Bacterial Growth & Nutrition Flashcards
Describe general mechanisms of toxin action.
- damage cellular membrane (ex: staphylococcus aureus alpha-toxin)
- inhibit protein synthesis (ex: shiga toxin)
- activate host cell receptor => pathological signaling cascade (ex: C. diff)
Describe the role of type III secretory apparatus in gram negative bacterial pathogenesis.
- composed of rings on the membranes and a hollow tube that acts as a needle
- effector proteins are transferred from the bacteria into the injected host cell
Describe and outline the mechanisms of DNA, protein, and peptidoglycan synthesis. Identify specific steps that can be interrupted by antibiotic drugs.
DNA REPLICATION
- carried out by DNA polymerase
- both strands act as templates
- novobiocin and synthetic quinolones inhibit DNA gyrase (disentangles finished replication products; unique from eukaryotic DNA gyrase)
PROTEIN SYNTHESIS
- mRNA is translated by the ribosomes
- mRNA transcription and translation are coupled (occur simultaneously)
- antibiotics target the ribosome (erythromycin, tetracycline, streptomycin, spectinomycin)
PEPTIDOGLYCAN SYNTHESIS
- subunits synthesized in cytoplasm
- transferred across membrane by carrier proteins
- cross-linked to existing peptidoglycan on outer membrane (facilitated by penicillin-binding proteins that make and break linkages during peptidoglycan maturation)
- penicillin inhibits penicillin binding proteins (various drugs attack at each of these steps)
List the major steps in metabolism. How is this useful in understanding pathogenesis and treatment?
- nutrient molecules enter cell
- central metabolic pathways partially convert to energy by breakdown
- fermentation or respiration to remove more energy
USEFUL B/C
- knowing requirements for energy production shows which environment best suits infection for that pathogens
- identification of pathogen by preferred method of energy production
- identifying toxic by-products of metabolism allows us to use reagents to combat bacterial defenses against them
Describe the siderophore system.
- siderophores are secreted by host cells
- sequester divalent cations in the ECF (ex: iron) to keep the free amount limited
- bacteria have evolved to take in siderophore-cation complexes
- dissociates in the cytoplasm
- frees up nutrients for energy
Define and differentiate between fermentation and respiration. Describe the relevance of each in pathogenesis and diagnosis.
RESPIRATION
- def: electron transport and oxidative phosphorylation (via proton gradient)
=> drugs: disintegrate the cell envelope => destroy the gradient => kill cell
- causes buildup of ROS that must be removed by peroxidase (H2O2) and superoxide dismutase (superoxides)
=> drugs: H2O2 used as antimicrobial agent; overwhelms antioxidant enzymes
FERMENTATION
- less efficient
- anaerobic
- can measure metabolic products
Describe the possible outcomes when bacteria encounter a specific environments. - general stress response - pathogenic stress response => ex: location specific => ex: temporal
- general stress response: starvation (sporulation) and heat (heat shock proteins)
- pathogenic stress response: toxins and pili
=> salmonella enterica produces different type 3 systems and effectors depending on what location it inhabits
=> cholera must activates genes in a temporal sequence to induce pathogenesis (1. determine location. 2. adherence and colonization. 3. toxin)
List methods of entry for nutrients.
- facilitated diffusion
- active transport
- siderophore system
What factors determine rate of bacterial growth in cell culture?
- nature of medium and presence of necessary nutrients
- oxygen status
- temperatures
exotoxin examples
- botulinum does not grow well in the body so it doesn’t usually spread once inside; however, the exotoxin is very potent and can spread
- enterotoxin isn’t fatal but assists in spread of organism by expelling spores in feces
List the major cellular targets of antibiotics.
- peptidoglycan synthesis (penicillin)
- RNA polymerase
- cell membrane
- ribosome inhibitors
List types of adaptive responses.
- sporulation in response to starvation
- heat shock proteins in response to heat to protect
- DNA repair in response to mutagenesis
Recall the phases of growth in culture.
- lag phase - no growth
- exponential growth - doubles over time
- stationary phase - growth = death; due to decreasing nutrients and buildup of toxins
- death phase
