Carbapenamses in Antibiotic Resistance

8/9/2019 Carbapenamses in Antibiotic Resistance

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. . .R T V RAO MD

Carbapenamasesin

AntibioticResistance


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What are Carbapenems

Carbapenems are a class of beta-lactam antibiotics with a broadspectrum of antibacterial activity.

They have a structure that rendersthem highly resistant to beta-

lactamases. Carbapenems

antibiotics were originallydeveloped from thienamycin, anaturally-derived product ofStreptomyces cattleya


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Carbapenems - Structure

Carbapenems arestructurally verysimilar to the

pencillins, but thesulfur atom inposition 1 of thestructure has

been replacedwith a carbonatom, and hencethe name of the

group, the


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Drugs belong to the

carbapenem class: Imipenem

Meropenem

Ertapenem

DoripenemPanipenem/ betamipron


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Background of

Carbapenamases Carbapenem-resistant

Enterobacteriaceae (CRE) areusually resistant to all -lactamagents as well as most otherclasses of antimicrobial agents. The

treatment options for patientsinfected with CRE are very limited.Healthcare-associated outbreaks ofCRE have been reported


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Discovery of

Carbapenamases In 1996, the first isolate of KPC-producing bacteria was discovered ina clinical specimen ofK pneumoniae

from a hospital in North Carolinainvolved in the Intensive CareAntimicrobial Resistance Epidemiology(ICARE) surveillance program. KPCs

were infrequently isolated until 2001,when KPC-producingEnterobacteriaceae were reported inseveral extended outbreaks in

metropolitan hospitals of New York


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Carbapenemases are produced byseveral commonly infecting Gram

Negative Bacteria

Carbapenemases are known to exist inseveral different species of gram-negative bacilli including species ofEnterobacteriaceae and Pseudomonasaeruginosa. However,carbapenemases are more common inlactose-fermenting species of

Enterobacteriaceae (e.g., K.pneumoniae and E. coli) than in non-lactose fermenting Enterobacteriaceae(e.g. Serratia marcescens and some

Enterobactericae spp.) and P.aeru inosa.


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How Carbapenamase

resistance is initiated Carbapenem resistance in

Enterobacteriaceae occurs when an

isolate acquires a carbapenemaseor when an isolate produces anextended-spectrumcephalosporinase, such as an AmpC-

type -lactamase, in combinationwith porin loss. In the United States,the most common mechanism ofcarbapenem resistance is the

Klebsiella pneumoniae


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Carbapenamases a Global

Problem The resistance toCarbapenems hasemerged worldwide

and thepredominantmechanism ofresistance is

attributed by theproduction ofvariousCarbapenems-

hydrolyzing -


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Carbapenems used as importantlife saving option

Carbapenems are often used asantibiotics of last resort for treatinginfections due to multidrug-resistant

gram-negative bacilli, because theyare stable even in response toextended-spectrum and AmpC -lactamases. However, gram-negative

bacilli producing the acquired metallo--lactamases (MBLs) IMP and VIMhave been increasingly reported inAsia and Europe and more recently,

they have been detected in Canada


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Carbapenem Resistance:

MechanismsEnterobacteriaceae Cephalosporinase + porin loss

Carbapenemase

P. aeruginosa Porin loss

Up-regulated efflux

Carbapenemase

Acinetobacterspp. Cephalosporinase + porin loss

Carbapenemase


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Transposons and Integronscontribute for spread of resistance,

The genes of these

MBL enzymes areoften plasmidborne and areassociated with

mobile geneticelements(transposons andintegrons),

making them


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CarbapenamasesClassification Enzyme Most Common Bacteria

Class A KPC, SME,IMI, NMC,

GES

Enterobacteriaceae(rare reports in P. aeruginosa)

Class B(metallo- -lactamse)

IMP, VIM,GIM, SPM

P. aeruginosaEnterobacteriaceaAcinetobacterspp.

Class D OXA Acinetobacterspp.


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Carbapenamases are complex in

Mechanisims Carbapenamases constitute the mostversatile family of -lactamases belongingto molecular classes A, B and D and are

capable of hydrolyzing almost all -lactams.Given their zinc dependent hydrolyticactivity, Carbapenamases of class B isdesignated as metallo--lactamases(MBL) that include, for example, IMP, GIM,

SIM, SPM, and VIM carbapenemases, andthese MBL enzymes have been reported inP.aeruginosa and other multidrug resistant

pathogens


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Carbapenamases are

spreading faster A new class of bacterial enzymescapable of inactivatingCarbapenems, known as Klebsiella

pneumoniae Carbapenamases(KPCs), has rapidly spread in theUnited States and continues to be

extensively reported elsewhere inthe world. KPCs are class ACarbapenamases that reside ontransferable plasmids and can

hydrolyze all pencillins,


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Klebsiella pneumoniaeCarbapenamases

KPC-producing organisms continuesto evolve. Although most KPCs aredetected in isolates ofKlebsiella

and Escherichia coli, KPCs havebeen extensively reported in othergenera of the Enterobacteriaceae

family, such as Proteus,

Serratia, Salmonella, andCitrobacter.


