Micro & ABx Flashcards
Virulence Facotr
Any pathogen component that aids in establishment of an infection (colonization, immune evasion, entry or exit from a host)
May not be essential for viability but is important in pathogenesis
What genera of bacteria does not contain peptidoglycan?
Mycoplasma
Gram +
Cyctoplasmic membrane surrounded by many layers of peptidoglycan
Distributed through these layers are teichoic and lipotechoic acids (only found in Gram + bacteria - promote birulence by aiding attachement to host structures and increasing viability)
Endotoxin
Lipopolysaccharide (LPS) exhibited on the outer leaflet of Gram negative bacteria
Stimulates the innate immune response
Gram-negative
Glycocalyx
“slime layer”
Loose layer of polysaccharides the surround bacteria - helps bacteria attach/adhere to surfaces and aids in biofilm formation
K antigen
Capsular polysaccharide
Capsule - outside of cell wall
Anti-phagocytic
Pili/fimbrae
Filamentous appendages that help bacteria sense and attach to their environment (including host cells)
H antigen
Flagella
What propels bacteria during chemotaxis?
Rotation of their flagella
Plasmids
Small, circular, extrachromosomal DNA - often contain virulence genes
Bacterial ribosomes
Sed rate
70s
(50s+30s)
Spores
Found in Gram-positive rods (clostridium and bacillus)
Facultative vs. obligate intracellular bacteria
Facultative - can grow extracellularly in the environment or lab and also grow inside of a host cell in the body
Obligate - cannot be grown on artificial culture medium - require host (in lab and in the body)
Most bacterial pathogens are?
In response to environmental oxygen
Facultative anaerobes
Have enzymes that protect from oxygen free radicals (superoxide dismutase, catalase, etc.)
Bacterial environmental sensing
Two-component signal transduction systems:
Sense the environment (histidine kinase)
Relay signals inwards (response regulator)
Influcne movement, gene regulation, and virulence factor expression
What are the function of siderophores
Acquisition of iron from host complexes via secreted bacterial molecules possessing a high affinity for iron ions
Fastidious bacteria
Can not grow without specific nutrient supplementation on aritificial media
Describe the Gram-negative cell envelope starting with the layer closest to the cytoplasm and moving to the external environment
Inner Membrane -> Periplasm -> Peptidoglycan -> Outer Membrane
Primary secretion system used by Gram-positive bacteria
The general secretory pathway
Primary secretory system for Gram-negative bacteria
Type III secretion system (T3SS)
Major virulence factor for Gram-negative pathogens
Referred to as a needle-like apparatus
T3SS effector molecules - numerous functions - bacterial attachemnt, immune system evasion, promotes interaction w/ host cell cytoskeleton, and cytotoxicity.
O-antigen
Lipopolysaccharide (LPS)
What is the only bacteria that utilizes sterols?
Mycoplasma
Bacterial chromosome
1-5 million bp (small)
Single, circular, haploid chromosome that lacks introns
Lipid A
Lipid component of endotoxin responsible for the toxicity of gram-negative bacteria
Most interior portion of LPS
Regulons
Functional groups consisting of several operons - the promoters driving these different operon are coordinately regulated (turned on and off at the same time)
Reverse mutations
Change the phenotype of a mutant back to that of the wild-type
True reversions - return genotype back to wild-type
Supressor mutations - return phenotype, not genotype to wild-type
Prototrophic bacteria
Baceria that can synthesize all essential nutrients
Conditional mutations
Mutations that produce proteins that are functional only under specific environmental conditions
Auxotrophs
Mutant bacteria that have lost the ability to synthesize all essential nutrients - must obtain nutrients or precursors from their environment
Bacterial single strand repair
Excision repair
Photoactivation
Bacterial double strand repair
Mismatch repair (recombinatorial repair)
Error-prone repair - emergency system that only bacteria use (damaged DNA is replaced with random sequences)
Bacterial recombination
Positive regulation of operon
System that directly increases RNA polymerase affinity for a particular promoter
Activator proteins turn this system on
Negative regulation of operon
System that directly decreases RNA polymerase affinity for a particular promoter
Repressor proteins turn this system off
Cis- acting elements
DNA sequence elements that must be present on the same piece of DNA w/ the gene of interest to function on that gene
Promoters
Operators
Enhancers
Terminators
During which phase of growth are bacteria most likely to begin forming spores
The stationary phase (nutrients/resources are becoming scare, there is also accumulation metabolic by-products/waste)
Trans-acting factors
Encode gene products that can act from a distance and upon genes located on different pieces of DNA (most are proteins)
Repressors
Activators
Co-repressors
Inducers
What cis-acting element is composed of RNA sequences
Terminators are RNA sequences (encoded in the DNA) that tell the RNA polymerase to stop at the end of a gene or operon
Activator vs. inducer
Both trans-acting factors
Activator - proteins that bind to the enhancer, promoter, and/or operator sites in a gene and increases the affinity in which RNA polyerase binds to promoter sequences
Inducer - factors (often metabolites) that either bind to activator proteins and activate them or bind to repressors and inactivate them
In bacteria, what factors recognize cis-DNA at the Pribnow box?
