BJ NewcomerResident Seminar

July 7, 2011

Brief history of MRSA Index case Characterization of LA-MRSA MRSA ST398

• Pigs• Cattle• Foodstuffs• Zoonotic potential www.ashleyhardin.wordpress.com

Gram (+), A-T rich cocci Coagulase positive Most important human Staph. species 1 of 3 major veterinary Staph.

pathogens• Cellulitis• Osteomyelitis• Pododermatitis• MASTITIS

www.randstarteam.blogspot.com

MRSA contains mecA which conveys methicillin resistance

mecA encodes for penicillin-binding protein (PBP2a)

PBPs normally present in membrane

PBP2a decreasedaffinity for β-lactams

Penicillin binding protein

Nestorovich E M et al. PNAS 2002;99:9789-9794

First isolated in UK hospital 1961 1970 – Emerged in U.S. Most prevalent nosocomial infection

• Hospital-acquired MRSA (HA-MRSA) In 2005: 278,000 cases

• ~95,000 serious infections• ~20,000 deaths

www.freewebs.com

Most early HA-MRSA belonged to only 5 CC’s

Possessed larger SCCmec types (I-III)• Afford resistance to most clinically available abx

Risk factors• Prolonged abx therapy• Prolonged hospitalization• ICU care• Surgical procedures

Common cause of:• Wound dehiscence• Thrombophlebitis• UTI’s

www.brettwilliams.wordpress.com

Mid 1990’s MRSA infections increasingly documented in non-hospitalized patients• Community-acquired MRSA

(CA-MRSA) Most possess smaller

SCCmec types (IV, V)• Greater suscept. to common

abx Distinct genetic lineage

from HA-MRSA Certain strains toxigenic

• Panton-Valentine leukocidin (PVL)

• Phenol-soluble modulin (PSM)

1972 – MRSA first isolated from livestock• Mastitic cow in Belgium• Concluded isolate was of human origin

1990’s - increased isolation from companion animals• Coincided with increase of CA-MRSA

www.webweaver.nu

July 2004: MRSA cultured from routine pre-op screening in 6 month old girl • No history of traveling, hospital admission

Repeated decolonization attempts unsuccessful

Parents subsequently found to be colonized

Voss, A, et al. Emerg Infect Dis. 2005 Dec;11(12):1965-6.

www.flickr.com

Family lived on farm and raised pigs Nov 2004 – pigs tested

• Initially, nares of 10 pigs cultured - All MRSA negative

• Subsequently, 30 perineal cultures- 1 MRSA positive culture

Identical strain in pigs, child, and parents

www.clker.com/clipart-29067.htmlVoss, A, et al. Emerg Infect Dis.

2005 Dec;11(12):1965-6.

Jan 2005 – 2nd pig farmer found colonized• Different region

Feb 2005 – Son of swine veterinarian colonized

Admitted to hospital, nurse colonized Veterinarian colonized

No clinical signswww.stealstreet.com

Regional farmer’s meeting

26 pig farmers screened – throat and nares

6/26 (23%) MRSA colonized

Frequency >760x higher than Dutch population

www.cutcaster.comVoss, A, et al. Emerg Infect Dis.

2005 Dec;11(12):1965-6.

Pulsed-field gel electrophoresis (PFGE)• Digestion with restriction endonuclease

(SmaI)• Separation of DNA fragments by electric

pulses• Current gold standard

Pulsed-field gel electrophoresis (PFGE)• Digestion with restriction endonuclease

(SmaI)• Separation of DNA fragments by electric

pulses• Current gold standard

www.bio.davidson.edu/courses/genomics/method/pulse_field.html

Multi-locus sequence typing (MLST)• Sequencing of 7 housekeeping genes• Grouped into clonal complexes (CC)

spa-typing – Staphylococcal protein A gene (spa)• Profile of repeats within gene

SCCmec typing• mec complex – contains mecA gene• ccr complex – responsible for mobility

Non-typeable by standard PFGE Almost all strains in CC398 (ST398) General absence of PVL and other

virulence factors Virulence/resistance obtained through

mobile genetic elements (MGE’s)• Staphylococcal chromosomal cassette (SCC)• Plasmids via bacteriophages (transduction)

Conjugative plasmids, transformation, transposons and staphylococcal pathogenicity islands (SaPIs) uncommon

Five SCCmec types based on differences in mecA and ccrC genes

www.staphylococcus.net

Types I-III often larger, common in HA-MRSA

Types IV, V more common in CA-MRSA

Type IV predominates in human medicine

MRSA ST398: type Vwww.staphylococcus.net

 

38 kb type V SCCmec mecA – confers methicillin resistance The ccrC gene encodes recombinase