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Located on plasmids; conjugative andnonconjugative

blaKPC is usually flanked by transposonsequences

blaKPC reported on plasmids with:

Normal spectrum -lactamases Extended spectrum -lactamases Aminoglycoside resistance

K le b sie lla p n e u m on iaeC arb ap en am ases


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Emerging Carbapenem Resistance

in Gram-Negative Bacilli Significantly limits treatment options for

life-threatening infections

No new drugs for gram-negative bacilli

Emerging resistance mechanisms,carbapenemases are mobile,

Detection of carbapenemases andimplementation of infection controlpractices are necessary to limit spread


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KPCs in

EnterobacteriaceaeSpecies CommentsKlebsiella spp. K.pneumoniae-cause of outbreaks

K.oxytoca-sporadic occurrence

Enterobacterspp. Sporadic occurrenceEscherichia coli

Salmonella spp.

Citrobacter freundii

Serratia spp.

Pseudomonas aeruginosa Columbia & Puerto Rico


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Pseudomonas aeruginosaCarbapenamases

KPC resistance hasbeen reported ininherently

resistantorganisms suchas

Pseudomon

as from Trinidad,an isolate ofmultidrug-resistant

Pseudomonasaeruginosa that


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Special antibiotic sensitivity testing isemerging need in Microbiology

laboratories Supplemental

testing, inaddition to the

routinesusceptibilitytests of isolates,has becomenecessary inorder to detectthe deluge ofbeta-lactamasesand

carbapenemases


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When to Suspect a KPC-

Producers Enterobacteriaceae especiallyKlebsiella pneumoniae that areresistant to extended-spectrum

cephalosporins:

MIC range for 151 KPC-producingisolates

Ceftazidime 32 to >64 g/ml Ceftriaxone 64 g/ml

Cefotaxime 64 g/ml

Variable susceptibility to cefoxitin and


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Modified HodgeTest for

CarbapenemaseDetection in

Enterobacteriacea


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The Modified Hodge

TestThe Modified Hodge Test is aphenotypic confirmatory test forCarapnemase activity and is

indicated when there is a positivescreening test and resistance to oneor more agents in cephalosporin

subclass III (i.e., cefoperazone,cefotaxime, ceftazidime, ceftizoxime,and ceftriaxone) Be aware thatimipenem disk tests perform poorly as

a screen for carbapenemases.


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CLSI Recommends

CLSI Recommends doing ModifiedHodge test before reportingCarbapenam susceptibility results

if results are elevated butsusceptible to Carbapenam byMinimum inhibitory concentration.

The results ofintermediate orresistance to Carbapenems neednot be tested with MHT


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The Modified Hodge Test

(MHT) The Modified Hodge Test (MHT)

detects carbapenemase productionin isolates of Enterobacteriaceae

Carbapenemase production isdetected by the MHT when the test

isolate produces the enzyme andallows growth of a carbapenemsusceptible strain (E.coli ATCC25922) towards a carbapenem disk


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The Carapnemase is detected byantibiotic sensitivity patterns

Carbapenemaseproduction isdetected by theMHT when the testisolate producesthe enzyme andallows growth of acarbapenem

susceptible strain(E.coli ATCC25922) towards acarbapenem disk.

The result is a

characteristiccloverleaf-like


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Step 1 and 2 of MHT

Prepare a 0.5

McFarlanddilution of theE.coli ATCC25922 in 5 ml ofbroth or saline.

Dilute 1:10 byadding 0.5 ml ofthe 0.5 McFarlandto 4.5 ml of MHB

or saline.


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Step 3 and 4 of MHT

Streak a lawn of the1:10 dilution ofE.coli ATCC 25922

to a Mueller Hintonagar plate andallow to dry 35minutes.

Place a 10 gmeropenem orertapenemsusceptibility diskin the center of thetest area.


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Protocols in Modified HodgeTest


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K.pneumonia showingCarbapenem resistance


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Step 5 and 6 of MHT

In a straight line, streak test organismfrom the edge of the disk to theedge of the plate. Up to four

organisms can be tested on thesame plate with one drug.

Incubate overnight at 35OC 2OC in

ambient air for 1624 hours

Modified Hodge Test


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Modified Hodge Test

Lawn ofE. coliATCC 259221:10 dilution of a0.5 McFarland suspension

Imipenem disk

Test isolates

. , , - .Described by Lee et al CMI 7 88 102.2001


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Observation for

Carbapenamases detectionby HMT After 1624 hours

of incubation,

examine theplate for a cloverleaf-typeindentation at the

intersection ofthe test organismand the E. coli25922, within the

zone of inhibition

of the


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MHT detection (photo courtesy of CDC)

The MHT performedon a 100 mmMHA plate. (1) K.

pneumoniaeATCCBAA 1705,

positive result K.pneumoniaeATCC

BAA 1706,negative result;and a clinicalisolate, positive

result312


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A Positive HMT test

MHT Positive testhas a clover leaf-like indentationof the E.coli25922 growingalong the testorganism growthstreak within the

disk diffusionzone. A positive MHT

indicates thatthis isolate is

producing a


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A negative HMT Test

MHT Negative test has no growthof the E.coli 25922 along thetest organism growth streakwithin the disc diffusion.

