Exam 1: Intro to ID Flashcards
Which bacteria retain crystal violet and iodine (stain purple): Gram + or Gram -?
Gram +
*note that Gram - bacteria are counterstained with safranin dye and appear pink/red
How does the Gram + bacteria’s peptidoglycan cell wall vary from Gram - bacteria?
Gram + bacteria: Have a thick peptidoglycan cell wall which is why they retain crystal violet
Gram - bacteria: Have a thin peptidoglycan cell wall
What are atypical bacteria?
Bacteria that do not stain using a Gram-stain
What are Acid-Fast Bacilli (AFB)?
Bacteria resistant to decolorization procedures by acids/ethanol
What is an example of an Acid-Fast Bacilli (AFB)?
Mycobacterium species
Most medically important Gram + pathogens are what type?
Cocci
(most bacilli are contaminants/ normal flora)
Which cocci species form clusters?
Staphylococcus
Which cocci species form pairs/chains?
Streptococci
Enterococci
The catalase test is used to differentiate between which two species?
-Staphylococci
-Streptococci
The coagulase test is used to differentiate between which two species?
-Staphylococcus aureus
-Coagulase-negative staphylococcus (CoNS)
alpha-hemolytic bacteria appear in which part of the body?
Oral flora
beta-hemolytic bacteria appear in which part of the body?
Skin, Pharynx, Genitourinary
gamma-hemolytic bacteria appear in which part of the body?
Gastrointestinal
What are the HACEK organisms?
-Haemophilus
-Actinobacillus
-Cardiobacterium
-Elkenella
-Kingella
Most Gram (-) pathogens are what?
Bacilli
Lactose fermentation is used to identify which two Gram (-) groups?
-Enterobacterales (enteric gram-negative rods or lactose fermenting gram-negative rods)
-Non-fermenting gram-negative rods
The oxidase test is used to distinguish which two Gram (-) groups?
Enteric lactose fermenters
Non-enteric lactose fermenters
What are fastidious organisms?
Slow growers
-require special supplement media
Review:
Lecture 2 Slide 18 for normal flora
What are Penicillin-Binding Proteins (PBP’s)?
Enzymes vital for cell wall synthesis, cell shape, and structural integrity
*beta lactams bind here
*largest drug target
What are 3 examples of Penicillin-Binding Proteins (PBP’s)?
Transpeptidases
Carboxypeptidases
Endopeptidases
Binding to which segments of Penicillin-Binding Proteins (PBPs) result in a bactericidal effect?
1A
1B
2
3
What is the specific job of the most important Penicillin-Binding Proteins: Transpeptidases?
Catalyze the final cross linking in the peptidoglycan structure
What is the cytoplasmic membrane?
Acts as a selective barrier
-certain drugs must pass through to reach their target site
What is the Peptidoglycan Layer (Cell Wall)?
Permeability barrier for large molecules
*PBPs: proteins essential for cell-wall synthesis
*G(+): thick
*G(-): thin
What is the Outer Membrane composed of (gram-negative bacteria only)?
Lipopolysaccharides (LPS): mediate immune response and sepsis
Porins: hydrophilic channels that permit diffusion of essential nutrients and small hydrophilic molecules
What is the Periplasmic Space?
Gram (+): Compartment between the cell membrane and cell wall
Gram (-): Compartment between the cell membrane and outer membrane
*Vital for bacterial protein secretion, folding, and quality control
*Acts as a reservoir for virulence factors
What is intrinsic resistance?
A bug is always resistant to a given antibiotic
What is acquired resistance?
A bug is initially susceptible to a given antibiotic, but develops resistance due to some mechanism
What are the possible mechanisms of Intrinsic resistance?
-Absence of target site
-Bacterial cell impermeability
What are the possible mechanisms of Acquired resistance?
-Mutation in bacterial DNA (spontaneously vs selective pressure)
-Acquisition of new DNA [chromosomal or extrachromosomal [plasmid])
What are examples of Intrinsic Resistance?
Cephalosporins vs Enterococci
B-lactams vs Mycoplasma
What are examples of Acquired Resistance?
-Stable derepression of AmpC
-Acquisition of KPC gene in GNRs
What are the 3 genetic elements involved in acquired resistance?
-Plasmid
-Transposons
-Phages
What is a plasmid?
-Self-replicating, extrachromosomal DNA
**Transferable between organisms
-One plasmid can encode resistance to multiple antibiotics
What are transposons?
“jumping genes”
-Genetic elements capable of translocating from one location to another
*Move from plasmid to chromosome or vice versa
-Single transposons may encode multiple resistance determinants
What are phages?
Viruses that can transfer DNA from organism to organism
What are the 3 ways that acquired resistance can occur?
Conjugation
Transduction
Transformation
What is conjugation?
