This discrepancy is probably due to differences in the IgG
binding site of the spa gene, which is outside of the X region.
Bsp143I is an endonuclease enzyme that digests the
GATC sequence in DNA, which is used in several studies
(10, 11). However, this is the first time this enzyme is applied
for digestion of the spa gene for S. aureus typing.
Using this method, we were able to divide the S. aureus
isolates to seven types. In a similar study in India on 149
isolates of S. aureus, PCR product of the spa gene was digested
with HaeII enzyme and five types were identified.
In other studies using HaeII enzyme in Germany and Iran,
14 and seven types were diagnosed, respectively (4, 12).
These findings imply that efficacy of the Bsp143I enzyme
in digesting the S. aureus spa gene is similar to HaeII enzyme.
In accordance with a previous research, we found
that variation of the spa types among MSSA is more
than MRSA isolates, insomuch all the seven spa types
were present in MSSA isolates, but only four (types1-4)
were seen in MRSA. Fenner et al. diagnosed 65 and 42
spa types among 101 MSSA and 200 MRSA isolates, respectively
(13). Strommenger et al. demonstrated that
the types variations among 283 MSSA isolates (128 types)
was more than the variations among 1176 MRSA isolates
(121 types) (14). Methicillin resistance is a relatively new
phenomenon caused by acquiring the mecA gene by S.
aureus; thus, many strains of S. aureus may not still have
enough time to acquire the resistance genes. On the
other hand, believing that only some S. aureus strains
have the ability to obtain the mecA gene, just certain
types of S. aureus can be MRSA and diversity of the spa
types is less than MSSA (8).
Variety of the S. aureus strains spa types isolated in this
study among patients and healthy carriers was statistically
significant. Although distribution of the type 1 spa gene
was similar in both patients and healthy carriers, the frequency
of type 3 among carriers was significantly more.
This probably means fewer virulence of type 3 spa. Although
it easily colonized in the noses of health care
workers, it was not important in the pathogenesis. Further
studies are recommended to identify its frequency
and possible reasons for its decreased pathogenicity.
Our results showed that the Bsp143I enzyme is a useful
tool for digestion of the spa gene and typing of S.
aureus. The spa types variations among MSSA were more
than MRSA isolates.