A negative MHT indicatesthat this isolate is notproducing a

carbapenemase


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Quality control strains in

Modified Hodge test Perform quality control of the

Carbapenems disks according toCLSI guidelines.

Perform quality control with each run.

MHT Positive Klebsiella

pneumoniae ATCC BAA-1705 MHT Negative Klebsiella

pneumoniae ATCC BAA-1706


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CLSI guidelines for

Carbapenamases detection CLSI has published guidelines fordetection of isolates producingcarbapenemases (CLSI document

M100) . For isolates that testsusceptible to a carbapenem butdemonstrate reduced susceptibilityeither by disk diffusion or MICtesting, performing a phenotypictest for carbapenemase activity, theModified Hodge Test (MHT), is

recommended


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Testing with ertapenem ormeropenem

The procedure described by Landman etal. describes using a 10-g imipenem

disk for step 1. However, there arespecies of Enterobacteriaceae whichhave intrinsic mechanisms ofresistance to imipenem other than a

carbapenemase (See CLSI documentM100, Appendix G). Therefore,ertapenem or meropenem mayprovide more specific selection foracquired carbapenem resistance in

Enterobacteriaceae


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New CLSI

guidelinesNonsusceptibleInterpretive

Category


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NonsusceptibleInterpretive Category

. used for organisms that haveonly a susceptible interpretivecategory, but not intermediate

or resistant interpretivecategories (ie, susceptible-onlyinterpretive category). Asusceptible-only interpretive

category may be applied to newantimicrobial agents for whichno resistant isolates have beenencountered at the time the

initial interpretive criteria are


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NonsusceptibleInterpretive Category

The isolates that test with an MICabove the susceptible interpretivebreakpoint are designated as

nonsusceptible. A designation ofnonsusceptible does notnecessarily mean that aresistance mechanism exists in

the isolate. The MIC of the isolatein the nonsusceptible range maybe within the previouslyrecognized wild-type distribution

of susceptibility results; however,


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Interpretation/ResultsConveyed to Infection Control Departments

Report all culturesthat are positivefor CRE or

carbapenemase-producingEnterobacteriaceae to the

appropriateinfection controlpersonnel.


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Patients infected will be dealt withcaution to prevent spread

patients colonized with carbapenem-resistant or Carbapenamases-

producing Enterobacteriaceae inthe intestinal tract and the Patientswho grow these organisms should

be placed on Contact Precautionsto prevent transmission of theresistant bacteria

Laboratories should create


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Laboratories should createprotocols for detection of CRE

The exact procedure for confirmationof CRE or carbapenemase-

production should be laboratory-specific and chosen based uponlaboratory workflow and the typesof isolates causing clinical infections

in the patient population served. Itmay be helpful to refer to the CLSIguidelines for identification ofcarbapenemase production in

isolates that test susceptible to


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Follow contact Precautions

ContactPrecautionsshould be

implemented forall patients withpositive culturesfor CRE or

carbapenemase-producingEnterobacteriaceae


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Hand washing can saveseveral patients


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Care of the patients colonized withCarapnemase resisistant

Enterobactericae Patients colonized with CRE are

thought to be a source oftransmission in the healthcare

setting . Identifying patients whoare colonized with CRE and placingthese patients in isolationprecautions may be an importantstep in preventing transmission


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Detection of Antibiotic resistancepatterns is more than past

Resistance to our beta-lactam andcarbapenem antibiotics is becomingdaunting for antimicrobial therapy

for infections involving theEnterobacteriaceae. Similarly,laboratory testing to detect theseresistance mechanisms is becomingmore complex and perplexing formicrobiology laboratories.


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Automation has limited usein Carbapenamases detection Automated testing

alone will notdetect all of theresistance patterns

that occur viabeta-lactamasesandcarbapenemases.Failure to detectorganisms withthese enzymes canresult in erroneousreports that wouldindicate an isolateis susceptible tobeta-lactam and/or


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Detection of Drug resistance helps tocontrol the spread of Hospital acquired

infections In addition to the riskof compromisedcare of the patient,when pathogens

with theseenzymes goundetected,necessaryinfection controlmeasures areprecluded, therebyallowing the risk ofthese resistant

organisms


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Created by Dr.T.V.Rao MD fore learning in

Microbiology

Email [email protected]

Carbapenamses in Antibiotic Resistance

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