SEHH2235 Lecture 5: Infection and Antimicrobial Agents PDF

SEHH2235 Introduction to Pathophysiology and Pharmacology Lecture 5 Infection and Antimicrobial Agents 1  Learning outcomes By the end of this lecture, students should be able to: 1. Differentiate types of pathogens...

SEHH2235 Introduction to Pathophysiology and Pharmacology Lecture 5 Infection and Antimicrobial Agents 1  Learning outcomes By the end of this lecture, students should be able to: 1. Differentiate types of pathogens 病原體 2. Identify types of antimicrobial agents 抗菌劑 3. Classify types of antibiotics and actions 4. State the development of antibiotic Resistance 2  Common Pathogens (1) Viruses 咽喉炎 (2) Bacteria (3) Fungi 瘧疾 (4) Protozoa human African trypanosomiasis 非洲人類錐蟲病 蛔蟲 (5) Worms 絛蟲 (蠕蟲) 3  Processes of Infection by Microorganisms  Colonization Pathogens present on or in body without tissue invasion Source of cross infection to other  Invasion Resist host defenses; attaches to host cells through adhesion molecules and receptors Opportunity for cell injury, alteration in function or cell death  Multiplication Uses host nutrients and environment, or cell organelles, for reproduction Tissue damage, cell alterations or cell death and disease symptoms  Spread Migrates locally or through bloodstream and lymphatics Local or systemic manifestations of disease through cell injury or effect of toxins 4  (1) Viral infections  Some viral infections are infected for life, they CANNOT be eradicated and can be reactivated when immunity is low 人類免疫缺乏病毒 e.g. Human Immunodeficiency Virus infection: HIV‐1/HIV‐2 人類單純疱疹病毒 e.g. Herpes simplex virus (HSV) infection: HSV‐1, HSV‐2  HSV‐1 & HSV‐2 are highly contagious: spread through contact & saliva HSV‐1: cold sores HSV‐2: most genital herpes  Treatment: Anti‐viral drugs (Antibiotics CANNOT kill viruses!) E.g. acyclovir / aciclovir (Zovirax)  taken up selectively by HSV‐infected cells  inhibits viral DNA polymerase to inhibit viral replication Cold sore (DNA replication  new cell) HSV1 infection 5 (2) Bacterial infections Bacterial Grouping by: (a) Shapes & arrangements  Filamentous bacteria (mycelium; eg. Mycobacterium tuberculosis)  True bacteria (cocci, bacilli, vibrio, spirilla) 球菌 雙球菌 鏈球菌 球菌 球桿菌屬 弧菌 芽孢桿菌 Vibrio cholera 四球菌 霍亂弧菌 八疊球菌 葡萄球菌 螺菌 螺旋體 6 (2) Bacterial infections Bacterial Grouping by: (a) Gram Staining  Gram staining differentiates bacteria by chemical and physical properties of their cell walls  Gram-positive bacteria possess a thick layer of peptidoglycan in their cell walls  Gram negative bacteria only have a thin layer of peptidoglycan but possess a lipopolysaccharide (LPS) coat in the outer membrane.  LPS consists of lipid A, a core polysaccharide and an O antigen  LPS coat is also known as endotoxin 內毒素 Gram positive Gram negative 7 Gram‐positive cell wall Gram‐negative cell wall 8 (2) Bacterial infections  Bacteria are also categorized by Gram stain test  Gram‐negative bacteria: do not retain crystal violet dye (Pink)  Gram‐positive bacteria : retain crystal violet (Blue) 脫色 複染 9  (3) Fungal infections  Large microorganisms with thick cell walls  Single‐celled: yeast; multi‐celled: mold/mould  Polysaccharides cell wall – resistant to antibiotics that lyse bacterial wall (e.g. penicillin and cephalosporin) Able to adapt to host environment e.g. wide temperature variations, digest keratin, low oxygen Able to suppress host immune defenses 栓劑  Vaginal infection caused by Candida albicans can be treated by antifungal cream, suppository or tablets. E.g.: 白色念珠菌 butoconazole (Gynazole‐1) clotrimazole (Gyne‐Lotrimin) fluconazole (Diflucan)  Scalp infection 頭皮感染 ketoconazole (Nizoral) 10  Types of Antibiotics  Bactericidal 殺菌 – bacteria killing  Bacteriostatic 抑菌 – prevents growth  rely on patient’s immune system to kill and remove the microorganisms (not useful in immunodeficient patients)  Broad spectrum:  act against a large group of bacteria  Narrow spectrum:  act against a limited group of bacteria  Antibiotics: antibacterial (some are also antiparasitic)  e.g. metronidazole (Flagyl) is antiparasitic & antibacterial microorganisms reduce metronidazole to its active form, which inhibits their DNA synthesis (only useful to treat susceptible organisms) Sir Alexander Fleming (1881‐1955) Known for discover of penicillin treat certain gastric/intestinal ulcers caused by a bacteria (Helicobacter pylori) Nobel Prize in Physiology or 幽門螺旋菌 Medicine (1945) 11  What is Antibiotics? Antibiotics are bactericidal or bacteriostatic depending on their mechanisms of action Basic mechanisms of 1 example antimicrobial actions each A Inhibits synthesis of A A A bacterial cell wall B Inhibits bacterial protein synthesis C Inhibits bacterial nucleic acid replication and C synthesis B D D Interferes with bacterial folic acid metabolism (for C DNA synthesis) E Damages bacterial cytoplasmic membrane 12  A Inhibits synthesis of bacterial cell wall l抑制細菌細胞壁的合成 C C Inhibits bacterial A nucleic acid replication and synthesis抑 C 制細菌核酸複製和 合成 B D D Interferes with bacterial folic acid metabolism B B 干擾細菌葉酸代謝 A Inhibits bacterial protein synthesis B 抑制細菌蛋白質合成 E PABA: Para-aminobenzoic acid  Main component of folic acid 葉酸 E Damages bacterial cytoplasmic membrane 破壞細菌細胞質膜 13  A Inhibits synthesis of bacterial cell wall C C Inhibits bacterial A nucleic acid replication and synthesis C B D D Interferes with bacterial folic acid metabolism B B A Inhibits bacterial protein synthesis B E E Damages bacterial cytoplasmic membrane 14 Bacterial cell wall synthesis 1. Alanine molecules are added to a carbohydrate tripeptide to form a "T" shaped cell wall precursor. This reaction is inhibited by D-cycloserine. 2. The precursor is transported across the plasma membrane by a carrier. Vancomycin inhibits the transport process. 3. The transporter is recycled to the inside of the cell to carry other precursors. Bacitracin inhibits this step. 4. The precursor is linked to the existing cell wall structure by transpeptidase. b tell Penicillins, cephalosporins, imipenem and aztreonam inhibit the transpeptidase. Transpeptidase is one of several penicillin binding proteins and is not the only site of penicillin action. Because human cells lack cell walls, they are generally unaffected by inhibitors of cell wall synthesis. This explains why penicillins and cephalosporins have few side effects. James Olson. Clinical Pharmacology Made Ridiculously Simple 2nd Edition (A) Inhibition of Bacterial Cell Wall Synthesis: (A1) Penicillins (盤尼西林類/青黴素) Penicillins eg. amoxicillin (Amoxil), ampicillin (Omnipen, Principen)  discovered in 1940, derived from moulds  the least toxic antibiotic  against Gram +ve & some Gram –ve bacterial  contain β‐lactam rings in their structure  penicillins weaken cell wall of Gram +ve bacteria It binds to and inhibits penicillin‐binding proteins (PBPs) on bacterial cell wall. PBPs are key enzymes for building bacterial cell wall  Penicillins weaken cell wall of Gram +ve bacteria  prevent cross-link of peptidoglycan layers  bacterial cell wall becomes weakened  bacterial cell lysis due to high internal osmotic pressure 15 (A) Inhibition of Bacterial Cell Wall Synthesis: (A2) Penicillinase‐resistance penicillins  Bacteria become resistant to penicillins by producing β‐lactamase (or penicillinase)  an enzyme that destroy penicillins by cutting the ‐lactam ring  Therefore, penicillins are ineffective against resistant bacteria that contain β – lactamase  Higher Generation “‐cillin” group antibiotics:  Oxacillin, cloxacillin, nafcillin, methicillin are used for penicillin‐resistant staphylococcus Semi‐synthetic penicillins: Augmentin Augmentin = clavulanic acid (β‐lactamase inhibitor) + amoxycillin Precaution: Penicillin is a common cause of drug allergy, causes hemorrhage and anaphylaxis 16 17 (A) Inhibition of Bacterial Cell Wall Synthesis: (A3) Cephalosporins (頭孢子菌素類)  First‐generation: “ceph‐”; Later generations: "cef‐“ [e.g. Cefaclor (Ceclor)]  A family of chemically modified penicillin  Bactericidal, same mode of action as ‐lactam antibiotics  But less susceptible to penicillinases or β‐lactamase  10% patients, who are allergic to penicillin, are also allergic to cephalosporin  Drug action similar to penicillin‐group antibiotics  Because Penicillins and Cephalosporins share the same core β‐lactam ring structure. 18 (A) Inhibition of Bacterial Cell Wall Synthesis: (A4) Vancomycin (萬古黴素)  Specifically used for serious resistant staphylococcal infection 金黃色葡萄球菌  e.g. Methicillin‐Resistant Staphylococcus aureus (MRSA) infection  Used only when culture and sensitivity test confirm the need Boucher, H.W.; et. al., Clin. Infect. Dis. 2009, 48, 1. of use  Commonly given I.V. as it is absorbed poorly in the GI  Adverse reactions 發燒 嗜酸性粒細胞增多 中性粒細胞減少 聽力損失  Fever, eosinophilia, neutropenia, hearing loss  Red man syndrome: rash with severe hypotension with rapid I.V. 19 Bactericidal Drugs that Work at the Cell Wall Drug Mechanism Penicillins and Cephalosporins Inhibits crosslinking of cell wall components Vancomycin Prevents transfer of cell wall precurser from plasma membrane to cell wall Bacitracin Inhibits recycling of the carrier which transports cell wall precursers across the plasma membrane. Carbapenem Inhibits crosslinking of cell wall components. Imipenem/Cilastatin (Primaxin) Meropenem (Merrem) Monobactam Aztreonam (Azactam) Penicillinases and penicillinase-resistant β-lactamase inhibitor (Clavulanic acid) Top: Penicillins destroy bacteria after binding to penicillin binding proteins (PBPs). Middle: Penicillinases are enzymes produced by bacteria that destroy penicillins by cleaving the beta-lactam ring of the drug. Penicillins are "lured" into the active site because they are chemically similar to penicillin binding proteins. Bottom: Clavulanic acid is a "decoy" drug that enhances the activity of penicillins. Clavulanic acid binds to the active sites of penicillinases rendering the enzyme inactive. James Olson. Clinical Pharmacology Made Ridiculously Simple 2nd Edition  A Inhibits synthesis of bacterial cell wall C C Inhibits bacterial A nucleic acid replication and synthesis C B D D Interferes with bacterial folic acid metabolism B B A Inhibits bacterial protein synthesis B E E Damages bacterial cytoplasmic membrane 20 (B) By stopping protein synthesis in bacteria (50S ribosome subunits) (B1) Macrolides (大環內酯類)  Suffixes end with “‐mycin” (eg. erythromycin, clarithromycin)  Broad spectrum  Both bactericidal & bacteriostatic in Gram +ve & Gram –ve bacteria (depending on concentration and types of bacteria)  Inhibit RNA‐dependent protein synthesis by acting on 50S ribosome  Buffered or enteric coated to prevent destruction by gastric acid so that it can be absorbed in the duodenum  Used in patient who’s