Chemotherapy of microbial diseases

1. Chemotherapy of microbial diseases 殷明 2011.11

2. 一些事实数据 1940年前，小儿肺炎、痢疾、伤寒、斑疹伤寒、鼠疫、霍乱、白喉、疟疾——不治之症 1930-1949 上海传染病死亡率 565/10万 1990 0.52/10万 1949年，中国人平均寿命 39岁 2004年，中国人平均寿命72岁（日本82岁）

3. GENERAL PRINCIPLES OF ANTIMICROBIAL THERAPY

4. Introduction • Mechanism of action • Antibiotic Resistance • General principles of clinical use

5. Definition • In the strictest sense, antibiotics are antibacterial substances produced by various species of microorganisms (bacteria, fungi, and actinomycetes) that suppress the growth of other microorganisms. • Common usage often extends the term antibiotics to include synthetic antimicrobial agents, such as sulfonamides and quinolones.

6. classification according to the actions against the type of organism • Antibacterial • Antiviral • Antifungal

7. The discovery of Penicillin • 1928: Alexander Fleming discovered the first antibiotic. • He observed that Penicillium fungus made an antibiotic, penicillin, that killed S. aureus. • Two Oxford University specialists Dr Howard W Florey and his German associate Dr Ernest Boris Chain spent month after month attempting to extract the essential substance from Fleming's mould. • On 12 February, 1941, the first dose of isolated penicillin was injected into a human being • Nobel Prize for Medicine in 1945

9. Antibiotics • Most significant discovery of modern medicine • Save millions of lives

10. Academic terms • Antimicrobial spectrum • Bactericidal-MBC, bacteriostatic-MIC • Therapeutic index: LD50/ED50 • Post antibiotic effect

11. Concept 1: antibiotic spectrum • Different antibiotics target different kinds of bacteria • Antimicrobial spectrum Antimicrobial spectrum of a drug means the species of microorganisms that the drug can inhibit or kill. • Narrow spectrum The agents act against a single or limited group of microorganisms (isoniazid: mycobacteria ) • Extended spectrum The agent that are effective against gram-positive organisms and also against a number of gram-negative bacteria (ampicillin). • Broad spectrum The agent affect a wide variety of microbial species (tetracycline)

12. Concept 2: Bacteriostatic vs. Bactericide • Antibiotics differ by mode of action • Bacteriostatic: arrest the growth or replication of the microorganism. Sulfanilamide • Bactericide: The agents which can kill the microorganisms are called bactericidal drugs; a drug may be bacteriostatic for one organism but bactericidal for another. Fluoroquinolones, Penicillins, …

13. Concept 3:Bactericidal-MBC, bacteriostatic-MIC Chemotherapy index (CI) To evaluate the safety of chemotherapeutic drugs, the value is LD50/ED50 Minimal inhibitory concentration (MIC) MIC is the lowest concentration of antimicrobial agents that prevents visible growth in 18-24 hours incubation.

15. Concept 4:Post antibiotic effect • The antibiotic inhibits microbial multiplication beyond the time when the MIC is reached in plasma. • Aminoglycosides • Macrolides • Allows reduction in dosing schedule

16. Mechanism of action

17. CLASSES OF ANTIBIOTICS • Inhibitors of cell wall synthesis • Agents that interfere with cell membrane permeability • Inhibitors of nucleic acid synthesis or activity • Inhibitors of protein synthesis • Inhibitors of bacterial metabolism • …

18. Antimicrobial site of action

20. β-lactam antibiotics Cell Wall Synthesis Inhibitors • Penicillins青霉素 • Cephalosporins 头孢菌素 • Vancomycin万古霉素 • Bacitracin杆菌肽

21. Peptidoglycan（肽聚糖） is a 3D molecule Cross links are both horizontal and vertical between glycan chains stacked atop one another.

22. Gram negative cell structure

23. Antimicrobials acting on the bacterial cell wall • Interfere with synthesis of peptidoglycan layer in cell wall • eventually cause cell lysis • bind to and inhibit activity of enzymes responsible for peptidoglycan synthesis • “penicillin-binding proteins”(transpeptidase)

24. β-Lactams 内酰胺 • β-lactams inhibit transpeptidase. • Only effective against rapidly growing organisms that synthesize peptidoglycan. • The size, charge and hydrophobicity of the molecule determines the extent of its antibacterial activity.

25. There is no molecule similar to peptidoglycan in humans, making drugs that target cell wall synthesis very selective in their toxicity against bacteria.

26. Antimicrobials acting on the cell membrane • amphotericin两性霉素: binding to the sterol-containing membranes of fungi • polymyxins多粘菌素: acting like detergents and disrupt the Gram negative outer membrane. • Not used parenterally because of toxicity to mammalian cell membrane • fluconazole and itraconazole: interfering with the biosynthesis of sterol in fungi

27. Bacteriostatic inhibitors of protein synthesis • Board Spectrum: tetracyclines 四环素, chloramphenicol 氯霉素 • Moderate: macrolides 大环内酯 • Narrow: clindamycin 克林霉素 peroperties • Suppress bacterial growth and replication but do not kill • Second-line agents

