Seminar 4

MRSAMethicillin resistant S. aureus

Mon – 4/30/2012

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Outlines • Introduction • Abbreviation • The basic Biology of Staphylococcus aureus• History of MRSA• Molecular basis for virulence factors and resistance• Epidemiology• Clinical Manifestations • Laboratory Diagnosis• Treatment• prevention and control

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Abbreviations/Definitions• MRSA = methicillin resistant Staphylococcus aureus• MSSA = methicillin sensitive S. aureus• HA = healthcare associated• CA = community associated• Colonization = organism is on or in the body but not

causing disease– 30% of people are carriers of MSSA– 1.5% of people are carriers of MRSA

• Infection = organism is present and causing signs and symptoms of disease

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S. aureus – the pathogen

• Microbiology – Gr+ cocci with many virulent factors (toxins and enzymes)

• Frequent nosocomial- and community-acquired pathogen

• Mode of transmission – contact

• Clinical manifestations:– Skin and soft tissue infections– Pneumonia– Osteomyelitis / Arthritis– Bacteremia / Sepsis – Endocarditis– Toxin-mediated disease: TSS, Food

poisining

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Summary of Virulence Determinants Of Staphylococcus aureus

• http://textbookofbacteriology.net/staph.html

http://textbookofbacteriology.net/http://textbookofbacteriology.net/staph.htmlstaph.html

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What Is MRSA?

• MRSA is “Methicillin Resistant S. aureus• Is a bacteria that is resistant to a synthetic penicillin-

methicillin. • MRSA causes a variety of disseminated, lethal infections

in humans.• Has the ability to easily transfer resistant genes to other

species directly and indirectly• Overuse of antibiotics imposes selective pressures which

mediates the acquisition of resistance

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Microbiology of MRSA

• Caused by changes in penicillin binding proteins

• Generally resistant to all B-lactam antibiotics• May be resistant to TMP/Sulfa, Tetracyclines,

Quinolones• Vancomycin resistance has been reported

(VISA, GISA)

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How “Tough” is MRSA?

• Staphylococci can survive many extreme environmental conditions.

• The bacteria can be cultured from dried clinical material after several months, are relatively heat resistant, and can tolerate high salt media.

So, “What Do we Do?”• You can not get rid of MRSA; you can only control

it.

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Risk factors for MRSA

CA-MRSA

• Skin, soft tissue infection

• ???

HA-MRSA

• Previous contact with health care system

• Longer hospitalization• ICU admission or

invasive procedures• Ab Rx.

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CA-MRSA: 1996-2008Changing definitions

• No contact with health-care facilities in prior 6-12 m.– Maybe more than 1y.

• Resistant only to b-lactams, but not to other classes.– Resistant to quinolones, macrolides and

others

• SCCmec IV– and V … and VI…

X X

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How is MRSA spread?1. Direct contact with infected or colonized host

-human-to-human contact2. Contaminated intermediate surfaces

-hand towels-faucets-tub/shower

3. Airborne fluid droplets

How did CA-MRSA evolve?•Recent evolution of CA-MRSA from common MSSA?

•“Hospital escape” of unsuccessful HA-MRSA

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MRSA – a nosocomial pathogenUntil ~1996

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Pets’/Animals’ Roles in MRSA Transmission

• In several studies, it has been found that farm owners, veterinary clinicians, and pet owners are at greater risk for MRSA infection

• In particular, there have been documented MRSA transmission to humans from:– Dogs– Cats– Horses– Pigs

• It is often noted that animals, especially pets, can serve as “reservoirs of infection”

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Antimicrobial resistance of S. aureus - history

200320001990198019701960

Introduction of Methicillin – ‘59

Epidemic spread of MRSA, Europe, India, Australia, USA

MRSA single clone theory Lacey & Grinsted, ‘73

Cloning of mecA

Matsuhashi ‘86

SCCmec sequenced Ito ‘99

1st MRSA isolate ‘61

2nd wave of epidemic MRSA (MDR), USA,

Australia, Ireland

Worldwide dissemination

Increasing reports - CA-MRSA

1st VISA, Japan ‘97 1st VRSA, USA ‘02

SA genome sequence, Kuroda ‘01

CA-MRSA sequence, Baba ‘02

CA-MRSA in Australia

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S. aureus Nasal ColonizationNational Health and Nutrition Examination Survey 2001-02

