Antibiotic Sensitivity Antibiotic Sensitivity Testing 2017 Update Testing 2017 Update

Margie A. Morgan, PhD, MT(ASCP), D(ABMM)Margie A. Morgan, PhD, MT(ASCP), D(ABMM)

Antibiotic Classes Penicillins

◦ Penicillin◦ Amoxicillin◦ Ampicillin◦ Amp/Clavulanate◦ Amp/Sulbactam

Anti-Pseudomonal Penicillins◦ Piperacillin/Tazobactam◦ Ticarcillin/Clavulanate

Anti- Staph Penicillins◦ Nafcillin◦ Oxacillin◦ Cloxacillin◦ Dicloxacillin

These antibiotics and those listed on the next slide have a beta lactam ring structure – aka beta lactam antibiotics

Antibiotic Classes (2) Carbapenems

◦ Imipenem◦ Meropenem◦ Ertapenem◦ Dorapenem

Monobactam ◦ Aztreonam

Cephalosporins ◦ First generation

◦ Cefazolin◦ Second generation

◦ Cefotetan◦ Cefoxitin Cefuroxime

◦ Third generation◦ Cefotaxime Ceftriazone◦ Ceftazidime Cefpodoxime

◦ Fourth generation◦ Cefepime Ceftaroline

Antibiotic Classes (3) Fluoroquinolones

◦ Ciprofloxacin◦ Levofloxacin◦ Moxifloxacin

Aminoglycosides◦ Gentamicin◦ Tobramycin◦ Amikacin

Trimethoprim/ sulfamethozaxole

Macrolides◦ Azithromycin◦ Clarythromycin◦ Erthromycin

Tetracyclines◦ Tetracycline◦ Minocycline◦ Doxycycline

Lincosamide◦ Chloramphenicol

The Four Major The Four Major mechanisms of antibiotic mechanisms of antibiotic resistanceresistance

Enzymatic cleavage Enzymatic cleavage leads to inactivation of antibioticleads to inactivation of antibiotic◦ Active Beta lactamases and amino-glycoside modifying enzymes Active Beta lactamases and amino-glycoside modifying enzymes

Altered receptorsAltered receptors/binding proteins preventing attachment of antibiotics /binding proteins preventing attachment of antibiotics to the bacterial surfaceto the bacterial surface◦ Penicillin binding proteins (PBPs)Penicillin binding proteins (PBPs)◦ Mechanism for Strep pneumoniae resistance to penicillin and MRSA Mechanism for Strep pneumoniae resistance to penicillin and MRSA

resistance to methicillinresistance to methicillin

Altered permeabilityAltered permeability/influx and efflux pumps stopping passage through /influx and efflux pumps stopping passage through porins – gram negative bacilli porins – gram negative bacilli ◦ Pseudomonas aeruginosa resistance to amino-glycosidesPseudomonas aeruginosa resistance to amino-glycosides

Bypass of a metabolic blockBypass of a metabolic block/metabolic block imposed by antibiotic /metabolic block imposed by antibiotic ◦ Enterococcus resistance to TMP/SXTEnterococcus resistance to TMP/SXT

The Rules for Susceptibility The Rules for Susceptibility TestingTesting

CLSICLSI – Clinical Laboratory Standards Institute Approved standards for the – Clinical Laboratory Standards Institute Approved standards for the testing & reporting of susceptibility results/ updated yearlytesting & reporting of susceptibility results/ updated yearly

1.1. Charts with appropriate antibiotics to testCharts with appropriate antibiotics to test2.2. How to interpret the laboratory resultsHow to interpret the laboratory results3.3. QC standards and proper testing proceduresQC standards and proper testing procedures

Methods/Bacteria in Methods/Bacteria in ReviewReview

Susceptibility testing methodsSusceptibility testing methods

1. Kirby Bauer disk diffusion (KB)1. Kirby Bauer disk diffusion (KB)

2. E Test Strip Minimum inhibitory concentration (MIC )2. E Test Strip Minimum inhibitory concentration (MIC )

3. Broth dilution Minimum inhibitory concentration (MIC)3. Broth dilution Minimum inhibitory concentration (MIC)

4. Beta lactamase enzyme detection4. Beta lactamase enzyme detection

Resistant Bacteria of ImportanceResistant Bacteria of Importance MRSA MRSA methicillin resistant Staphylococcus aureusmethicillin resistant Staphylococcus aureus VRE VRE vancomycin resistant enterococcusvancomycin resistant enterococcus ESBLESBL Extended Spectrum Beta Lactamase Gram neg rodsExtended Spectrum Beta Lactamase Gram neg rods KPCKPC Klebsiella pneumonia Carbapenemase or Klebsiella pneumonia Carbapenemase or CRE CRE Carbapenamase Resistant EntericsCarbapenamase Resistant Enterics Streptococcus pneumoniaeStreptococcus pneumoniae Neisseria gonorrhoeaeNeisseria gonorrhoeae

