and morphology and how closely they are related. This group is three genera: Bacteroides, Prevotella and Porphyromonas. They all fit these criteria: no spores, pleomorphic, normal flora of respiratory and GI tract as well as the female genital tract. They normally don’t cause problems. The important groups are the Bacteroides fragilis and the Prevotella melaninogenica, which are more commonly involved in infections. Above the diaphragm you think of P. melaninogenica and below the diaphragm you think B. fragilis, so it ‘s colon associated or oral associated. There are some other niches, like the female genital tract has particular species of Prevotella.
Again, abscess formation, mixed flora sometimes also mixed with facultative organisms are characteristic of anaerobic infections.
14. This is not a mixed flora; this is necrotizing fasciitis caused by Bacteroides fragilis. This is the same sort of flesh-eating bacteria like Streptococci. It’s the same idea: fasciitis is fasciitis. It’s not as toxic as the streptococci, but it can cause this. This is an example of introducing bacteria that are normally part of our flora into a place they don’t belong and you get infection and disease.
15. This is the bad outcome of that. You can’t leave dead tissue; you get devitalized tissue in this sort of condition. You have to remove it, so this guy will have additional surgery to get rid of black tissue, which is dead.
16. Fusobacterium is the long fusiform rods. Fusiform means pointed. They are pointed at the ends. They are pleomorphic, virtually all of these are pleomorphic. This is distributed in the upper respiratory and GI tracts. Pleomorphic means the same organism can have multiple shapes.
17. Already talked about pulmonary abscess. This is lower lung abscess, probably a result of aspiration like the circumstances already described.
18. Fusobacteria are pointed. There’s nothing unique about them when they grow on plates, except that they would not have grown unless you collected them properly and they did anaerobic cultures in the lab.
19. Of the gram-positive bacteria, there are some of the more classic diseases. Actinomyces are a group of higher order bacteria that are strict anaerobes; they cannot be exposed to oxygen at all. If they are exposed to oxygen, more than likely they will not live. This is the most common species, A. israelii. They are very slow growing. Most of the bacteria we deal with grow a colony in 18-24 hours on a plate. It may take 3-4 days for Actinomyces to multiply enough to make colonies. What that means is that if you ever suspect this is a part of an infection, you have to let the lab know to hold these longer and not to look at them early in their incubation. Taking them out might kill them if they haven’t grown enough.
They create draining sinuses with sulphur granules. If you were to aspirate this organism, it makes an abscess in your lung and it can come out and causes sinus in the chest walls. Out of that drains material and pus, including the organisms that are in small colonies like little sand grains. They are the organism microcolonies covered in host material. The original ones seen were yellow, so they were called sulphur granules. They can be yellow, white, or different colors, but that’s a characteristic. This is mostly associated with oral and respiratory. The copper IUD’s can get colonized and have to be removed, but the major problems are in the oral and respiratory tract.
20. Dacryocystitis is not a serious condition. This is A. israelii and the sulphur granules are blocking the tear ducts and they can’t function. Prior to the (availability of) haemophilus influenza B vaccine a child may look like this, so it would require a differential diagnosis between dacryocyctitis and haemophilus infection. It’s important when you’re dealing with people to know their immunization history. If the child had not been immunized you would want to look into that. The treatment is to get those things (bacteria?) out of the tear duct.
21. The classic condition of Actinomycosis: Lumpy Jaw. This guy is asymmetric; normal face on one side and greatly swollen on the left side.
22. Not the same patient, but the same process. Looking down at the root of the crown and looking at the x-ray, you see the roots and the bone are being eaten away. An abscess forms down there and is quite painful. People will come in to have it looked at and if you leave it alone they make these draining sinuses. This will come out the side of the jaw. If it’s opened up and put some gauze on it, the gauze soaks up the fluid and you can capture the sulphur granules and diagnose without having to go into the abscess inside, but not everyone waits this long. This is the classic description of Actinomyces israelli infection.
23. These are the sulphur granules, about the size of a grain of sand. The picture is black and white, so they may or may not be colorless. They are important to look at and crush into a gram stain. In the gram stain they are filamentous branching rods. There are fungal infections that also cause draining sinuses, generally not in the oral cavity, but elsewhere and they make sulphur granule-type material. The treatment for a fungal versus bacterial infection is quite different. It’s important that the lab looks to be sure they have a bacteria or fungus.
24. The closer view shows that in culture they look long and branched, kind of unusual for bacteria, but the size is 1-2 microns in diameter. That is bacterial size. Fungi are roughly 10 times larger, so size can be important when you look at things with similar morphology. You may see in the future that staphylococcus is a certain size and yeast is about 10-15 times bigger, but they both are round, so you can be fooled. When it’s grown (this is an old culture) it makes what’s called a “molar tooth colony.” The colony looks like a molar.
25. There are less important, nuisance anaerobes and they fall in the gram-positive bacilli category. They can be part of the mixed flora but the others we’ve discussed, the gram-negatives, are more important in the pathogenesis. This can be a nemesis in the lab because they are normal skin flora. It’s aerotolerant and it grows down in the hair follicles. It’s a problem because we get blood cultures in the lab and if someone doesn’t decontaminate the area properly, there are two things they can put in there. There’s staphylococcus epidermis, which most of us have on our skin and propionobacteium; it causes confusion. Staph can cause true infection, for example, of artificial heart valves or artificial joints. So you don’t know did it come from the skin or from somewhere else? Propionobacteria are easier, except they show up about day 4-5 of the incubation. Clinician is told they have a gram-positive rod in the blood culture and they have to do something about it until they get a final answer because there are other gram-positive rods that can cause a problem. We try to stress to the medicine people and nurses … it depends on who collects the blood. Phlebotomists specialize in it, so you get lower contamination. Nurses are OK and less often the clinician does it, but whoever does can save the lab trouble by doing it right.