Emerg Infect DisEIDEmerging Infectious Diseases1080-60401080-6059Centers for Disease Control and Prevention19116081266068207-164710.3201/eid1501.071647Letters to the EditorSCCmec Typing in Methicillin-Resistant Staphylococcus aureus Strains of Animal OriginSCCmec Typing in MRSA Strains of Animal OriginJansenMarc D.BoxAdrienne T.A.FluitAd C.University Medical Center Utrecht, Utrecht, the NetherlandsAddress for correspondence: Ad C. Fluit, Department of Medical Microbiology, Rm G04.614, University Medical Center Utrecht, PO Box 85500, Utrecht 3508 GA, the Netherlands; email: a.c.fluit@umcutrecht.nl12009151136137van LooI , HuijsdensX , TiemersmaE , de NeelingA , van de Sande-BruinsmaN , BeaujeanD , Emergence of methicillin-resistant Staphylococcus aureus of animal origin in humans.Emerg Infect Dis. 2007;13:1834–9.18258032Keywords: Staphylococcus aureusSCCmecanimalletterTo the Editor

Van Loo et al. described the presence of staphylococcal cassette chromosome mec (SCCmec) type III in some methicillin-resistant Staphylococcus aureus sequence type (ST) 398 isolates related to pig farming (1). SCCmec types are based on the allotype of ccr genes and the mec gene complex. Class A mec has intact mecI/R regulator genes. Type III SCCmec has type 3 ccr genes and class A mec complex, whereas type V SCCmec contains ccrC and class C mec (2,3). The authors typed SCCmec of the isolates by the method of Zhang et al. (4), in which type III is defined by amplification of a 280-bp fragment located in the junkyard region. This fragment is found in SCCmer that is associated with SCCmec type III.

We have typed SCCmec of the same 4 isolates that were reported to be SCCmec type III positive by using the primer sets defined by Ito et al. (2,3) and Lim et al. (5) for ccr types 1–3 and ccrC and 4 additional primers developed at our institute (Table) in single PCRs. All ST398 isolates were PCR negative when primers specific for SCCmec type III were used, but PCR positive with the ccrC-specific primers. DNA sequencing confirmed the product as ccrC. Further, the isolates did not have a class A mec complex, a requisite for SCCmec type III, because a mecI-specific PCR was negative for these isolates. In addition, Southern hybridizations with digoxigenin-dUTP–labeled PCR fragments obtained with our primer pair specific for ccr3 and primers for ccrC (3) showed no hybridization with the ccrA/B3 probe (except for the positive control). All of the ST398 isolates hybridized with the ccrC-specific probe.

Primers used to type SCC<italic>mec</italic> of MRSA ST398 isolates*
GenesPrimer namePrimer sequence (5′ → 3′)
ccrA/B1ccr1B-forCTT TCA CGA TAG ACA CAG
ccr1B-rev
TAA AAG AAG TTC ATA GCC GTT AAA TTG G
ccrA/B2ccr2B-forGCA TTC ATC ATC AAT CAA AAT G
ccr2B-rev
CTA TAA CCT TCT GTG CTT TGC A
ccrA/B3ccr3B-forTCC GTA ATA AGA AGC AAC TTC AC
ccr3B-rev
ACT ATA GCC TTC AGT ACT TTG GA
ccrA/B4ccr4B-forTGA AGA AGC ACA AGA GCG GC
ccr4B-revCTG CAC CAC ATT TTG GGC AC

*SCCmec, staphylococcal cassette chromosome mec; MRSA, methicillin-resistant Staphylococcus aureus; ST, sequence type.

We conclude that on the basis of generally accepted definitions SCCmec type V is present in these ST398 pig-farming–related isolates, not SCCmec type III. Therefore, researchers should be aware that some typing methods may lead to inadequate results.

Suggested citation for this article: Jansen MD, Box ATA, Fluit AC. SCCmec typing in methicillin-resistant Staphylococcus aureus strains of animal origin [letter]. Emerg Infect Dis [serial on the Internet]. 2009 Jan [date cited]. Available from http://www.cdc.gov/EID/content/15/1/136.htm

This research was supported by the Department of Medical Microbiology, University Medical Center, Utrecht, the Netherlands.