Preparation of Bacteria Preparation of Bacteria for all Susceptibility for all Susceptibility MethodsMethods

Pure culture of one organismPure culture of one organism Log phase growth of bacteria - 16-24 hrs oldLog phase growth of bacteria - 16-24 hrs old Methods test for stasis not killingMethods test for stasis not killing Standardized suspension of bacteria: Standardized suspension of bacteria:

◦ O.5 McFarland Standard – Barium sulfate solution that O.5 McFarland Standard – Barium sulfate solution that equals the turbidity of 10 8 bacteria/mlequals the turbidity of 10 8 bacteria/ml

◦ Alternative method – use spectrophotometer Alternative method – use spectrophotometer

Incubation at 35 °C in room air (or CO²) for 18- 24 hrsIncubation at 35 °C in room air (or CO²) for 18- 24 hrs

This is a 0.5 McFarland Standardwhich is a turbidity standard made fromBarium sulfate – the turbidity is equal to10 8 CFU/ml bacteria

Quality ControlQuality ControlVerificationVerification: Before testing patients: Must correctly test multiple QC : Before testing patients: Must correctly test multiple QC strains for 20 consecutive days or 3 replicates for 5 days. This is to strains for 20 consecutive days or 3 replicates for 5 days. This is to make sure you can perform the tests correctly.make sure you can perform the tests correctly.

ATCCATCC strains of bacteria (American Type Culture Collection) If QC strains of bacteria (American Type Culture Collection) If QC strains are within limits - you can then do Weekly quality control on all strains are within limits - you can then do Weekly quality control on all lots of cards, disks, plates in uselots of cards, disks, plates in use◦ Data must be recorded and reviewed monthly by supervisorData must be recorded and reviewed monthly by supervisor

If weekly QC results are out of control:If weekly QC results are out of control:◦ Immediately repeat/ inform supervisorImmediately repeat/ inform supervisor◦ If repeat is OK – continue routine testingIf repeat is OK – continue routine testing◦ If repeat is NOT OK – must investigate/document/ repeat 5 times to If repeat is NOT OK – must investigate/document/ repeat 5 times to

start routine testing. All repeats must be in controlstart routine testing. All repeats must be in control

Agar Disk Diffusion (Kirby Agar Disk Diffusion (Kirby Bauer) Bauer)

Qualitative Susceptibility method Qualitative Susceptibility method Mueller Hinton agar –with or without bloodMueller Hinton agar –with or without blood

◦ 150 mm plate diameter150 mm plate diameter◦ 4mm in depth4mm in depth◦ Agar specifically balanced in Ca+ and Mg+, Agar specifically balanced in Ca+ and Mg+,

◦ if the ions are too high % amino-glycosides test falsely resistant,if the ions are too high % amino-glycosides test falsely resistant,◦ if the ions too low % falsely susceptible amino-glycoside resultsif the ions too low % falsely susceptible amino-glycoside results

Streak bacteria on plate with cotton tipped swabStreak bacteria on plate with cotton tipped swab

Apply 6mm paper disks that contain single antibioticApply 6mm paper disks that contain single antibiotic Incubate for 16-24 hrs at 35*CIncubate for 16-24 hrs at 35*C Measure zone of diameter of inhibition of growth (mm)Measure zone of diameter of inhibition of growth (mm)

Kirby Bauer disk Dispenser

Each cartridge is a separate antibiotic

Growth inside a zone is consideredresistance

Measure the diameter of the zone of inhibition

Watch out for double zones

Proteus will swarmInto a zone

Kirby Bauer (KB)Kirby Bauer (KB) Theory: Concentration gradient created with the diffusing Theory: Concentration gradient created with the diffusing antibiotic and the increasing number of bacteria growing on antibiotic and the increasing number of bacteria growing on the agar, this determines the zone size of inhibition around the agar, this determines the zone size of inhibition around disk. disk.

