microbio ch 7 & 20

what are the 5 actions of antimicrobial drugs?

1. alter membrane permeability

2. prevent cell wall synthesis

3. damage proteins/prevent protein synthesis

4. damage nucleic acids/prevent nucleic acid synthesis

5. inhibit essential metabolites

bacteriocidal

cell death

bacteriostatic

inhibit cell reproduction, which causes the population to dwindle

controlling microbial growth: cold

exposing microbes to temperatures below their optimal range by refrigeration/freezing slows down growth

controlling microbial growth: heat

exposing microbes to temperatures above their optimal range inhibits protein synthesis, leading to cell death

controlling microbial growth: filtration

small pores in filters physically prevent microbes from passing through, preventing spread

desication

removing water from cells, which disrupts metabolic processes leading to cell death

disinfectant vs antiseptic

both kill microorganisms, but antiseptics are safe to use on living tissue and disinfectants are used on non-living objects

controlling microbial growth: phenol

disrupts the plasma membrane

controlling microbial growth: alcohol

denatures proteins and disrupts the plasma membrane

controlling microbial growth: aldehydes and heavy metals

denatures proteins and enzymes

controlling microbial growth: soaps/detergents

mechanical removal of microbes by scrubbing

how do sulfa drugs control microbial growth

inhibits folic acid synthesis

folic acid

used by microbes to synthesize nucleic acid and proteins

why are sulfa drugs safe for humans but kill bacteria?

humans do not make folic acid but obtain it from diet
bacteria can only make folic acid and slufa drugs block the folic acid synthesis pathway leading to lysis

folic acid synthesis

synthetase enzyme combines 3 substrates pteridine, PABA, and glutamic acid to make folic acid

sulfanilamide

a sulfa drug that is a competitive inhibitor for PABA
binds to synthetase to prevent PABA and pteridine from binding, inhibiting folid acid synthesis and preventing nucleic acid/protein synthesis

beta-lactam: entering gram positive bacteria

beta-lactam can easily penetrate gram positive bacteria despite having many layers of peptidoglycan because they lack a thick outer membrane

beta-lactam: entering gram negative bacteria

beta-lactam cannot easily penetrate gram negative bacteria because they have a thick outer membrane

to be effective, beta-lacatam must?

1. penetrate cell peptidoglycan layers
2. keep the beta-lactam ring intact
3. bind to transpeptidase

what does the beta-lactam ring do in bacteria?

enters bacterial cells and binds to transpeptidase (competitive inhibition), preventing it from linking peptidoglycan layers and inhibiting cell wall synthesis (causes lysis)

transpeptidase

an enzyme that links NAG/NAM chains with amino acids during peptidoglycan synthesis

how does penicillin work to control microbial growth?

prevents cell wall synthesis

beta-lactam resistance: alter transpeptidase structure

1. a beta-lactam resistant cell lyses and releases its genetic material
2. other bacterial cells take up the resistant gene
3. transpeptidase structure is altered and has less affinity for beta-lactam

beta-lactam resistance: producing beta-lactamase

bacterial cell acquires another cell's genes which code for beta-lactamase enzymes that destroy the beta-lactam ring

what are the 4 mechanisms of action for antimicrobial resistance?

1. block entry
2. inactivation by enzymes
3. alteration of target molecule
4. efflux/active transport out via pump mechanism

anitibiotics that inhibit cell wall synthesis

1. penicillin
2. polypeptide antibiotics
3. antimycobacterial antibiotics

antibiotics that inhibit protein synthesis

1. "-mycin" drugs
2. tetracycline

antibiotics that destroy the plasma membrane

polymyxins

antibiotics that inhibit nucleic acid synthesis and transcription

1. nalidixic acid
2. ciprofloxacin

antibiotics that inhibit metabolite synthesis

sulfonamides