Lecture 3 MRSA Methicillin resistant S. aureus Tues – 1/15/2008

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 Toxins: cytotoxins, superantigens, enterotoxins, TSST-1, exfoliative toxins, Panton-Valentine leukocidin Enzymes: protease, lipase, hyaluronidase

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 carriage

Risk groups with high carriage rates Diabetes Mellitus Dialysis patients HIV Chronic skin diseases IV Drug abusers Health care workers (?)

Antimicrobial resistance of S. aureus - history SA genome sequence, Kuroda ‘01 CA-MRSA sequence, Baba ‘02 Cloning of mecA Matsuhashi ‘86 SCCmec sequenced Ito ‘99 MRSA single clone theory Lacey & Grinsted, ‘73 1960 1970 1980 1990 2000 2003 1st MRSA isolate ‘61 1950 penicillinase found in E.coli (before use of penicillin) rapidly moved to S.aureus 59 introduction in Europe, 61 first MRSA in UK. 61 introduction in USa – FIRST mrsa in USA – 1968. 2004 – 60% of SA in ICU in USA = MRSA. Epidemic spread of MRSA, Europe, India, Australia, USA 2nd wave of epidemic MRSA (MDR), USA, Australia, Ireland Increasing reports - CA-MRSA Worldwide dissemination CA-MRSA in Australia Introduction of Methicillin – ‘59 1st VISA, Japan ‘97 1st VRSA, USA ‘02

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. capable of cell wall synthesis in absence of all other PBPs.

MRSA - mechanism of resistance Modifying enzymes Degrading enzymes Target Change Efflux pumps

Genetic Mechanisms Horizontal vs. Vertical transmission Mutation Plasmid transfer Transformation Large genetic mobile elements (cassettes)

MRSA – mechanism-II mecA is part of a large, mobile, genetic element – Staphylococcal cassette chromosome mec (SCCmec)

SCCmec cassette A unique class of mobile genetic element (21-67kb)  ccr complex (type2) Mec complex (class B) orfX IS 1272 mecR1 mecA IS431mec 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) Primary mode of spread – clonal expansion, but how is an MRSA strain “born”: Transduction by one of the many phages. It has been estimated that only 20 times did SA acquire SCCmec A unique class of mobile genetic element that Contains no phage-related genes, no transoposases. Origin of SCCmec - unknown, but they are disseminated widely among Staphylococcal strains. Location of integration site of SCCmec near the origin of replication Ccr complex enables movement of the cassette

The mec Complex S. aureus contains only class A & B.  ccr complex (type2) Mec complex (class B) orfX IS 1272 mecR1 mecA IS431mec S. aureus contains only class A & B. Class C mainly in S. haemolyticus Class D in S. hominis

    TypeI SCCmec (34kb) TypeII SCCmec (53kb) ccr complex (type 1) mec complex (class B) TypeI SCCmec (34kb) orfX mecR1  R-I ccrA1 ccrB1 mecA  IS1272 IS431mec TypeII SCCmec (53kb) mec complex (class A) ccr complex (type 2) orfX pUB110  ccrA2 ccrB2 Tn554 IS431mec  mecI mecR1 IS431mec mecA Type III SCCmec (67kb) mec complex (class A) ccr complex ccr complex (type3) orfX SCCmecI= Mec complex type B: mecI and 3’ region of mecR1 are deleted SCCmec2 & 3: mec Complex A ISI431 encode tobra Res Tn554 - encode Eryth R ŸTn544 cadium R ccrA3 Tn554 mecI mecA pT181 mer Tn554 ccrB3 mecR1 IS431mec IS431 IS431 ccr complex (type2) Mec complex (class B) orfX IS 1272 mecR1 mecA IS431mec Type IV SCCmec (24kb)  

Genetic organization of SCCmec type I-VI de Lencastre et al. 2007 SCCmecI= Mec complex type B: mecI and 3’ region of mecR1 are deleted SCCmec2 & 3: mec Complex A ISI431 encode tobra Res Tn554 - encode Eryth R ŸTn544 cadium R

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

Prevalence of MRSA in USA (cumulative data 1998-2005) / Shorr CID 2007 Ip – in patient Op - outpatient

MRSA among S. aureus isolates in Europe

MRSA – a nosocomial pathogen Until ~1996

CA-MRSA – an emerging infection JAMA 1998 CID 2004 EID 2003

CA-MRSA: 1996-2008 Changing 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

Community acquired MRSA (CA-MRSA)/ Weber. CID 2005

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.

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:… (closely related genetically strains)

Antibiotic consumption and MRSA, an ecologic study (EID 2004)

Changing Epidemiology of MRSA / Crum et al. Am. J. Med 2006

CA-MRSA infections in Texas (2002-2004) / Kaplan et al. CID 2005

MRSA in the Netherlands 76 isolates randomly picked. SCCmec in 46. Most are CA-MRSA – emerging! HA-MRSA – most from abroad.

How did CA-MRSA evolve? Recent evolution of CA-MRSA from common MSSA? “Hospital escape” of unsuccessful HA-MRSA

SCCmec Type IV = “Mobile mec”  ccr complex (type2) Mec complex (class B) orfX IS 1272 mecR1 mecA IS431mec 24kb Small Size Novel SCCmec type Smaller – more efficient horizontal transfer

Resistance and virulence US300 Major CA-MRSA clones in US: US300 & US400 US300 – the most common single clone of CA-MRSA SCCmec IV Resistant to ciprofloxacin (mutation in gyrA) Many strains acquired MDR by plasmides (tetK, erm ) Several mobile genetic elements Several Toxins

Resistance and virulence Panton Valentine leukocidine A pore forming cytotoxin Strains containing pvl genes were associated with severe SST – infections Direct role of pvl – still controversial

ACME – arc gene cluster Complete genome sequence of US300 / Diep et al ACME – arc gene cluster Complete genome sequence of US300 / Diep et al. Lancet 2006 Arginine Catabolic Mobile Element: virulence/strain survival factor Different from native arc gene carried by all S. aureus Highly similar to ACME from S. epidermidis Arginine deiminase pathway Inhibits the nitric oxide production Allows survival in low ph, anaerobic conditions Enhances fitness: enhances potential to grow and survive within a host

ACME (Arginine Catabolic Mobile Element) – arc gene cluster

ACME positive isolates in UK / Ellington et al. JAC 2008 ST8 (US300) ST8 ACME neg ST97

How do we control MRSA? Hospitals: Community: Infection control!!! Antibiotic control?? Community: ?????

Treatment of MRSA CA-MRSA Clindamycin ?? TMP-SMX? Rifampin? Vancomycin (high ery-R suggests inducible clinda-R) TMP-SMX? Rifampin? Vancomycin HA-MRSA Vancomycin Linezolid Daptomycin Daptomycin – cyclic lipopeptide Oxazolidinone – linezolid (zyvox) 2000 approved, 2001 first case of resistance