Sigma (σ) factors recognize cis-DNA sequences in the promoter (-10 and -35 regions-referred
to as the Pribnow box).
Once the σ-factor is bound to
DNA, RNA polymerase (RNAP) is recruited to that site and transcription can begin. Sigma-factor/DNA interaction puts the RNA polymerase in the correct
position and is required for transcriptional initiation.
What determines bacterial transcription frequency?
Ultimately determine by how tightly RNA polymerase is bound (holoenzyme binds to the promoter DNA)
RNAP/DNA affinity:
Increase - activator binding
Decreased - repressor binding
lac repressor
Negative regulation
If there is not lactose present, the lac repressor binds to the operator site and reduces RNAP binding
When lactose (inducer) binds the repressor, its affinity for the operator site is reduced - falls off - allows RNAP to bind the lac promoter
Catabolite activator protein (CAP)
Postive regulation of lac operon
When CAP is bound to cAMP, it binds to the lac promoter and increases RNAP activity
When glucose is present, the amount of cAMP in the cell is low, reducing CAP-mediated activation of lac gene transcription
The level of cAMP is inversely regulated by glucose.
High glucose = low cAMP
Low glucose = high cAMP
Attenuation
Operan gene regulation
Requires simultaneous transcription and translation of the mRNA - used to tightly regulate several bacterial AA biosynthetic operons (i.e. Trp and His operons)
Trp operon
Increased [Trp]intracell - Trp binds Trp repressor (TrpR) protein which suppresses transcription initiation (negative regulation)
Decreased [Trp]intracell - ribosome stalls at the Trp codons b/c it can’t find a charged trp-tRNA but the polymerase continues transcription
Leader region 2 base-pairs to region 3 which blocks formation of the terminator structure - transcript is elongated to the end of the operon and Trp biosynthetic enzymes are translated from the full-length mRNA
What part of the Trp operon contains an attenuator site?
The Trp RNA leader sequence contains an attenuator site which contains two adjacent Trp codons (in region 1)
Horizontal gene transfer
Moving genetic information between bacteria (transformation, conjugation, and transduction)
Bacillus antracis
Capsule
poly D-glutamic acid capsule instead of polysaccharide capsule
Temperate phage
A phage that can undergo both lysogenic and lytic replication
A mutation occurs in the TrpR gene preventing it from binding tryptophan. What would be the consequence of the mutation on regulation of the trp operon in a cell with plenty of tryptophan present?
TrpR would not bind to the trp operator and attenuation would prevent expression of the trp operon.
Amino acid based vs glycolytic based operons
AA - +/- regulation and attenuation
Glycolytic - only +/- regulation
Virulent phage
Only undergoes lytic replication cycle
Helper phage
Phage that provides an essential function for the lytic replication of a defective phage
Specialized transduction
occurs when the genome of a temperate phage is incorrectly excised from the host genome prior to initiation of the lytic cycle. In this case a small piece of host DNA adjacent to the phage genome integration site is excised along with the phage genome. The incorrectly-excised phage genome (with a bit of
host DNA attached to one end) is packaged into a phage capsid and transferred into any new host cell that the transducting phage infects
Why does heat shocking a bacterial colony indicate whether a lytic phage is present?