CLSI charts used to interpret the measured zone sizes as CLSI charts used to interpret the measured zone sizes as Sensitive, Intermediate or ResistantSensitive, Intermediate or Resistant

Cannot directly compare zone sizes between antibiotics– Cannot directly compare zone sizes between antibiotics– ◦ ex: ZID of 21mm zone size is as sensitive as a GM of 14mm ex: ZID of 21mm zone size is as sensitive as a GM of 14mm

- zone sizes differ for organism/antibiotic combinations- zone sizes differ for organism/antibiotic combinations◦ Regression analysis can be used to calculate MIC value Regression analysis can be used to calculate MIC value

related to KB zone sizerelated to KB zone size

E TestE TestQuantitative MIC SusceptibilityQuantitative MIC Susceptibility

Calibrated plastic strips impregnated with one antibioticCalibrated plastic strips impregnated with one antibiotic◦ concentration gradient (mcg/ml) embedded in plasticconcentration gradient (mcg/ml) embedded in plastic

Diffusion gradient created as antibiotic diffuses into agar Diffusion gradient created as antibiotic diffuses into agar in an elliptical shapein an elliptical shape

MIC (minimum inhibitory concentration) is where the MIC (minimum inhibitory concentration) is where the ellipse ends on the plastic stripellipse ends on the plastic strip

Good method for slower growing fastidious organisms Good method for slower growing fastidious organisms

.

E Test method

E test method

Susceptibility result =Where growth crossesThe plastic strip

E test for Strep pneumoniae

Low concentration

High concentration

MIC value

MIC value

Penicillin

Cefotaxime

Broth DilutionBroth DilutionQuantitative Susceptibility MethodQuantitative Susceptibility Method

Bacteria inoculum: 0.5 McFarland standard – further diluted to 5x10Bacteria inoculum: 0.5 McFarland standard – further diluted to 5x105 5

organisms /ml organisms /ml in broth in broth Suspension is inoculated into tubes or micro titer trays containing Suspension is inoculated into tubes or micro titer trays containing growth medium and known 2 fold dilutions (mcg/ml) of antibioticsgrowth medium and known 2 fold dilutions (mcg/ml) of antibiotics

Each horizontal row is a uniqueEach horizontal row is a unique

antibiotic – growth causes antibiotic – growth causes

turbidity in the wellsturbidity in the wells Lowest dilution of antibioticLowest dilution of antibiotic

with No Growth (clear well)= with No Growth (clear well)=

MIC value.MIC value.

Broth Dilution DefinitionsBroth Dilution Definitions MIC MIC = lowest concentration of antibiotic inhibiting growth = lowest concentration of antibiotic inhibiting growth MBCMBC = lowest concentration of antibiotic killing 99.9% = lowest concentration of antibiotic killing 99.9%

Antibiotic toleranceAntibiotic tolerance – Ratio of MBC/MIC (>=32) – Ratio of MBC/MIC (>=32)◦ MBC = 16 MIC= 8 16/8= 2 MBC = 16 MIC= 8 16/8= 2 No ToleranceNo Tolerance◦ MBC = 128 MIC = 8MBC = 128 MIC = 8 128/2 = 64128/2 = 64 Tolerance*Tolerance*

◦ *This means bacteria will tolerate the antibiotic and not be killed*This means bacteria will tolerate the antibiotic and not be killed

Siemens Microscan walkawayAST system

BD Phoenix AST system

Biomerieux Vitek2 AST

Automated IdentificationSusceptibility Testing Systems (AST)

Disk test for Beta lactamase Disk test for Beta lactamase Detection (Cefinase Test)Detection (Cefinase Test)

Add bacteria to filter paper impregnated with NitrocefinAdd bacteria to filter paper impregnated with Nitrocefin (yellow colored/chromogenic cephalosporin substrate)(yellow colored/chromogenic cephalosporin substrate) Incubate at room temp (@ 1 minute) and observe Incubate at room temp (@ 1 minute) and observe

for color change from yellow to redfor color change from yellow to red Beta lactamase enzyme of bacteria breaks down the beta Beta lactamase enzyme of bacteria breaks down the beta lactam ring of Nitrocefin to produce a red end productlactam ring of Nitrocefin to produce a red end product Detects resistance to Ampicillin/Penicillin/1Detects resistance to Ampicillin/Penicillin/1stst gen Cephalosporin gen Cephalosporin in Haemophilus, N. gonorrhoea , Moraxella catarrhalis, in Haemophilus, N. gonorrhoea , Moraxella catarrhalis, Enterococcus, and anaerobic gram negative rodsEnterococcus, and anaerobic gram negative rods

