Antibiotic Antibiotic Sensitivity Sensitivity

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

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 leads to inactivation of antibioticEnzymatic cleavage leads to inactivation of antibiotic Beta lactam and aminoglycoside antibioticsBeta lactam and aminoglycoside antibiotics Active Beta lactamases and amino-glycoside modifying Active Beta lactamases and amino-glycoside modifying

enzymes enzymes Altered receptors/binding proteins preventing Altered receptors/binding proteins preventing

attachment of antibiotics to the bacterial surfaceattachment of antibiotics to the bacterial surface Altered Penicillin binding proteins Altered Penicillin binding proteins Strep pneumonia resistance to penicillinStrep pneumonia resistance to penicillin MRSA resistance to methicillinMRSA resistance to methicillin

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

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

The Rules for The Rules for Susceptibility TestingSusceptibility Testing

1. CLSI – Clinical Laboratory Standards 1. CLSI – Clinical Laboratory Standards Institute Approved standards for the Institute Approved standards for the testing & reporting of susceptibility testing & reporting of susceptibility results/ updated yearlyresults/ 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 QC standards and proper testing

proceduresprocedures

2. Susceptibility Tests are tests of 2. Susceptibility Tests are tests of bacterial stasis – not killingbacterial stasis – not killing

Methods/Bacteria in Methods/Bacteria in ReviewReview

METHODSMETHODS1. Kirby Bauer disk diffusion1. Kirby Bauer disk diffusion2. E Test Strip Minimum inhibitory concentration (MIC )2. E Test Strip Minimum inhibitory concentration (MIC )3. Broth dilution Minimum inhibitory concentration 3. Broth dilution Minimum inhibitory concentration (MIC)(MIC)4. Beta lactamase enzyme detection4. Beta lactamase enzyme detection

RESISTANT BACTERIA IN THE NEWSRESISTANT BACTERIA IN THE NEWS 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 KPC KPC Klebsiella pneumonia Carbapenemase or CRE Klebsiella pneumonia Carbapenemase or CRE

(Carbapenamase Resistant Enterics)(Carbapenamase Resistant Enterics) Streptococcus pneumoniaStreptococcus pneumonia Neisseria gonorrhoeaeNeisseria gonorrhoeae

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

MethodsMethodsRequires pure culture of one organism onlyRequires pure culture of one organism only Log phase growth of bacteria - 16-24 hrs oldLog phase growth of bacteria - 16-24 hrs old Standardized suspension of bacteria must be Standardized suspension of bacteria must be

prepared using: prepared using: O.5 McFarland Standard – Barium sulfate solution O.5 McFarland Standard – Barium sulfate solution

that equals the turbidity of @ 10 8 bacteria/mlthat equals the turbidity of @ 10 8 bacteria/ml Alternative method – use spectrophotometer Alternative method – use spectrophotometer

Incubation of tests are at 35 *C in room air Incubation of tests are at 35 *C in room air (some require CO2) for 18- 24 hrs(some require 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 Control for all Quality Control for all methodsmethodsBefore you can test patients: Must test multiple QC strains for Before you can test patients: Must test multiple QC strains for

20 consecutive days or 3 replicates for 5 days plan. This is to 20 consecutive days or 3 replicates for 5 days plan. This is to make sure you can perform the tests correctly.make sure you can perform the tests correctly.

The QC values must be within CLSI established limits using The QC values must be within CLSI established limits using ATCC strains of organisms (American Type Culture ATCC strains of organisms (American Type Culture Collection) If QC strains are within limits - you can then do Collection) If QC strains are within limits - you can then do Weekly quality control on all lots of cards, disks, plates in useWeekly quality control on all lots of cards, disks, plates in use Data must be recorded and reviewed monthly by Data must be recorded and reviewed monthly by

supervisorsupervisor 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 If repeat is NOT OK – must investigate/document/ repeat 5

times to start routine testing. All repeats must be in times to start routine testing. All repeats must be in controlcontrol