Becuase heat shocking the bacteria also heat shocks the phage, causing it to enter the lytic cycle of viral - causes the infected bacterial cells to lyse (evident upon viewing growth plate)
Most common disease presentation of Staphylococcus aureus
Skin/soft tissue
Gram (+) cocci in clusters
Facultative anaerobe
Most common disease presentation of Streptococcus pyogenes
Respiratory
Catalase (-)
aka Strep A
Gram (+) cocci in chains
Does not have catalase (differentiates from S. aureus)
Sensitive to Bacitracin disk
Most common disease presentation of Neisseria meningitidis
CNS
Gram (-) cocci
Most common disease presentation of Legionella pneumonphilia
Respiratory
Gram (-) Bacilli
Most common disease presentation of Streptococcus pneumonia
Respiratory
Gram (+) diplococci
Most common disease presentation of Streptococcus agalactiae
CNS
aka Strep B
Most commonly infantile meningitis - agalactia = without milk (infant does not feed)
Gram (+) cocci chains
Does not have catalase
Resistant to bacitracin
Hippurate (+)
cAMP test (+)
Most common disease presentation of Clostridium perfringen
GI and soft-tissue
Gram (+) Bacilli
Spore-forming (but rarely observed)
Non-motile
Encapsulated
Anaerobic
Most common disease presentation of Haemophilus influenzae
Respiratory
Gram (-) coccobacillus
Also CNS
Both catalase and oxidase (+)
Hib is most common and feared
Can colonize - if found in throat/nasopharynx
Disease state - found in CSF/blood/synovial joint
Most common disease presentation of Clostridium difficile
GI
Gram (+) Bacilli (pleomorphic)
Spore-forming (sub-terminal)
Obligate anaerobe
Motile
Ubiquitous in nature
Most common disease presentation of Campylobacter jejuni
GI
Gram (-) Bacilli - seagull ribbone shaped
Also CNS and skeletal/joint
Micro-auerophilic
Thermophilic
Oxidase and catalase (+)
Most common disease presentation of E. coli
GI and GU/Renal
Gram (-) Bacilli
Also Respiratory
Most common disease presentation of Salmonella enterica
GI
Gram (-) Bacilli
Also Skeletal/Joint
Transmission: improperly cooked food and animal contact
Most common disease presentation of Shigella spp.
GI
Gram (-) Bacilli
Also Skeletal/Joint
Most common disease presentation of Pseudomonas aeruginosa
Respiratory/GU/Renal/CV and skin/soft tissue
Gram (-) Bacilli
Most common disease presentation of Bacteroides fragilis
Skin/soft tissue
Gram (-) Bacilli
Associated with 80% of intra-abdominal infections
Polysaccharide capsule
Resistance to penicillin
Susceptible to metronidazole, carbapenems, piperacillin-tazobactam
Most common disease presentation of Fusobacterium spp.
Skin/soft tissue
Oppurtunistic - normal flora of oropharynx, GI, and female GU
Gram (-) rod
Clindamycin sensitive
Make significant amounts of butyric acid (differentiates it from other anaerobes)
What Gram (+) cocci can commonly become systemic?
S. aureus and Streptococcus pyogenes
What Gram (-) Cocci can become systemic?
Neisseria meningitidis
Mycobacterium tuberculosis
Acid fast (+) - does not Gram stain
Aerobic bacilli - thin branching filaments
First-line Tx: Isoniazid, rifampin, ehtambutol, and pyrazinamide
Mycoplasma pneumoniae
Atypical pneumonia - walking pneumonia
Community-acquired respiratory distress syndrome toxin (CARDS toxin) - ADP-ribosylating and vacuolating cytotoxin - swelling of airway and nuclear fragmentation of airway epithelia (contributes to ciliostasis)
Does not have peptidoglycan
Only bacteria thats lipid bilayer contains sterols
PPG backbone
Alternating units of N-acetrylglucosamine (NAG) and N-acetylemuramic acid (NAM)
Cross-linking between tetrapeptide side-chains form meshwork of PPG chains
What PPG monosaccharide is specific to bacteria?
