History and Mechanisms of Chemotherapy and Antibiotics

1. MICROBIOLOGY – ALCAMO LECTURE: Chemotherapeutic Agents and Antibiotics

2. Chemotherapeutic Agents and Antibiotics • For centuries, doctors thought that drastic measures were necessary to save a patient from infectious disease: • Purges and bloodlettings • Large doses of chemicals • Ice water baths • Starvation • These treatments probably made a bad situation worse

4. Chemotherapeutic Agents and Antibiotics • In 1825, doctors in Boston and London wanted to see what would happen if these treatments were not given • They found that no treatment at all was better • For the next 60 years it became the doctor’s job to diagnose disease, explain it to the family, and sit by caring for the patient

5. Chemotherapeutic Agents and Antibiotics • Late 1800’s – germ theory of disease • Doctors understood where disease comes from but could do little • Tuberculosis killed 1 of every 7 people that died • Streptococcal heart valve disease, pneumonia, and meningitis killed many

8. Chemotherapeutic Agents and Antibiotics • 1940’s – chemotherapeutic agents and antibiotics were discovered • Doctor’s learned that they could kill bacteria in the body without harming the body itself • Doctors were altering the course of disease which made a dramatic change in the world

13. Chemotherapeutic Agents & Antibiotics • Must be more harmful to MO than host cells • Chemotherapy only helps the immune system to control the infection • The immune system ultimately stops MOs

14. Chemotherapeutic Agents • Produced in lab, inorganic chemicals • Sulfur, Arsenic, Quinine, Nicotinic Acid • Still major medical applications • Can be quite toxic to patient

15. Antibiotics • Originally: Chemical produced by an MO which inhibits growth of other MOs • Now synthesized in labs, Organic Chem

17. Chemotherapeutic Agents & Antibiotics • Have anti-metabolite mechanisms • Select for specific MO according to which life process you need to disrupt: • Protein synthesis • Cell Wall structure • Cell membrane structure • RNA or DNA synthesis • Chemical reactions

19. History of Chemotherapy • Paul Ehrlich – worked with stains and dyes and found out they had antimicrobial properties • Collaborated with Sahachiro Hata to produce Salvarsan – 1st chemotherapeutic drug (cured syphilis) • Problems: • Local reaction at injection site • Church wanted syphilis to be a deterrent to immoral behavior

20. History of Chemotherapy • For the next 20 years, German scientists kept testing dyes for antimicrobial properties • Gerhard Domagk tested prontosil dye on his own daughter when she became ill with septicemia and she recovered

21. Sulfa Drugs • It was determined that the active ingredient in prontosil is sulfanilimide • In 1940, D.D. Woods and E.M. Fildes proposed a mechanism of action for sulfa drugs • It showed how they could interfere with bacterial metabolism without damaging host tissues

22. Competitive Inhibition • Bacteria need folic acid to produce nucleic acids (DNA and RNA) • Bacteria have an enzyme to make folic acid – they can’t get folic acid from environment like we do • This enzyme joins PABA with 2 other components to make folic acid • Sulfanilimide looks like PABA and enzyme will bind to it instead of PABA

24. Sulfa Drugs • Bactrim: • Sulfamethoxazole • Used for urinary tract infections and pneumonia • Gantrisin: • Sulfisoxazole • Used for vaginal infections, conjunctivitis and toxoplasmosis

25. Antibiotics • Word means “against life” • Chemical products or derivatives of certain organisms that are inhibitory to other organisms • How did organisms gain the ability to produce antibiotics? • Random genetic mutation • Evolutionary advantage

26. Antibiotics • Mainstay for help with bacterial infections. Used for some fungal and protozoal infectionsUseless on viruses (2ndary Bact Inf) • Usually safe/effective, some patients dangerously hypersensitive

27. Alexander Fleming • Discovered antibiotics • One of his agar plates containing staphylococci became contaminated with a green mold • He noticed the staphylococci didn’t grow near the mold • He identified the mold as a species of Penicillium and he named its substance penicillin

28. Zone of Inhibition

29. Penicillin • Isolated from a fungus - Penicillium • First antibiotic, 1940’s • Interferes with cell wall synthesis • Effective against G+ MOsFew G- with massive doses • “Cillins: a very large family of drugs

