Microbiology - Block 2 - Antibiotics

davidwurbel7's version from 2016-03-11 12:15

Inhibitors of Bacterial Cell Walls


Question Answer
Target of beta-lactam drugs + vancomycinPeptidoglycan
Inhibit transpeptidase-carboxypeptidase enzyme that cross-links the peptide chainsBeta-Lactams
Penicillins, Cephalosporins, Carbapenems, MonobactamBeta-Lactams
Binds to D-Alanine – D-Alanine interfering with cross-linkingVancomycin
Target of aminoglycosides, tetracyclines, chloramphenicol, macrolides, lincosamides, linezolid, streptogramins70s Ribosomes
Target of fluoroquinolones + RifampinNucleic Acid
Target of trimethoprim + metronidazole + sulfonamides + pyrimethamineFolic Acid Synthesis
Inhibits a wide range of gram-positive and gram-negative bacteriaBroad-Spectrum Antibiotic
Active against a limited variety of bacteriaNarrow-Spectrum Antibiotic
Inhibit growth of bacteriaBacteriostatic
Cause death of the bacteriaBacteriocidal
Combination of 2 antibiotics that have enhanced bactericidal activity than activity of each single drugAntibiotic Synergism
Aminoglycosides, Tetracyclines, Chloramphenicol, Macrolides, Lincosamides, Linezolid, StreptograminsAT CELLS
Beta-lactams, Vancomycin, Bacitracin and CycloserineBacterial Cell Wall Synthesis Inhibitors
Hydrolysis of antibiotic by Beta-lactamases, Alteration of PBPs and Reduced permeability of Gram negative outer membraneMechanisms of Bacterial Resistance to B-Lactams
Cleaves at the base of the beta-lactam ring between the nitrogen and the carbon double bound to oxygenBeta-lactamases


Question Answer
Penicillin G and Penicillin V only work on these types of bacteriaGram (+) and Spirochetes
Amoxicillin and Ampicillin work on these types of bacteriaGram (+) and a few Gram (-)
Drug of choice for Pseudomonas infectionPiperacillin
Drug of choice for SyphilisPenicillin G
Drug of choice for Rheumatic feverPenicillin G
Drug of choice for Listeria meningitis and Enterococcal infectionsAminopenicillins (Amoxicillin and Ampicillin)
Ureidopenicillins and Carboxypenicillins are type ofExtended Spectrum Penicillins
Piperacillin and MezlocillinUreidopenicillins
Carboxycillin and TicarcillinCarboxypenicillins
Methicillin, Nafcillin, Oxacillin, Cloxacillin and DicloxacillinPenicillinase-Resistant Penicillins
Clavulanate, Sulbactam, TazobactamBeta-Lactumase Inhibitors
Amoxicillin + Clavulanate, Ampicillin + Sulbactam, Piperacillin + Tazobactam, Ticarcillin + TazobactamPenicillin + Beta-Lactamase Inhibitor
Amoxicillin + ClavulanateAugmentin
Drug of choice for Staph aureus skin infections and abcessesNafcillin
Drug of choice for MRSAVancomycin
Mechanism of resistance to methicillinModified PBPs

Route of Administration for Penicillins

Question Answer
Route of administration of Penicillin GIV, IM
Route of administration of Penicillin VPO
Route of administration of AmoxicillinPO, IV
Route of administration of AmpicillinIV, PO
Route of administration of methicillin, nafcillin and oxacillinIV
Route of administration of cloxacillin and dicloxacillinPO
Route of administration of cephalexinPO
Route of administration of cefazolinIV, IM


Question Answer
Cephalexin and cefazolin1st Generation Cephalosporins
Uses for skin & soft tissue infections caused by S.pyogenes/Staph.aureus1st Generation Cephalosporins
Cefuroxime and cefoxitin2nd Generation Cephalosporins
2nd Generation Cephalosporins are effective againstHEN PEcKS
Haemophilus influenzae, Enterobacter, Neisseria, Proteus, E.coli, Klebsiella, SerratiaHEN PEcKS
Cefotaxime, Ceftriaxone and Ceftazidime3rd Generation Cephalosporins
Drug of choice for PseudomonasCeftazidime
Penetrate blood-brain barrier and concentrate in CSF3rd Generation Cephalosporins
Drug of choice for empiric treatment in adults against bacteria meningitisCeftriaxone
Drug of choice for empiric treatment in pediatrics against bacteria meningitisCefotaxime
Drug of choice for gonorrhoeaeCeftriaxone
Cefepime4th generation Cephalosporins
Empirical treatment of nosocomial infections by suspected beta-lactamase-producing bacteriaCefepime
Ceftaroline5th generation Cephalosporins
Can be used against MRSA/MRSE infections but vancomycin is still drug of choiceCeftaroline
Cross-allergenicity in patients with penicillin allergiesCephalosporins
Organisms not covered by cephalosporinsListeria monocytogenes, Atypical bacteria (Chlamydia, Mycoplasma), MRSA (exception; ceftaroline coveres MRSA) and Enterococci

