Nester's Microbiology Chapter 20

acquired resistance

resistance that develops due to genetic changes, including mutation and horizontal gene transfer

antibiotic

a compound naturally produced by molds or bacteria that inhibits the growth of or kills other microorganisms

antimicrobial medication

an antibiotic or other chemical that acts by inhibiting or killing microorganisms and is used to treat an infectious disease; also called an antimicrobial drug

antiviral medication

a chemical that acts by interfering with the infection cycle of a virus and is used to treat a viral infection; also called an antiviral drug

broad-spectrum antimicrobial

an antimicrobial medication that is effective against a wide range of microorganisms, often including both Gram-positive and Gram-negative bacteria

chemotherapeutic agent

a chemical used to treat disease

intrinsic resistance

resistance due to inherent characteristics of the organism

narrow-spectrum antimicrobial

an antimicrobial medication that is effective against a limited range of microorganisms

R plasmid

a plasmid that encodes resistance to one or more antimicrobial medications

selective toxicity

the substance causes greater harm to the microbes than to the human host

therapeutic index

the lowest dose toxic to the patient divided by the dose typically used for therapy

narrow spectrum antimicrobials

affect a narrow range of bacteria and are therefore less disruptive to normal flora

antagonistic

counteracting combinations

synergistic

combinations in which the activity of one medication enhances the activity of the other

additive

combinations that are neither synergistic or antagonistic

dysbiosis

an imbalance in the microbial population

B-lactam antibiotics

penicillins, cephalosporins, carbapenems, and monobactams; have a shared structure

penicillin binding proteins (PCBs)

a group of enzymes that catalyze the formation of peptide bridges between NAM molecules on the chains

natural penicillins

narrow-spectrum antibiotics, effective against Gram positive and a few gram negative bacteria. Bacterias that produce penilcilinase are resitant

penicillinase-resistant penicillins

include methicillin and dicloxacillin.

broad-spectrum penicillins

active against penicillin-sensitive gram positive bacteria and also active against many gram negative bacteria. include ampicillin and amoxicillin

extended-spectrum penicillins

greater activity against most of the Enterobacteria as well as Pseudomonas aeruginosa. Have less activity against gram positive bacteria. Include ticarcillin and piperacillin

penicillins + B-lactamase inhibitor

a combination of agents. An example is Augementin, a combination of amoxicillin and clavulanic acid

cephalosporins

structure protects them against certain B-lactamases. Some are not very effective against Gram-positive bacteria, because the antibiotics have a low affinity for their PBPs.

carbapenems

effective against a wide range of gram negative and gram positive bacteria. not inactivated by the extended spectrum B-lactamases produced by certain gram negative bacteria, usually reserved as a last resort treatment. include imipenem, ertapenem, meropenem, and doripenem. There are bacteria that are resistant to these and almost all other medications

monobactam

primarily effective against Enterobacteriaceae. only azetreonam. bacteria that produce B-lactamases or certain carbapenemases are resistant

glycopeptide antibiotics

interfere with petidoglycan synthesis by binding to the amino side chain of NAM molecules, blocking the formation of cross-links between adjacent glycan chains. Affective only against gram positive bacteria. low therapeutic index. includes vancomycin and telavancin

bacitracin

inhibits cell wall biosynthesis by interferring with the transport of peptidoglycan precursors across the cytoplasmic membrane. its toxicity limits it to topical use.

aminoglycosides

bacterial antibiotics that irreversibly bind to the 30S ribosomal subunit causing it to distort and malfunction. Can cause severe side effects including damage to the inner ear and the kidney. Generally not effective against anaerobes, enerococci, and streptococci because they enter the cell during respiratory metabolism. sometimes used synergistically with penicillin. Include streptomycin, gentamycin, tobramycin, and neomycin

tetracyclines

reversibly bind to the 30S ribosomal subunit blocking the attachment of tRNA and preventing translation from continuing. effective against certain Gram-positive and gram negative bacteria. has a long half life. includes doxycycline

glycylcyclines

a wider spectrum of activity than tertracyclins. effective against many bacteria that have developed resistance to the tetracyclines. example is tigecycline

macrolide

reversibly bind to the 50S ribosomal subunit and prevent the continuation of translation. medication of choice for patients allergic to penicillins, bacteriostatic against many gram positive bacteria, but do not pass through the outer membrane of gram negative bacteria. include erythromycin, clarithromycin, and azithromycin.