0

5

10

15

20

25

30

35

40

45

50

1--5 6--11 12--19 20--29 30--39 40--49 50--59 60--69 70+

Age (years)

Pre

va

len

ce

(%

)

Male

Female

S. aureus: 32.4% = 89.4 M people

MRSA: 0.8% = 2.3 M people

MRSA colonization associated with age >= 60 years & being female04/10/23 15

Prevalence of MRSA 2006

Grundmann, Lancet 2006

Transformation

Plasmidtransfer

Genetic Mechanisms Horizontal vs. Vertical transmission

Mutation

Large genetic mobile elements (cassettes)04/10/23 17

Horizontal Gene Transfer-Another Mechanism For Resistance

http://www.bioteach.ubc.ca/Biodiversity/http://www.bioteach.ubc.ca/Biodiversity/AttackOfTheSuperbugsAttackOfTheSuperbugs

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MRSA – mechanism – I

• Horizontally transferred DNA element - SCCmec.

• Site specific recombination.

• mecA gene encodes PBP2a.

• PBP2a = 78 KDa PBP - capable of cell wall synthesis.

• PBP2a has low affinity for all -lactams.

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MRSA - mechanism of resistance

1. Modifying enzymes

2. Degrading enzymes

3. Target Change

4. Efflux pumps

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MRSA – mechanism-II

• mecA is part of a large, mobile, genetic element – Staphylococcal cassette chromosome mec (SCCmec)

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SCCmec cassette

• A unique class of mobile genetic element (21-67kb) • Resembles a pathogenicity island, but with no virulence

genes.• Ccr complex: ccrA & ccrB encode recombinase A & B enable

SCCmec to integrate into the chromosome in correct orientation.

• Mec complex: encodes β-lactam resistance and its inducible regulation + transposons + integrated copies of plasmids that carry various resistance genes (non-b-lactam)

ccr complex (type2)Mec complex (class B)

orfX

IS 1272mecR1

mecA IS431mec

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Origin of SCCmec and the mec gene

• Single clonal origin theory• Hiramatsu et al. 1996: Clonal diversity: different

strains developed independently

• Origin of mecA gene - horizontal transfer from:– SCN – S. scuiri– Enterococcus hiriae

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Clonal spread of MRSA

• Spread is mainly clonal. Only few clones are the cause of most infections.

• Major cause for clonal spread: lapses in IC

• Yet - role of Ab pressure:…

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mecA gene carried on SCCmecMSSA acquired the mecA gene

encodes a PBP with low affinity for penicillin (PBP2a)

Carried on a large chromosomal element (SCCmec)

Integrates into chromsome in orfX site specific int

mecA (complex A, B and C)

20 kb-60kb

ccr recombinase genes (allotypes A, B, C and complex 1,2,3,4,5,)

orfX

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Currently identified SCC mec types in S. aureus strains

SCCmec types ccr gene complexes mec gene complexes strains

I 1 (A1B1)* B NCTC10442, COL

II 2 (A2B2) A N315, Mu50, Mu3, MRSA252, JH1, JH9

III 3 (A3B3) A 85/2082

IV 2 (A2B2) B

CA05, MW2, 8/6-3P, 81/108, 2314, cm11, JCSC4469, M03-68, E-MRSA-15, JCSC6668, JCSC6670

V 5 (C1) C2 WIS(WBG8318), TSGH17, PM1,

VI 4 (A4B4) B HDE288

VII 5 (C1) C1 JCSC6082

VIII 4 (A4B4) A C10682, BK20781

IX 1(A1B1) C2 JCSC6943

X 7(A1B6) C1 JCSC6945

XI 8(A1B3) E LGA25104/10/23 26

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http://www.sccmec.org/Pages/SCC_ClassificationEN.html

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One last Mechanism

• MRSA has shown variability in its resistance to erythromycin by two mechanisms, one of which can be transferred to clindamycin.

