E3 Flashcards
What are common methods for identification and classification of bacteria?
- microscopy: morphologys and staining properties
- bacterial Ag: Ab to detect H,K,O
- detect bacterial nucleic acids; PCR, sequencing
- culture: metabolic properties, biochemical testing
- Ab response to bacteria: ELISA, western blot, immunostaining
What is a cocci?
Sphere
What is a bacilli?
Rod- straight or curved
What is a spirochetes?
Spiral
What are the layers of a gram positive bacterial cell wall?
Thick peptidoglycan
plasma membrane
What are the layers of a gram negative cell wall?
Thick outer membrane
thin peptidoglycan
periplasmic space
plasma membrane
What are the steps of a gram stain?
- Crystal violet turns everything purple
- Precipitate with gram iodine = still purple
- Decolorizer = crystal violet can’t get out of gram positive bilayer so it stays purple
- safranin red = turn gram negative pink
What is the function and importance of peptidoglycan?
In both gram +/- organisms
- unique to bacteria for drug targeting
- layer provides protection: osmotic and physical bilayer
What is the structure of peptidoglycan?
- linear chains of NAG and NAM with Beta 1-4 linkages
- tetrapeptide crosslinks linear polymers
- pentaglycine bridge in some gram +
What effects does peptidoglycan have?
Proinflammatory
- activate complement
- bind pattern recognition receptors to trigger inflammatory cytokines
What are the components of a gram-positive envelope?
- Peptidoglycan: many layers with crosslinks
- teichoic and lipoteichoic acid: which attach peptidoglycan to membrane, attach to other bacteria and host cells, and are virulence factors
What are the components of a gram-negative envelope?
- peptidoglycan: greatly reduced in comparison to gram+, in periplasmic space
- surrounded by outer membrane rich in porins and lipopolysaccharide
What are the components of a gram-negative outer membrane?
- stiff sack for structure and permeability barrier
- rich in porins = metabolites
- LPS in outer leaflet
What are the components of lipopolysaccharide/endotoxin?
- Lipid A: endotoxin activity = proinflammatory cytokines
- Core polysaccharide: 9-12 sugars for structure and rigidity
- O Ag: linear polysaccharide allows distinguish between organisms
What are the effects of LPS/endotoxin?
- bind CD14 and TLR4 on phagocytes
- activate immune system
- cause inflammation through TNF-a, IL-1, IL-6
What are acid-fast bacteria?
- mycobacteria and nocardia
- mycolic acid: LBCFA thick waxy cell wall
- slow growing and difficult for nutrition to get in
- difficult for Ab to get in
What are the components of an acid-fast bacterial wall?
- inner plasma membrane overlaid with peptidoglycan
- lipoarabinomannan (LAM): related to LPS
- arabinogalactans: branched polysaccharides that bind to mycolic acid
- mycolic acid: waxy
What is the purpose of pili/fimbrae?
- protein subunits (pilin) form hollow tube
- common or somatic: sued in attachement
- sex: 1/cell used in gene transfer, plasmid transfer
What is the purpose of flagella?
- locomotion
- different arrangements = identification
- virulence = able to dessimate more easily if can migrate through tissues
What is a capsule/K-Ag?
- loose polysaccharide layer surrounding some gram + or - bacteria
- hydrophilic
- aides in protection from immune system
What is a biofilm?
Organized community of microbial cells that has a capsule/slime layer over the entire population.
What is an endospore?
- in some gram + in harsh environment
- convert from vegetative to dormant
- give rise to single bacteria when environment favorable
- dehydrated, with single copy of chromosome
- Ca bind to dipicolinic acid to stabilize genome
- inner membrane peptidoglycan layers with outer keratin coat
What do endospores mean for human pathology?
- spores can be aeroslized
- found in variety of environments for extended times
- must sterilize surfaces
- can exist for centuries
What is the main difference between bacteria and eukaryotes?
The metabolic differences between these two cell types can be utilized for the development of antibacterial therapies
What are the different phases of the optimal growth curve for bacteria?
- Lag: initial period of adaptation. sensitive to antimicrobials. little cell division
- exponential: multiply rapidly by binary fission. most susceptible to certain antibiotics
- stationary: nutrients depleted. stopped but not dying. sporulation begins
- decline: more bacteria killed than division
What is obligate aerobic?
exclusively uses respiration to meet its energy need
What is obligate anaerobic?
exclusively uses fermentation to meet its energy need
What is microaerophilic?
Grow best at low O2 but can grow without O2 as well
What are the two enzymes present in aerobic bacteria?
Catalase and superoxide dismutase
What is the function of catalase?
H2O2 = water + O2
What is the function of superoxide dismutase?
detox superoxide anion
What is respiration?
substrate oxidation coupled to electron transport
- aerobic = O2 final acceptor
- anaerobic = other final acceptor
- efficient ATP generation
What is fermentation?
Anaerobic process, metabolic intermediate derived from fermentable substrate end products can be measured
Is aerobic or anaerobic more efficient?
