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Bacterial Diseases Ans.pdf

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MICB 202
Tracy Kion

1 Bacterial Diseases Review Questions - Topic 1. 1. The bacteria could pass right through the gastrointestinal tract or it could colonize and become part of the normal flora. If the bacteria are pathogenic in nature, the bacteria could infect the gastrointestinal tract. The interactions between the pathogen and host might result in the occurrence of disease. 2. Different body parts experience different levels of moisture, temperature, and access to nutrients such as molecular oxygen. The area of the armpit is much warmer and moist relative to the skin on the arm. Different areas of the digestive tract have different pH; some bacteria are better suited for a neutral pH, others are better suited for a more acidic pH. Certain parts of the body are always sterile (except in pathogenic events); these areas include the bloodstream, muscle tissue, other internal tissues, brain, bone, and lower respiratory tract. With the exception of the lower respiratory tract, these areas of the body are not in direct contact with the environment. The lower respiratory tract is kept sterile because of ciliated epithelial cells (that sweeps anything trapped in mucous up towards the upper respiratory tract) and the alveolar macrophages that would engulf bacteria. 3. Bacteria that are embedded deep within the biofilm have less access to nutrients (which may include molecular oxygen). As a result, these bacteria are less metabolically active, may not be dividing, and so are less susceptible to antibiotics. This might suggest to a doctor, that the duration of antibiotic treatment may need to be extended – once the bacteria on the outer surface are killed off, the ones that were at the bottom may start to grow – they would then become more susceptible to the antibiotic. The bacteria embedded deep in the biofilm are also protected from the antibiotic, because the antibiotic may not be able to penetrate deep into the film, or it may be bound by substances that make up the extracellular polymeric substance (EPS). 4. Antiseptics are compounds that are intended to be used on living tissue. It kills or inhibits the growth of microorganisms but is considered sufficiently non-toxic such that it can be applied to living tissue. Disinfectants are compounds that are intended to be used on inanimate (non-living) objects such as floors, toilets etc. It is a compound that is intended to kill microorganism, but it may be too toxic to put on living tissue (i.e., it would kill eukaryotic cells too). If it were my knee, I’d go with the antiseptic. 5. A broad spectrum antibiotic is effective against many different species of bacteria – it is effective against both Gram–positive and Gram–negative bacteria. Selective toxicity refers to the ability of a compound to inhibit or kill pathogenic microorganisms without adversely affecting the host. 2 6. Could easily be done by setting up a table. How antibiotic affects Exists in human Why we can use it pathogen RNA synthesis Yes Our RNA polymerase (RNAP) has a different structure than bacteria’s RNAP – the antibiotics don’t bind to our RNAP Protein synthesis Yes Our ribosomes have a different structure – the antibiotics don’t interact with our ribosomes Cell wall biosynthesis No We don’t have a cell wall. Folic acid metabolism No We need to get folic acid from our diet – we can’t make our own DNA replication Yes Our DNA gyrase has a different structure that doesn’t interact with the antibiotic Destabilize cytoplasmic Yes The antibiotic would not be able to act membrane with the membrane of eukaryotic cells 7. The antibiotic should be soluble in the body fluids, and should be able to reach the infection site quickly, and in sufficiently high enough concentration. To do this, it has to remain in the body for a reasonable amount of time (i.e., it can’t be excreted into the urine within a few minutes of ingesting it, or breakdown too quickly). It should also have no or minimal amount of side effects – it if caused nausea, then a person may not take the medication as needed. If it caused vomiting, it may not have been in the body long enough to be absorbed. If it causes diarrhea, it may lead to other problems or may result in non- compliance by the patient. It can’t trigger allergic responses – that would definitely not be good for the person, as it would likely be a systemic response. It shouldn’t be something that the bacteria could easily develop a resistance to (this may be hard to design) and it should act against most pathogenic bacteria (not all antibiotics do – sometimes it is necessary or advantageous to use an antibiotic that targets specific groups of pathogens. 