Direct contact or mating via sex pili
-DNA shared via mobile genetic elements (MGE) such as plasmids or transposons
Most common
What is transduction?
Transfer of genes between bacteria by bacteriophage (viruses)
What is transformation?
Transfer or uptake of “free floating” DNA from the environment
-DNA is integrated into host DNA
Which of the following describes the difference between Gram-positive and Gram
negative bacteria?
a) Gram-positive have a thin cell wall; Gram-negative have a thick cell wall
b) Gram-positive have a thick cell wall; Gram-negative have a thin cell wall
c) Gram-positive have porin channels; Gram-negative lack porin channels
d) Gram-positive have PBP; Gram-negative lack PBPs
B) Gram-positive have a thick cell wall, Gram-negative have a thin cell wall
What are the 4 mechanisms of antibiotic resistance?
Efflux pumps (pump it out)
Drug inactivating enzyme (chew it up)
Modified drug target (change it up)
Altered cell wall protein/decreased porin production (do not let it in)
What is a B-lactamase?
An enzyme that hydrolyzes the beta-lactam ring by splitting the amide bond
*Inactivates drugs
*These are produced by bacteria as a resistance mechanism against beta-lactam antibiotics
*beta-lactam antibiotics are the largest and safest drug class so we do not want resistance to occur against these
What are the 2 ways that B-lactamases can be classified?
Ambler class: classified according to amino-acid structure (Class A-D)
Bush-Jacoby-Medeiros: classified according to functional characteristics
What are the 2 types of B-lactamase?
Serine beta-lactamases: serine residue at the active site
Metallo-beta-lactamases (MBL): zinc residue at the active site
*see lecture 2 slide 31 for picture
What 3 types of B-lactamases are considered Ambler Class A?
Narrow-spectrum B-lactamases
Extended-spectrum B-lactamases (ESBL)
Serine carbapenemases
What is the function of Narrow-Spectrum B-lactamases and which bacteria produce them?
-Hydrolyze Penicillin
-Produced by Enterobacterales
What is the function of Extended-Spectrum B-lactamases (ESBL)?
-Hydrolyze narrow + extended spectrum-B-lactam antibiotics
-Hydrolyze most penicillins, cephalosporins, and monobactams
In which pathogens is the CTX-M enzyme of ESBLs most commonly found?
Escherichia coli
Klebsiella pneumoniae/oxytoca
Proteus mirabilis
What are the treatments for ESBLs?
Carbapenems (meropenem, imipenem, doripenem, ertapenem)
Note that non-B-lactam antibiotics are an option depending on infection source and susceptibility
*Piperacillin/tazobactam are an option for urinary sources only
What enzyme is an example of an Extended-spectrum B-lactamase (ESBL)?
CTX-M-15
What is the function of Serine carbapenemases?
B-lactamase that hydrolyzes carbapenems
What enzymes are examples of serine carbapenemases?
KPC-1
KPC-2
KPC-3
What 6 pathogens is the KPC enzyme commonly found in?
-K. pneumoniae
-K. oxytoca
-E. coli
-E. cloacae
-E. aerogenes
-P. mirabilis
What are the treatment options for Carbapenemase?
B-lactams: ceftazidime/avibactam, meropenem/vaborbactam, imipenem/cilastatin/relebactam
(B-lactam + B-lactam inhibitor)
Non-B-lactams: Plazomicin, Eravacycline, Omadacycline
Which B-lactamase is considered Ambler Class B?
Metallo-B-lactamases
What is the function of Metallo-B-lactamases?
Hydrolyze carbapenems
*confer resistance to all B-lactams except monobactams (aztreonam)
What enzyme is an example of a Metallo-B-lactamase?
NDM-1
What are the treatment options for Metallo-B-lactamases?
LIMITED -no B-lactamase inhibitors will work
-Cefiderocol
-Aztreonam + Ceftazidime/Avibactam
Which B-lactamase is considered Ambler Class C?
Cephalosporinases
What kind of resistance do cephalosporinases produce?
Inducible
What enzyme is an example of a cephalosporinase?
Amp-C
What are the 3 mechanisms of AmpC production?
**Inducible via chromosomally encoded AmpC genes
(if you put a patient on a drug that induces this then the patient gets worse)
Non-inducible chromosomal resistance via mutations (rare)
Plasmid-mediated resistance
What pathogens is AmpC found in?
Hafnia alvei
Enterobacter cloacae
Citrobacter freundii
Klebsiella aerogenes
Yersinia enterocolitica
(HECK-Yes)
*these are the only bacteria that can induce AmpC, must know these for treatment
What are the possible treatments for AmpC?
*Cannot use older B-lactamase inhibitors
*Can use newer ones: avibactam, vaborbactam, relebactam
How is AmpC induced?
