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Therapeutics V > Intro to ID Part 2 > Flashcards

Intro to ID Part 2 Flashcards

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1
Q

What color are gram-positive bacteria in a gram stain?

A

Purple

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2
Q

What color are gram-negative bacteria in a gram stain?

A

Red/pink

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3
Q

What color are atypical bacteria in a gram stain?

A

Do not stain

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4
Q

What are acid-fast bacilli?

A

Resistant to acids/ethanol based decolorization procedures

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5
Q

Gram-positive morphology

A

-Most medically important pathogens are cocci rather than bacilli
-Gram-positive bacilli should be interpreted with clinical context

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6
Q

Which gram-positive bacteria appear in clusters?

A

Staphylococcus

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7
Q

Which gram-positive bacteria appear in pairs/chains?

A

Streptococci and enterococci

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8
Q

Which gram-positive bacteria are catalase positive?

A

Staphylococcus

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9
Q

Which gram-positive bacteria are catalase negative?

A

Streptococcus and enterococcus

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10
Q

Gram-negative morphology

A

Bacilli predominant pathogen

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11
Q

What do oxidase tests tell you about gram-negative bacteria?

A

Help distinguish between enteric vs. non-enteric lactose fermenters

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12
Q

What are fastidious organisms?

A

-Slow growers
-Require special supplemental media

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13
Q

What is the difference between gram-positive and gram-negative?

A

Gram-positive has a thick wall while gram-negative has a thin wall

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14
Q

What are penicillin-binding proteins?

A

-Enzymes vital for cell wall synthesis, cell shape, and structural integrity (transpeptidases)
-Numbered according to molecular weight
-Differ from one bacterial species to another
-Binding to PBPs 1A, 1B, 2 and 3 result in bactericidal effect
-Transpeptidase most important PBP

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15
Q

Definition of intrinsic resistance

A

Always resistant to given antibiotic

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16
Q

Mechanism of intrinsic resistance

A

-Absence of target site
-Bacterial cell impermeability

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17
Q

Definition of acquired resistance

A

Initially susceptible but develop resistance due to some mechanism

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18
Q

Mechanism of acquired resistance

A

-Mutation in bacterial DNA (spontaneously vs selective pressure)
-Acquisition of new DNA (chromosomal or extrachromosomal [plasmid])

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19
Q

Plasmid definition

A

-Self-replicating, extrachromosomal DNA
-Transferable between organisms
-One plasmid can encode resistance to multiple antibiotics

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20
Q

Transposon definition

A

-“Jumping genes”
-Genetic elements capable of translocating from one location to another
-Move from plasmid to chromosome or vice versa
-Single transposon may encode multiple determinants

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21
Q

Phages definition

A

Viruses that can transfer DNA from organism to organism

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22
Q

Conjugation definition

A

-Direct contact or mating via sex pili
-Most common
-DNA shared via mobile genetic elements (MGE), such as plasmids or transposons

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23
Q

Transduction definition

A

Transfer of genes between bacteria by bacteriophages (viruses)

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24
Q

Transformation definition

A

-Transfer or uptake of “free floating” DNA from the environment
-DNA is integrated into host DNA

