Cephalosporins, Resistance in Gram Negative Bacteria

8/7/2019 Cephalosporins, Resistance in Gram Negative Bacteria

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Dr.T.V.Rao MD

Dr.T.V.Rao MD 1


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Introduction to Cephalosporins..

Cephalosporins werefirst isolated fromcultures of

Cephalosporiumacremonium from asewer in 1948 byItalian scientist,Giuseppe Brotzu

The first agent cephalothin

(cefalotin) was launched by

Eli Lilly in 1964 Dr.T.V.Rao M

D 2


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B-Lactam antibiotics ( similar topenicillin's)Broad spectrum in action.Act by inhibition of cell wall synthesisBactericidal

Inactive against : enterococci, MRSA,legionella , mycoplasma, chlamydia spp.Widely used in surgical procedures to reduce

the risk of post operative infections

Cephalosporins .

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The site of action of beta-lactam antibiotics is thepenicillin binding proteins (PBPs) on the inner surface ofthe bacterial cell membrane that are involved in thesynthesis of the cell wall

Cephalosporins are bactericidal agentsAll bacterial cells have a cell wall that protects them.

Cephalosporins disrupt the synthesis of the

peptidoglycan layer of bacterial cell walls, which causesthe walls to break down and eventually the bacteria die.

Antimicrobial activity ofCephalosporins

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Classification is based onspectrum of activity

Cephalosporins are groupedinto "generations" basedon their spectrum ofantimicrobial activity.

The first cephalosporins were

designated first generationwhile later, more extendedspectrum cephalosporinswere classified as secondgeneration cephalosporins.

So continued Generations

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Basis of Classification

Each newer generation ofcephalosporins hassignificantly greatergram-negative

antimicrobial propertiesthan the precedinggeneration

Fourth generationcephalosporins, however,have true broad spectrumactivity

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1st

generationCephalosporins

First generation cephalosporinsare moderate spectrum agents

Effective against gram +ve aerobes

They are effective for treating

staphylococcal andstreptococcal infections andtherefore are alternatives forskin and soft-tissue infections,as well as for streptococcal

pharyngitis.

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Dr.T.V.Rao MD 8

CefadroxilCephalexin

Cephaloridine

Cephalothin

Cephapirin

Cefazolin

Cephradine

The 1st

generationcephalosporins are:


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Active against G+ cocci ( except. Enterococci & MRSA):s.pneumoniae, s.pyogenes,s. aureus,

S. epidermidisIndicated for streptococcal pharyngitis ( e.g.

cephalexin)Commonly used ( eg. Cefazolin) as prophylactic for

surgical procedures.Modest activity against G- bacteria

1st Generation

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2nd


Their antibacterial spectrumis broader than that of 1st

generation cephalosporinsand includes some gram -ve

pathogens They are also more resistant

to beta-lactamase

They are useful agents for

treating upper and lowerrespiratory tract infectionsand sinusitis

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2nd generation cont...

These agents are alsoactive against E. coli,Klebsiella and Proteus,

which makes thempotential alternativesfor treating urinary tract

infections caused bythese organisms

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Dr.T.V.Rao MD 12

2nd Generation Cephalosporins

..

CefoxitinCefuroxime

Cefuroxime axetilCefaclor

Cefprozil


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3rd


They have anextended spectrum

of action againstgram -veorganisms

Resistant to beta-lactamases

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3rd generation cont...

The parenteral thirdgeneration cephalosporins(ceftriaxone and cefotaxime)have excellent activity

against most strains ofStreptococcus pneumoniae,including the vast majorityof those with intermediateand high level resistance topenicillin

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Third Generation Cephalosporins

CeftriaxoneCefotaxime

CeftazidimeCefoperazoneCefixime

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THIRD GENERATION

They have enhanced G- activity, H. influenza, N.meningitidis, N.gonorrhea, P. aeruginosae, M.catarrhalis, E.coli, most Klebsiella

Ceftriaxone has long half-life . Not advised inneonates (interferes with bilirubin metabolism )

Cefotaxime preferred in neonate ( does not interferewith bilirubin metabolism ), as may ceftriaxone.Ceftazidime & cefoperazone have excellent activity

against P.aeruginosa.Cefixime has similar activity to amoxicillin &

Cefaclor for actute otitis media

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4th

generationcephalosporins

4th

generation cephalosporinsare extended spectrum agentswith similar activity againstgram-positive organisms asfirst generation cephalosporins.