This test does NOT detect Extended Spectrum Beta Lactamase This test does NOT detect Extended Spectrum Beta Lactamase enzyme produced by enteric gram negative rodsenzyme produced by enteric gram negative rods

Beta lactamase Beta lactamase detection tidbitsdetection tidbits Haemophilus influenzae Haemophilus influenzae

◦ In US, approx 28% are beta lactamase producers and therefore, In US, approx 28% are beta lactamase producers and therefore, resistant to Ampicillinresistant to Ampicillin

Bacteroides fragilis groupBacteroides fragilis group◦ Primary resistance mechanism is beta lactamase production Primary resistance mechanism is beta lactamase production

>95% of strains are resistant to Pencillin>95% of strains are resistant to Pencillin

Moraxella catarrhalisMoraxella catarrhalis◦ >90% beta lactamase positive /Ampicillin resistant>90% beta lactamase positive /Ampicillin resistant

Methicillin Resistant Staph Methicillin Resistant Staph aureus (MRSA)aureus (MRSA)

Test for oxacillin (OX) resistance - it is more stable for testing Test for oxacillin (OX) resistance - it is more stable for testing than methicillin in the laboratorythan methicillin in the laboratory

OLD OLD - If - If OX is resistantOX is resistant - S. aureus is reported as a MRSA - S. aureus is reported as a MRSA NEW - resistanceNEW - resistance testing for Cefoxitin is more reliable and a testing for Cefoxitin is more reliable and a preferred way to confirm MRSApreferred way to confirm MRSA

All cephalosporin antibiotics are reported resistant for MRSA All cephalosporin antibiotics are reported resistant for MRSA and should never be used for therapyand should never be used for therapy

Resistance mechanism by Resistance mechanism by penicillin binding proteins (PBPs)penicillin binding proteins (PBPs)◦ PBPs bind penicillin and related antibioticsPBPs bind penicillin and related antibiotics◦ The binding prevents disruption of the peptidoglycan synthesis in the The binding prevents disruption of the peptidoglycan synthesis in the

Staph aureus cell wallStaph aureus cell wall◦ PBPs are produced by the PBPs are produced by the mecA genemecA gene

Oxacillin KB disk = resistantMRSA

Cefoxitin KB disk Newer method –more sensitive screen for MRSACefoxitin (FOX) KB = sensitive S. aureus

Methods to Detect Methicillin and Oxacillin Resistance - MRSA

Oxacillin Testing is no longer the preferred method for detection

Clindamycin Induction Test Clindamycin Induction Test – – The D testThe D test

This test determines if Staph aureus, including MRSA, is This test determines if Staph aureus, including MRSA, is susceptible to Clindamycin more reliably than testing susceptible to Clindamycin more reliably than testing Clindamycin resistance by KB or MICClindamycin resistance by KB or MIC During antibiotic therapy, S aureus isolates resistant to During antibiotic therapy, S aureus isolates resistant to Erythromycin possess enzymes that can be induced to Erythromycin possess enzymes that can be induced to make the S. aureus also resistant to Clindamycinmake the S. aureus also resistant to Clindamycin Clindamycin is often used to treat serious soft tissue Clindamycin is often used to treat serious soft tissue infections with MRSA – so reliable testing necessaryinfections with MRSA – so reliable testing necessary

D test Negative- round Clindamycin zone

Kirby Bauer zone around Clindamycin will be Kirby Bauer zone around Clindamycin will be blunted to form a D if Clindamycin can be blunted to form a D if Clindamycin can be induced by Erythromycin to be resistant – so induced by Erythromycin to be resistant – so called INDUCIBLE RESISTANCE.called INDUCIBLE RESISTANCE. Clindamycin should be reported as resistant by Clindamycin should be reported as resistant by clindamycin induction and not used for therapyclindamycin induction and not used for therapy

The D Test

EnterococcusEnterococcus All are intrinsically resistant to:All are intrinsically resistant to:

◦ CephalosporinsCephalosporins◦ Clindamycin Clindamycin ◦ Trimethoprim/sulfamethoxazole Trimethoprim/sulfamethoxazole

Synergistic antibiotic therapy can be important for the Synergistic antibiotic therapy can be important for the treatment of Enterococcustreatment of Enterococcus◦ Ampicillin plus Gentamicin is synergistic = increased Ampicillin plus Gentamicin is synergistic = increased

killing potential in combination killing potential in combination ◦ Important for endocarditis therapy Important for endocarditis therapy

