**9. Phenotypes associated with sRNA expressions**

The expression pattern of sRNAs is different in normal compared with SCV (small colony variants) phenotypes of *S.aureus* clinical isolates from the osteomyelitis patients [72]. Different characteristics of SCV strain are slow growth, low pigment production, lower hemolytic activity, lower susceptibility pattern to aminoglycosides, low production of toxins and improved intracellular persistence [73]. Usually, the normal phenotypes are considered as virulent strain and SCVs are considered as persister cells. RNA III expression is a phenotypic-specific, as it is detected in normal phenotypes but not in SCV phenotypes [74]. The absence of


#### **Table 2.**

*Factors used by* S.aureus *to counter host defense mechanism.*

Staphylococcus aureus *and Virulence-Related Small RNA DOI: http://dx.doi.org/10.5772/intechopen.98520*

RNAIII sRNA in SCV phenotypes may be the reason for the reduced production of toxins and less virulence. Several PI encoded sRNAs' expression pattern is switched off in the SCV phenotypes during the late growth phase. Also, the less expression profile of SprS in the SCV phenotypes may also be responsible for their less pathogenicity in comparison to the normal phenotypes [75] (**Table 2**).

It has been reported that there is an up-regulation of Sau-13 in normal phenotypes, whereas it is down-regulated in the SCV phenotypes. Sau-13 involve in ion transport and other metabolism by its antisense function against the precursor phoB. But Sau-66 sRNA up-regulated in SCV phenotypes only and down-regulated in normal phenotypes [95]. Sau-66 has antisense region on a gene encoding protein which is involved in folate biosynthesis. Sau-66 has a major impact on the formation of thymidine autotrophs in SCV phenotypes in purine biosynthesis pathway because folate is a carbon donor [96].