• Relatively stable

Schijffelen et al. BMC Genomics 2010, 11:376

GENE FUNCTION/PHENOTYPE

ampA Apramycin resistance

blaZ β-lactam resistance

cfr multiple-antibiotic resistance

copA copper resistance

dfrG trimethoprim resistance

dfrK trimethoprim resistance

erm (A) macrolide/lincosamide resistance

erm(C) macrolide/lincosamide resistance

erm(B) macrolide/lincosamide resistance

erm(T) macrolide/lincosamide resistance

fexAchloramphenicol/florfenicol

resistance

mecA methicillin resistance

tet(K) tetracycline resistance

tet(L) tetracycline resistance

tet(M) tetracycline resistance

vga(A) virginiamycin resistance

vga(C) virginiamycin resistance

Plasmids form accessory genome

Convey resistance or virulence

Lacking from most MRSA ST398 isolates

Multiple-abx resistance• Tetracyclines – always• Macrolides,

lincosamides, etc• +/- fluoroquinolones

Predominant MRSA strain in swine• Other recent reports limited to human strains

Most reports from Europe• The Netherlands• Germany• Belgium

Limited reports elsewhere

• Canada• Singapore• USA

www.netherlands.world-guides.com

Carriage rates vary considerably• 10% in Denmark (n=100)• 24.9% in Canada (n=285)• ~40% in The Netherlands, Germany

Farm prevalence• 66% in Denmark (n=3)• 45% in Canada (n=20)• 68% in Belgium (n=50)

Study differences• 81% vs 23% MRSA (+) farms in The Netherlands

www.prlog.org

Survey of 2 production systems in IA, IL• Comprise ~90,000 animals

Nasal swabs from 299 swine, 20 workers MRSA prevalence

• 49% in swine (147/299)• 45% in workers (9/20)

MRSA (+) only on Farm A• 70% in swine (147/209)• 64% in workers (9/14)

Smith, TC, et al, PLoS One. 2009;4(1):e4258www.needalittleadvice.com

Isolates tested by PFGE• Non-typeable by smaI, typeable by EagI

MLST revealed clonal isolates• Not related to common IA isolates• MRSA ST398

Isolates PVL negative Workers and swine apparently unaffected

www.thepigpage.com

Early Belgian study (Willems, 2007) : • risk for piglets > sows or fattening pigs

Canadian study (Weese, et al, 2009) :• Low prevalence in piglets (<10%)• Prevalence peaked at 64% (42 d)• Dropped to 41% at study end (70 d)

Other studies show no effect

www.thisisstaffordshire.co.uk

Similar results in USA study

Smith, TC, et al, PLoS One. 2009;4(1):e4258

LA-MRSA first detected in mastitic milk Few published reports of MRSA (+)

cattle• MRSA (+) milk/nasal swab samples in France (Alves, et al., 2009)

MRSA ST398 found in mastitic milk in S. Korea (Lee 2006, Moon 2007)

• Quarter level prevalence very low (<0.2%)

www.farmville.wikia.com

MRSA ST398 never detected in US milk 357 isolates of S. aureus from 24 NC

dairy herds (Anderson, et al., 2006)

• No MRSA isolates Comprehensive study by NAHMS 2009 (Virgin, et al., 2009)

542 bulk milk tank samples (17 states)

• No MRSA

www.scientificamerican.com

Due to elaboration of enterotoxins• Symptoms generally mild• Often undiagnosed

One report of MRSA food poisoning (Jones, et al., 2002)

• Contaminated coleslaw• Isolate from hospital origin

No reports of LA-MRSA food intoxication

www.mylot.com

MRSA ST398 never detected in US food

Spain survey (Lozano,

et al., 2009):• 318 raw meat

samples• Chicken, pork, veal,

lamb, poultry, rabbit, game

• 2 MRSA ST398 (+) samples: pork and veal www.venere.com

Dutch survey (de Boer, et al., 2009):• 2217 raw meat samples• beef, pork, veal, lamb/mutton, chicken,

turkey, fowl and game • Incidence highest in poultry and veal• Also found in turkey, lamb and sheep meat

www.thefreedictionary.com

Apparent capacity to transfer with close animal contact• Especially swine workers

Also demonstrated in veal farming• Lone report of LA-MRSA carriage

Unknown mechanism No increased risk for dairy/beef farmers

www.Ft.com

Pig health conference in Denmark Nasal/throat swab from 272

registrants 34 (12.5%) MRSA (+) from 9

countries• 31/34 MRSA ST398

Wulf, et al., Clin Microbiol Infect. 2008 Jan;14(1):29-34

www.bacontoday.com

Survey of US Veterinary Teaching Hosp.

70 S. aureus isolates, 9/70 MRSA 9 (+)’s: 4 EQ, 4 CN, 1 FE No MRSA ST398

Prevalent colonizer of swine • Less common in other livestock

Poor host specificity• Capable of transfer to humans• Higher prevalence in livestock workers

Reports of associated disease rare Potential to acquire virulence or resistance factors

www.clker.com

Veterinary University of Austria• 140 swabs of wounds/incisions • 25 (+) MRSA, 7 MRSA ST398• All contracted after admission

Faculty of Vet Medicine, Ghent University• 110 horses screened• 12 (+) MRSA ST398• 1 infected wound

www.itstrulyrandom.com

Cultured from foot ulcer (The Netherlands 2008)• 5 other patients

colonized• No pig or cattle

contact 3687 MRSA isolates

– Canadian D-labs (2010)• 5 MRSA ST398

samples• No livestock contact

12 yr old Spanish girl• Skin lesion (2010)• Near pig farm• 2 types isolated

Croatian pig farmer bitten on arm (2008)• Complicated soft

tissue infection

www.northernvirginiamag.com