allergic to penicillin  Adverse drug reactions: GI distress  Should be taken with food 21 (B) By stopping protein synthesis in bacteria (30S ribosome subunits) (B2) Aminoglycoside (氨基糖苷類 抗生素)  Suffix also ends in “‐mycin”  eg. amikacin, streptomycin, gentamicin, neomycin and tobramycin  Bactericidal by interfering translation:  disturbing peptide elongation at the 30S ribosomal subunit  causing inaccurate mRNA translation leading to production of truncated proteins that bear altered amino acids at particular points  highly toxic antibiotics  used in the treatment of infections caused by Gram‐negative bacteria 腎毒性 神經毒性 耳毒性  cause nephrotoxicity, neurotoxicity & ototoxicity 損害腎功能 前庭和耳蝸功能障礙  impair renal function, vestibular & cochlear dysfunction Selman Abraham Waksman1888–1973 Nobel Prize in Physiology/Medicine (1952) 22 (B) By stopping protein synthesis in bacteria (30S ribosome subunits) (B3) Tetracyclins (四環素)  Bacteriostatic 尋常性痤瘡(青春痘)  Commonly used for treating acne vulgaris (Propionibacterium acnes)  NOT for pregnant or breast feeding women, nor for children under 8 years of age  It is calcium binding  cause permanently mottle and discoloration of teeth and decreases skeletal growth in children 齒永久斑點和變色 23 (B) By stopping protein synthesis in bacteria (50S ribosome subunits) (B4) Chloramphenicol (氯黴素)  Given orally / for eye infection  Used in patients allergic to tetracycline  Suppress bone marrow  agranulocytosis 粒細胞缺乏症  Safety concerns  no longer a first‐line agent 24  A Inhibits synthesis of bacterial cell wall C C Inhibits bacterial A nucleic acid replication and synthesis C B D D Interferes with bacterial folic acid metabolism B B A Inhibits bacterial protein synthesis B E E Damages bacterial cytoplasmic membrane 25 (C) Inhibitors of DNA synthesis by inhibiting DNA gyrase (C) Fluoroquinolones (氟喹諾酮類)  DNA gyrase: an essential enzyme of replicating DNA 1st Gen: nalidixic acid, oxolinic acid, piromidic acid 2nd Gen: ciprofloxacin, lomefloxacin, nadifloxacin, norfloxacin, cinofloxacin (second gen end with suffix “‐floxacin”)  DNA gyrase is an enzyme that relieves strain while DNA is unwound for transcription or DNA replication through cutting and rejoining the DNA  Fluoroquinolones are bactericidal as it inhibits the ligase activity of DNA gyrase to prevent rejoining of DNA  DNA fragmentation is resulted  Broad spectrum Gram +ve & Gram –ve bacterial  For bone and joint infections , bronchitis, UTI, pneumonia  Adverse Drug Reaction: GI distress, dizziness, tendon rupture, crystalluria with high dose at alkaline pH 肌腱斷裂 結晶尿  Patient teaching: stay well‐hydrated 26  A Inhibits synthesis of bacterial cell wall C C Inhibits bacterial A nucleic acid replication and C synthesis B D D Interferes with bacterial folic acid metabolism B B A Inhibits bacterial protein synthesis B E E Damages bacterial cytoplasmic membrane 27 (D) Prevent growth of microorganisms by inhibition of Folic acid metabolism (D) Sulfonamides / Sulfa drugs (磺胺類) co‐trimoxazole (a combination of a sulfa drug and a folate antagonist) for infections like Pneumocystis carinii  Bacteriostatic  First antibiotics (1932) used systemically  Broad spectrum against Gram +ve & Gram –ve bacteria 大腸桿菌  Often used to treat UTI by Escherichia coli and for prophylactic infections 預防性感染  Blocks folic acid synthesis  Crystalluria 結晶尿 and kidney stones may occur during excretory phase DNA synthesis  Patient teaching: adequate fluid intake to flush the urinary tract 28  A Inhibits synthesis of bacterial cell wall C C Inhibits bacterial A nucleic acid replication and C synthesis B D D Interferes with bacterial folic acid metabolism B B A Inhibits bacterial protein synthesis B E E Damages bacterial cytoplasmic membrane 29 (E) Damages bacterial cytoplasmic membrane (E) Polymyxin (多粘菌素) Polymyxin B (polymyxin b sulfate for injection, IM, IV)  Bactericidal  Only used as the last resort if other antibiotics are ineffective or are contraindicated.  