• 1. Efflux pump - encoded by msrA gene; confers resistance of e-mycin, but not clindamycin

• 2. erm gene - erythromycin ribosomal methylase; mutation to clinda resistance may develop during clinda therapy

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S. aureus - Epidemiology

• Epidemiologic niche: – Nasal carriage (anterior nares)– GI tract (rectal)– Perineal– Throat

• Nasal carriage – 30% of adults– 20% Persistant carriers– 60% Transient carriers– 20% Never carriers

• Nosocomial transmission – transient hand carriage04/10/23 30

Frequency of Staphylococcus aureus colonization in carriers on various body sites

Nose 100%

Skin chest 45%

Perineum 60%Ankle 10%

Axilla 19%

Hand 90%

Forearm 45%

Dancer S. Importance of environment in Methicillin Resistant Staphylococcus aureus acquisition: the case for hospital cleaning Lancet 07:70241-4

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Intracellular Persistence

• MRSA may survive within host cells such as phagocytes. May be found in chronic infections such as osteomyelitis, prosthetic joints, and skin infections.

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Predisposing Factors Of Susceptibility

• Integument injury• Burns and trauma• Foreign objects• A history of chronic Infections• Hormonal changes and stress• Immunocompromised

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Risk groups with high carriage rates

• Diabetes Mellitus• Dialysis patients• HIV• Chronic skin diseases• IV Drug abusers• Health care workers (?)

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Who Is At Risk? – 5”C”

• The 5 C’s– Crowding– Contact (frequent)– Compromised skin– Contaminated surfaces and shared items– Cleanliness or lack of

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Contaminated Surfacesand Shared Items

Frequent Contact

Cleanliness

Crowding

Compromised Skin

Factors that Facilitate Transmission

Antimicrobial Use

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Laboratory Diagnosis And Susceptibility Testing Of

Methicillin-Resistant Staphylococcus aureus (M.R.S.A.)

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Conventional approaches for:o Identification of S.aureus

o Routine microscopy, culturing & susceptibility testing

o Slide coagulase testo Tube coagulase testo Latex agglutination tests o DNase and heat-stable nuclease tests o Commercial biochemical tests o Molecular tests

o Methicillin/oxacillin susceptibility testing

o Dilution methods (MICs) o Breakpoint methods o Disc diffusion o Agar screening methodo E-test method (Diffusion & dilution)

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Detection of MRSA in screening samples

Conventional approaches

Solid agar media e.g (MSA), contains

o An indicator to distinguish S. aureus

o Inhibitory substanceso NaCl, ciprofloxacin, polymyxin-B, aztreonam

o And methicillin, oxacillin or,more recently, cefoxitin to select methicillin-resistant strains

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Enrichment

Enrichment broths have commonly been used to increase the sensitivity of screening by allowing small numbers of MRSA to grow during overnight incubation before subculture on a screening agar medium.

Enrichment media generally contain additional NaCl and may also contain methicillin, oxacillin or, more recently, cefoxitin to add selectivity

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Culture Detection of MRSA

• Clinical and Laboratory Standards Institute (CLSI) recommends:– Cefoxitin disk screen test– Latex agglutination test for PBP2a

– 6 ug/ml oxacillin in Mueller-Hinton agar with 4% NaCl

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D-zone test for Inducible Clindamycin Resistance

CCE

-Perform on erythromycin-resistant, clindamycin-susceptible S. aureus isolates-Clinical implications unclear, but treatment failures have occurred-Does not require pre-treatment or co-treatment with erythromycin in vivo

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erm gene Detection

• The D test - place a pair of erythromycin and clindamycin disks on a plated dish.

