Chapter 14. Bugs that Resist Drugs

Transcription

1 Chapter 14 Bugs that Resist Drugs

2 See website Learning Objectives Important Terminology Power point- posted after chapter is completed

3 What happened to Carlos Don, Rebecca Lohsen, Ricky Lannetti? Carlos Don, sixth grade Rebecca Lohsen, high school student Ricky Lannetti, college student

4 Prokaryotic Cells Fimbriae Nucleoid Ribosomes Plasma membrane Bacterial chromosome (a) A typical rod-shaped bacterium Cell wall Capsule Flagella 0.5 µm (b) A thin section through the bacterium Bacillus coagulans (TEM)

5 Characteristics of Prokaryotic Cells vs Eukaryotic Cells Prokaryotic Cells No nucleus Cell wall Small No organelles Single-cells Eukaryotic Cells- animal and plant cells Nucleus Organelles complex

6 MRSA Methicillin-resistant Staphylococcus aureus (MRSA) Infectious bacterium that has become widespread in recent years and that is difficult to treat with most existing antimicrobial drugs Centers for Disease Control in 2007 study, 94,000 people get sick each year, kill about 19,000 Formerly outbreaks were primarily in hospitals

7 A major public health concern New high-risk groups: day care workers, prisoners, etc. Young healthy people are now getting sick Robert Daum, a professor of microbiology, states WE NEED A PLAN OF ATTACK NOW

8 Staph the microbe MRSA infection is caused by Staph Several species of staph bacteria can cause human disease Concerns over S. aureus, that has developed resistance to antibiotic drugs that normally kill them- penicillin and cephalosporins MRSA or drug-resistant staph How did it get the name methicillin resistant?

9 Staphylococcus aureus S. aureus is a bacterium that can be passed from person to person by direct contact or through shared, contaminated items such as towels and bars of soap.

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11 Staphylococcus aureus Staph bacteria are harmless to most people who carry them. Between 30% and 40% of the population carries staph on their skin or in their noses.

12 Staphylococcus aureus Some staph bacteria have developed resistance to antibiotic drugs that once effectively killed them. About 1% of the population carries drugresistant strains of staph. If you carry staph and aren t sick, you are colonized but not infected. Could have many different types of staph, including (MRSA), and not become ill. Can pass to others that become ill.

13 Staphylococcus aureus Every one of us has probably had staph In otherwise healthy people, staph infection usually causes only minor skin eruptions such as boils or pustules that can resemble spider bits.

14 Staphylococcus aureus People with weakened immune systems are at especially high risk of developing severe diseases such as pneumonia, infections of the bloodstream, or infections of surgical wounds caused by staph. Some disorders: Lupus, AIDS, Diabetes Elderly and children o&feature=related

15 Staphylococcus aureus In recent years there have been several cases of healthy people becoming severely ill from MRSA infection Most likely because they were infected by an especially deadly strain of drug-resistant staph. Healthy person can become more severely ill: Procedure that weaken the immune system Break in skin that becomes infected with staph

16 Staph bacteria How do they cause illness? Multiply on or in human tissues. Secrete toxic substances that harm human cells damage organelles, membranes, etc. Range of diseases due to different strains differ in their genetic makeup or DNA MRSA is a combination of unique strains of bacteria. Some more deadly than others- drug-resistant strains Recently more healthy people are becoming ill due to an especially deadly strain of MRSA Ricky s had the flu? Was the flu caused by MRSA??

17 Antibiotics Antibiotics are chemicals that either kill bacteria or slow their growth by interfering with the function of essential bacterial cell structures. Certain microorganism, such as the fungus Penicillium, produce compounds that kill bacteria 1928, Alexander Fleming isolated penicillim Many antibiotics are now synthesized

18 Drug-resistant stains of Staph They are resistant to class of antibiotic drug called betalactams Penicillin, cephalosporin antibiotics (methicillin) Beta- lactams are the most commonly prescribed class of antibiotics Interfere with the bacteria s ability to synthesis a cell walls. Water flow in by osmosis? What is osmosis and what caused the water to flow in??? Non-beta lactam drugs are used as a treatment for MRSA vacomycin. Not always effective. Did Ricky or Rebecca respond to vacomycin?

19 Carlos had pneumonia. What this caused by MRSA? 85% of the causes occur in patients who are hospitalized or in people with immune compromised, or health care worker. What are some of the factors that may determine if the medicine works or not?