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

Procedure: Qualitative Susceptibility method Procedure: 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 Streak bacteria on plate with cotton tipped swabswab

Apply 6mm paper disks that contains single Apply 6mm paper disks that contains single antibioticantibiotic

Incubate for 16-24 hrs at 35*CIncubate for 16-24 hrs at 35*C Measure zone of diameter of inhibition of growth Measure zone of diameter of inhibition of growth

(mm)(mm)

Kirby Bauer disk DispenserEach Cartridge is a separate antibiotic

Kirby Bauer Disk Diffusion

Measure diameter in mm– across center of theDisk – for each antibiotic disk

Colonies growing into zones is considered Resistant to that antibiotic

Growth inside a zone is considered

resistance

Measure diameter of the Zone of inhibition in mm

Double zoning - measure the inside zoneWatch out! The sensi could Be mixed – NEVER read a mixed sensi!

Proteus swarms into zone and is not considered as resistant

Kirby Bauer (KB)Kirby Bauer (KB) Concentration gradient created with the Concentration gradient created with the

diffusing antibiotic and the increasing number diffusing antibiotic and the increasing number of bacteria growing on the agar, this of bacteria growing on the agar, this determines the zone of inhibition around disk. determines the zone of inhibition around disk.

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

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

of 14mm - zone sizes differ for organism/antibiotic of 14mm - zone sizes differ for organism/antibiotic combinationscombinations

Regression analysis can be used to calculate MIC Regression analysis can be used to calculate MIC value related to KB zone sizevalue related to KB zone size

E TestE TestQuantitative MIC SusceptibilityQuantitative MIC Susceptibility

Calibrated plastic strips impregnated with Calibrated plastic strips impregnated with one antibiotic/concentration gradient one antibiotic/concentration gradient (mcg/ml) embedded in plastic / carefully (mcg/ml) embedded in plastic / carefully placed on the agar surfaceplaced on the agar surface

Gradient created as antibiotic diffuses into Gradient created as antibiotic diffuses into agar in an elliptical shapeagar in an elliptical shape

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

Useful for any organism but a method of Useful for any organism but a method of choice for slow growing fastidious organisms choice for slow growing fastidious organisms

E Test method

E test method

Susceptibility result =Where growth crossesThe plastic strip

E test for Strep pneumonia susceptibility

Low concentration

High concentration

MIC value

MIC value

Broth DilutionBroth DilutionQuantitative Susceptibility MethodQuantitative Susceptibility Method

Bacteria inoculum: 0.5 McFarland Bacteria inoculum: 0.5 McFarland standard – further diluted to 5x10standard – further diluted to 5x105 5

organisms /ml organisms /ml in broth in broth Suspension is inoculated into tubes Suspension is inoculated into tubes

or micro titer trays containing or micro titer trays containing growth medium and known 2 fold growth medium and known 2 fold dilutions (mcg/ml) of antibioticsdilutions (mcg/ml) of antibiotics

Doubling dilution MIC TrayEach row has one antibiotic in >= 4 dilutions

Broth Dilution Broth Dilution DefinitionsDefinitions

MIC MIC = lowest concentration of antibiotic inhibiting = lowest concentration of antibiotic inhibiting growthgrowth 2 fold dilutions: 2 fold dilutions: 1 2 41 2 4 88 16 32 64 128 mcg/ml 16 32 64 128 mcg/ml GrowthGrowth No growth No growth MIC = 8 mcg/mlMIC = 8 mcg/ml

MBCMBC - Minimum - Minimum bactericidalbactericidal concentration determined concentration determined by the subculture of the contents of the wells that show no by the subculture of the contents of the wells that show no growth to solid agar - the lowest concentration of growth to solid agar - the lowest concentration of antibiotic that kills 99.9% of original inoculum is the MBC.antibiotic that kills 99.9% of original inoculum is the MBC. 8 168 16 3232 64 128 64 128 32mcg/ml = MBC32mcg/ml = MBC Growth Growth No Growth No Growth