• Flattening of the clindamycin zone confers a positive test, i.e. inducible clinda resistance

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Molecular Identification and Strain Typing of MRSA

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Typing Techniques1. Plasmid Profile Analysis

– Several limitations2. Enzymatic Restriction (REA)

– Difficult (RFLP)3. Hybridisation with a Nucleic Acid Probe (Southern Blotting)

– Ribotyping yields good reproducibility and discriminatory power for epidemiological characterizations of MRSA

4. Pulsed-Field Gel Electrophoresis (PFGE) ex; ( SmaI-PFGE)– The discriminatory power is equal to or superior to phenotypic techniques as well as to genotypic

techniques such as ribotyping, RAPD, PCR-RFLP and inter-IS 256 PCR – has been sug-gested to be a gold standard for typing of MRSA

5. Polymerase Chain Reaction (PCR)– SCCmec typing– Spa typing– RAPD (Random Amplified Polymorphic DNA)

• discriminatory power will still remain poor– Repetitive Palindromic Extragenic Elements PCR (Rep-PCR) high discriminatory power

6. Multilocus Sequence Typing (MLST)

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Advantages of MRSA PCR

• Rapid Identification of carriers– 2 hours PCR– 24-72 hours Culture

• Swift implementation of appropriate interventions• Limits unnecessary preemptive isolation• Limits unnecessary antibiotic use• Identifies MRSA in mixed populations

– Methicillin resistant coagulase negative Staph– mecA negative Staph

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Molecular methods

• To detect genes which identify strains as S. aureus – (nuclease (nuc), coagulase (coa), protein A (spa), femA

and fem B and mecA)

• Generally only applicable to identification of purified cultures of staphylococci, and therefore they should not be used directly on samples.

• Most molecular methods for identification of S. aureus have been PCR based.

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Why Utilize Molecular Testing?

• Rapid diagnosis• Cost effective• Highly specific• Improved patient care• Provides ultimate resolution• No outside interference from medication or

treatments can alter the testing results

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MRSA PCR Procedure

• Specimen preparation• Concentration• Lysis-DNA extraction• Reconstitution of molecular reagents• Real-time PCR• Automated results• Full run time < 2 hours

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MRSA PCR vs. CultureMethod Sensitivity % Specificity %

Culture 78-80% 99%

PCR 93% 96%

PPV: 94%

NPV: 98%

Detection limit: 325 MRSA per swab

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MRSA Strain Typing

• MRSA is a clonal organism• Very useful for epidemiology

– Strain types between patients– Monitor trends in types– Track seasonal outbreaks– Database of samples for long term studies

• Trace infection source– Patient-Patient / Patient-Caregiver

• Determine if HA or CA MRSA

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Resolution of Typing Methods

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Pulsed Field Gel Electrophoresis

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PFGE Results

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Approach to Laboratory identification of MRSA• Sensitivity Testing:

a) Conventional methods

b) Automated systems

c) Quenching fluorescence method • Serological Identification• Genotyping Identification (Molecular method)• Direct identification of MRSA in blood cultures • Identification of MRSA in endotracheal aspirates and other

clinical samples

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Dilution methods

Broth micro dilution:o No single set of test conditions is suitable for detection of all resistant

strains.

o The CLSI(NCCLS)method :

o The CLSI method, which requires the use of MH broth with 2% NaCl, an inoculum of 5 x105 cfu/mL and incubation at 33–35°C for 24 h, is the only defined method

o Tray should include

o a growth control (no antimicrobial agent), o a sterility control (not inoculated at all) & +ve controlo positive MRSA control strain = Staph.aureus NCTC 6571

o An oxacillin MIC of ≤ 2 μg /ml indicates that the strain is susceptible and

> 2 μg /ml resistant.