Vancomycin Resistant Vancomycin Resistant Enterococcus (VRE)Enterococcus (VRE) Acquired resistance to vancomycin –Acquired resistance to vancomycin –

◦ Plasmid mediated vanA associated with E. faecium Plasmid mediated vanA associated with E. faecium ◦ Plasmic mediated vanB associated with E. faecalis Plasmic mediated vanB associated with E. faecalis

Detected by KB, automated AST systems, and Etest methodsDetected by KB, automated AST systems, and Etest methods Drugs of choice limited if VRE detected – Drugs of choice limited if VRE detected –

◦ Linezolid Linezolid ◦ Synercid for E. faecium onlySynercid for E. faecium only

Major infection control issue!! Major infection control issue!! ◦ Rectal colonization can contaminatie the environment and Rectal colonization can contaminatie the environment and

lead to transmission to surrounding patientslead to transmission to surrounding patients◦ Most infections related to ICU stays and long Most infections related to ICU stays and long

hospitalizations hospitalizations ◦ Not virulent but problematic in immune suppressedNot virulent but problematic in immune suppressed

Extended Spectrum Beta Extended Spectrum Beta LactamaseLactamase[ESBL][ESBL] Enzymes produced by Enteric Gram negative bacilliEnzymes produced by Enteric Gram negative bacilli

◦ Confer resistance to Cephalosporins, Penicillins and Confer resistance to Cephalosporins, Penicillins and Monobactam (Aztreonam) by opening the beta lactam ring Monobactam (Aztreonam) by opening the beta lactam ring and inactivating the antibioticand inactivating the antibiotic

◦ ESBLs do not attack Cephamycin (cefoxitin, cefotetan) or the ESBLs do not attack Cephamycin (cefoxitin, cefotetan) or the Carbapenem antibiotic classesCarbapenem antibiotic classes

Plasmid mediated CTX-M beta lactamases are the most Plasmid mediated CTX-M beta lactamases are the most common in the US currently, but many more ESBL types common in the US currently, but many more ESBL types worldwide worldwide

Therapy for ESBL producing gram negative rods:Therapy for ESBL producing gram negative rods:◦ Carbapenems: Imipenem, Meropenem, Doripenem, Carbapenems: Imipenem, Meropenem, Doripenem,

ErtapenemErtapenem

ESBL Susceptibility ESBL Susceptibility PatternPattern Escherichia coli – ESBL CTX-M PositiveEscherichia coli – ESBL CTX-M Positive

◦ Ampicillin Ampicillin RR◦ Cefazolin Cefazolin RR◦ Gentamicin Gentamicin RR◦ Cefotetan Cefotetan S S (Cephamycins are not cephalosporins)(Cephamycins are not cephalosporins)◦ Cefotaxime Cefotaxime RR◦ Ceftazidime Ceftazidime RR◦ Cefpodoxime Cefpodoxime R R ◦ Piperacillin Piperacillin RR◦ Pip/Tazobactam SPip/Tazobactam S /R (?) /R (?) Tazobactam is a beta lactam blockerTazobactam is a beta lactam blocker◦ Imipenem Imipenem S S **(Carbapenem) – Antibiotic of choice**(Carbapenem) – Antibiotic of choice

Detecting ESBL in the laboratory

Standard of Practice:Standard of Practice:◦ CLSI established new Cephalosporin MIC and KB CLSI established new Cephalosporin MIC and KB

breakpoints to safely detect ESBL activitybreakpoints to safely detect ESBL activity◦ New MIC breakpoints are one to three doubling dilutions New MIC breakpoints are one to three doubling dilutions

lower than previously used and lower than previously used and ◦ New KB zones for susceptible are largerNew KB zones for susceptible are larger◦ These values were adjusted to aid laboratories in the These values were adjusted to aid laboratories in the

detection of ESBLdetection of ESBL

Molecular testing needed for confirmation of actual enzyme Molecular testing needed for confirmation of actual enzyme present (CTX-M)– beyond the scope of most clinical present (CTX-M)– beyond the scope of most clinical laboratorieslaboratories

Positive ESBL Double Disk TestPositive ESBL Double Disk Test*Older method for ESBL Detection*Older method for ESBL Detection – – observe action of the Beta lactam observe action of the Beta lactam enzyme blockerenzyme blocker

ResistantCefotaxime

ResistantCeftazidime

SusceptibleCeftazidime plusClavulanic acid (beta lactam blocker)

