Staphylococcus aureus is a well known agent as commensal organism lived on the human skin and as a leading cause of human disease. This bacterium responsible for a variety of disorders ranging from superficial skin infections up to serious abnormalities such as pneumonia, Bacteremia and Endocarditis and Staphylococcus aureus colonizes the anterior nares of 20% - 80% of the human population [1] [2] .

There are many molecular methods that have been employed to type, differentiate and group the S. aureus isolates, such as pulsed-field gel electrophoresis (PFGE), which have been used as the gold-standard method [3] , Multilocus Sequence Typing (MLST), coa typing, phage typing and SCCmec typing. Sequence-based methods have been developed to provide fast, unambiguous, and exportable typing data. Among them, the sequence determination of the polymorphic X region of spa gene or short sequence repeat (SSR) region of the protein A gene (spa) has been proposed as an alternative to current techniques for the typing of S. aureus [4] [5] .

The X region of spa gene as an epidemiological marker initially was employed in 1994 by Frenay and his colleague. The X region was amplified and its size estimated by electrophoresis [6] .

In 1996, the same group improved the technique by performing sequence analysis of the X region [7] . Since then many researchers have evaluated the usefulness of this technique for diverse epidemiological purposes and its credibility for S, typing. They found also it is a cost effective and simple method to apply.

Koreen et al. stated that the spa typing was shown to have a higher potential discriminatory power than other typing methods such as, microarray, multilocus enzyme electrophoresis (MLEE), Pulsed field gel electrophoresis (PFGE) and coa typing [8] . Based on these later findings we chose the spa typing method to type S. aureus in our region.

The aim of this study was to compare the S. aureus spa types isolated from healthy carrier and patients, also among MRSA and MSSA isolates.

Rapid and accurate determination of the different Staphylococcus aureus isolated from patients and carriers are a great help in understanding the epidemiology of this bacteria and its infection control [7] .

PFGE is still considering the gold standard in molecular typing, owing to its excellent discriminatory ability [11] , but the main disadvantages of this technique are related to the technical demands, the costs of the equipment, the time and labor required. Accordingly, there is a need for a rapid, inexpensive, and reliable method in routine epidemiological surveillance. Several PCR-based methods have been applied for molecular typing, for example PCR-RFLP, AP-PCR, MLST, SCCmec, coa typing and spa typing based on sequencing. In this study we used spa typing, due to its high degree of polymorphism in X region, for discrimination of different S. aureus isolated from patient, healthy carriers and between MRSA and MSSA.

In a study Nuno A. Faria and et al. (2008) used different method for typing 116 MRSA isolates and found that there were 32, 34, and 51 types in PFGE, MLST and spa methods respectively. This result indicated that discriminatory effect of Xr spa typing is more powerful even than PFGE and MLST [12] .

In our pervious study PCR-RFLP method on spa gene indicated that only 8 types out of 190 isolates are S. aureus [13] . In another survey conducted in India by this method only 5 spa types were detected [14] , but in this present study spa typing was carried out based on its Xr region sequencing and found about 50 spa types. This means PCR-RFLP spa gene had lower discriminative effect than Xr spa sequencing method, therefore Xr spa sequence typing preferred to PCR-RFLP method of spa gene.

We found that the spa types distribution in MSSA (44 types) was significantly more than MRSA (21 types) isolates. Nuno A. Faria et al. showed spa types among 116 MRSA isolates and 82 MSSA isolates was 51 and 55, respectively (Faria et al. 2008) and Strommenger et al. (2006) in a study on 283 MSSA and 1176 MRSA isolates found 128 and 121 types, respectively [3] . These latter findings are in accordance with our data which mean that the distribution of spa types in MSSA is much higher than MRSA types.

We were not able to find any spa types which we confidently label it as MRSA, although t037 was the most common type among MRSA isolates in our region but it was also found among 15 MSSA isolates. In contrast, most isolates belonging to type t937 were MSSA and a few of them belong to MRSA, and this difference was statistically meaningful. The common spa types in MRSA isolates in different region was not similar, in study conducted by Strommenger in Germany, common types were t032 and t003 in MRSA and t008 in MSSA isolates [15] and in Larry Koreen study the common type was t033 [8] . Based on these latter findings the prominent spa type of S. aureus are varied in different parts of the world.

We detected that some spa types, t021, t330, t267, t436, t1149, t2313, are conclusively found among MSSA isolates. Based on our findings the question is whether this observation is due to any relation between these types and sensitivity to methicillin or it is an accidental phenomenon? Answering to this question requires a larger sample population.

The distribution of spa types among S. aureus which were isolated from healthy carrier, and patients, was similar. The most common types among healthy carriers and patients were t937 and t037 respectively. Although none of spa types was restricted to either of patients or healthy carriers, but some spa types t012, t267 and t660 predominantly detected in patients and some other spa types including t701, t779 and t2313 were more common in healthy carriers. Spa type t660 only was detected in children less than 3 years old, can this type be considered as a marker of infection on children? To answer these question extensive studies on this spa type are suggested.

We found seven new spa types in our region where out of them five types exclusively were isolated from patients, and further studies are required to address the key role played by these 5 spa types in pathogenicity, virulence and toxicity of S. aureus.