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Micro240 > Gram negative review > Flashcards

Gram negative review Flashcards

1
Q

In which way does Ab act on bacteria

A

-blocking ability to form peptidoglycan so it cant synthesize its cell wall
-entering the cell and binding with cytoplasmic membrane - destabilizes it causing it to leak out and the bacteria dies
-binding to 30s or 50s ribosomal subunit interfering with bacterial protein synthesis
-interfering with how the bacteria synthesizes nucleic acid by blocking the enzymes during DNA un/winding during replication or by binding to RNA polymerase which prevents RNA synthesis
-inhibiting metabolic pathway or folic acid synthesis - needed for NA synthesis , cant replicate - die

focus on the cephalosporins

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2
Q

What are CEPHALOSPORINS

A

-bactericidal beta lactam ABtics from fungus acremonium and they disrupt cell wall synthesis

-1st gen are active against GP with the next generations more active against GN except 4th which are extended spectrum agents and 5th gen that are resistant against MRSA

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3
Q

Drugs that have FA, PHA, or PHRA are

A

1st generation except Cefaclor

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4
Q

Drugs that end in IME, ONE, TEN

A

3rd generation except Cefuroxime which is a 2nd gen

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5
Q

Drugs with PI

A

4th gen

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6
Q

Drugs with ROL

A

5th generation

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7
Q

Bacteriostatic:

A

inhibits growth but doesn’t kill organism

Hosts immune system will kill organism already weakened by antibiotic.

SXT is static when it us used alone and becomes cidal when with others

l

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8
Q

Bactericidal:

A

Antibiotic kills the organism
Streptogramins (cidal when used together)

Vanco is cidal to Staph and Strep but static to entercocci

Location also makes AB cidal or static for example - Nitrofurantoins iare cidal in treating urinary infections

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9
Q

MAIN MODES OF ANTIBIOTIC RESISTANCE

A

intrinsic or acquired

-Activation of drug Efflux pumps- channels that take antimicrobial agent out of the cell
-Inactivation of Drug by Enzymes - Beta lactamase
-Inhibition of Drug uptake
-Alteration of Drug target- if it cant bind it cant work

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10
Q

Intrinsic R

Acquired R:

A

Intrinsic R - R mechanism on original bacterial chromosome - natural , passed to daughter cell , resistance in all genes

Acquired R: changes to original genome - bacteria becomes R
-acquired through mutation where original genes are altered with no new genes are acquired
-Transferable so new genes are acquired through plasmids or transposons (IC concern)

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11
Q

What is gene regualtion

A

each time the bacteria expresses the gene it gets tired because making and expressing take energy
so they have gene regulation which lets bacteria control when to express the gene

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12
Q

Genes can be Constitutive or Inducible

A

Constitutive: Expressed all the time - resistance to AB
-(e.g. erythromycin R by erm gene – methylation of RNA)

Inducible: R expressed only in the presence of inducer
-turned on in response to environment
Inducible: (e.g. erythromycin inducible resistance of clindamycin expressed only in the presence of erythromycin).

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13
Q

R By Mutation

A

Alters genes already there–no new genes added
Spontaneously
Errors in DNA replication
Physical, chemicals, toxins, damage DNA
Exposure to antibiotic

Mutations passed through normal bacterial replication

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14
Q

resistance by transference of mobile genetic elements via

A

Plasmids, Transposons, Phages

How they work - Horizontal transfer

Transduction -resistance genes are transferred from one germ to another- Phages

Conjugation - R genes can be transferred between germs when they connect- plasmid (pilze)
the new bacteria will make the pilze and pass it on

Transformation - R genes released from Live or dead germs that are picked up by another germ
Exposed to naked fragments of DNA inthe cell

Transposition-with transposons - jumping genes because they can move from one to another .

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15
Q

WHAT IS BACTERIAL PERSISTENCE

if bacteria are exposed to AB

A

R bacteria survive– S ones die.
Only R ones left to replicate –eventually all bacteria in that population become R.

All bacteria are S, but some become dormant because of stress - presister cells
-AB only kill bacteria that are actively replicating (non persisters)
-liver persister cells restart replication after the AB exposure is finished
Persistent bacteria can stay in host for long time - leads to overuse of antibiotics.

