**1. Introduction**

Bowel preparation refers to the mechanical cleansing of the bowel through the oral, rectal route, or a combined route. It has been in use for many decades as a part of preoperative preparation before elective colorectal surgery. However, the scientific basis of this practice is still debatable [1]. The infectious complication and anastomotic leak (2.7–20%) are the significant issues with colorectal surgery. These lead to increased morbidity in terms of postoperative ileus (10–30%), surgical site infection (6.5–20%), re-admission rate (8.1–11.8%), and an increase in the length of hospital stay (LOS) [1–7]. Colonic bacterial flora is one of the major causes of infectious complications in colorectal surgery, but the effective way to reduce the bacterial load is still debatable [8]. Preoperative bowel preparation is one of the techniques

frequently studied to reduce these colonic bacterial florae. It is not easy to indicate when mechanical bowel preparation (MBP) was first used in colorectal surgery and is still the subject of debate.

Nevertheless, it is believed that preoperative mechanical bowel preparation (MBP) removes stool content and associated bacterial load, thereby reducing surgical site infection (SSI). The other benefit of MBP is easier bowel manipulation during surgery [9]. Subsequently, nonabsorbable antibiotics were added to reduce the bacterial load further. Since 1970, MBP plus poorly absorbed prophylactic oral antibiotics (POA) and intravenous antibiotics effective against intestinal microorganisms were accepted before elective colorectal surgery [10]. However, the effect of antibiotics is believed to last beyond the surgical intervention and can influence the structure and function of the gut microbiome [11]. The human intestine possesses millions of microbial genes, known as microbiome [12]. These microbiomes are highly specific, which is the reason for the conflicting data of MBP or the combination of MBP with POA [13]. Multiple clinical trials have been conducted to determine the best strategy for bowel preparation, but their results are controversial [14–16]. Since 1980, the evidence of Enhanced Recovery After Surgery (ERAS) and the successful outcome of emergency colorectal surgery has led to the belief that MBP can be omitted.

Many RCTs have failed to demonstrate any protective benefit of isolated MBP against infective complications or anastomotic leaks. On the contrary, the patients exhibited a paradoxical increase in postoperative ileus. Data from the late twentieth century studies suggest that the elimination of MBP does not increase morbidity. This gradually led to a trend of avoiding MBP routinely. Nevertheless, most of these studies have not combined the POA with MBP. Preoperative POA use has also decreased as surgeons started following ERAS. But the use of POA has not disappeared completely [17–20]. There is a resurgence of bowel preparation because of the high risk of surgical site infection after colorectal surgery. Since 2013, clinical guidelines have been changing, and a combination of MBP and POA is now recommended [21–23]. A number of retrospective studies and meta-analyses have been done after 2014, which have shown that preoperative MBP and POA following colorectal surgery reduce postoperative surgical site infection [24–28].

There are various methods of bowel preparation before elective colorectal surgery. These include MBP alone without a preoperative POA, MBP with preoperative POA, preoperative POA alone without MBP, and preoperative enema alone without MBP and POA. However, there is no consensus on the optimal type of bowel preparation, and it generally depends on the treating surgeon's preference and the patient's prognosis [29]. However, most surgeons prefer preoperative POA with MBP in elective colorectal surgery.