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Interpretive Criteria (in μg /ml) for Oxacillin MIC Tests

Susceptible Intermediate Resistant

S. aureus ≤ 2.0 μg /ml N/A ≥ 4.o μg /ml

CoNS ≤ 0.25 μg /ml N/A ≥ 0.5 μg /ml

N/A = not applicable

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• BSAC method:

o M-H agar or Columbia agar with 4% NaCl

o CLSI (NCCLS) only M-H agar with 2 % NaCl

o Spot inoculum of 104 cfu/mL

o Sensitivity at 24 hrs incubation is variable, 48hrs incubation often required for an

o acceptable result.o The BSAC requires incubation at 30°C, while

the NCCLS requires 33–35°C.

o An oxacillin MIC of ≤ 2 μg /ml indicates that the strain is susceptible and > 2 μg /ml resistant.

o In the BSAC method a methicillin MIC of o ≤ 4μg /ml indicates that the strain is susceptible

and > 4μg /ml resistant,

Agar dilution MethodAgar dilution Method

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Breakpoint methods

Breakpoint methods include both agar and broth methods

Similar to dilution MIC methods but test only the breakpoint concentration (2 ug /ml oxacillin, 4 ug /ml methicillin)

The breakpoints for S. aureus are different from those for coagulase-negative staphylococci (CoNS).

Susceptibility and resistance breakpoints

Methicillin : ≤ 4 and ≥ 16 ug /ml Oxacillin & nafcillin: ≤2 and ≥ 8 ug /ml

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Disc diffusion

• Breakpoint methods include both agar and broth methods and are essentially similar to dilution MIC methods but test only the break point concentration

o Tests batteries : o 1µg oxacillin disk o 5µg methicillin disk

o “Cefoxitin” (30ug) disc diffusion tests are more reliable than those with oxacillin.

o No special medium or incubation temperature is required. o Many different combinations of conditions have been recommended for

disc diffusion.

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Discs tests for methicillin Resistance

Solid agar Media: • Iso-sensitest agar with the ‘1st line’ set of antibiotics, including

5ug methicillin disc. 30°C incubation for a full 24 hrs.• Use M-H agar at 35°C for 24 hrs. some batches of MH not

perform reliably ( Qc with control strains)• Use M-H or Columbia agar added with 5% NaCl. Incubate at

35°C for 40hrs.• Use IST agar with a final salt conc. of 4%. Incubate at 30°C for

18-24 hrs. • Run a quality control batch with known sensitive & resistant

strains.

Ref : Mackie & McCartney 4th edition

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Disc diffusion cont….

Interpretation:

o Most true methicillin-/oxacillin-resistant isolates give no zone. ( Homo-resistance)

o Sometime isolates give borderline suscp (small zones) due to hyper-production of B-lactamase resulting in inactivation of oxacillin. (sometimes give no zone and will therefore be falsely reported as MRSA.)

o Heterogeneously resistant to penicillinase-stable penicillins,

o Only 1 daughter cell out of 104 to 106 cells appears phenotypically resistant by routine antimicrobial susceptibility tests.

o For this reason, methicillin or oxacillin resistance is not detected well by some susceptibility testing systems.

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N/A = not applicable

Interpretive Criteria (in mm) for Cefoxitin Disk Diffusion Test

Susceptible* † Resistant

S. aureus ≥ 20 mm   ≤ 19 mm

CoNS ≥ 25 mm   ≤ 24 mm † There is no intermediate category with the cefoxitin disk diffusion test

Interpretive Criteria (in mm) for Oxacillin Disk Diffusion Tests

Susceptible Intermediate Resistant

S. aureus ≥ 13 mm 11-12 mm ≤ 10 mm

CoNS ≥ 18 mm N/A

≤ 17mm

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Left plate : A methicillin (oxacillin)-susceptible S. aureus (zone of inhibition within susceptibility range)

Right plate : A methicillin (oxacillin)-resistant S. aureus (zone of inhibition is less than the susceptibility range)

Although the zone of inhibition is at the borderline for resistance (12 mm); the presence of small colonies within the zone of inhibition (yellow arrows) indicates the presence of heteroresistant strains. The interpretation here, therefore, is "methicillin-resistant" staphylococci

????

M-H agar plate

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Chromogenic agar medias Recently developed chrom agars with cefoxitin as a selective

agent.

o MRSA Select CHROMagar MRSAo MRSA ID Bio-Connectionso Bio-Rad BioMerieux

Ciprofloxacin-resistant MRSA medium

This medium shows improved specificity when compared with traditional media. Sensitivity is also improved but requires 48hrs incubation to achieve >85%.

