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Flashcards in Antibiotic review Deck (9)
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Review antibiotic resistance mechanisms

Bacteria develop ability to hydrolyze these drugs using β lactamase

confers resistance to penicillin

e.g. E. coli, Staph epidermidis, Pseudomonas aeruginosa, Klebsiella pneumoniae

add β lactamase inhibitor e.g. clavulanic acid in amoxicillin-clavulanate (Augmentin)

Genetic mutation of mecA

carried by Staphylococcal cassette chromosome (SCCmec) mobile genetic unit

a bacterial gene encoding a penicillin-binding protein (PBP2a). 

PBP2a has reduced affinity for antibiotics

confers resistance to methicillin, oxacillin, nafcillin

e.g. MRSA

SCCmec type IV has less genetic elements and is specific to CA-MRSA, making CA-MRSA less multi-drug resistant

Altered cell wall permeability

confers resistance to tetracyclines, quinolones, trimethoprim and β lactam antibiotics

Creation of biofilm barrier provides an environment where offending bacteria can multiply safe from the hoste immune system


Staph epidermidis

Active efflux pumps

confers resistance to erythromycin and tetracycline

e.g. msrA gene in Staph

Altered peptidoglycan subunit (altered D-alanyl-D-alanine of NAM/NAG-peptide) 

confers resistance to vancomycin

e.g. vancomycin resistant enterococcus (VRE) 

Ribosome alteration

erm gene confer inducible resistance to MLS (macrolide lincosamide streptogranin) agents via methylation of 23s rRNA

demonstrate using D zone test  

for inducible clindamycin resistance in Staph and beta hemolytic Strep


Review Pennicillin


interferes with bacterial cell wall synthesis

Subclassification and tested examplesnatural

penicillin G


methicillin (Staphcillin)


ampicillin (Omnipen, Polycillin)


Review Fluuroquinolones


blocks DNA replication via inhibition of DNA gyrase 

Side effects

inhibit early fracture healing through toxic effects on chondrocytes 

increased rates of tendinitis, with special predilection for the Achilles tendon. 

tenocytes in the Achilles tendon have exhibited degenerative changes when viewed microscopically after fluoroquinolone administration.

recent clinical studies have shown an increased relative risk of Achilles tendon rupture of 3.7. 

Subclassification and tested examples

ciprofloxacin (Cipro)

levofloxacin (Levaquin)


Review aminoglycosides



inhibition of bacterial protein synthesis 

work by binding to the 30s ribosome subunit, leading to the misreading of mRNA. This misreading results in the synthesis of abnormal peptides that accumulate intracellularly and eventually lead to cell death. These antibiotics arebactericidal.

Subclassification and tested examples

gentamicin (Garamycin)


Review Vancomycin


gram-positive bacteria



an inhibitor of cell wall synthesis 


increasing emergence of vancomycin-resistant enterococci has resulted in the development of guidelines for use by the  (CDC) 

indications for vancomycin  

serious allergies to penicillins or beta-lactam antimicrobials 

serious infections caused by susceptible organisms resistant to penicillins (MRSA, MRSE)

surgical prophylaxis for major procedures involving implantation of prostheses in institutions with a high rate of MRSA or MRSE


Linezolid Mechanism of action

Linezolid binds to the 23S portion of the 50S subunit and acts by preventing the formation of the initiation complex between the the 30S and 50S subunits of the ribosome 



Splenectomy patients or patients with functional hyposplenism require the following vaccines and/or antibiotics 

Pneumococcal immunization

Haemophilus influenza type B vaccine

Meningococcal group C conjugate vaccine

Influenza immunization

Lifelong prophylactic antibiotics (oral phenoxymethylpenicillin or erythromycin)


antibiotic resistance examples

After the introduction of penicillins, bacteria developed the ability to hydrolyze these antibiotics using B-lactamase. In response, penicillinase-stable antibiotics were developed, the first of which was methicillin, since replaced with oxacillin and nafcillin. Drug resistance to this class of antibiotics is achieved via a genetic mutation of mecA encoding an altered penicillin binding protein. The gene product of this mutation, PBPa has a low affinity for these antibiotics and cannot be inhibited by them. Altering cell wall permeability is found in resistance to tetracyclines, quinolones, and trimethoprim, as well as B-lactam antibiotics. Biofilm barriers are produced by bacteria such as salmonella. Active efflux pumps provide resistance to erythromycin and tetracycline, and altering the peptidoglycan subunit is found in resistance to vancomycin.


antiobiotic mechanism of action overview

Antibiotics exert their effects via five basic mechanisms: (1) Inhibition of cell wall synthesis (cephalosporins, penicillins, vancomycin, imipenem). (2) Increasing cell membrane permeability (Bacitracin). (3) Ribosomal inhibition (gentamycin, erythromycins, linezolid, tetracyclines). (4) interference with DNA metabolism (quinolones), and (5) antimetabolite action (Trimethoprim).