Mechanisms of Antimicrobial Resistance (Final Exam)

Antibiotic resistance can develop through ______ in the organism or ______ from other organisms or the environment.

random mutations, acquisitions

What are some examples of inappropriate use of antibiotics?

- Use as additive in livestock

- Use in domesticated animals

Innate/intrinsic resistance occurs to a particular ______ or ______.

antibiotic, class

Obligate anaerobes possess innate resistance to ______.

aminoglycosides

Gram negative bacteria are innately resistant to ______.

vancomycin

Innate resistance can occur through ...

- Lack of affinity to bacterial target

- Inaccessibility into bacterial cell

- Extrusion via exporters

- Enzymes that inactivate the drug

What are some mechanisms of acquired resistance?

- Spontaneous mutations

- Acquisition of antimicrobial resistance (AR) genes from other organisms

Transfer of antibiotic resistance genes can occur through ...

- Conjugation

- Transduction

- Transformation

Conjugation requires ______ contact of organisms of the same or different species.

cell-to-cell (transfer through pili)

The donor cell in conjugation provides a ______ to the recipient.

mobile genetic element

Transduction occurs through a ______ injecting donor DNA into the recipient cell that will be incorporated into the recipient DNA.

bacteriophage

Once it lyses, the donor DNA will become ______ and spread their DNA again.

bacteriophages

Transformation occurs when donor cells are ______, releasing genetic content into its surroundings.

lysed

This exogenous DNA can be taken up and incorporated into a ______.

recipient genome

What are the mobile genetic elements?

- Plasmid

- Transposon

- Integron

A plasmid is a small extrachromosomal DNA molecule (circular) within a cell that can ______ independently.

replicate

A transposon is a small piece of DNA that inserts itself into another place in the ______.

genome

An integron is a genetic unit that can capture and incorporate gene cassettes by ______.

recombination

Integrons can carry multiple ______ with different resistances.

cassettes

Plasmid-mediated resistance can occur naturally, expecially in ______.

GNR

Plasmids frequently mediate resistance to ______.

multiple drugs

Porin mutations can prevent _______ and ______ from entering their target GNRs.

beta lactams, fluoroquinolones

Efflux pumps pump substances ______ via active transport.

out of the cell

Most efflux pumps operate via a ______ system.

tripartite

This tripartite system consists of ...

RND, MFP, OMP proteins

MDR P. aeruginosa possess multiple ______ that can have overlap of target substances.

efflux pumps (mexAB, mexCD, mexXY)

Beta-lactamase enzymes circulate in the ______ of GP organisms.

periplasmic

These beta-lactamase enzymes bind and inactivate the antibiotic by hydrolyzing the ______.

beta-lactam ring

MRSA resistance occurs through alteration in the ______.

penicillin-binding protein (PBP)

The ______ gene is carried on the Staphylococcal cassette chromosome.

mecA

The mecA gene encodes an additional PBP2a, which has a lower affinity for all ______.

beta-lactam antibiotics

MRSA Screening Methods

- Cefoxitin disk or MIC screen

- Oxacillin - salt agar

- Detection of PBP2a via lateral flow IA

- Molecular test for mecA

The mexC homologue of mecA causes resistance to ...

Cefoxitin and oxacillin (sometimes susceptible)

The only way to identify mecC is through ______.

molecular detection

Vancomycin inhibits enterococci by binding to the ______ terminus of cell wall precursors.

D-alanyl-D-alanine

Vancomycin-Resistant Enterococci (VRE) has a ______ terminus instead of the D-alanyl-D-alanine terminus.

D-alanyl-D-lactate

The D-alanyl-D-lactate terminus has a lower ______ for vancomycin.

binding affinity

VRE screening can be done through ...

- Chromogenic media

- BEA with 6ug/mL vanco

- MIC or disk diffusion testing

What are the three forms of vancomycin resistance and their genes?

- High level resistance >64ug/mL (vanA)

- Low-level resistance 16-512ug/mL (vanB)

- Intrinsic low-level resistance 2-32ug/mL (vanC)

______ and ______ vancomycin resistance genes are acquired via plasmids.

vanA, vanB

(Most common in E. faecium and E. faecalis)

vanC is mostly found in ...

