Ch 9 General Characteristics Of Antimicrobial Drugs

Front 1

cell wall synthesis inhibition

Back 1

• penicillins
• cephalosporins
• vancomycin

Front 2

protein synthesis inhibition

Back 2

• aminoglycosides
• tetracyclines
• macrolides
• chloraphenicol

Front 3

nucleic acid synthesis inhibition

Back 3

• quinolones and fluoroquinolones
• rifampin
• less selectively toxic because they can affect both bacterial and eukaryotic cell function
• target topoimerase, DNA polymerase, RNA polymerase

Front 4

cell membrane disruption

Back 4

polymyxin B

Front 5

antimetabolites

Back 5

• sulfonamides, trimethoprim, dapsone, isonizid
• similar in structure to substrate of target enzyme
• compete with a natural substrate for binding at active site
• binding to enzyme inhibits enzyme activity
• broad spectrum; bacteriostatic

Front 6

narrow spectrum antibiotics (10)

Back 6

• penicillin G
• penicillin V
• methicillin
• vancomycin
• streptomycin
• norfloxacin
• ciprofloxacin
• polymyxin B
• dapsone
• isoniazid

Front 7

penicillins

Back 7

• cidal; cell wall synthesis inhibition
• inhibit transpeptidation enzymes involved in cross-linking the polysaccharide chains of peptidoglycan > osmotic lysis
• have a beta-lactam ring
• can cause allergic rxns but least toxic
• narrow spectrum: penicillin G, penicillin V, methicillin
• broad spectrum: ampicillin, carbenicillin

Front 8

cephalosporins

Back 8

• cidal; cell wall synthesis inhibition
• beta-lactam ring; inhibit transpeptidation enzymes involved in cross-linking the polysaccharide chains of peptidoglycan > osmotic lysis
• allergic rxns, thrombophlebitis, renal injury
• broad spectrum: cephalothin, cefoxitin, cefaperazone, ceftriaxone

Front 9

vancomycin

Back 9

• cidal; cell wall synthesis inhibition
• peptide portion prevents transpeptidation of peptidoglycan subunits binding to D-Ala-D-Ala amino acids at the end of peptide side chains; different binding site than penicillins
• tinnitus, deafness, renal toxic, allergic rxns
• narrow spectrum: cancomycin

Front 10

aminoglycosides

Back 10

• cidal; protein synthesis inhibition
• bind to small ribosomal subunit (30S) & interfere w/ protein synthesis directly & by causing a misreading of mRNA
• ototoxic, renal damage, loss of balance, nausea, allergic rxns
• narrow spectrum: streptomycin
• broad spectrum: neomycin, kanamycin, gentamicin

Front 11

tetracyclines

Back 11

• static; protein synthesis inhibition
• bind to small ribosomal subunit (30S) & interfere w/ protein synthesis directly & by causing a misreading of mRNA
• gastrointestinal upset, teeth discoloration, renal & hepatic injury
• broad spectrum: oxytetracycline, chlorotetracycline

Front 12

macrolides

Back 12

• static; protein synthesis inhibition
• bind to the 23S rRNA of large ribosomal subunit (50S) to inhibit peptide chain elongation during protein synthesis
• gastrointestinal upset, hepatic injury, anemia, allergic rxns
• broad spectrum: erythromycin, clindamycin

Front 13

chloramphenicol

Back 13

• static; protein synthesis inhibition
• bind to the 23S rRNA of large ribosomal subunit (50S) to inhibit peptide chain elongation during protein synthesis
• depressed bone marrow function, allergic rxns; increased side effects
• broad spectrum: chloramphenicol

Front 14

quinolones and fluroquinolones

Back 14

• cidal; nucleic acid synthesis inhibition
• inhibit DNA gyrase and topoisomerase II; block DNA replication
• tendonitis, headache, light-headedness, convulsions, allergic rxns
• narrow spectrum: norfloxacin, ciprofloxacin
• broad spectrum: R-Cin, rifacilin, rifamycin, rimactane, rimpin, siticox

Front 15

polymyxin B

Back 15

• cidal; cell membrane disruption
• binds to plasma membrane and disrupts its structure and permeability properties
• severe kidney damage, drowsiness, dizziness
• narrow spectrum: polymyxin B, polymyxin topical ointment (mycobacterial infections, principally leprocy)

Front 16

sulfonamides

Back 16

• static; antimetabolites
• inhibit folic acid synthesis by competing with p-aminobenzoic acid (PABA)
• nausea, vomiting, diarrhea; hypersensitivity rxns
• broad spectrum: silver sulfadiazine, sulfamethoxazole, sulfanilamide, sulfasalazine
• synergistic effect w/ trimethoprim

Front 17

trimethoprim

Back 17

• static; antimetabolites
• inhibit folic acid synthesis by inhibiting the enzyme tetrahydrofolate reductase
• nausea, vomiting, diarrhea; hypersensitivity rxns
• broad spectrum: trimethoprim
• synergistic effect w/ sulfonamides

Front 18

dapsone

Back 18

• static; antimetabolites
• thought to interfere with folic acid synthesis
• back, leg, or stomach pains, discolored fingernails, lips, or skin; breathing difficulties, fever, loss of appetites, rash, fatigue
• narrow spectrum: dapsone (mycobacterial infections, principally leprosy)

Front 19

isoniazid

Back 19

• cidal; antimetabolites
• exact mechanism unclear but thought to inhibit lipid synthesis (mycolic acid)
• nausea, vomiting, liver damage, seizures, pins and needles in extremities
• narrow spectrum: isoniazid (mycobacterial infections, principally tuberculosis)

Front 20

disk diffusion test

Back 20

used for rapidly growing microbes; the wider the zone around the disk the more susceptible the pathogen is to the antibiotic

1. inoculate surface of MUeller Hinto agar plate w/ bacteria
2. allow agar surface to dry
3. place antibiotic infused test disks onto agar surface
4. incubate plates 16-18 hrs at 35degC
5. measure Zone of Inhibition
6. determine MLC - plot zone diameter on MIC chart

Front 21

dilution susceptibility test

Back 21

can be used to determine the minimal lethal concentration & minimal inhibitory concentration

1. inoculate broth tubes containing serially diluted antibiotic
2. incubate cultures in antibiotic tubes for 16-20 hours
3. determine MIC - tube w lowest antibiotic [C] with there was no growth
4. inoculate fresh broth tubes (no antibiotics) with samples that did not grow in tubes with antibiotics
5. incubate cultures in broth without antibiotics

Front 22

therapeutic index

Back 22

ratio of toxic dose to therapeutic dose

Front 23

locations where bacteria may display decreased susceptibility

Back 23

abscesses and biofilms

Front 24

What processes will antimetabolites that block the folic acid pathway disrupt?

Back 24

DNA synthesis

purine synthesis

pyrimidine synthesis

Front 25

The Etest

Back 25

best used for anaerobic bacteria that do not grow well in broth culture

1. inoculate surface of the agar plate with bacteria
2. place Etest strips on surface of agar plate in a radial pattern
3. incubate plates for 24-48 hours
4. determine MLC - find point of intersection between inhibition zone and test strip values