SusceptibleCefotaxime plusClavulanic acid (betaLactam blocker

Why all the fuss about ESBLs? GNRs with ESBL phenotypes >=10% in US and the numbers are increasing

Limited treatment options ◦ Carbapenems: meropenem, imipenem, ertapenem

Risk factors:◦ Long hospital stay – particularly in the ICU◦ Central lines◦ Issues with the intestine◦ Long term care facility◦ Ventilator assistance

Carbapenemases - CRE Carbapenem antibiotics currently have the highest spectrum of activity against multi-drug resistant GNRs

But the worst scenario has come true – Appearance of Carbapenem-hydrolyzing-beta-lactamases which confer resistance to a broad spectrum of beta lactam antibiotics – making GNR pan resistant

CRE – Carbapenemase Resistant Enteriobacteriaceae Two CREs are getting the most attention:

◦ KPC – “Klebsiella pneumoniae carbapenemas most common in the US◦ NDM-1 – New Delhi metallo-beta-lactamase has received much press.

Recognized in 2009. Resistance determinants are numerous and great concern about its spread.

Infections with CRE producing GNRs - 50% fatality rate

Most sensitive screen to detected CRE is an Ertapenem MIC test. However, all Carbapenem antibiotics will show elevated MICs in the resistance range.

Treatment of CRE:Polymyxins (Colistin and Polymyxin B) These antibiotics are +/- toxic and problematic for therapy.

Carbapenemase Resistant Enterics (CRE)Laboratory Testing

OLD Method to Detect OLD Method to Detect CRE/KPC/NDM-1CRE/KPC/NDM-1Modified Hodge Test Modified Hodge Test Observe growth on this plate:Background is lawn of E. coli.Patient GNR streaks hug the Imipenem disc in the center of the plate. (A, B, C , D and E)

A = Hodge Test PositiveTherefore, it is a CRE!Shoulder effect around streak of test organism (arrow)

Negative = “B”No shoulder effect, this organismis not a CRE

Lawn of E. coli

Streaks of patient GNR

Streptococcus pneumoniae Streptococcus pneumoniae and resistance to Penicillin and resistance to Penicillin (PEN)(PEN)

Two step resistance test – old wayTwo step resistance test – old way◦ Step 1Step 1 - - Oxacillin KB Oxacillin KB disk testing performeddisk testing performed◦ If resistant to Oxacillin, possible resistance to PENIf resistant to Oxacillin, possible resistance to PEN◦ Step 2Step 2 –Confirm PEN resistance by MIC test –Confirm PEN resistance by MIC test◦ MIC value determines susceptibility or resistanceMIC value determines susceptibility or resistance

Best method – Primary test is to perform a Penicillin MIC Best method – Primary test is to perform a Penicillin MIC test by E Test or broth dilutiontest by E Test or broth dilution

KB method cannot be used to test PEN against Strep KB method cannot be used to test PEN against Strep pneumoniae, under predicts resistancepneumoniae, under predicts resistance

Strep pneumoniae MIC Strep pneumoniae MIC valuesvalues

CLSI interpretation of AST dependent on the site of infectionCLSI interpretation of AST dependent on the site of infection◦ CSFCSF Blood/RespBlood/Resp◦ Sensitive <=0.06 mcg/mlSensitive <=0.06 mcg/ml <=2 mcg/ml<=2 mcg/ml◦ Intermediate 0.12 - 1 mcg/mlIntermediate 0.12 - 1 mcg/ml <=4<=4◦ Resistant Resistant >= 2 mcg/ml>= 2 mcg/ml >=8>=8

High level PEN resistance is <=10% in USHigh level PEN resistance is <=10% in US◦ If Pen resistant- antibiotics of choice become 3If Pen resistant- antibiotics of choice become 3rdrd gen gen

Cephalosporin, vancomycin or quinolone Cephalosporin, vancomycin or quinolone

Neisseria gonorrhoeae (GC)

Increasing resistance of GC over last two decades◦ 1980’s beta lactamase producing - Penicillin resistance◦ By 2000, the quinolones were resistant due to the acquisition of

mutations that altered the binding sites◦ Currently Cephalosporins (Ceftriaxone & Cefixime) are the

mainstay for therapy in the US – however resistance to these antibiotics are becoming common in Asia. ◦ Resistance due to Penicillin Binding Proteins (PBPs) and over production of

efflux pump◦ Detection of resistance in the USA could be problematic due to

our reliance on amplification testing for STD diagnosis that only test for GC and not for resistance markers