Which one of the following Gram positive organism is most common cause of UTI among sexually active women :
**Core Concept**
Gram-positive bacteria are a type of bacteria that have a thick peptidoglycan cell wall, which is visible under a microscope as a purple-staining layer. In the context of urinary tract infections (UTIs), certain Gram-positive bacteria are more commonly associated with infections in women, particularly those who are sexually active.
**Why the Correct Answer is Right**
The correct answer is **Enterococcus faecalis**, a Gram-positive coccus that is commonly found in the gastrointestinal tract and can cause UTIs, especially in women who are sexually active. This organism can ascend from the vagina into the urinary tract, leading to infection. The pathogenesis of E. faecalis UTIs involves the adhesion of bacteria to the uroepithelial cells, followed by the production of virulence factors such as hemolysin and aggregation substance.
**Why Each Wrong Option is Incorrect**
**Option A:** *Escherichia coli* (E. coli) is a Gram-negative bacterium that is the most common cause of UTIs in women, but it is not Gram-positive. While E. coli can cause UTIs in sexually active women, it is not the correct answer in this case.
**Option B:** *Staphylococcus saprophyticus* is a Gram-positive bacterium that can cause UTIs, particularly in young, sexually active women. However, it is not the most common cause of UTIs in this demographic.
**Option C:** *Staphylococcus aureus* is a Gram-positive bacterium that is more commonly associated with skin and soft tissue infections, rather than UTIs.
**Clinical Pearl / High-Yield Fact**
In sexually active women, UTIs caused by Gram-positive bacteria such as E. faecalis can be more challenging to treat than those caused by E. coli, as they may be resistant to commonly used antibiotics.
**Correct Answer:** B. *Staphylococcus saprophyticus*.