These antimicrobial agents usually interfere with bactral physiology (e.g. Macrolids [erythromicine], Clindamycin, Sulfamethoxazole, Trimethoprim, the Tetracyclines, and Chloramphenicol

Bacteriostatic: antimicrobial agents that inhibit growth and/or reproduction of infecting agent, but fail to actually kill the bactra

E.g. the -lactam antibiotics (penicillin & cephalosporin), vancomycin, aminoglycosides (gentamycin), and fluoroquinolones (ciprofloxacin)

Bacteriocidal: Antimicrobial agent capable of causing irreversible dmg or death to organism

Antimicrobials may be bacteriostatic @ low conc but bacteriocidal @ high conc

b/c @ cidal doses, it may be toxic to host tooMost commonly, the inhibitory conc is used to quantitate the activity of an agent against an organism (aka Minimal Inhibitory Concentration [MIC])

A factor that affects whether a drug is bacteriostatic or bacteriocidal is the antimicrobial concnetration @ the site

Distinguish b/w bacteriostatic and bacteriocidal-

Most interfere w/ peptidoglycan synth These agents include the -lactam antibiotics (penicillin, cephalosporin, monobactams, carbapenems) and the glycopeptides (vancomycin)

Polysaccharide portion of peptidoglycan structure is made of repeating units of NAG-NAM

However, -lactam antibiotics, like penicillin, binds irreversibly @ the active site of the enzyme that cross links the peptidoglycan st rands --> bactral cell wall is prevented from forming

The bactral cell wall is complete when crosslink b/w 2 peptide chains + the NAG-NAM backbone

Mech of action:

Penicillin (there are different CLASSES of penicillin)

Cephalosporin (cephalosporins are categorized by "generations"; each generation gets stronger

Monobactams (Aztreonam): active against aerobic gram- bacilliCarbapenems: active against essentially all pathogenic org (these are the tanks of the antibiotics)

4 main -lactams

Glycopeptides (Vancomycin): Effective against ONLY Gram+

Interfere w/ cell wall synthesis (most common)1.

Interfere w/ formation of 30S initiation complex or 50S ribosome = interferes w/ formation of 70S ribosome (found in prokaryo tic cells and not euk)Block the elongation process of assembling amino acids into a polypeptide

Can interfere w/ protein synthesis of bactra by:

Aminoglycosides (gentamycin, tobramycin, amikacin, streptomycin): interferes w/ 30S [bacteriocidal]

Linezolid: binds to 23S portion of the 50S subunit [bacteriostatic]; however, should only be used against Gram+ bactra that a re resistant to other antibioticsMacrolids (erythromycin, azitheromycin, clarithoromycin): Acts by binding to 23S rRNA of the 50S subunit [bacteriostatic]

Lincosamides (clindamycin): similar to macrolidsChloramphenicol: binds 23 rRNA; special note for this is that it is effective against many Salmonella; this is used when othe r antibiotics are contraindicated [bacteriostatic]

Tetracyclines: inhibit bactral protein synth by blocking 30S subunit [bacteriostatic]

Main antibiotics that interfere in this way:

Interfere w/ protein synthesis (second most common mech)2.

Bacitracin (topical): disrupt cytoplasmic membraneAnti-fungals: alter the sterol structure and fxn (cholesterol-like structure found in fungi)

Interfere w/ cytoplasmic membrane fxn3.

Quinolones/fluorquinolones (ciprofloxacin "cipro", levofloxacin, norfloxacin): inhibit DNA gyrase or topoisomerase req for DN A supercoiling [bacteriocidal]

Metronidazole: metabolic cytotoxic byproducts that disrupt DNA [bacteriocidal]

Interferes w/ DNA

Used for TBRifampin: binds to DNA-dependent RNA polymerase --> inhibit RNA synthesis [bacteriocidal]

Bacitracin (topical): inhibit RNA transcription [bacteriocidal]

Interferes w/ RNA

Interfere w/ nucleic acid synth4.

Sulfonamides [bacteriostatic] and Dapsone [bacteriocidal]: prevent synth of folic acidTrimethoprim: prevent synth of folic acid [bcateriostatic]

Used to treat UTI, middle ear infections, bronchitis, traveler's diarrhea, and shigellosis

Triimethoprim + Sulfamethoxazole used in combination: synergistic effects cause bacteriocidal

Interfere w/ metabolic pathway5.

Antibiotics inhibit or kill bactra by one of 5 main mechs

List the 5 modes of action of antibiotics drugs on the bactral cell, and give an example of each-

Learning Objectives

Condensed NotesSaturday, August 23, 2014 8:57 PM

Microbiology Page 1