**Core Concept**
The use of antibiotics in surgery is a critical aspect of preventing surgical site infections (SSIs). Prophylactic antibiotics are administered to reduce the risk of infection in patients undergoing surgical procedures, especially those with a high risk of SSI.

**Why the Correct Answer is Right**
Prophylactic antibiotics are recommended for colorectal surgery due to the high risk of SSI associated with this type of procedure. The American Society of Health-System Pharmacists (ASHP) and the Infectious Diseases Society of America (IDSA) recommend the use of prophylactic antibiotics in patients undergoing colorectal surgery to reduce the risk of SSI. This is because the colon is a rich source of bacteria, and the risk of SSI is higher in colorectal surgery compared to other types of surgery.

**Why Each Wrong Option is Incorrect**
**Option A:** No prophylaxis for clean contaminated surgery - This is incorrect because prophylactic antibiotics are recommended for clean-contaminated surgeries, which include procedures where the respiratory, alimentary, genitourinary, or oropharyngeal tract is entered under controlled conditions and without unusual contamination. Colorectal surgery is an example of a clean-contaminated surgery.
**Option B:** No prophylaxis for gastric ulcer surgery - This is incorrect because prophylactic antibiotics are not routinely recommended for gastric ulcer surgery unless there is a high risk of SSI, such as in cases of perforated gastric ulcers.
**Option D:** Local irrigation with antibiotic contraindicated when systemic antibiotics given - This is incorrect because local irrigation with antibiotics is not contraindicated when systemic antibiotics are given. In fact, local irrigation with antibiotics is often used in conjunction with systemic antibiotics to enhance the effectiveness of prophylaxis.

**Clinical Pearl / High-Yield Fact**
It is essential to note that the timing of prophylactic antibiotic administration is critical, and antibiotics should be administered within one hour before the surgical incision to be effective. This is because the risk of SSI is highest within the first hour after the surgical incision.

**✓ Correct Answer: C. Prophylaxis for colorectal surgery**