They also have a greaterresistance to beta-lactamasesthan the third generationcephalosporins.

Many can cross blood brain

barrier and are effective inmeningitis.

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4th

GenerationCephalosporins...

Cefepime

CefluprenamCefozopran

CefpiromeCefquinome

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Fourth Generation

Cefipime

Active against G+ bacteria> than Cefazolin againsts. pyogenes,S.pneumoniae but lower

against s. aureus.Similar to cefotaximeagainst E.coli & K.pneumoniae but < for p.aeruginosa.

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They are organic acids and are hydrophilic

They generally have poor oral bioavailability as theyunstable in acid environments

They are readily excreted by the kidneys, via tubularsecretion in the proximal convoluted tubule. This resultsin high concentrations of the drug in urine.

Exceptions are:

Cephalexin which is stable in acid and so suitable for oraldosing.

Cefoperazone is excreted in bile rather than in urine.

Pharmacokineticconsideration

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Why Cephalosporins are Widely

Prescribed Antibiotics

Broad spectrum of activity

Stability to -lactamase

Oral and parenteral preparations

Widely accepted

Treats day to day as well asserious infections

High safety profileDr.T.V.Rao MD 21


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Dr.T.V.Rao MD 22

Cephalosporins-Limitations

Emerging resistancepatterns

III & IV generation

cephalosporins wereavailable only as

parenteral formulations

Pharmacoeconomics


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Why detect ESBL producers?

ESBL producers may:

Appear Sensitive to some cephalosporins in

vitro

Show major inoculum effects

Fail in therapy, despite appearingsusceptible

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Detection Strategy: step 1

Ref http://www.hpa.org.uk

Screen Enterobacteriaceae with : Cefpodoxime- best general ESBL substrate

Cefotaxime & ceftazidime- good substrates for

CTX-M & TEM/SHV, respectively

Spread of CTX-M into community meansscreening must be wider than before

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Detection of ESBLs: step 2

Seek ceph/clavsynergy in ceph Risolates

DoublediscCombinati

on discEtest

Ref http://www.hpa.org.ukDr.T.V.Rao MD 25


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Double Disk Method

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Etest for ESBLs

Cefotaxime

Cefotaxime+

ClavulanateDr.T.V.Rao MD 27


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Methods optimised for E. coli & Klebsiella

More difficult with Enterobacter

clavulanate induces AmpC; hides ESBL

Best advice is to do synergy test (NOT

SCREEN) with 4th gen cephalosporins

Pitfalls in ESBL detection

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Synergy tests with 4-gen cephalosporins

Cefepime/clav (Mast & AB Biodisk)

Cefpirome clav (Oxoid)

Devt. driven by spread of clonal E. aerogenes withTEM-24 in Belgium & France

Sensitivity for weak ESBLs remains to be proven

Cefpirome & cefepime products need comparison

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Bacteria not to test for ESBLsAcinetobacter

Often S to clavulanate alone

S. maltophilia+ve result by inhibition of L-2

chromosomal -lactamase,ubiquitous in the species

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Briefly, revising breakpoints involves systematic reviewof microbiological, pharmacologic, and clinical data.Recognized experts, sponsors (pharmaceutical industry),and regulators participate in the process which includesdiscussions at public meetings of the CLSI Subcommitteeon Antimicrobial Susceptibility Testing that take placetwice a year. When establishing original breakpoints for

new agents, controlled clinical trial data are required

Role of CLSI in Revising Breakpoints in AntibioticResistance

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Follow the New GuidelinesCLSI 2010

Guidelines forcephalospins forEnterobacteriaceae inaccordance with the 2010

Clinical LaboratoryStandards Institute (CLSI)recommendations. Thefollowing changes will be

made to comply with theCLSI.

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Why do breakpoints sometimesneed to be revised?

Breakpoints need to berevised due to changingresistance mechanisms andbacterial population

distributions, changingscience leading to a betterunderstanding of thepharmacologic determinantsof clinical response, and

adoption of best practicesby clinicians.

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Enterobacteriaceae -Rapid Spread of resistance The rapid and disturbing

spread of:

extended-spectrum -lactamases

AmpC enzymes carbapenem resistance

metallo--lactamases

KPC and OXA-48 -

lactamases quinolone resistance

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What breakpoints were revised in 2010?