Antibiotic toleranceAntibiotic tolerance - MBC/MIC ratio >=32 - MBC/MIC ratio >=32 MBC = 128 MIC= 2 128/2= 64 MBC = 128 MIC= 2 128/2= 64 ToleranceTolerance

Siemens Microscan walkawayAST system

BD Phoenix AST system

Biomerieux Vitek2 AST

Disk test for Beta Disk test for Beta lactamase Detection lactamase Detection

(Cefinase Test)(Cefinase Test) Add bacteria to filter paper impregnated with Add bacteria to filter paper impregnated with NitrocefinNitrocefin

(yellow colored/chromogenic cephalosporin)(yellow colored/chromogenic cephalosporin) Incubate at room temp (@ 1 minute) and observe for Incubate at room temp (@ 1 minute) and observe for

color change from yellow to redcolor change from yellow to red

Positive result is color changePositive result is color change to red to red – – Bacteria beta lactamase enzyme breaks down the beta lactam ring of Bacteria beta lactamase enzyme breaks down the beta lactam ring of

Nitocefin to produce a red end productNitocefin to produce a red end product Detects resistance to Detects resistance to

Ampicillin/Penicillin/Cephalosporins in Haemophilus, Ampicillin/Penicillin/Cephalosporins in Haemophilus, Neisseria gonorrhoea , Moraxella catarrhalis, Neisseria gonorrhoea , Moraxella catarrhalis, Enterococcus, and anaerobic gram negative rodsEnterococcus, and anaerobic gram negative rods

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

Beta lactamase detection Beta lactamase detection tidbitstidbits

Haemophilus influenza Haemophilus influenza In US, approx 28% are beta lactamase In US, approx 28% are beta lactamase

producers therefore, resistant to Ampicillinproducers therefore, resistant to Ampicillin Bacteroides fragilis groupBacteroides fragilis group

Primary resistance mechanism is beta Primary resistance mechanism is beta lactamase production –lactamase production –

>95% of strains are resistant to Pencillin>95% of strains are resistant to Pencillin Moraxella catarrhalisMoraxella catarrhalis

>90% beta lactamase positive /Ampicillin >90% beta lactamase positive /Ampicillin resistantresistant

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

In the laboratory you test oxacillin (OX) because it is In the laboratory you test oxacillin (OX) because it is more stable for testing than methicillin more stable for testing than methicillin

If If OX is resistantOX is resistant the S. aureus is reported as a MRSA the S. aureus is reported as a MRSA Cefoxitin resistanceCefoxitin resistance testing is also a very reliable and testing is also a very reliable and

a preferred way to confirm a S. aureus to be a MRSAa preferred way to confirm a S. aureus to be a MRSA All cephalosporin antibiotics are reported as resistant All cephalosporin antibiotics are reported as resistant

when reporting results for MRSA and should never be when reporting results for MRSA and should never be used for therapyused for therapy

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

in the Staph aureus cell wallin the Staph aureus cell wall PBP are produced by the PBP are produced by the mecA genemecA gene

Oxacillin KB= resistant

Newer and moresensitive method to screen for MRSA is using a Cefoxitin KB to determine Methicillin resistance

Methods to Detect Methicillin and Oxacillin Resistance

Oxacillin is no longersuggested by CLSI for detecting MRSA

Clindamycin Induction Clindamycin Induction TestTest

Also known as the D testAlso known as the D test This test accurately determines if Staph aureus, This test accurately determines if Staph aureus,

including MRSA, is susceptible to Clindamycinincluding MRSA, is susceptible to Clindamycin During antibiotic therapy, S aureus isolates During antibiotic therapy, S aureus isolates

resistant to Erythromycin possess enzymes that resistant to Erythromycin possess enzymes that can be induced to make the S. aureus also can be induced to make the S. aureus also resistant to Clindamycinresistant to Clindamycin

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. Clindamycin called INDUCIBLE RESISTANCE. Clindamycin should be reported as resistant by clindamycin should be reported as resistant by clindamycin induction and not used for therapy. Clinda is induction and not used for therapy. Clinda is often used to treat skin infections.often used to treat skin infections.