28. Antimicrobials acting on protein synthesis • Target the bacterial ribosome. • Bacterial – 70S (50S/30S) • Mammalian – 80S (60S/40S) • High levels may interact with mammalian ribosomes. • Binding to 30s Subunit • Aminoglycosides氨基糖苷 (bacteriocidal) • tetracyclines 四环素 • Binding to the 50s subunit • chloramphenicol 氯霉素 macrolides (erythromycin红霉素, clarithromycin克拉霉素, azithromycin阿齐霉素)

29. Antimicrobials acting on nucleic acid synthesis • Inhibitors of DNA replication • Quinolones (e.g.ofloxacin，氧氟沙星) inhibit DNA-gyrase回旋酶 • Orally active, broad spectrum • Damage to DNA • Metronidazole甲硝唑(anti-anaerobes) • nitrofurantoin呋喃妥因Inhibitors of Transcription • rifampicin (key anti-TB drug) inhibits bacterial RNA polymerase • flucytosine氟胞嘧啶，incorporated into yeast mRNA

30. Antimicrobials acting on Folic acid synthesis • Inhibitors of precursor synthesis • sulphonamides & trimethoprim are synthetic, bacteriostatic agents • used in combination in co-trimoxazole（复方磺胺甲噁唑 ） • Sulphonamides inhibit early stages of folate synthesis（二氢叶酸合成酶） • dapsone(氨苯砜), an anti-leprosy drug • Trimethoprim inhibits final enzyme in pathway, dihydrofolate reductase（二氢叶酸合成酶）　 • Pyrimethamine（乙胺嘧啶）

31. Mechanism of sulfonamides • 蝶啶＋ →二氢蝶酸→二氢叶酸→四氢叶酸 ↑↑ 二氢蝶酸合成酶 二氢叶酸还原酶 sulfonamides TMP（甲氧苄啶） Dapsone氨苯砜 pyrimethamine （乙胺嘧啶） methotrexate

32. Antibiotic Resistance

33. 2010年英国媒体：南亚发现新型超级病菌，产生NDM-1（New Delhi metallo-β-lactamase-1，新德里金属-β-内酰胺酶-1 ），抗药性极强。 • Superbug： Escherichia coli and Klebsiella pneumoniae 克雷伯肺炎杆菌

34. 日本科学家拍摄到的“超级细菌”照片

35. Antibiotic resistance • Definition: a microorganism is able to survive exposure to an antibiotic. • 1940’s, penicillin-resistant bacteria, 1% • 21st century, 耐苯唑西林金黄色葡萄球菌（MRSA: methicillin-resistant Staphylococcus aureus): 80-92% • 耐万古霉素肠球菌（VRE），耐氨基糖苷类的高耐株（high-level aminoglycoside resistant, HLAR）：0-8%，60-80% • 2002.7: 美国center for disease control (CDC)公布第一株真正的耐万古霉素（MIC>128 mg/L）的葡萄球菌 Bacteria

36. 金黄色葡萄球菌：获得性耐药株的新挑战 39thICAAC1999 ？ VRSA 1996 VISA 1975 多重耐药MRSA 1961 古典的MRSA 1944 耐青霉素的金黄色葡萄球菌 VISA: Vancomycin-intermediate Staphylococcus aureus 万古霉素中介耐药葡萄球菌 VRSA: vancomycin-resistant Staphylococcus aureus 1960 1970 1980 1990 2000

37. antibiotic era 抗生素时代 form 1940s: Penicillin was tested clinically and mass produced to 1975 • Post-antibiotic era 后抗生素时代 multi-drug resistance 多药耐药

38. The kinds of antibiotic resistance (1) Intrinsic resistance （天然/固有耐药）： genes in chromosome (2) Acquired resistance （获得性耐药）: genes in plasma • transfer of antibiotic resistance: • transformation 转化 • conjugation 接合 • transduction 转导

39. Mims C et al. Medical Microbiology. 1998.

40. mechanisms of resistance • Inactivating enzymes: hydrolases; synthases • Targets changes: protein structure change; production of protective protein • Decrease of antibiotics: increased efflux system; decreased permeability to antibiotics • Change of metabolic pathways; trapping mechanism; formation of biofilm

41. Resistance to antibiotics

42. Mechanisms of resistance • Modification or bypass of target • by mutation or acquisition of extrinsic DNA

43. Resistance Mechanisms • β-lactamase – hydrolyze the β-lactam ring. • Penicillinase –Staph • Alteration of penicillin-binding protein (PBP) affinity. (Strep. Pneumo., MRSA)

45. Antibiotics in theCommunity • 75% of antibiotics prescribed for respiratory tract infections • 50% of antibiotic prescriptions are inappropriate • Most respiratory tract infections are caused by viruses • Antibiotics do not work against viruses

46. Antimicrobial selection • Identify the infecting organism • Drug sensitivity of the infecting organism • Host factors – site of infection, status of patient, safety of the agent, cost therapy

47. Delaying the emergence of resistance • Prescribed only when needed • Narrow-spectrum: Cultures must be obtained prior to initiation of therapy • Adequate dosage • Limit use of newer drugs • Minimize giving antibiotics to livestock

48. Antibiotic combinations Severe infection Mixed infections Prevention of resistance – tuberculosis Decreased toxicity Enhanced antibacterial action

49. Appropriate prophylactic use • Before surgery • Prevent bacterial endocarditis • Protect fetus of an HIV-infected pregnant woman • Prevent TB

50. Quinolones, sulfonamides and other synthetic antibacterial drugs