Referencesvan Loo I, Huijsdens X, Tiemersma E, de Neeling A, van de Sande-Bruinsma N, Beaujean D, Emergence of methicillin-resistant Staphylococcus aureus of animal origin in humans.Emerg Infect Dis 2007;13:1834–918258032Ito T, Katayama Y, Asada K, Mori N, Tsutsumimoto K, Tiensasitorn C, Structural comparison of three types of staphylococcal cassette chromosome mec integrated in the chromosome in methicillin-resistant Staphylococcus aureus.[erratum in Antimicrob Agents Chemother, 2001;45:3677] Antimicrob Agents Chemother 2001;45:1323–36 10.1128/AAC.45.5.1323-1336.200111302791Ito T, Ma XX, Takeuchi F, Okuma K, Yuzawa H, Hiramatsu K Novel type V staphylococcal cassette chromosome mec driven by a novel cassette chromosome recombinase, ccrC.Antimicrob Agents Chemother 2004;48:2637–51 10.1128/AAC.48.7.2637-2651.200415215121Zhang K, McClure JA, Elsayed S, Louie T, Conly JM Novel multiplex PCR assay for characterization and concomitant subtyping of staphylococcal cassette chromosome mec types I to V in methicillin-resistant Staphylococcus aureus.J Clin Microbiol 2005;43:5026–33 10.1128/JCM.43.10.5026-5033.200516207957Lim TT, Chong FN, O’Brien FG, Grubb WB Are all community methicillin-resistant Staphylococcus aureus related? A comparison of their mec regions.Pathology 2003;35:336–43 10.1080/003130203100015049812959761In ResponseHuijsdensXandervan LooIngeKluytmansJanInstitute for Public Health and the Environment, Bilthoven, the Netherlands (X. Huijsdens)University Hospital Maastricht, Maastricht, the Netherlands (I. van Loo)Amphia Hospital, Breda, the Netherlands (J. Kluytmans)Medical Microbiology and Infection Control, VU Medisch Centrum, Amsterdam, the Netherlands (J. Kluytmans)Address for correspondence: Xander Huijsdens, National Institute for Public Health and the Environment (RIVM), Diagnostic Laboratory for Infectious Diseases and Perinatal Screening, Pb 22, PO Box 1, 3720 BA Bilthoven, the Netherlands; email: xander.huijsdens@rivm.nl

We thank Jansen et al. for their comments about the SCCmec types of sequence type (ST) 398 methicillin-resistant Staphylococcus aureus (MRSA) isolates (1). For SCCmec typing of MRSA, several different PCR methods have been published. We originally chose the SCCmec PCR developed by Zhang et al. (2) because at that time it was the method of choice in many published papers. Fluit et al. questioned whether the SCCmec type III isolates were correctly typed (1). To prove that the results of typing these 4 isolates were incorrect, these researchers performed several different SCCmec PCRs, including a PCR with primers they developed themselves. In addition, Southern hybridization was done. The results showed that SCCmec III ST398 MRSA isolates should be typed as SCCmec type V. In this conclusion we agree with the authors. It seems clear that Zhang’s method incorrectly identified 4 of the animal-related ST398 isolates as SCCmec type III instead of SCCmec type V. Whether all ST398 MRSA are SCCmec type IV or V remains unclear. Recently, an article by Nemati et al. was published in which ST398 MRSA was also typed as SCCmec III (3). However, in that study the SCCmec typing method of Zhang was also used.

In conclusion, the choice of SCCmec typing method is directly related to obtaining accurate SCCmec results for ST398 isolates. To date, almost all animal-related ST398 MRSA isolates are SCCmec types IV and V.

ReferencesJansen MD, Box ATA, Fluit AC SCCmec typing in methicillin-resistant Staphylococcus aureus strains of animal origin.Emerg Infect Dis 2009;15:136 10.3201/eid1501.07164719116081Zhang K, McClure JA, Elsayed S, Louie T, Conly JM Novel multiplex PCR assay for characterization and concomitant subtyping of staphylococcal cassette chromosome mec types I to V in methicillin-resistant Staphylococcus aureus.J Clin Microbiol 2005;43:5026–33 10.1128/JCM.43.10.5026-5033.200516207957Nemati M, Hermans K, Lipinska U, Denis O, Deplano A, Struelens M, Antimicrobial resistance of old and recent Staphylococcus aureus isolates from poultry: first detection of livestock-associated methicillin-resistant strain ST398.Antimicrob Agents Chemother 2008;52:3817–9 10.1128/AAC.00613-0818663024