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MRSA on MRSA ID medium MRSA grow as distinct denim blue colonies(Oxoid Chromogenic MRSA Agar).

CHROMagar™ Staph aureus

•S.aureus –• mauve

• Other bacteria –• blue, colorless or inhibited

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Agar screening method o The method recommended by the CLSI requires

suspending the test organism to the density of a 0.5 McFarland standard (1.5x108) and inoculating an M-H agar containing 4% NaCl and 6 µg/ml oxacillin or10 µg/ml methicillin

o Inoculum preparation :o Overnight cultures on blood agar and turbidity

adjusted to be equivalent to that of a 0.5 McFarland std (108 cfu/mL) in tryptone Soya broth.

o The Inoculum is spotted on Plates incubated at 35°C for 24 h (additional 24 h if no growth)

o Any growth other than a single colony is indicative of resistance.

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Enrichment• Enrichment of screening swabs is more sensitive than direct

plating and may be particularly useful for screening in some high-risk groups of patients.

• Enrichment media generally contain additional NaCl and may also contain methicillin, oxacillin & recently cefoxitin.

• Broth bases used have included nutrient broth, tryptone Soya broth, MH broth, BHI broth and Robertson's cooked meat medium.

• Indicator-enrichment media (broth containing carbohydrate, indicator and antibiotics) may be useful in providing an indication of the presence of MRSA after overnight incubation.

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MIC by E-test method

• It gives an MIC result and is affected by test conditions in a similar way to other MIC and diffusion methods

• It requires MH agar with 2% NaCl • An inoculum density equivalent to 0.5–1.0 McFarland standards,

application of inoculum with a swab & incubation at 35°C for 24 h. • The Etest has an advantage over other MIC methods in that it is as

easy to set up as a disc diffusion test.

– MRSA the oxacillin MIC is ≥ 16 ug/ml – MSSA isolates the MIC is ≤ 1 ug /ml– Cefoxitin Etest MICs for mec A-positive strains are ≥ 16 ug/ml , while

cefoxitin Etest MICs for mec A-negative strains are ≤ 4 ug/ml

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Automated Methods

Automated systems commonly used in North America.

Vitek/Vitek2 (BioMérieux) Phoenix (Becton Dickinson) & Baxter Microscan (Dade Behring)

All systems include methods based on the principle of micro broth dilution tests for methicillin/oxacillin susceptibility and are generally reported to be reliable for S. aureus although a small number of incorrect results, mostly false resistance, have been reported.

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Quenching fluorescence method

With the Crystal MRSA method (Becton Dickinson) inhibition of growth of an isolate by oxacillin is indicated by the quenching of fluorescence of an oxygen-sensitive fluorescent indicator by oxygen remaining in the broth.

In the presence of an actively metabolizing organism oxygen is consumed, which allows the fluorescence to be observed under a UV light source.

The method is reasonably reliable but requires several hours of incubation i.e. 4 hrs @ 35°C.

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Serological Identification

Latex agglutination: Commercially available as a kit from several suppliers

Principle:o Based on detection of PBP2a o Extraction of PBP2a from suspensions of colonies & detection of the

protein by agglutination with latex particles coated with monoclonal antibodies to PBP2a.

o Isolates producing small amounts of PBP2a may give weak agglutination reactions or agglutinate slowly.

o Reactions tend to be stronger if PBPa production is induced by growth of MRSA in the presence of a penicillin.

o Rare isolates may give negative reactions.

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Molecular Methods

• Resistance to penicillinase-resistant penicillin is generally related to the presence of the “mecA gene”.