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16
Q

BETA LACTAM ANTIBIOTICS

A

B lactam drugs are used to treat Enterobacterales
-BL ring differ in the side rings and side chains
-all bind to PBPs in bacterial cell wall
-prevents bacteria from making its cell wall - death

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17
Q

Antibiotics with beta lactam ring

A

Penicillins, ampicillins, piperacillin
1st, 2nd, 3rd generations of cephalosporins
2nd, 3rd are oxyimino-cephalosporins
Monobactam (Aztreonam)
Carbapenems (Imipenem, meropenem, ertapenem)

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18
Q

RESISTANCE TO β-LACTAMS

A

-production of β-lactamases that hydrolyze the β-lactam ring and now it cant bind PBP

19
Q

2 CLASSIFICATION SCHEMES OF β-LACTAMASES
Ambler classification

A

Based on amino acid sequence of enzyme

Divided more into
Class A, C, and D (serine beta lactamases) where serine is the active site where the B lactam attaches and gets hydrolyzed

Class B - Class B (metallo-beta lactamases) zinc ions used as active site where β-lactam drug attaches & gets hydrolyzed

20
Q

2 CLASSIFICATION SCHEMES OF β-LACTAMASES
Bush-Jacoby classification

A

Based on which antibiotic(s) it hydrolyzes & if is inhibited by BL inhibitor like clavulanic acid, tazobactam or EDTA

divided into Groups 1-4
Group 2 has many subgroups

21
Q

β-LACTAMASE INHIBITORS

A

-Clavulanate, sulbactam or tazobactam that block activity of certain beta-lactamases
- can be used in combination with B lactam AB to treat orgs that make B lactamase- efficiency enhanced

Amoxicillin-Clavulanic acid
Ampicillin-Sulbactam
Piperacillin-Tazobactam

-combos can block penicillinases but NOT Amp-C BL or carbapenemases
-Can’t treat ESBL’s with these because ESBL that appear S in vitro testing may be R in vivo so treatment may fail

22
Q

BETA LACTAMASE NITROCEFIN (CEFINASE) TEST

A

-Nitrocefin disk (chromogenic cephalosporin)
-Beta lactamase hydrolyzes beta-lactam ring of nitrocefin.
Disk changes color from yellow to pink/red.
-Positive means R to penicillinase-susceptible-penicillins like amox, or amp
-Not carbapenems, monobactams or glycopeptides because they have multiple resistance mechanisms or mutiple B lactam enzyme being made - test is unreliable
-Not used to test for ESBL or carbapenemase producers

23
Q

What can the NITROCEFIN (CEFINASE) TEST be used for

A

-N. Gonorrhoeae or meningitidis (if pos is resistance to penicillin)
-H. influenzae (if pos is resistance to ampicillin)
-Staphylococcal/Enterococcal (if pos is resistance to penicillin)- staph needs to be induced to make its B lactamase by being grown in the presence of Peni or Oxa
-Bacteroides spp.

24
Q

RESISTANCE IN ENTEROBACTERALES

A

E. coli, Klebsiella pneumoniae, Proteus mirabilis
-can be found in soil, water or intestines
-resistance due to production of BL enzyme is of most concern.
-known for nosocomial infections
-Beta-lactam drugs used to treat
-Increased R = increased morbidity & mortality, longer hospital stays & increased costs.
-Extended spectrum β lactamases producing (ESBL)- & carbapenemase-producing (CPE) Enterobacteriales, are multidrug-resistant.

25
Q

WHAT IS AN ESBL

A

GNB that produce BL, R to extended spectrum of antibiotics.
-R to penicillins, 1st, 2nd & most 3rd gen cephalosporins
-But R to cefoxitin depends on Class of ESBL
-Doesn’t affect carbapenems (Mero) unless it is a carbapenemase producer
-only those on plasmid are of IC concern
- 3 Classes of ESBL A, C & D as per Ambler
-Class B but these are always CPE
-Differentiated by whether are inhibited by clavulanic acid, tazobactam or EDTA