Carbapenems and Monobactams

Question Answer
Beta-lactam antibiotics. Resistant to most beta-lactamases. Most broad spectrum of all antibioticsCarbapenems
Always used in combination with CilastinImipenem
Beta-lactam antibiotic. Resistant to most beta-lactamases. Narrow spectrum - only Gram-negative aerobic bacteriaAztreonam
Reserved for treatment of hospital-acquired multi-drug resistant Gram-negative bacteria (including Pseudomonas). Can be given to patients allergic to penicillinAztreonam


Question Answer
Glycopeptide that binds to D-Ala – D-Ala terminal of peptidoglycan side chain, which leads to inhibition of cross-linking of side chainsVancomycin
Narrow spectrum - only Gram-positive bacteriaVancomycin
DOC for MRSA/MRSE infectionsVancomycin
A switch from D-Alanine > D-Alanine to D-Alanine > D-LactateMechanism of Vancomycin Resistant Bacteria
Drug of choice to treat VRSA / VSEStreptogramins (Quinupristin-Dalfopristin)
Extensive antibiotic usage may lead to overgrowth of Clostridium difficile (GPR) in the gut which causes antibiotic-associated/pseudomembranous colitis which is treated with thisOral Vancomycin

Inhibitors of Bacterial Protein Synthesis

Question Answer
Aminoglycosides and Tetracyclines target this subunit of the bacteria ribosome30S Subunit
Chloramphenicol, Erythromycin (Macrolide), Linezolid, Lincosamide (Clindamycin) and Streptogramins target this subunit of the bacteria ribosome50S Subunit


Question Answer
Gentamicin, Neomycin, Amikacin, Tobramycin, Streptomycin, Kanamycin, NetilmicinGNATS KaN't
Aminoglycosides passage across inner cytoplasmic membrane requires O2-dependent aerobic process so they are not effective against this group of bacteriaGram Negative Bacteria
Aminoglycosides are not effective against this type of bacteriaAnaerobic Bacteria
Aminoglycosides penetration is enhanced when co-administered with a cell-wall synthesis inhibitorGram Positive Bacteria
Mechanism of action bind irreversibly bind 30s ribosomal unit, leading to inhibition of protein synthesisAminoglycosides
Poorly absorbed orally, best used parenterally (IV or IM)Aminoglycosides
Spectrum of activity & uses of this class has good activity against aerobic/facultative gram-negative bacteria especially when combined with a beta-lactamAminoglycosides
Phosphorylation, Adenylation & AcetylationResistance Mechanism


Question Answer
Group of antibiotics with bacteriostatic activityTetracyclines
Includes Tetracycline, Doxycycline, Minocycline and DemeclocyclineTetracyclines
Blocks aminoacyl t-RNA from binding to mRNA-30s ribosome complex and prevents addition of amino acidsTetracyclines
Broad spectrum and atypical bacteria such as Chlamydia, Rickettsia, MycoplasmaTetracyclines
Contraindicated in pregnant women and children below 14 years of ageTetracyclines
Side effects include Photosensitivity to UV, yellowish-brown discoloration of teeth in fetus and young children and skeletal deformity and growth retardation in fetus and children up to 14 years oldTetracyclines
Antibiotic comes into the bacteria and is then immediately pumped out of the bacteria (efflux pump)Resistance Mechanism


Question Answer
Broad-spectrum, bacteriostatic drug with a MOA that inhibits protein synthesisChloramphenicol
Adverse effects include bone marrow suppression and aplastic anemiaChloramphenicol
Not widely used in clinical setting due to high toxicityChloramphenicol