30. This bacterium is lysing because an antibiotic disrupted its cell wall. Why doesn’t the antibiotic lyse human cells?

31. Disadvantages of Penicillin • 1. Anaphylaxis or allergy • Swelling of the eyes or wrists • Flushed or itchy skin, hives • Shortness of breath • 2. Penicillin-resistant bacteria • Produce penicillinase, an enzyme that converts penicillin into a useless compound • Use too many antibiotics – natural selection of antibiotic resistant bacteria

32. Semi-synthetic Penicillins • In the 1950’s the beta-lactam nucleus of the penicillin molecule was identified and synthesized • New penicillins were created by attaching different groups to this nucleus: Ampicillin Amoxicillin

33. Cephalosporin • Isolated from a fungus - Cephalosporium • Interferes with cell wall synthesis • Similar to Penicillin – can be used in allergic persons and with resistant MOs • Interferes with some G+ and some G- MOs

34. Streptomycin • Isolated from a filamentous (mold-like) soil bacteria - Streptomyces • Attaches to ribosomes, blocks messenger RNA • Carefully used, toxic side effects (deafness) • “Mycins” a very large family of drugs • Neosporin contains Neomycin

35. Chloramphenicol • Streptomyces’ 2nd family of drugs:Original Prod: Chloromycetin • 1st “Broad Spectrum” AntibioticWide variety of G+ and G- MOs • Interferes with protein synthesis, ribosomes blocked from mRNA

36. Tetracycline • Broad spectrum antibiotics • Can be taken orally and were used widely in the 1950’s and 1960’s • Overused, so normal flora was eliminated from the intestines • Then fungi (Candida albicans) flourished and antifungal antibiotics had to be taken • Also caused gray-brown tooth discoloration

37. Antimicrobial Drugs • Chemotherapy: The use of drugs to treat a disease • Antimicrobial drugs: Interfere with the growth of microbes within a host • Antibiotic: A substance produced by a microbe that, in small amounts, inhibits another microbe • Selective toxicity: A drug that kills harmful microbes without damaging the host

38. The Action of Antimicrobial Drugs • Bactericidal • Kill microbes directly • Bacteriostatic • Prevent microbes from growing

39. Antibiotic Assays • 1. Tube dilution method – determines the smallest amount of antibiotic necessary to inhibit a test organism • Prepare a set of tubes with different concentrations of an antibiotic • The tubes are inoculated with the test organism, incubated and examined for growth • Extent of growth gets lower with increasing concentration of antibiotic • When growth fails to occur – you have reached the minimum inhibitory concentration (MIC)

41. Antibiotic Assays • 2. Agar or disk diffusion method – operates on the principle that antibiotics will diffuse from a paper disk into agar medium containing test organisms • Inhibition is observed as a failure of an organism to grow in the region of the antibiotic

42. Kirby-Bauer Test • 1. Pour agar into plate and inoculate with test organism • 2. Apply paper disks containing known concentrations of antibiotics to the surface • 3. Incubate plate • 4. Compare diameters of zones of inhibition to a standard table to determine if test organism is susceptible **If organism is susceptible, it will be killed in patient’s blood stream if experimental concentration of antibiotic is reached

43. The Disk-Diffusion Method

44. Antibiotic Resistance and Abuse • During past 25 years, a large # of bacterial species have evolved with resistance to drugs and antibiotics • Resistant organisms are responsible for human diseases in: • Intestines, lungs, skin, urinary tract • Common diseases that used to be easy to treat with a single dose of antibiotics are now hard to treat: • Bacterial pneumonia, strep throat, gonorrhea

45. Antibiotic Resistance and Abuse • How do MOs acquire resistance?: • Production of enzymes capable of destroying antibiotic (penicillinase) • Changes in permeability of cell wall • Resistance to drug’s activity by bypassing a normal metabolic pathway and creating an altered one (new way to produce folic acid)

47. Antibiotic Resistance and Abuse • Antibiotic resistance may develop: • Normally - mutation • From doctors prescribing too many antibiotics – forced evolution • From hospitals using too high doses of post-surgery antibiotics – forced evolution • From livestock feeds which contain 40% of all antibiotics produced in U.S. – forced evolution

48. Antibiotic Resistance and Abuse • Can resistance be transferred?? • Researchers have transferred antibiotic resistance genes from one bacterial species to another using plasmids • There is potential for the transfer of antibiotic resistance from a harmless bacterium to a pathogenic bacterium • Result – disease and death

50. Antibiotic Resistance and Abuse • Antibiotics have been known as miracle drugs – they are overworked miracles • Suggestions have been made to control their use as strictly as narcotics are controlled • But, antibiotics are abused in 3rd world countries where they are sold over-the-counter