8. The antibiotics target both pathogens and the bacteria of the normal flora. If a significant proportion of the normal flora bacteria are eliminated because of the antibiotic, it reduces the microbial antagonism and makes it easier for pathogens to colonize in the host (including opportunistic pathogens). This would mean that the normal flora that was occupying space and using up nutrients aren’t there any more, so a(n) (opportunistic) pathogen can more easily infect a person. If a person has been taking antibiotics for a long time, it would suggest they are not in good health, and that their immune system make not be working adequately to deal with the infection, so they may be more susceptible to opportunistic pathogens anyway. 9. The child was likely infected, inadvertently, by a hospital worker. The hospital worker may have tended to the first sick child, or cleaned the room of the first child, and ended up with some of the MRSA on their hands. They may have then tended to the second child (without washing their hands first) and transmitted the bacteria to the second child which then developed the infection. They may have touched a door handle, light switch etc., which was then touched by someone else who had contact with the second child. It is possible that the MRSA bacteria could have been transmitted to the door handle or light 3 switch by the parents of the first sick child, which was then picked up and transmitted by the hospital worker. 10. The first postulate, that the pathogen is found only in those that are ill, but not in healthy is not true in at least two situations. There are people that carry pathogenic bacteria as part of their normal flora; the bacteria do not cause disease in them, but may cause disease in other people if the bacteria is transmitted to them. These people are known as “carriers”. Also, bacteria of the normal flora can cause disease if they get into a part of the body where they are normally not present (i.e., skin bacteria causing ear infections, bacteria from the gastrointestinal tract causing urinary tract infections). The second postulate, that the bacteria must be isolated and grown in pure culture is not always true. Many bacteria cannot be grown in culture (i.e., we can’t reproduce their growth requirements in a petri dish), and others cannot be grown as pure cultures. Viruses cannot be “grown” as pure cultures – there are always cells present to support their replication. The third postulate, that the bacteria must be inoculated into a healthy animal, which must then develop the same disease, as the original subject is not always true. Some bacteria cause disease only in humans, but not animals (it may be part of the animal’s normal flora), or they cause a different disease in animals that what is observed in humans (see the example in the Salmonella section of the notes). Bacterial Diseases Review Questions - Topic 2 - Neisseria gonorrhoeae Case Study. 11. Bacteria are specific to the type of cells they adhere to, so not all bacteria adhere equally well to epithelial cells. The reason why adherence is important, is that in order to colonize, the bacteria must remain at a particular site. Many natural bodily functions (such as intestinal peristalsis, flow of urine, movement of ciliated cells, sloughing off of dead skin cells) are intended to remove bacteria that try to interact with the body surfaces. 12. When a person is infected with N. gonorrhoeae, the initial immune response is an inflammatory response. This accounts for much of the initial symptoms and the discharges associated with infections. However, many people are asymptomatic and may be unaware that they are infected. Men may experience painful urination and urethral discharge of pus. Women might present with cervical-vaginal discharge, painful urination if a urethral infection is present, abnormal menstral bleeding and pelvic pain. However, many men and women are asymptomatic and may be unaware that they are infected. For some people, the infection is may be cleared by the inflammatory immune response, so the person is completely recovered. The infection may be cleared more quickly by using the appropriate antibiotics. The complications that occur are not equal for men and women. Both genders may suffer from gonococcal arthritis if the bacteria disseminates through out the body. Women may suffer chronic pelvic inflammatory disease (PID) which is a caused when the bacteria disseminate into the uterus and fallopian tubes – this may result in sterility. An infected 4 women that gives birth may transmit the bacteria to the eyes of the infant, causing ophthalmia neonaturm; however, silver nitrate or antibiotic drops are placed in the eyes of ALL newborns to protect against this. This is because women can be asymptomatic and be unaware that she is infected. 13. N. gonorrhoeae is unusual in that it appears as a Gram-negative diplococci – Gram- negative diplococci are not part of the normal flora of the genitourinary tract. The reason why it might not be useful for diagnosing N. gonorrhoeae infections in females, is that the vagina already has a lot of bacteria as part of the normal flora – it might not be possible to see a few Gram-negative diplococci in the field of view of the microscope – the vast majority of bacteria in the field of view will be from the normal fl
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