A. Nucleic acid hybridization

• Earliest Molecular Probe Methods: – P.F.G.E.– Radiolabelled (P32, I125) OR – Digoxigenin (DIG)-labelled DNA probes

B. Amplification Methods:

• PCR Assays: • Real-Time PCR -Addition of single set of Primers. • Gold standard method• Determine staphylococcal chromosomal cassette carrying the mecA

methicillin-resistant gene (SCCmec) type•

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Multiplex PCR and gel electrophoresis for identifying the mecA gene in Staph. species. Two distinct polymerase chain reactions are performed: one amplifies a portion of the 16S ribosomal RNA gene unique to Staphylococcus species, and the second amplifies a segment of the mecA gene. Lane 1: a strain of methicillin-resistant S. aureus is identified; electrophoretic bands of appropriate size appear for the 16S ribosomal DNA (rDNA) and mecA. Lane 2: a methicillin- susceptible S. aureus is identified; an electrophoretic band for 16S ribosomal DNA is present, but there is no band for mecA. Lane 3: is a negative control (reagents only), and Lane 4: contains DNA fragment standards. Bp =base pair.

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Direct identification of MRSA in blood cultures

Branched DNA Method: • A commercially available non-PCR-based method (Chiron

Diagnostics, East Wampole)• Detecting the mecA gene directly from blood cultures containing

Staphylococcus species.• Amplification of a signal & not target nucleic acid. • Signal generation is proportional to the amount of mecA gene

sequences in the sample, which in turn is proportional to the number of staphylococcal cells used in the assay.

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DNA is released from staphylococcal cells and hybridized to both capture probes and target probes. bDNA molecules (amplifiers) are then hybridized to target probes. Enzyme-labeled probes are subsequently hybridized to the bDNA amplifier. A chemiluminescent substrate dioxetane is added, and emitted light is measured.

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Identification of MRSA in endotracheal aspirates and other clinical samples

• Rapid and specific detection of MRSA colonization of the upper and lower respiratory tract is of particular importance for critically ill mechanically-ventilated patients in intensive care units.

• A 6 h multiplex PCR procedure (targeting the femA and mecA genes) has been used successfully to identify MRSA in endotracheal aspirates from mechanically-ventilated patients

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Clinical Manifestations of MRSA Infection

1. A localized, superficial abscess or – Skin/soft tissue infection– Pneumonia

1. Invasion of lymphatic, blood, and major organs– Endocarditis– Bone infection

– bloodstream infections

– pneumonia

– meningitis

– toxic shock syndrome

– surgical wound infection

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How do MRSA infections present?

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Superficial Infections

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Scalded Skin Syndrome: Classic Toxic Shock

www.aafp.org/afp/ 20000815/804.htmlwww.aafp.org/afp/ 20000815/804.html

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Systemic S aureus In the Lower spine

» .

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Systemic Menstrual Toxic Shock By MRSA

• Most major organs fail with disseminated MRSA (TSS-1)

www.web.net/terrafemme/ cashnightmare.htm 04/10/23 88

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Approach to Therapy

• Principles of management:• Obtain specimens for culture of all skin

infections

• Drain purulent collections and provide thorough wound care

• Know the organism resistance patterns for the community

• Make reliable plans for reassessment

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Approach to Therapy

• Selecting antibiotic therapy:• Is the infection suspected to severe or non

severe?

• What can I empirically treat with until I have culture-proven MRSA?

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Approach to Treatment

• Empiric treatment of non-severe illness (outpatient tx):

• dicloxacillin, cephalexin, augmentin or clindamycin• bactrim - avoid if suspecting skin infection by other

pathogens, specifically group A Streptococcus

• Culture-proven MRSA:• Clindamycin if D-test is negative, bactrim, minocycline

and linezolid

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Biotechnology: Current Drug Treatments For MRSA

• MRSA Drugs of Choice: • Linezolid-Protein synthesis inhibitor Daptomycin-

Causes membrane depolarization in bacteria-so no membrane transport

• Vancomycin-Acts by interfering with the construction of cell wall. Still works well with other antibiotics

• Alternatives: Synercid, Rifampin• Third-Line agents: TMP-SMX (Sulfa)

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Biotechnology: Drugs In Development

• Oritavancin-Binds to normal cell wall precursors

• Tigecyclin-Works on efflux pumps• Dalbavancin- Bacteriacidal

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Biotechnology: A Novel Vaccination For S. aureus

• Development of StaphVAX®, a polysaccharide conjugate vaccine against S. aureus infections

• The results of the phase 3 clinical trials of the vaccine (Staph VAX) will be presented 2006 according to the NIH.

