Volume 15, Number 1—January 2009
Letter
SCCmec Typing in Methicillin-Resistant Staphylococcus aureus Strains of Animal Origin
To 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.
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.
Acknowledgment
This research was supported by the Department of Medical Microbiology, University Medical Center, Utrecht, the Netherlands.
, and Ad C. Fluit
References
- van 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;13:1834–9.PubMedGoogle Scholar
- Ito 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. DOIPubMedGoogle Scholar
- Ito 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. DOIPubMedGoogle Scholar
- Zhang 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. DOIPubMedGoogle Scholar
- Lim 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. DOIPubMedGoogle Scholar
Table
Cite This ArticleRelated Links
In Response: 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.
References
- Jansen MD, Box ATA, Fluit AC. SCCmec typing in methicillin-resistant Staphylococcus aureus strains of animal origin. Emerg Infect Dis. 2009;15:136. DOIPubMedGoogle Scholar
- Zhang 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. DOIPubMedGoogle Scholar
- Nemati 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. DOIPubMedGoogle Scholar
Table of Contents – Volume 15, Number 1—January 2009
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Please use the form below to submit correspondence to the authors or contact them at the following address:
Ad C. Fluit, Department of Medical Microbiology, Rm G04.614, University Medical Center Utrecht, PO Box 85500, Utrecht 3508 GA, the Netherlands;Ad C. Fluit, Department of Medical Microbiology, Rm G04.614, University Medical Center Utrecht, PO Box 85500, Utrecht 3508 GA, the Netherlands;
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;
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