26
Q

CLASS A ESBL

A

-Serine based beta lactamases.
-Plasmid encoded so R is transferrable
-common families of ESBL in this class are TEM-3, SHV-2, CTX-M, in Klebsiella, E. coli & P. mirabilis (indole neg proteus)
-Provides R to penicillins, beta lactam/beta lactam inhibitor combinations, all cephalosporins + monobactam.
-Sensitive to cefoxitin
-Inhibited by clavulanic acid but not EDTA

27
Q

AMP C BETA LACTAMASE

A

-low levels in all Enterobacterales & some other GN other than salmonella and klebsiella
-Production is intrinsic and sometimes inducible.

found in SPICE orgs
Serratia spp
Providencia spp
Indole positive Proteus: Morganella, P. vulgaris, Edwardsiella
Citrobacter freundii
Enterobacter spp
Hafnia, Acinetobacter, Cronobacter, & rarely Pseudomonas.

all bL AB must be treated at R even if they test as sus

28
Q

CLASS C ESBL THAT ARE S.P.I.C.E

A

-AMP C is an Ambler Class C ESBL (needs serine to break up BL AB.
-Serine based, & not inhibited by β-lactamase inhibitors.
-Gene for AMP C production is intrinsic -on organism chromosome (if on chromo then it wont transfer gene)
-
-AMP C BL production usually inducible – Organism must be grown in the presence of antibiotic (cefoxitin is strong inducer).
-May test S to beta lactam drugs but are really R (inducible resistance)

29
Q

WHAT ABOUT CLASS C NOT SPICE?

A

-gene can make Amp C that can move to a plasmid
-transfer ability to make Amp C BL to organisms other than SPICE
-K. pneumoniae, E. coli, K. oxytoca, Salmonella, P. mirabilis
-produces large amounts of AMP C BL that is not inducible
-still serine based & not inhibited by beta lactam inhibitors
-still R to extended spectrum of penicillin, cephalosporins, monobactams & cefoxitin

30
Q

CLASS A & C ESBL

A

-Klebsiella, E. coli & P. mirabilis that have acquired both Class A & a Class C ESBL via plasmid
-Co express both A & C ESBL
-PCT shows potentiation with 1 or both of the 3rd gen cephalosporins with clavulanic acid
-But cefoxitin is R
-reported as resistant all β-lactams and β-lactam/β-lactamase inhibitor combinations except carbapenems

31
Q

HOW DO WE KNOW WE HAVE A CLASS A ESBL VS A SPICE

A

-Check organism identity, is it a SPICE?
Examine AST results
-Check for R to 3rd Gen cephalosporins –are indicator drugs of possible ESBL or SPICE
-Examples: ceftazidime, cefixime, cefpodoxime, cefotaxime or ceftriaxone
-SPICE Class C, may not show R to 3rd Gen cephalosporin or other beta lactams because resistance may be inducible, so even if tests as S, will be R

32
Q

IF YOU HAVE A SPICE

A

-No further testing required.
-Make sure that any reportable penicillin, cephalosporin and β-lactam/β-lactamase inhibitor combinations are resulted as R even if they test as S.
-Check the Susceptibility reporting document to make sure you’re reporting all the correct antibiotics.
-Don’t forget to add amikacin & meropenem.
-Add comment to the front of the work card comment section:
“This organism harbors a broad-spectrumβ-lactamase and should be considered resistant to all β-lactams and β-lactam/β-lactamase inhibitor combinations except carbapenems”

33
Q

WHAT ABOUT CLASS D ESBL?

A

-OXA beta lactamases
-P. aeruginosa & Acinetobacter -hospitals dont check for resistance because these two are highly resistant
-Serine based & mostly plasmid encoded
-Resistance to penicillin, oxacillin all cephalosporins + monobactam
-No R against cefox or cabapenems
-Poorly inhibited by any beta lactamase inhibitors
-Not actively checked for or reported because these organisms are already known to be very resistant.
-No need to confirm the Class of ESBL by PCT.
-Report correct antibiotics & add a comment indicating that it is a multidrug resistant organism (MDR)

33
Q

IF YOU HAVE NON-SPICE ORGANISM THAT IS POSSIBLE ESBL

A

-phenotypic confirmatory test (PCT) to confirm.
-Determines whether you have a Class A, Class C or Class A & C ESBL
-By whether inhibited by BL inhibitors combined with BL drug & whether S or R/I to FOX