They are neurotoxic and nephrotoxic.  Actions: Disrupt both outer and inner membranes once it binds to lipopolysachharide (LPS) in the outer membrane of Gram –ve bacteria.  Against Gram –ve bacteria, especially acute infection (urinary tracts, meninges) by multiple drug- resistant Pseudomonas aeruginosa or carbapenemase-producing Enterobacteria species 綠膿桿菌 30 (E) Damages bacterial cytoplasmic membrane (E) Polymyxin (多粘菌素) General mode of Biophysical mechanism of action for polymyxin-induced membrane damage polymyxin action in general membrane Original Modified Lipid A Lipid A 31  Mechanisms of Antibiotic Resistance Bacterial have developed mechanisms to prevent the antibiotic from reaching to its target by decreasing the uptake of antibiotics. One of the most successful strategy is to produce enzyme that inactivate the antibiotics by adding specific chemical group to the compound or that destroy A common strategy is to avoid the molecule itself, rendering the antibiotic to reach its binding antibiotic unable to interact with its site, resulting in decreased target. affinity for the antibiotics. Production of complex bacterial machineries capable to extrude a toxic compound out of the cell can also result in antimicrobial resistance. Many classes of efflux pumps are characterized in both Gram –ve and Gram +ve bacteria. 32 Mechanisms of Antibiotic Resistance: Superinfection  A second infection superimposed on an earlier one (esp. by a different microbial agent), that is resistant to the antibiotics used against the first infection  The more the bacteria is exposed to an antibiotic, the greater the chance it can defense against antibiotics  Superinfection occurs when a large dose of antibiotics is used an antibiotic is used long term broad‐spectrum antibiotics are used to work against different strains of bacteria  Overuse of antibiotics has resulted in: Pseudomonas become resistant to cephalosporins Candida albicans becomes resistant to tetracycline 33 Antibiotics use can cause fatal infection: Clostridium difficile  Clostridium difficile is a bacterium that causes an infection of the large intestine (colon).  C. difficile bacteria usually live harmlessly in the bowel along with lots of other types of bacteria.  They become a problem when the balance of bacteria changes (antibiotics killing other bacteria but not C. difficile).  Infection can cause high fever, diarrhoea, stomachache and loss of appetite.  Toxic Megacolon and sepsis can be resulted from serious C. difficile infection. They often lead to ICU admission and sometimes death is resulted.  Treatment: 1. Stop the course of current antibiotics, if possible 2. 10-day course of another antibiotic that can treat C. difficile 3. If recurrent for more than 2 times, faecal microbiota transplant is indicated 33  References Norris, T.L. (2019). Porth’s pathophysiology: concepts of altered health states (10th ed.). Philadelphia: Wolters Kluwer. McCance, K.L. & Huether, S.E. (2019). Pathophysiology: the biology basis for disease in adults and children (8th ed.). St. Louis: Mosby Elsevier. Moreau, D. (2009) Clinical pharmacology made incredibly easy! (3rd ed.).LWW. Keogh, J. (2010) Pharmacology Schaum’s Outlines McGrawHill 34