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21 Antibiotics Antibiotics have been effective in treating most common bacterial infections (staph), but soon after antibiotics were in general use, microorganisms that could survive antibiotics began to emerge. Drug-resistant bugs People are treatable but with fewer options Sometimes nothing works - death

22 Acquiring resistance Bacteria might never grow resistant to drugs if not for random mutations that create new alleles and generate genetic diversity. Bacteria can acquire mutations when their DNA replicates during reproduction. Define mutation Define alleles

23 Bacteria reproduce asexually by binary fission a type of asexual reproduction in which one parental cell divides into two. Acquiring resistance

24 Unlike sexual reproduction, in which gametes from two parents fuse, asexual reproduction does not require a partner. Acquiring resistance

25 Acquiring resistance During binary fission, a single parental cell simply replicates its single chromosome, grows in size, and then splits into two daughter cells, each with a copy of the parental DNA. iwc

26 Acquiring resistance Each time DNA is replicated, there is a chance that genetic mutations will occur, New alleles will then be carried into each daughter cell. Because bacteria reproduce much more rapidly (20 minutes) than other organisms, they accumulate mutations at a relatively high rate. New population is a few days. Do mutations occurs in sexual producing organisms? Why are we diverse?

27 Acquiring resistance A bacterium can also acquire new alleles through gene swapping, in which bacteria can swap pieces of DNA with other bacteria. Remember DNA encodes for what the carries out the functions of the cell?

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29 How populations evolve Any organism can undergo genetic changes that gives it new traits An entire population of organisms with a new trait can arise when the environment favors that trait- advantageous to organism A population is a group of organisms of the same species living together in the same geographic area. (pond water, prairie, etc.)

30 How populations evolve An entire population of organisms with a new trait can arise only when the environment favors that trait that is, when carrying the specific trait is advantageous to the organisms carrying it.

31 How populations evolve When a population s environment favors some traits over others, the frequencies of the alleles that code for those traits in the population change over time. Bacteria populations with and without antibiotics This change in the frequency of alleles in the population over time is called evolution.

32 How populations evolve An organism s ability to survive and reproduce in a particular environment is call that organism s fitness. The greater an organism s fitness, the more likely that alleles carried by that organism will be passed on to future generations and increase in frequency.

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34 Antibiotic-Resistance trait Becomes common trait Reproductive edge in an environment in which antibiotic use has been rampant In some cases, even though they are resistant to antibiotics they may now reproduce slower.

35 Patterns of natural selection Ultimately, interplay between an organism s traits and its environment is what determines what traits will predominate in any population. Organisms can be fit in one environment and not in another. This process of differential survival and reproduction of individuals within a population in response to environmental pressure is known as natural selection.

36 How populations evolve When natural selection favors some traits over others, the population shows adaptation. In other words, specific advantageous traits become more common in a population over time.

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39 How populations evolve Note that evolution by natural selection occurs in populations, not individuals. Individual organisms do not experience a change in allele frequencies over time. Therefore, individual organisms do not evolve.

40 Natural selection occurs in patterns Scientists have defined three major patterns of natural selection.

41 Natural selection occurs in patterns Directional selection occurs when organisms with phenotypes at one end of a spectrum are favored by the environment. From populations sensitive to drugs to ones that resist drugs

42 Natural selection occurs in patterns Stabilizing selection occurs when organisms with phenotypes near the middle of the phenotypic range of variation are favored by the environment.

43 Natural selection occurs in patterns Diversifying selection occurs when organisms with phenotypes at both extremes of the phenotypic range of variation are favored by the environment.

44 MRSA Would Carlos, Rebecca, Ricky have survived if we didn t use so many different antibiotics??? MRSA first emerged in hospitals in 1960s Remember new strains may not sicken the patient but can be passed on others that may become very ill. Hand-washing important in hospitals Strains in community appear different than strains in the hospital (USA3000 is more virulent than other strains necrotizing fasciitis)

45 Stopping superbugs Because the use of antibiotics can drive bacterial populations to evolve resistance, antibiotic resistance is inevitable. The best way to control resistance is to change practices that enable resistant strains to thrive.

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47 Superbugs Over 200 species of bacteria cause human diseases Salmonella, Pneumonia, tuberculosis, gonorrhoeae Getting harder to treat Salmonella food poisoning- drug-resistance Humans have contributed to the resistance by haphazard use and overuse of antibiotics Agriculture shrimp in the news???? Vaccines??? Haemophilus influenza - pneumonia