N-acetylmuramic acid
PPG tetrapeptide side-chains
D-AA’s and diaminopimelic acid (m-DAP)
m-DAP is found only in Gram (-) bacteria
PPG Biosynthesis
- Glucoasamine is converted to MurNAc (NAM)
- A pentapeptide side-chains is added to NAM
- NAM-pentapeptide is attached to a bactoprenol carrier in the cytoplasmic membrane
- NAG is attached to NAM-pentapeptide forming subunit
- Some bacteria add additional AA’s to the side-chain at the 3rd position of the peptide to lengthen the cross-link
- The bactoprenol carrier translocates the PPG subunit outside of the cell. It is attached to the existing PPG backbone
- Side-chains are crosslinked by carboxypeptidase and transpeptidase
Enzymes that crosslink PPG
aka penicillin binding proteins (PBP)
Carboxypeptidase - breaks bond b/w fourth and fifth AA’s (D-ala/D-ala)
Transpeptidase - forms bond between the D-ala (fourth) and L-lys (Gram-positives) or m-DAP (Gram-negatives) in the third position of the AA side-chain
When PBPs are bound to beta-lactam abxs - no longer cross-link PPG - results in bacterial lysis due to osmotic pressures
Autolysins
Bacterial PPG
Degrade PPG - even if synthesis stops
PPG as a bacterial PAMP
Stimulates immune response through TLR-2 and nucleotide oligomerization domain-like receptors (NODs) leading to macrophage stimulation, cytokine production, and complement activation
LPS domains
- Lipid A domain - stimulates TLR-4
- Core region - maintains permeability of outer membrane
- O-antigen - shields bacterial surface proteins and prevents immune recognition
O-antigen can be used in serotyping
Maximal TLR-4 stimulationg by LPS
Requires:
- Disaccharide (GlcN-GlcN)
- Two phosphates
- Six fatty acyl chains (12-14 carbon lengths)
ABx resistance
Intrinsic resistance (lack ABx target or targest is inaccessible)
ABx target mutations
Horizontal gene transfer
Macrolide resistance
Methylation of 23S rRNA prevent ABx binding but does not interfere with ribosome function
Also confers resistance to other 50S subunit inhibitors
Beta-lactamases
Enzymes that hydrolyze the beta-lactam ring - prevents interaction with PBPs
Bacterial tetracycline resistance
Mg-chelated tetracyclines are exported via the tetA efflux pump
Kirby-Bauer Disk Diffusion Test
Epsilometer test (E-test)
D test
Inducible clindamycin resistance
A 67-year-old male was brought to the emergency department with severe dehydration from vomiting and watery diarrhea. Two days ago, he had eaten at a local restaurant and had a traditional Thanksgiving meal that included turkey, stuffing, potatoes, and green beans. A bacterium was identified as the causative agent, which was a Gram (-) bacillus. Which of the following bacteria is MOST LIKELY responsible for this infection?
Campylobacter jejuni
A patient has a pus-filled boil on his back that has been drained. A sample was taken for laboratory culture and a Gram (+) coccus was identified as the causative agent. This bacterium was found to be resistant to penicillin. Which of the follow bacteria is MOST LIKELY responsible for this infection?
Staphylococcus aureus
An 18-year-old male presents to the emergency department with a severe headache, light sensitivity, and a stiff neck. The physician in charge obtains spinal fluid and a Gram stain is performed. The results suggest the etiologic agent is Neisseria meningitidis. Which of the following Gram stain and cellular morphologies would the physician most likely have seen in the CSF?
Gram (-) cocci
A 24-year-old female presents with her third urinary tract infection of the year. Which of the following bacteria is MOST LIKELY causing her infections?
Escherichia coli
A 10-year-old boy is taken to his pediatrician for a sore throat, headache, and icky feeling. Several of his classmates have the same symptoms. His immunizations are up-to-date. A throat culture is performed and the next day, Gram (+) cocci are identified from bacterial colonies that are beta hemolytic. Which of the following bacteria fit this profile?
Streptococcus pyogenes