MCB2004 Final Exam Review Lecture 26 27 Antimicrobial Drugs I II 1 Describe selective toxicity spectrum of activity and explain why most antibiotics are specific for bacteria Selective toxicity a drug that kills harmful microbes without killing the host Spectrum of activity broad spectrum effective against many species Narrow spectrum effective against a few or a single species Drug should affect microbial physiology that does not exist or is greatly modified in humans i e peptidoglycan difference in ribosome structure biochemical pathways absent in humans 2 Name the microbes that produce the most antibiotics Gram positive rods bacillus subtilis and paenibacilus polymyxa Bacitracin and Polymyxin Actinomycetes Gentamycin Streptomycin Neomycin Chloramphenicol etc Fungi Penicillin Cephalothin Griseofulvin 3 Identify five modes of action of antimicrobial drugs a b c d e Inhibition of cell wall synthesis Inhibition of protein synthesis Inhibition of replication and transcription Injury to plasma membrane Inhibition of synthesis of essential metabolites 4 List the advantages of each of the following over penicillin semisynthetic penicillins cephalosporins and vancomycin a Semisynthetic penicillins Oxacillin narrow spectrum only gram positives but resistant to penicillinase Ampicillin extended spectrum many gram negatives b Cephalosporins more effective against gram negatives c Vancomycin important last line against antibiotic resistant S aureus 5 Explain why INH and ethambutol are antimycobacterial agents INH inhibits mycolic acid synthesis and ethambutol inhibits incorporation of mycolic acid 6 Describe modes of action of aminoglycosides tetracyclines chloramphenicol macrolides polymyxin B bacitracin neomycin rifamycins and quinolones a Aminoglycides streptomycin neomycin gentamycin i Change shape of 30S subunit b Tetracyclines ii Broad spectrum 1 Side effect hearing loss i Broad spectrum ii Interferes with tRNA attachment c Chloramphenicol i Broad spectrum ii Binds 50S subunit inhibits peptide bond formation d Macrolides e Polymxyin B i Gram positives ii Binds 50S prevents translocation i Topical ii Combined with Bacitracin and Neomycin in over the counter preparation Neosporin f Bacitracin i Gram positives ii Topical application iii Inhibits cell wall synthesis g Neomycin h Rifamycins i See above Inhibits RNA synthesis i ii Antituberculosis i Quinolones Inhibits DNA gyrase i ii Anti anthrax iii UTI s 7 Describe how sulfa drugs inhibit microbial growth Broad spectrum inhibit folic acid synthesis Sulfamethoxazole competitively inhibits the synthesis of dihydrofolic acid from PABA Trimethoprim competitively inhibits the synthesis of tetrahydrofolic acid 8 Explain the modes of action currently used in antiviral drugs Protease inhibitors inhibit attachment inhibit uncoating interferons prevent the spread of viruses to new cells 9 Describe two tests for microbial susceptibility to chemotherapeutic agents a Kirby Bauer Test multiple disks with different antibiotics size of cleared zones reflects relative sensitivity b E Test determines MIC Gradient of antibiotic in paper strip drug must be above MIC in order to be effective c Broth dilution test growth in all cells resistant No growth in any cells sensitive Decreased concentration across cells 10 Describe the mechanisms and causes for drug resistance A variety of mutations can lead to antibiotic resistance Resistance genes are often on plasmids or transposons that can be transferred between bacteria Mechanisms of drug resistance blocking entry inactivating enzymes alteration of target molecule efflux of antibiotic 11 Describe the underlying mechanisms of antiviral drugs See 8 12 Bactericidal and Bacteriostatic antibiotics Bactericidal antibiotics kill target organism Bacteriostatic antibiotics prevent growth of organism cannot kill organism immune system removes infection 13 The first antibiotic penicillin history and derivatives 1928 Fleming discovered penicillin produced by penicillium Florey and Chain conducted clinical trials in the 1940s Derivatives penicillinase resistant penicillins extended spectrum penicillins and penicillins lactamase inhibitors Lecture 28 Microbial Diseases of the Skin and Eyes 1 Describe the structure of the skin and mucous membranes and the way pathogens can invade the skin Three layers of skin epidermis dermis secretions perspiration and sebum portals of entry follicles and ducts subcutaneous layer Skin is inhospitable to most microbes dry salty body secretions lysozymes hydrolyze peptidoglycan fatty acids inhibit some pathogens defensins are antimicrobial peptides Mucous membranes line body cavities The epithelial cells are attached to an extracellular matrix Cells secrete mucous Some cells have cilia 2 Provide examples of normal skin microbiota and state the general locations and ecological roles of its members Normal skin flora gram positive streptococcus and staphylococcus low GC gram positive diphtheroids high GC gram positive anaerobic inhabit hair follicles can withstand drying fatty acids low pH high salt Some yeasts 3 Differentiate staphylococci from streptococci and name several skin infections caused by each a Staphylococcus i Low GC gram positive clusters ii Coagulase enzyme that clots fibrin in the blood iii Cause folliculitis furuncles boils carbuncles toxemias occur when toxins enter bloodstream scalded skin syndrome toxic shock syndrome 1 Folliculitis infections of hair follicles a Sty folliculitis of an eyelash b Furuncle abscess pus surrounded by inflamed tissue c Carbuncle inflammation of tissue under skin i Low GC gram positive chains ii Hemolysins beta alpha gamma hemolysis iii Classified into groups according to hemolytic enzymes and surface b Streptococcus antigens 1 Group A 2 Groups B C and O iv Many virulence factors M proteins extracellular enzymes and toxins v M protein on surface anti complement anti phagocytosis vi Cause impetigo isolated pustules erysipelas caused by Group A beta hemolytic strep toxin Invasive group A streptococcal infections vii 1 Streptokinases hyalurodinase exotoxin A super antigen cellulitis necrotizing fasciitis flesh eating 4 List the causative agent mode of transmission and clinical symptoms of Pseudomonas dermatitis otitis externa and acne Gram negative aerobic rods five groups unusual metabolism grow on traces of organic substance in soap liner adhesive Environmental soaps and water opportunists medical devices contact solutions Cause dermatitis
View Full Document
Unlocking...