-Enzyme production increases in the presence of certain beta-lactam agents
-Initially, the gene for beta-lactamase production is REPRESSED, goes to an inducer, and the gene is DEREPRESSED, leading to increased beta-lactamase production
-Remove the inducer and the gene is repressed, beta lactamase production goes back to low levels
-Genetic mutation leads to the gene being derepressed, stable derepression, and high level beta-lactamase production continuously
-Different beta-lactams induce AmpC beta-lactamases to varying degrees
*see lec 2 slide 41+42
Which drug is a weak inducer of AmpC and has a high susceptibility to AmpC hydrolysis?
Ceftriaxone
What is a stably derepressed AmpC mutant?
Organism initially tests susceptible but then subsequently tests as resistant
-this occurs in 20-40% of cases treated with 3rd generation cephalosporins
What is the treatment for stably derepressed mutants?
Cefepime
JH is a 65 YOM admitted with pyelonephritis (infection in the kidney) and started on IV ceftriaxone.
However, he soon develops a fever and becomes hypotensive. Blood cultures are taken and result
for E. cloacae.
Q1)What could explain his sudden decompensation?
a) E. cloacae harbors an ESBL gene and this was induced with ceftriaxone treatment
b) E. cloacae harbors a KPC gene and this was induced with ceftriaxone treatment
c) E. cloacae harbors an AmpC gene and this was induced with ceftriaxone treatment
d) E. cloacae harbors a NDM gene and this was induced with ceftriaxone treatment
c) E. cloacae harbors an AmpC gene and this was induced with ceftriaxone treatment
2) What antibiotic change do you recommend?
a) Switch to Piperacillin/tazobactam
b) Switch to Cefepime
c) Switch to Ceftazidime
d) Switch to Aztreonam
b) Switch to Cefepime
(see stably derepressed mutants)
Which B-lactamase is considered Ambler Class D?
OXA-type
What are the functions of OXA-type B-lactamases?
Hydrolyze:
-oxacillin
-oxyimino B-lactams
-carbapenems
*can ether hydrolyze a very broad or narrow range of beta lactams depending on which one it is
What enzyme is an example of an OXA-Type B-lactamase?
OXA-48
In which pathogens are OXA-type B-lactamases typically found?
Acinetobacter baumannii (A. baumannii)
Pseudomonas aeruginosa
What are the treatment options for OXA-Type B-lactamases?
Limited
-Cefiderocol
-Sulbactam/durlobactam
What are 4 important points to remember about Carbapenem Resistance?
-Resistance is associated with the loss of our safest last line of defense
-Cross resistance to other antibiotic classes is very prevalent
-Resistance can be due to beta-lactamase or non-beta-lactamase causes (porin channels, efflux pumps)
-Carbapenem-resistant Enterobacterales (CRE) does not mean carbapenemases are present
JM is a 45 YOM admitted with fever, chills, urinary frequency and urgency. Blood cultures are collected and 12
hour after admission rapid diagnostic testing identifies E.coli, CTX-M (+) in 4/4 bottles.
Q1) What type of antibiotic resistance is present?
a) Non-CP CRE
b) ESBL
c) NDM
d) KPC
b) ESBL
JM is a 45 YOM admitted with fever, chills, urinary frequency and urgency. Blood cultures are collected and 12
hour after admission rapid diagnostic testing identifies E.coli, CTX-M (+) in 4/4 bottles.
Q2) What is the recommended treatment option?
a) Meropenem
b) Meropenem/vaborbactam
c) Aztreonam + Ceftazidime/avibactam
d) Piperacillin/tazobactam
a) Meropenem
Another source of enzymatic inactivation causing resistance is Aminoglycoside-Modifying Enzymes. This is the most common method of ___________ resistance.
aminoglycoside
What are the 3 mechanisms by which resistance through aminoglycoside-modifying enzymes can occur?
Acetylation
Nucleotidylation
Phosphorylation
How do aminoglycoside-modifying enzymes work?
Modify aminoglycoside structure by transferring the indicated chemical group to a specific side chain
(impairs cellular uptake and/or binding to ribosome)
What is the mechanism of resistance of vancomycin in enterococci species?
Altered Target Site: Cell Wall Precursor
-vancomycin binds to D-alanine-D-alanine terminus of peptidoglycan precursors
-inhibits cell wall synthesis
*Resistance alters D-Ala-D-Ala to D-Ala-D-Lac or D-Ala-D-Ser
What genes mediate vancomycin resistance through altered cell wall precursor?
VanA
VanB
Vancomycin resistance through altered cell wall precursors, mediated by VanA and VanB, produces what?
Vancomycin-Resistant Enterococcus (VRE)
What is the treatment for Cell Wall Precursor altered target site?
-vancomycin resistance
Daptomycin
Linezolid
When Penicillin Binding Proteins (PBPs) become an altered target site, what happens?