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Prevention and Control in Hospitals

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Standard precautions

• Hand hygiene

• PPE

• Laundry/linen

• Waste disposal

• Cleaning/disinfection

• Respiratory hygiene/cough etiquette

• Safe injection practices

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Prevention

• Draining infections must be kept covered

• Talk to your physician about wound management techniques

• Wash hands frequently with soap and water

• Avoid sharing personal items• Wipe objects down with alcohol.• Advise health care workers to wash their

hands before touching you or your hospital equipment

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Prevention

• 57% of patients receive inappropriate antiobiotic treatment of the index MRSA infection

• “Good judgment comes from experience, and a lot of that comes from bad judgment.”

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Prevention

• Surveillance cultures• Barrier precautions• Hand washing• Single bed facilities• Isolation of infected

patients

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How do we control MRSA?

• Hospitals: – Infection control!!!– Antibiotic control??

• Community:– ?????

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Inappropriate Use of Antibiotics

• Encourage over growth of resistant organisms – now have access to nutrients and space

• MRSA infections associated with B-lactam and quinolones allow rapid proliferation of an organism that may have been merely colonizing

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Changes In Practice

• Must rein in use of antibiotics • 55% of all RX for URI in US unnecessary• Avoid broad spectrum antibiotics• How long to treat?• Decrease antibiotic use in agricultural

industry.

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Control of MRSA in hospitals

1. Isolate patient who is colonized or infected in a private room. Cohort if no private room available

2. Contact precautions: wear gown, gloves upon entry to the room.

3. Hand Hygiene

4. Dedicated equipment, decontamination of environment

5. Screening for carriage: not universal

6. Decolonization with mupirocin, chlorhexidine wash: uncommon

7. Use Device bundles: CVC bundles, pneumonia bundle

8. Leadership and organizational culture.

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LONG TERM CARELONG TERM CARECommunityCommunity

Colonized/infected patients“RESERVOIR”

Susceptible patients

Antibiotic pressure

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Transmission in Healthcare

• Patients colonized and infected with MRSA are the reservoir

• Transmitted from one patient to another via HANDS of healthcare worker (HCW) due to transient colonization

• Contaminated environmental surfaces also source of transmission but less important than hands of HCW

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Clinical cultures focus here MRSA infected

We continue to ignore a major source of the problem

MRSA colonized

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That’s All Folks!! Any Questions????

Staph cells attaching photo courtesy of Dr. Sharon Staph cells attaching photo courtesy of Dr. Sharon Peacock- University of OxfordPeacock- University of Oxford

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References

• 1 Mitchell, David.MRSA.”what’s New”. Inoculum. Volume 8, number 2 (1999) 1-12.• 2 textbookofbacteriology.net/resantimicrobial.html• 3 healthsciences.columbia.edu/ dept/ps/2007/mid/2006/transcript_02_mid22.pdf • 4 http://www.bioteach.ubc.ca/Biodiversity/AttackOfTheSuperbugs• 5. Foster, Timothy. The staphylococcus aureus “superbug”.J. clin Ivestigation• Volume number114 (2004) 1693-1696.• 6. www.channing.harvard.edu/4a.htm• 7. ww.ncbi.nlm.nih.gov.• 8. www.aafp.org/afp/ 20000815/804.html• 9. Journal of Clinical Microbiology, June 2000, p. 2378-2380, Vol. 38, No. 6

0095-1137/04.00+0• 10. www.FDA.com (FDA archives)• 11.www.postgradmed.com/issues/2001/10_01/hoel.htm

12. www.cdc.gov/ncidod/hip/aresist/mrsa_CDCactions.htm• 13. www.medscape.com• 14 http://www.nabi.com/images/factsheets/fsStaphVAX.pdf

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MRSA Infection Control Strategies

• contact precautions• screening• decolonization

The End