Select cephalosporin andaztreonam breakpoints

for Enterobacteriaceaewere revised as notedbelow (for comparison,the old breakpoints are

included):

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-lactamases capable of conferring bacterialresistance to the penicillin's

first-, second-, and third-generation cephalosporins aztreonam

(but not the cephamycins or carbapenems)

These enzymes are derived from group 2b -lactamases (TEM-1, TEM-2, and SHV-1) differ from their progenitors by as few as one AA

Extended-Spectrum -Lactamases

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Until 2000, most ESBL producers were hospital Klebsiella

spp. with TEM and SHV mutant -lactamasesNow, the dominant ESBLs across most of Europe and

Asia are CTX-M enzymes, which originated as genetic

escapes from Kluyvera sppCurrently recognized as the most widespread and

threatening mechanism of antibiotic resistance, both inclinical and community settings 80% of ESBL-positive E. coli from bacteraemias in the UK and

Ireland are resistant to fluoroquinolones 40% are resistant to gentamicin

CTCTX-M-type ESBLs X-M-type ESBLs

Livermore, DM J. Antimicrob. Chemother2009

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Agent

CLSI 2009 CLSI 2010

S I R S I R

Cefazolin 8 16 32 1 2 4

Cefotaxime 8 16-32 64 1 2 4

Ceftriaxone 8 16-32 64 1 2 4

Ceftazidime 8 16 32 4 8 16

Aztreonam 8 16 32 4 8 16

Cefipime 8 16 32 8 16 32

Enterobacteriaceae: RevisedBreakpoints for Cephalosporins

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Agent Old (M100-S19) Revised (M100-S20)

S I R S I R

Cefazolin 18 15-17 14 NA NA NA

Cefotaxime 23 15-22 14 26 23-25 22

Ceftizoxime 20 15-19 14 25 22-24 21 Ceftriaxone 21 14-20 13 23 20-22 19

Ceftazidime 18 15-17 14 21 18-20 17

Aztreonam 22 16-21 15 21 18-20 17

S susceptible I Intermediate

R Resistant.

Disk diffusion breakpoints (mm):

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Agent M100-S19 M100-S20

S I R S I R

Cefuroxime 8 16 32 8 16 32

Cefepime 8 16 32 8 16 32

Cefotetan 16 32 64 16 32 64

Cefoxitin 8 16 32 8 16 32

S susceptible I Intermediate

R Resistant

Following MIC breakpoints were reevaluated forEnterobacteriaceae but were not revised

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Why were the breakpoints for cefepime andcefuroxime (parenteral) not revised?

The cefepime breakpointswere not revised based uponclinical trial data and PK-PD

evaluations. The clinical trialdata showed cefepimeefficacy for patients infectedwith isolates that testedcefepime susceptible (MIC8 g/ml), but produced anESBL


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Why are there no disk diffusion

breakpoints for Cefazolin?

Studies have not yet beencompleted to identify thezone diameter breakpointsthat correlate with the

revised MIC breakpoints forCefazolin. Initial studies didnot reveal clear zonediameter breakpoints anddisk diffusion testing of

Cefazolin may require a newdisk with alternate diskcontent.


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Cephalothin group

Cephalothin is nowclassified under Test/ReportGroup U forEnterobacteriaceae. Resultsfor cephalothin can be usedto represent activities ofseveral other oral FDA-approved agents fortreatment of urinary tractinfections which include

cefadroxil, cefpodoxime,cephalexin, and loracarbef.


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The ESBL testing recommendations were to be a shortterm solution to address a new mechanism of resistance.Subsequently, additional mechanisms of resistance havebeen identified (e.g., new types of ESBLs and AmpC-likeenzymes) and with increased frequency multipleenzymes are identified in a single isolate which cancomplicate ESBL testing (1). These issues coupled withimproved understanding of the PK-PD determinants of

efficacy with cephalosporins and monobactams resultedin the decision to revise the breakpoints.

Need for ChangingRecommendations

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The revised breakpoints eliminate the need toperform ESBL screen and confirmatory tests formaking treatment decisions. Phenotypic tests for ESBLdetection and confirmation are less accurate when

multiple enzymes are present (e.g., false-negative resultsoccur when isolates express both ESBLs and AmpC-typeenzymes) (13) and the presence of multiple enzymes aremore common in contemporary isolates (4, 8). The MIC of

an isolate correlates better with clinical outcome thanknowledge of resistance mechanisms (e.g., ESBLs)

Measuring the Revised Zones isAdvantageous

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Cephalosporins, Resistance in Gram Negative Bacteria