Outbreak of USA300-like MRSA colonization in a postpartum maternal and neonatal care center in Korea Misuk Ji 1*, Heungsup Sung 1, Ai-rhan Kim 2, Mi-Na Kim 1 1 Department of Laboratory Medicine and 2 Pediatrics, University of Ulsan College of Medicine and Asan Medical Center, Seoul, Korea

Background (1) USA300 CA-MRSA * clone (ST8) Widely disseminated within the United States Major pathogen causing skin and soft tissue infections in community settings Panton-Valentine leukocidin (PVL) toxin-positive Highly transmissible and virulent Continent-specific distribution In Korea, PVL-negative ST72 as the predominant CA-MRSA strain *Community-associated methicillin-resistant Staphylococcus aureus

Background (2) Two case reports of human infections caused by the USA300 in Korea Perianal abscess (2008) and pneumonia (2012), respectively Aim of the study To characterize PVL-positive MRSA isolates from surveillance cultures in a postpartum maternal and neonatal care center

Methods (1) From July to August 2011 Screening for MRSA colonization At 11 postpartum maternal and neonatal care centers in 11 regions of Korea: up to 20 neonates per center consecutively Collecting swab samples from the nares Transported to the laboratory in Tryptic Soy Broth containing 6.5% NaCl and 2 μg/mL of oxacillin Preincubated swabs subcultured on MRSASelect (Bio-Rad, USA)

Methods (2) Susceptibility testing For Presumptive MRSA colonies, identification and anti- microbial susceptibility testing were performed with MicroScan PBC28 panel (Siemens, USA) Detection of genes for virulence factors lukF-PV, lukS-PV (PVL) by PCR, eta, etb (exfoliative toxin) and tst (toxic shock syndrome toxin) by multiplex PCR Molecular characterizations SCCmec typing, agr typing, and pulsed-field gel electro- phoresis (PFGE) analysis, multilocus sequence typing (MLST)

Results (1) PVL-positive isolates identified from 15 newborns 15 out of 17 MRSA isolates in a single institution

Results (2) Cip, ciprofloxacin; Ery, erythromycin; Cli, clindamycin; Mup, mupirocin. Microbiological characteristics of 17 MRSA isolates from the single institution No. MLST sequence type PFGESCCmecagrPVLeta, etb, tst Resistant antimicrobials 1ST 8A0IV1+-Cip, Ery 2ST 8A0IV1+-Cip, Ery 3ST 8A0IV1+-Cip, Ery 4ST 8A0IV1+-Cip, Ery 5ST 8A0IV1+-Cip, Ery 6ST 8A0IV1+-Cip, Ery 7ST 8A0IV1+-Cip, Ery 8ST 8A0IV1+-Cip, Ery 9ST 8A0IV1+-Cip, Ery 10ST 8A0IV1+-Cip, Ery 11ST 8A0IV1+-Cip, Ery 12ST 8A0IV1+-Cip, Ery 13ST 8A0IV1+-Cip, Ery 14ST 8A0IV1+-Cip, Ery 15ST 8A0IV1+-Cip, Ery 16ST72A1IVA1--Cli I, Ery 17ST1A0IV1--Cip, Ery, Mup(I)

Results (3) PFGE patterns of PVL-positive MRSA isolates Same pulsotype (A0) Interpreted as the USA300 strain compared with USA300 image files The isolates seemed to be a USA300-like strain exhibiting PVL, ST8, and SCCmec IV PVL-negative MRSA isolate A1 : ST72 M * USA300 J Clin Microbiol. 2006;44(1): A1 A0

Results (4) Country (year)This studyKorea (2008)Korea (2012)Japan (2008)USA (2006) OriginCA-MRSA Age/Sexneonates76/F50/M3 mo/F- Infectioncolonizationperianal abscesspneumoniacervical abscess- Specimennasal swabdrained pus, bloodsputumdrained puswound or others Antimicrobial resistance Cip, EryEryCip, Ery, TetEry, Kan Ery (97%), Tet (17%), Lvx (16%) Comments postpartum maternal /neonatal care center suggested to be imported from Hawaii post-influenza suggested to be imported from California From the CDC strain collection (USA type strain) PVL+++++ Sequence typeST8 SCCmecIV IVA Comparison with other USA300 strains Cip, ciprofloxacin; Ery, erythromycin; Tet, tetracycline; Kan, kanamycin; Lvx, levofloxacin.

Conclusion The present study demonstrates the first clustering of USA300-like MRSA clone among the neonates in the community It was assumed that the cross-transmission of USA300-like MRSA would be the cause of that clustering within the institution, although index case was not found We need to pay attention to this issue, considering possibility of the spread of USA300 clone in Korea