D test PositiveBlunt D shaped CC zoneClindamycin has inducible resistanceD test Negative

Round CC zone

EnterococcusEnterococcus All naturally resistant to:All naturally resistant to:

CephalosporinsCephalosporins Clindamycin Clindamycin Trimethoprim/sulfamethoxazole Trimethoprim/sulfamethoxazole

Synergistic antibiotic therapy can be important Synergistic antibiotic therapy can be important for the treatment of Enterococcusfor the treatment of Enterococcus Ampicillin plus Gentamicin is synergistic and Ampicillin plus Gentamicin is synergistic and

often used to increase the killing potential often used to increase the killing potential 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 associtated with E. faecium Plasmid mediated vanA associtated with E. faecium Plasmic mediated vanB associated with E. faecalis Plasmic mediated vanB associated with E. faecalis

Not difficult to detect – vancomycin resistance easily Not difficult to detect – vancomycin resistance easily detected by KB, automated AST systems, and Etest detected by KB, automated AST systems, and Etest methodsmethods

Drugs of choice if VRE detected – Drugs of choice if VRE detected – Linezolid Linezolid Synercid for E. faecium onlySynercid for E. faecium only

Major epidemiology issues!! Major epidemiology issues!! Rectal colonization can contaminatie the environment Rectal colonization can contaminatie the environment

and lead to transmission to patientsand lead to transmission to 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 that are produced by Gram negative bacteriaEnzymes that are produced by Gram negative bacteria

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 inactivating the antibioticinactivating the antibiotic

Cannot attack cephamycins (cefoxitin, cefotetan) or the Cannot attack cephamycins (cefoxitin, cefotetan) or the carbapenems (imipenem, meropenem, ertapenem, doripenem)carbapenems (imipenem, meropenem, ertapenem, doripenem)

Generally susceptible to beta-lactamase inhibitors (tazobactam)Generally susceptible to beta-lactamase inhibitors (tazobactam) Plasmid mediated TEM, SHV, CTX-M beta lactamases Plasmid mediated TEM, SHV, CTX-M beta lactamases

are the most commonare the most common Therapy for ESBL producing gram negative rods:Therapy for ESBL producing gram negative rods:

Carbapenems: Imipenem, Meropenem, Doripenem, ErtapenemCarbapenems: Imipenem, Meropenem, Doripenem, Ertapenem Piperacillin/Tazobactam – Tazobactam blocks beta lactamase Piperacillin/Tazobactam – Tazobactam blocks beta lactamase

actionaction

ESBL Susceptibility ESBL Susceptibility PatternPattern

Escherichia coli – ESBL PositiveEscherichia coli – ESBL Positive Ampicillin Ampicillin RR Cefazolin Cefazolin RR Gentamicin Gentamicin RR Cefotetan Cefotetan S S (Cephamycins are not (Cephamycins are not

cephalosporins)cephalosporins) Cefotaxime Cefotaxime RR Ceftazidime Ceftazidime RR Cefpodoxime Cefpodoxime R R Piperacillin Piperacillin RR Pip/Tazobactam SPip/Tazobactam S (Tazobactam is a beta (Tazobactam is a beta

lactam blocker)lactam blocker) Imipenem Imipenem S S (Carbapenem)(Carbapenem)

Detecting ESBL in the laboratory

Suggested method:Suggested method: Cephalosporin MIC values and KB zone sizes Cephalosporin MIC values and KB zone sizes

established by CLSI to safely detect ESBL established by CLSI to safely detect ESBL activityactivity

New breakpoints are one to three doubling New breakpoints are one to three doubling dilutions lower than breakpoints and KB zones dilutions lower than breakpoints and KB zones for susceptible that were used for decadesfor susceptible that were used for decades

These values were lowered to aid laboratories These values were lowered to aid laboratories in the correct detection of ESBLin the correct detection of ESBL

Molecular testing needed for confirmation Molecular testing needed for confirmation – beyond the scope of most clinical – beyond the scope of most clinical laboratorieslaboratories