KB on MHA and adding 5 discs
35C, 02, 16-18hrs

34
Q

CARBAPEMEN ANTIBIOTICS

A

-Broad spectrum beta lactam antibiotics that are R to hydrolysis by most β-lactamases.
Includes: ertapenem, imipenem & meropenem
Used to treat serious infection with MDR or ESBL

35
Q

PCT INTERPRETATION

A

Measure zones
-if potentiation of ≥ 5mm between when drug tested alone and when drug tested with clavulanic acid –then the beta lactamase enzyme has been inhibited.

means ceftazidime works better on this organism when it is combined with the β-lactamase inhibitor = potentiation

Means β-lactamase enzyme was inhibited by clavulanic acid

36
Q

how orgs become resistant to CARBAPEMEN like enterobacc

CPE

A

Organisms become R by:
Production of carbapenemase.
Hyperproduction of AMP C or other ESBLs.
Altered porin (decreased uptake)or increased efflux (increased removal from cell).

37
Q

CARBAPENEMASE

A

-BL enzyme that hydrolyze all β-lactam antibiotics including carbapenems.
- not affected by BL inhibitors
- found on a plasmid (sometimes on chromosome).
-of infection control concern.
- significance to public health- are reportable to the Medical Officer of Health.

Some common abbreviations:
CPE: Carbapenemase producing Enterobacterales
CRE: Carbapenem resistant Enterobacterales
CRO: Carbapenem resistant organism

in vitro doesnt always doesnt match in vivo CPE testing

38
Q

MOST COMMON CLASSES OF CARBAPENEMASE

A

Class A:
KPC: K. pneumoniae serine carbapenemase, inhibited by CA & TZB, but not EDTA
KPC gene can be acquired by entero bac or ecoli, Pseudo, acino
-IC concern because it is found in the community as NF

Class D:
OXA-48 serine carbapenemase poorly inhibited by CA, TZB or EDTA

Class B:
NDM: New Delhi, VIM: Verona integron, & IMP: active on imipenem are metallo-carbapenemase that require zinc to hydrolyze
Are inhibited by EDTA but not CA or TZB

39
Q

HOW DO YOU KNOW YOU HAVE A POSSIBLE CPE

A

-Detected by routine susceptibility testing like KB or VITEK AST on an Enterobacterales.
-On any Enterobacterales (especially a possible ESBL or SPICE)- Check the meropenem result next.
-If meropenem R, means it might be a possible CPE
-Possible CPE must be confirmed by a mCIM test

40
Q

Modified Carbapenem Inactivation Method (mCIM)

A

0.5mcfld of possible CPE & add a 10-μg meropenem (MEM) disk to the suspension.

Incubate for 2 hours at 350 C, in O2.

Remove and set aside the MEM disk from the suspension.

Make a 0.5 McFarland suspension of known carbapenem susceptible indicator organism.

Swab entire surface of MHA plate for confluent growth with the suspension of the carbapenem susceptible organism.

Apply the MEM disk you set aside to the center of the MHA plate.

Incubate for 18 hours at 35oC, in O2

41
Q

IF YOU HAVE A CONFIRMED CPE

A

in the front of the card Org + Probable Carbapenemase producer
-report all AB + 2 extra meropenem & amikacin.
-R to any reportable penicillin, cephalosporin and β-lactam/β-lactamase inhibitor combination even if test S

Add 3 comments to the card

42
Q

WHAT IS THE eCIM TEST?

A

used with mCIM, to differentiate between metallo-β-lactamase class B or serine-based carbapenemase production A/D (Enterobacteriaceae only)

-mCIM tells you if the carbapemase is being produced but eCIM with mCIM differentiates between the classes;

-Detects meropenem disk inactivation in the presence of EDTA
-EDTA inhibits the activity of metallo-β-lactamases but not the serine based.
Valid only if mCIM is positive

-Metallo-β-lactamase positive: ≥ 5 mm increase in zone diameter for eCIM vs mCIM
-Means beta lactamase was inhibited by EDTA

Micro240 (7 decks)

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