Anaerobic less sufficient = 2ATP/glucose while TCA = 38ATP/glucose
What is unique of nucleic acid biosynthesis of bacteria?
-bacteria synthesize folate while humans gain from diet for synthesis of purines and thymidine
What is unique of bacterial DNA replication?
Topoisomerase II or IV are required for DNA recombination and repair and are target of quinolones.
What is unique of bacterial transcription and translation?
- 70S ribosomal subunit, humans have 80S
- occur simultaneous b/c no nuclear envelope
- inhibited by rifampin
What are the steps of peptidoglycan synthesis?
- activation of carbohydrate subunits by binding with UDP
- Pentapeptide added on independent of mRNA and ribosomes (ending with 2x D-ala)
- activated NAM-UDP transferred to bactophrenol with pyrophosphate link and UMP release
- NAG from NAG-UDP transferred to bactophrenol-NAM-pentapeptide
- bactophrenol carrier trasnports NAG-NAM across to outside membrane
- disacchardie attached to end of growing chain by transglycosylases
- pyrophosphobactophrenol is converted back to phosphobactophrenol and recycled
- transpeptidation: link peptide side chains at free amino of diamino and 3rd position so D-ala is released
What is transpeptidation?
-cross linking of peptide chains by peptide bond exchanger
-occurs on outer leaflet
=transpeptidase and carboxypeptidase (penicillin binding proteins) remove D-ala to limit cross links
What is a bacterial chromosome?
Large, circular DNA that comes in variety of sizes
What is a plasmid?
small DNA molecule separate from chromosome
- can be replicated or split
- can be incorporated into host
How do bacteria regulate gene expression of self?
- sensory proteins to detect environment
- highly regulated to prevent waste of energy
- regulon: a group of genes that are regulated as a unit and have further effectors on eachother
How do bacteria regulate gene expression on the population level?
low level low density autoinducers
-modify transcription
What is transformation in bacteria?
Uptake of free DNA from envrionment
-can gain new genes and resistance very quickly
What is conjugation in bacteria?
- acquisition of new DNA from another viable bacterium
- DNA transfer directly by sex pilus
- requires Fertility factor with tra genes for sex pilus and oriT for where break occurs
How does an F+ x F- conjugation occur?
- unidirectional
- f- goes to F+
- oRt transfers to cell then the enitre plasmid transfers over and circularizes
How does a Hfr x F- conjugation occur?
- F facor in chromosome
- form bridge
- DNA transfer begins with OriT
- bridge doesnt stay long enough for entire chromosome to transfer but enough for f factor to transfer
- no sex change occurs because no tra genes exchanged because they are at the end
What is transduction in bacteria?
- transfer of bacterial DNA via a bacteriophage
- lytic/virulent phage = lytic replication upon entry
- temperate phage = integration into chromosme and can excises and undertake lytic replication later
Why are lysogenic phages important?
- toxins are encoded on bacteriophage
- if give antibiotic that kill bacteria, cause increase in bacteriophage because senses state
- start replicating and increase genetic material of the phage
- upregulate the toxin and cause the disease to be much worse
What is intrinsic antibiotic resistance?
- not transferable horizontally between bacteria
- not increasing among bacterial populations
- ex: lack of Ab target (no cell wall in some species)
What is chromosome-mediated antibiotic resistance?
- through random mutation
- homologous recombination with antibiotic resistance gene
- mutation occurs in chromosome that allows bacteria to now be resistant
What is plasmid-mediated antibiotic resistance?
- genes encoding antibiotic resistance are located on a plasmid
- degrade/modify and antibiotic or an efflux pump to get it out of cell
- resistance factor R = what it needs for conjugation
- resistance determinant- drug for resistance
What are bacterial transposons?
- mobile DNA elements that can transfer themselves from one mol DNA to another
- in bacterial cells and viruses
- indirect repeat sequences on end
- gene for transposase the enzyme for transposon movement
- can contain a single or multiple antibiotic resistance genes
What are integrons?
- diverse group of genetic elements
- encode site specific recombination system
- can capture antibiotic resistance gene
- associated with large mobile genetic elements like plasmids or transposons
- important role in spread of drug resistance
What are pathogenicity islands?
- large transpsons
- large pieces of dna that dont normally carry antibiotic resistance
- carry virulence genes surrounded by insertion sequences that cause toxins and pili to hop between bacteria
What is selective toxicity?
leverage biochemical differences to kill or inhibit the growth of a microorganism without harming host cells
What is bacteriostatic chemotherapy?
stunts growth so immune system can come in and kill
What is bactericidal chemotherapy?
when immune system cant be counted on, used to kill bacteria
What are broad-spectrum antibiotics?
Cover a large spectrum of bacteria
- pro: more likely to cover unknown cause of infection
- con: possible disruption of normal microbiota
What are narrow-spectrum antibiotics?
Cover only a small subset of bacteria
- pro: avoids disruption of the normal microbiota
- con: must identify causitive agent to be confident of coverage
What is antibiotic synergism?
Combination of two antibiotics will enhance bactericidial activity