Question Answer
Erythromycin, Azithromycin, ClarithromycinMacrolides
MOA reversibly binding to 23s subunit of 50s and blocks polypeptide elongationMacrolides
Methylation of 23s rRNA, preventing binding by the macrolidesResistance Mechanism
Broad spectrum antibiotic for use in Upper respiratory tract infections - Sinusitis, otitis media, bronchitis. Treatment of community-acquired Atypical pneumonia - Legionella, Chlamydia pneumoniae, Mycoplasma. Can be used in patients allergic to penicillinsMacrolides


Question Answer
Inhibits protein synthesis by binding to 50s with very narrow spectrum only Gram-positive cocci - Staphylococci, Streptococci, EnterococciLinezolid
Linezolid reserved for treatment of infections caused by theseVancomycin Resistant Bacteria


Question Answer
MOA by blocking peptide transfer (translocation) at 50s ribosomal subunitClindamycin
Clindamycin is used mainly against Gram-negative Anaerobes
Side effect is Pseudomembranous colitis when this antibiotic is administeredClindamycin


Question Answer
Streptogramins are used together due toSynergistic
Drug of choice for Vancomycin-resistant Enterococci (VRE) and Vancomycin-resistant Staphylococci (VRSA)Streptogramins

Inhibitors of Nucleic Acid Synthesis

Question Answer
Two catergories - Inhibitors of folic acid synthesis or direct inhibitors of nucleic acid synthesisNucleic Acid Inhibitors
Bacteria synthesize this from precursors like para-aminobenzoic acid (PABA)Folate
Bacteria synthesize this which is required for nucleic acid precursors like thymidine, purines, methionineTetrahydrofolate (THF)
Bacteria require synthesize of this to be able to synthesis of Nucleic acidFolate

Folic Acid Synthesis Inhibitors

Question Answer
Sulfonamides inhibit this enzyme which converts para-aminobenzoic acid and pteridine to dihydropteroic acidPteridine Synthetase
Pteridine Synthetase which converts para-aminobenzoic acid and pteridine to dihydropteroic acid is inhibited bySulfonamides
Trimethoprim inhibit this enzyme which converts dihydrofolic acid to tetrahydrofolic acidDihydrofolate Reductase
Dihydrofolate Reductase which converts dihydrofolic acid to tetrahydrofolic acid is inhibited byTrimethoprim
Mechanism of action has a similar structure to PABA and competes with PABA in binding to enzyme and therefore impair folate synthesisSulfonamides
Fixed dose combination of sulfamethoxazole (SXT) & trimethoprim (TMP)Cotrimoxazole
Causes sequential block of folate metabolismCotrimoxazole
Drug of choice for Pneumocyctis jiroveciiCotrimoxazole
Drug of choice for uncomplicated UTICotrimoxazole


Question Answer
Bactericidal drugs that inhibit bacterial enzymes needed for DNA replication - DNA topoisomerase II (DNA gyrase) & DNA topoisomerase IVFluoroquinolones
Nalidixic acid and Norfloxacin1st Group Fluoroquinolones
Ciprofloxacin and Ofloxacin used mainly against Gram negative bacteria2nd Group Fluoroquinolones
Sparfloxacin and Gatifloxacin used against both Gram-negative & Gram-positives3rd Group Fluoroquinolones
For use against complicated UTICipro/Norfloxacin
For use against Typhoid feverCiprofloxacin


Question Answer
Bactericidal against anaerobic bacteria. Also effective against parasites (Giardia, Trichomonas)Metronidazole
The mechanism of action is it forms free radical toxic metabolites in bacterial cell damageMetronidazole
Can produce adverse reaction Disulfiram like reaction with alcohol. Presents as nausea, vomiting, headache, tachycardia, CV collapseMetronidazole
Metronidazole can produce an adverse reaction like reaction with alcohol which is similar to this medication. Presents as nausea, vomiting, headache, tachycardia, CV collapseDisulfiram

Mechanism of Drug Resistance

Question Answer
Bacteria modify porin channel frequency, or size of porins and selectivity prohibiting entry of drugsInhibition of drug uptake
VISA (vancomycin intermediate Staph aureus) have thicker cell walls trapping vancomycin Inhibition of drug uptake
Membrane proteins that pump out the drug. Results in low intracellular concentrations of drug that are insufficient to elicit an effectEfflux pumps
Destroying the active component of the drug. Usually by producing enzymes that modify the drugDrug Inactivation
Alteration in PBPs , Altered peptidoglycan, Alterations in subunits of DNA gyrase, Alteration in subunits of topoisomerase IV and Changes in RNA polymeraseModify the drug targets