E. gallinarium E. casseliflavus

Persistence in the ______ and frequent hand contamination are drivers of VRE transmission.

environment

VISA/VRSA (vancomycin intermediate/resistant S. aureus) is acquired via the ______ plasmid from enterococci.

vanA

(Hard to maintain in the organism; not a big threat)

Extended-Spectrum Beta-Lactamases (ESBL) are class A Ambler lactamases that hydrolyze ______ with an oxyimino side chain and ______.

cephalosporins, aztreonam

ESBLs are inhibited by ______ and ______.

clavulanic acid, tazobactam

ESBLs acquire resistance through ______ substitutions at specific positions.

single amino acid

TEM-3 ESBL confers resistance to ...

Ceftazidime, cefotaxime, ceftriaxone (all 3rd generation cephalosporins)

TEM-10 confers high level resistance to ______.

ceftazidime

(Common in U.S. with 12 and 26)

SHV-1 and SHV-2 ESBL differ by a single ______ change.

amino acid (238 Gly-->Ser)

CTX-M ESBL is ______ mediated.

plasma

CTX-M ESBL beta-lactamases are typically resistant to ______ and susceptible to ______.

cefotaxime, ceftazidime

CTX-M ESBL is found mainly in ______.

Enterobacterales

E. coli ST 131 is implicated in a lot of antimicrobial resistance in the ______.

U.S.

ESBL infections are more commonly seen in ______ patients.

hospitalized (indwelling medical devices, antibiotic exposure, etc.)

ESBLs are commonly treated with ______.

carbapenems

Common ESBL Enterobacterales

- E. coli

- K. pneumonia, oxytoca

- P. pirabilis

- Enterobacter

- Salmonella

Common ESBL non-fermenting GNB

- Acinetobacter

- P. aeruginosa

ESBL production can be detected via ...

- MIC, disk diffusion

- Chromogenic media

- PCR

- Microarrays (uncommon)

AmpC beta-lactamases are class C Ambler and are typically ______ mediated.

chromosomally (can be on a plasmid)

AmpC beta-lactamases hydrolyze broad and extended spectrum ______.

cephalosporins

AmpC beta-lactamases are not inhibited by ______.

beta-lactamase inhibitors

In some Enterobacterales, AmpC beta-lactamase expression is low but ______ in response to exposure to beta-lactams.

inducible

Carbapenemases are ______-hydrolyzing beta-lactams.

carbapenem

This occurs through ______ mutations causing impaired permeability.

porin

Patients with carbapenemase producing organisms have increased ______.

morbidity and mortality

Klebsiella pneumoniae carbapenemase (KPC) resides on a transmissible ______ that confers resistance to all ______.

plasmids, beta-lactans

What organisms are KPC found in?

- K. pneumoniae

- Enterobacterales

- Psuedomonas

- Acinetobacter

Metallo beta-lactamases are dependent on ______ for hydrolysis of beta-lactams.

zinc

Metallo beta-lactamases can be inhibited by ______.

EDTA

Metallo beta-lactamase organisms

Naturally occurring: Aeromonas, Chryseobacterium, S. maltophilia

Acquired: others

New Delhi MBL-1 (NDM-1) is ______ mediated, complex and unpredictable.

plasmid

NDM-1 has been identified in ...

- E. coli

- E. cloacae

- P. aeruginosa

- A. baumanii

Isolates with NDM-1 have ______ resistance.

broad

OXA-cabapenemases have weak carbapenem ______ activity.

hyrolytic

OXA-cabapenemases have no hydrolytic activity against ______

3rd/4th generation cephalosporins

Culture methods are easy to perform but there is no ______.

gold standard

What are some discrepancies between culture methods?

- Varied sensitivity/specificity

- Confirm carbapenem resistance

- Some media not reviewed by FDA

- Prolonged TAT

CLSI endorses ______ and ______ for culture methods for carbapenem resistance.

CarbaNP, mCIM

______ detection methods for CP-CRE are more rapid, more sensitive and specific than culture methods.

Molecular

______ can quickly identify resistance mechanisms in culture specimens.

Rapid lateral flow