chloramphenicol

binds to the 50S ribosomal subunit, preventing peptide bonds from being formed and blocking translation. bacteriostatic. active against a wide range of bacteria, but used as a last resort due to a rare but lethal side effect, aplastic anemia.

lincosamides

bind to the 50S ribosomal subunit and prevents contiuation of translation, bacteriostatic. Inhibit a variety of gram negative and gram positive bacteria. example is clindamycin

oxazolidinones

bind to the 50S ribosomal subunit, interferring with the initiation of translation. example linezoid. bacteriostatic against gram positive bacteria, useful against bacteria resistant to B-lactam antibiotics and vancomycin

pleuromutilins

bind to the 50S ribosomal subunit, preventing peptide bonds from being formed during translation. active against many gram positive bacteria. topical use

streptogramins

bind to the 50S ribosomal subunit. effective against a variety of gram-positive bacteria, generally reserved. Synercid consists of quinupristin and dalfopristin which work syngeristically to be bactericidal

fluoroquinolones

synthetic compounds that inhibit one or more group of enzymes called topoisomerases, which maintain the supercoiling of DNA. Bactericidal against a wide variety of bacteria including gram positive and gram negative. examples include ciprofloxacin and moxifloxicin

rifamycins

antibiotics that block bactericidal RNA polymerase from initiating transcription.bactericidal against many gram positive and some gram negative bacteria as well as members of the genus mycobacterium. example rifampin

metronidazole

a synthetic compound that interferes with DNA synthesis and function, but only in anaerobic microorganisms, since anaerobic metabolism is required to activate it. Once active it binds DNA, interfering with synthesis and causing damaging breaks.

co-trimoxazole

a medication in which the combination of a sulfonamide and trimethoprim act in synergisitc effect

sulfonamides/ sulfa drugs

inhibit the growth of many gram-positive and gram-negative bacteria. structurally similar to PABA, a substrate in the pathway fro folate biosynthesis.

trimethoprim

inhibits the bacterial enzyme that catalyzes a metabolic step following the one inhibited by sulfonamides

daptomycin

inserts into bacterial cytoplasmic membranes. not effective against gram- negative bacteria.

polymyxins

bind to the membranes of gram negative cells, also binds to eukaryotic cells to a lesser extent so is used topically

isoniazid (INH0

inhibits the synthesis of mycolic acids, a primary component of the cell wall of mycobacterium tuberculosis

ethambutol (EMB)

inhibits enzymes required for synthesis of other mycobacterial cell wall components

pyrazinamide (PZA)

inhibits enzymes used to restart stalled ribosomes

minimum inhibitory concentration (MIC)

the lowest concentration of a specific antimicrobial medication needed to prevent the visible growth of a given bacterial strain in vitro

minimum bactericidal concentration (MBC)

the lowest concentration of a specfic antimicrobial medicattion that kills 99.9% of cells of a given bacterial strain in vitro

Kirby-Bauer disc diffusion test

a relatively simple method routinely used to determine the susceptibility of a given bacterial strain to a variety of antimicrobial medications

zone of inhibition

the clear area in which no visible growth occurs

efflux pumps

systems that bacteria use to transport antimicrobials ajd other damaging compounds out of a cell

combination therapy

used because the chance of a cell simultaneously developing mutational resistance to multiple antimicrobial medications is extremely low

polyenes

a group of antibiotics produced by certain species of Streptomyces, bind to ergosterol, disrupting the fungal membrane. highly toxic to humans. examples Amphotericin B and nystatin

azoles

inhibit ergosterol synthesis. examples fluconazole, voriconazole, ketoconazole, miconazole, and clotrimazole

allylamines

inhibits an enzyme in the pathway of ergosterol synthesis. examples naftifine and terbinfine.

echinocandins

interfere with synthesis of the fungal cell wall component causing the cell to burst, example caspofungin

griseofulvin

targets cell division, interfers with the action of tubulin. only active against skin and nail infections

flucytosine

taken up by yeast cells then converted by yeast enzymes into an active form that inhibits nucleic acid synthesis