1. Summary of outcomes reported per study.

StudyID	SSI	Subdivision in incisional and organ/space SSI	Anastomotic leakage	Mortality	Mild and severe postoperative complications according to Clavien‐Dindo	Incidence of postoperative ileus	LOS	Side effect of Intervention	C. difficile‐related diarrhoea
MBP+oAB vs. MBP
Anjum 2017	yes	yes	no	no	no	no	no	no	no
Arezzo 2021	yes	no	yes	yes	yes	yes	yes	yes	yes
Espin‐Basany 2005	yes	no	no	no	no	yes	no	yes	no
Hata 2016	yes	yes	yes	no	no	yes	no	no	yes
Horie 2007	yes	no	yes	no	no	no	no	no	no
Ikeda 2016	yes	yes	yes	no	no	yes	yes	no	yes
Ishida 2001	yes	yes	yes	no	no	no	no	no	no
Kobayashi 2007	yes	yes	no	no	no	no	no	no	no
Lau 1988	yes	no	yes	no	no	no	yes	no	no
Lazorthes 1982	incorrect*	no	no	yes	no	no	incorrect**	no	no
Lewis 2002	yes	no	no	no	no	no	no	no	no
Oshima 2013	yes	yes	no	no	no	no	no	yes	no
Papp 2021	yes	yes	yes	yes	yes	yes	no	no	yes
Rybakov 2021	yes	yes	yes	no	yes	yes	no	no	incorrect***
Sadahiro 2014	yes	yes	yes	no	no	no	no	no	incorrect****
Takesue 2000	yes	no	yes	no	no	no	no	no	no
Uchino 2019	yes	yes	no	no	no	no	no	no	no
MBP+oAB vs. oAB
Ram 2005	yes	no	yes	yes	no	yes	yes	no	no
Suzuki 2020	yes	yes	yes	no	no	no	no	no	yes
Zmora 2003	yes	no	yes	yes	no	yes	incorrect**	no	no
MBP+oAB vs. nBP
Koskenvuo 2019	yes	yes	yes	yes	yes	yes	yes	yes	yes

* Wound infections were classified into major and minor, but only data from major wound infections are reported
**Only the numerical value given with no unit of measurement specified, no information about range or standard deviation
*** Detection of Clostridia in general, not specific for C. difficile
**** Detection rate of C. difficile toxin pre‐ and postoperatively, regardless of whether diarrhoea was present