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25
What are beta-lacatamases
Enzymes that hydrolyze beta-lactam ring by splitting amide bond (inactivates drug)
26
Classification systems for beta lactamases
-Ambler class -Bush-Jacoby-Medeiros
27
How are beta-lactamases classified based on the ambler classification system?
Classified according to amino-acid structure (class A-D)
28
How are beta-lactamases classified based on the Bush-Jacoby-Medeiros classification system?
Classified according to functional characteristics
29
What are the two types of beta-lactamases
-Serine beta-lactamases: serine residue at active site -Metallo-beta-lactamases (MBL): zinc residue at active site
30
Ambler class A beta-lactamases
-Narrow-spectrum beta-lactamases -Extended-spectrum beta-lactamases (ESBL) -Serine carbapenemases
31
Ambler class B beta-lactamases
Metallo-beta-lactamases
32
Ambler class C beta-lactamases
Cephalosporinases
33
Ambler class D beta-lactamases
OXA-type
34
What are extended-spectrum beta-lactamases?
-Plasmid-mediated enzymes that hydrolyze most penicillins, cephalosporins, and monobactams -Organisms with ESBL gene often harbor additional resistance genes
35
Most common extended-spectrum beta-lactamase enzyme
CTX-M
36
What organisms is the ESBL enzyme most prevalent in?
-E. Coli -Klebsiella pneumoniae/oxytoca -Proteus mirabilis
37
Treatment options for extended-spectrum beta-lactamase enzyme
-Treatment of choice: carbapenems -Non-beta-lactam antibiotics are an option depending on the infection source and susceptibility -Piperacillin/tazobactam is an option for urinary source only
38
What is carbapenemase?
-Most frequent cause of carbapenem-resistant enterobacterales (CRE) -Resistant to entire beta-lactam class
39
Most common carbapenemase enzyme
-Klebsiella pneumonia carbapenamse (KPC) -Plasmid-mediated enzyme; KPC-2 and KPC-3 most common variants
40
What bacteria is carbapenemase enzyme found in?
-K. pneumoniae -K. oxytoca -E. coli -E. cloacae -E. aerogenes -P. mirabilis
41
Treatment options for carbapenemases
-Beta-lactam with beta-lactamase inhibitor: ceftazidime/avibactam, meropenem/vaborbactam, imipenem/cilastatin/relebactam -Non-beta-lactam: Plazomicin, eravacycline, omadacycline
42
What are metallo-beta-lactamase
-Confer resistance to all beta-lactams except monobactams (aztreonam) -Harbor additional antibiotic-resistance genes to other antimicrobial classes
43
Most common metallo-beta-lactamase enzyme
New Delhi MBL (NDM)
44
Metallo-beta-lactamases treatment options
-Limited -Not inhibited by any beta-lactamase inhibitor -Cefiderocol; aztreonam + ceftazidime/avibactam
45
What organisms is metallo-beta-lactamases in?
-P. aeruginosa -Acinetobacter spp. -Enterobacterales
46
What are OXA-Type enzymes?
Large heterogenous group often accompanied by other beta-lactamase classes
47
What organisms are OXA-Type enzymes found in?
-Acinetobacter baumanii -Pseudomonas aeruginosa -Some enterobacterales such as klebsiella pneumonia
48
OXA-Type treatment options
-Extremely limited -Cefiderocol -Sulbactam/durlobactam
49
Mechanism of AmpC
Inducible via chromosomally encoded genes
50
Which beta-lactamase inhibitors can inhibit AmpC?
-Inhibited by newer beta-lactamase inhibitors: avibactam, vaborbactam, relebactam -Not inhibited by older beta-lactamase inhibitors (clavulanic acid, tazobactam, sulbactam)
51
What organisms is AmpC present in?
-Hafnia alvei -Enterobacter cloacae -Citrobacter freundii -Klebsiella aerogenes -Yersinia enterocolitica
52
Strong AmpC inducers with high susceptibility to AmpC hydrolysis
-Penicillin G -Ampicillin -First generation cephalosporins (cefazolin) -Cefoxitin
53
Weak AmpC inducers with high susceptibility to AmpC hydrolysis
-Second generation cephalosporins -Third generation cephalosporins (ceftriaxone) -Piperacillin/tazobactam -Aztreonam
54
Strong AmpC inducers with low susceptibility to AmpC hydrolysis
Carbopenems
55
Weak AmpC inducers with low susceptibility to AmpC hydrolysis
Cefepime
56
Treatment of AmpC
-Cefepime -Carbapenems -Non-beta-lactams (fluoroquinolones, trimethoprim/sulfamethoxazole, tetracyclines)
57
What are aminoglycoside-modifying enzymes?
Most common method of aminoglycoside resistance
58
Three mechanisms of aminoglycoside-modifying enzymes
-Acetylation -Nucleotidylation -Phosphorylation
59
Aminoglycoside-modifying enzyme mechanism
Modify aminoglycoside structures by transferring the indicated chemical group to a specific side chain -> impairs cellular uptake and/or binding to ribosome
60
What is a cell wall precursor?
Mechanism of vancomycin resistance in Enterococci species
61
Cell wall precursor mechanism
-Vancomycin binds to D-Alanine-D-Alanine terminus of peptidoglycan precursors -Resistance alters D-ala-D-ala to D-ala-D-lac or D-ala-D-ser -Mediated by VanA or VanB gene -> most common -Produces vancomycin enterococcus
62
Vancomycin resistance treatment
Daptomycin or linezolid
63
PBP alteration mechanism
Decreased ability of PBPs for antibiotic or change in amount of PBP produced by bacteria
64
Which bacteria has altered PBPs?
Methicillin-resistant staphylococcus aureus
65
Which gene expression causes alterations in PBPs?
mecA gene
66
Treatment for PBP alterations
-Ceftaroline -Ceftobiprole -Vancomycin -Daptomycin -Linezolid
67
How do PBP alterations effect streptococcus pneumoniae?
Confers penicillin and cephalosporin resistance
68
What is ribosomal target site alteration?
Responsible for macrolide resistance in S. pneumoniae
69
Which gene is responsible for ribosomal target site alterations?
ermB gene
70
Which antibiotics are ribosomal target site alterations resistant to?
-Clindamycin -Aminoglycosides in gram negatives
71
Which antibiotics are DNA gyrase/topoisomerase IV alterations resistant to?
Fluoroquinolones in gram-negative and S. pneumoniae
72
What is the mechanism of efflux pumps?
-Actively transport antibiotics OUT of periplasmic space -Overexpression can lead to a high level of resistance
73
Which bacteria do efflux pumps play an important role in?
-P. aeruginosa against carbapenems -S. pneumoniae against macrolide antibiotics
74
What are porin channels
-Porin channels are hydrophilic diffusion channels -Smaller, more hydrophilic antibiotics pass easier than larger, hydrophobic antibiotics
75
How do mutations effect porins?
Mutations result in loss of specific porins leading to antibiotics resistance
76
What bacteria are porin mutations most commonly seen?
-Enterobacterales -Carbapenem-resistant P. aeruginosa

Therapeutics V (52 decks)

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