Dolly, I just can’t quit you.
This week we studied pathogenesis and identification of microbes in the clinical setting. In order to cause disease, bacteria must:
- establish a reservoir
- Transmit and enter the body
- Attach and colonize
- Evade the immune system
- Multiply and spread
- Cause damage or disease
- Exit (I guess technically this isn’t a requirement, but it is if they want to move onto someone else)
Can you give examples of how bacteria do each of these things?
Toxins are of particular importance. We studied three kinds:
- Exotoxin (secreted from bacteria)
- Superantigen (a special type of exotoxin that causes an immune system response)
- Endotoxin (the toxic portion of the Gram- outer membrane, AKA Lipid A)
We then covered two ypes of bacterial infections, Salmonella and Strep.
There are some unusual things about each. Salmonella has the ability to live INSIDE of macrophages (a component of the immune system…. immune evasion!!) which is pretty rare.
The second part of the class was to cover how microbes are identified in the clinical setting.
Samples must be taken and handled appropriately, and the right test needs to be done to identify the causative agent of the disease. A lot of information can be found using:
- H&P
- Logic about the disease and source of microbe
- stains and microscopy
- Growth on selective and differential media
- Enzymatic tests
- Molecular tests
There are three things that we can use to identify a species of bacteria (or any pathogen):
- Identifying pathogen specific genomic sequences (using something like PCR, RFLP, etc)
- Identifying pathogen specific proteins
- Identifying the pathogen indirectly by assessing the patient’s immune response
We went over a variety of stains (simple and differential), used a dichotomous key to identify an unknown species of microbe, and looked more closely at how subtle genomic differences can be used to positively ID the species of bacteria.
I had a brain fart and completely forgot to include the slides about horizontal gene transfer in the student hand outs. Sorry!
Horizontal gene transfer, or the transfer of DNA from one unrelated bacteria to another (as opposed to vertical transfer which is from “mother” cell to “daughter” cells). Conjugation was especially highlighted… here’s an awesome video about why horizontal gene transfer is so important to the rise of antibiotic resistant bacteria!
There are several types of conjugation:
- Conjugation: The transfer of plasmids from F+ to F- bacteria
- Hfr conjugation: The F plasmid becomes integrated into the F+ bacteria’s chromosome and the bacteria tries to transfer over the ENTIRE CHROMOSOME to the F- recipient.
- F’ conjugation: The plasmid is integrated into the chromosome, and then pops back out, taking a little extra DNA with it. So, then the plasmid is transferred like in regular conjugation, but the recipient gets a little extra DNA too
Plasmids are VERY common in bacteria. They are also dsDNA and circular like the chromosome, but much smaller. They also carry useful, but non-essential information. Here are the types:
- R. Carries genes for antibiotic resistance
- F. Carries the genes necessary for conjugation. If you have it, you’re F+
- Col. Carries genes that kill other bacteria.
- Vir. Carries genes that are toxic to humans
- Met. Carries genes that are involved in metabolism
Next, we talked about bacteria in soil and aquatic ecosystems (mostly aquatic). How do bacteria adapt to the scarcity of nutrients in the ocean?
Ocean pollution was discussed and how that affects bacteria. What do you think would happen if the neuston was completely covered in oil or trash? How would that affect the food web? How can bacteria assist in cleaning up ocean oil spills? What’s being done about the ocean plastics? Without intervention, by 2050, there will be more plastic in the ocean than fish. You read that right.
Next we talked about how bacteria impact humans. We started off with our own resident microbes – our normal flora. We looked at concentrations and diversity at different sites on the body, and what these little symbionts do for us. What type of symbiotic relationship is this? They can contribute to obesity to. Obese mice seem to have more Firmicutes than Bacteroidetes, and lean mice are the opposite. If you take the feces from a fat mouse and put it into a lean mouse, that mouse will become fat too! Would the reverse work? Fecal transplantation could be the “weight watchers” of the future!
Living large…
Next we discussed how to make yogurt and cheese, which are kind of the same thing – only the former keeps the whey (liquid) in the product and the latter removes it. Probiotics (and prebiotics) were next on the menu, and we talked about their strengths (in people with intestinal dysfunction) and their weaknesses (healthy people). Do you take probiotics?
Next we talked about microbes and water, both drinking water and waste water. We learned that microbes are the main remover of organic contamination in waste water, and that bottled water is the biggest scam ever perpetrated on the American public.
Presented by Online Education
Things to focus on for today:
- DON’T focus too heavily on the individual infections (salmonella, strep, ) they were just examples
- Compare and contrast the three types of toxins
- Know how to use a dichotomous key
- Describe the disk diffusion test for antibiotic resistance
- Describe PCR and RFLP, how are they different? How are they similar?
- Wash your hands after taking a poop.
- Explain how bacteria contribute to nutrient cycling, especially the fixation of Nitrogen. Why is that one so important?
- Be able to describe the different types of conjugation discussed in class, including understanding of the terms F+, F-, F’ and Hfr
- Draw a diagram of conjugation, including who is capable of conjugating, what is transferred, how, and which direction the info flows
- Describe the characteristics of a plasmid, and know what type of information each plasmid carries (R, Col, F, etc)
- Describe where you would find bacteria in the marine food web, and which types of bacteria are where
- What are the benefits of a gut microbiome?
- Describe what bacteria do to produce yogurt and cheese.
Questions and comments? Leave them below… happy studying!