**Core Concept**
Acquired vesicoureteric reflux (VUR) is a condition where urine flows backward from the bladder into the ureters or kidneys, often causing urinary tract infections (UTIs). The primary goal of treatment is to prevent UTIs and their complications, such as pyelonephritis and kidney damage.

**Why the Correct Answer is Right**
Cotrimoxazole, a combination of trimethoprim and sulfamethoxazole, is a broad-spectrum antibiotic effective against a wide range of bacterial pathogens, including E. coli, which is the most common cause of UTIs in patients with VUR. In this scenario, Cotrimoxazole is the treatment of choice because it can effectively eliminate the infection and reduce the risk of recurrent UTIs. Additionally, it does not require ureteral instrumentation or surgery, making it a more conservative approach.

**Why Each Wrong Option is Incorrect**
**Option B:** Bilateral reimplantation of ureter is a major surgical procedure typically reserved for patients with severe, persistent VUR who have failed medical management and have developed recurrent UTIs or kidney damage. It is not the first-line treatment for acquired VUR with a UTI.
**Option C:** Injection of Collagen in the ureter is a minimally invasive procedure that can be used to treat VUR, but it is not the standard treatment for patients with a UTI. It may be considered in select cases where medical management has failed or as a bridge to more definitive surgical treatment.
**Option D:** Endoscopic resection of ureter is not a standard treatment for VUR or UTIs. This option may be a distractor for students who are not familiar with the nuances of VUR management.

**Clinical Pearl / High-Yield Fact**
In patients with VUR, the presence of a UTI is a strong indicator for the need for antibiotic prophylaxis to prevent recurrent infections and kidney damage.

**✓ Correct Answer: A. Cotrimoxazole**