The OLD method to detect ESBL

[double disk test] Test the susceptibility of a GNR

against a cephalosporin Compare this zone size (KB) or the

MIC value with the same GNR tested against the cephalosporin plus clavulanic acid (a beta lactam blocker)

If the zone size or MIC is considerably smaller with the cephalosporin alone, you have evidence for ESBL production by the GNR being tested

Positive ESBL Double Positive ESBL Double Disk TestDisk Test

ResistantCefotaxime

ResistantCeftazidime

SusceptibleCeftazidime plusClavulinic acid

SusceptibleCefotaxime plusClavulinic acid

Why all the fuss? Gram neg rods with ESBL phenotypes

>=10% Left with limited treatment options

/Carbapenems such as Imipenem Risk factors for development of

colonization or infection Long hospital stay – particularly in the ICU Central lines Issues with the intestine Long term care facility Ventilator assistance

Carbapenemases Carbapenem antibiotics have an important role – they

retain therapeutic activity against resistant ESBL gram negative rods

When carbapenem antibiotics are also inactivated – headed toward extreme resistance

Carbapenem-hydrolyzing-beta-lactamases confer resistance to a broad spectrum of beta lactamase substrates including carbapenems (CRE – Carbapenemase Resistant Enterics)

Two CRE are getting the most attention: KPC – Klebsiella pneumoniae carbapenemase is the most

common in the USA NDM-1 – New Delhi metallo-beta-lactamase has received

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

Carbapenemase producing GNR

Risk Factors Acquisition of genes from other bacteria while

on very broad spectrum antimicrobial therapy Severe illness Mechanical ventilation Organ transplantation Medical care in India or Pakistan (NDM-1) Can carry as normal intestinal flora

(colonization) Fatality rates in infections can reach 50%

Most sensitive screen and the first Carbapenem to show subtle resistance by increase in MIC value is Ertapenem. However. most Carbapenems will show elevated MICs in the resistance range.

This class can be difficult to detect. MIC values can be at the “breakpoint” for resistance

Polymyxins (Colistin and Polymyxin B) used for therapy. This class is 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-1

Modified Hodge Test Modified Hodge Test Observe growth on this plate:Background is lawn of E. coliTest GNR streaks hug the Imipenem disc in the middle of the plate. (A, B, C , D and E)

Hodge Test Positive = “A”CRE positiveShoulder effect around streak of test organism

Negative = “B”No shoulder effect

Lawn of E. coli

Streaks of test GNR

Streptococcus pneumonia Streptococcus pneumonia and resistance to Penicillin and resistance to Penicillin

(PEN)(PEN) Two step resistance testing can be usedTwo step resistance testing can be used

Step 1Step 1 - - Oxacillin KB Oxacillin KB disk testingdisk testing If resistant to Oxacillin possible resistance to If resistant to Oxacillin possible resistance to

PENPEN Step 2Step 2 -Must confirm PEN resistance by MIC -Must confirm PEN resistance by MIC

test methodtest method MIC value determines susceptibility or MIC value determines susceptibility or

resistanceresistance Best most direct method one step- Perform Best most direct method one step- Perform

a Penicillin MIC test by E Test or broth a Penicillin MIC test by E Test or broth dilutiondilution

[cannot use KB to test Penicillin][cannot use KB to test Penicillin]

Strep pneumonia MIC Strep pneumonia MIC valuesvalues

Penicillin MIC values – CLSI has set Penicillin MIC values – CLSI has set interpretation depending on site of interpretation depending on site of infectioninfection 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 High level PEN resistance is uncommon, usually <= 10%uncommon, usually <= 10% If resistant to Penicillin antibiotics of If resistant to Penicillin antibiotics of

choice become Cefotaxime, vancomycin or a choice become Cefotaxime, vancomycin or a quinolone quinolone

Neisseria gonorrhoeae (GC)

Increasing resistance of GC over last two decades 1980’s beta lactamase producing strains emerged

eliminating Penicillin for therapy 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 (PBP) 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