B-lactam resistance
Why do alterations in Penicillin Binding Proteins (PBPs) lead to B-lactam resistance?
Decreased affinity of PBPs for antibiotic
OR
Change in the amount of PBP produced by bacteria
What gene causes B-lactam resistance due to alterations in Penicillin Binding Proteins (PBPs)?
mecA gene
Besides B-lactam resistance, what else can the mecA gene indicate?
mecA+
means PBP2A+
means patient has MRSA
(methicillin-resistant staphylococcus aureus)
*PBP2A has resistance to B-lactams
What is the treatment for mecA + resistance?
Ceftaroline
Ceftobiprole
Vancomycin
Daptomycin
Linezolid
Alterations in PBP in Streptococcus pneumoniae can result in what?
Penicillin and Cephalosporin resistance
What gene is responsible for Altered Ribosomal Target Sites?
ermB gene
How can efflux pumps lead to resistance?
Efflux pumps actively transport antibiotics out of the periplasmic space
-overexpression leads to high-levels of resistance
Efflux pump overexpression is an important resistance mechanism for what pathogens?
P. aeruginosa against carbapenems
S. pneumoniae against macrolide antibiotics
How can porins cause resistance?
Porin channels are hydrophilic diffusion channels
-the rate of antibiotic diffusion depends on porin + antibiotic physiochemical characteristics
-smaller, more hydrophilic antibiotics pass through easier than large, hydrophobic ones
**Mutations can result in loss of specific porins which leads to antibiotic resistance
Porin channel mutations that cause resistance are most commonly seen in which pathogens?
Enterobacterales
Carbapenem-resistant P. aeruginosa
What is the mechanism of Staphylococcus aureus resistance to beta-lactams?
a) mecA gene
b) VanA gene
c) ermB gene
d) KPC gene
a) mecA gene
What is Pharmacokinetics (PK)?
Process by which the drug enters and leaves the body based on ADME
What is Pharmacodynamics (PD)?
Describes the biochemical and physiological response of the drug and its mechanism of action
What is bactericidal?
KILLING of the organism by acting on areas such as the cell wall, cell membrane, bacterial DNA, etc
What is bacteriostatic?
INHIBITING BACTERIAL REPLICATION without killing the organism by inhibiting protein synthesis
What is the Cmax?
The highest drug concentration
(peak)
What is the AUC?
Overall drug exposure over a certain time
What is the MIC?
Minimum inhibitory concentrations
What is the Post Antibiotic Effect (PAE)?
Continued growth inhibition for a variable period after the concentration at the site of infection has decreased below the MIC
What does Concentration Dependent mean?
Maximize concentration at binding site
What does Time Dependent mean?
Optimize duration of exposure at binding site
What does a large Cmax/MIC mean?
Greater killing
*Correlates with increased area under the curve
Which antibiotics have time-dependent PD?
All B-lactams
(penicillin, cephalosporin, carbapenem, monobactam)
*Vancomycin
Which antibiotics have concentration dependent PD?
Fluroquinolones: Levofloxacin, Ciprofloxacin
Aminoglycosides: Gentamicin, Tobramycin, Amikacin
*Daptomycin
The time that free drug concentration remains above MIC correlates with what?
Clinical and Microbiological outcomes
For what percent of the time do we want the free drug concentration to be above the MIC in:
-Carbapenems
-Penicillins
-Cephalosporins
to maximize fT>MIC?
Carbapenems >/=40%
Penicillin >/= 50%
Cephalosporins >/=60%
What are the strategies to maximize fT>MIC?
(free drug concentration > MIC)
Increase dose, same interval
Same dose, shorter interval
Continuous infusion
Prolonged infusion
How is vancomycin’s PD different than other antibiotics?
Time-dependent bactericidal activity
Long post-antibiotic effect for gram-positive organisms
What target is used for vancomycin PD?
AUC/MIC
Goal: 400-600
What AUC/MIC is considered elevated and has a high risk of nephrotoxicity?
> /= 600-700
Which of the following describes the PK/PD parameters of meropenem?
a) Time-dependent antibiotic; fT>MIC 40% of the dosing interval
b) Concentration dependent antibiotic; fAUC/MIC
c) Time-dependent antibiotic; fT>MIC 80% of the dosing interval
d) Concentration dependent antibiotic; Cmax/MIC
a) Time-dependent antibiotic; fT>MIC 40% of the dosing interval
What are the predictive PK/PD parameters for aminoglycosides + Daptomycin?
Peak/MIC
AUC/MIC
What are the predictive PK/PD parameters for B-lactams?
T>MIC
What are the predictive PK/PD parameters for fluoroquinolones + vancomycin?
AUC/MIC
Is vancomycin bacteriocidal or bacteriostatic?
Cidal (slowly)
