[[Billede:Escherichia coli Gram.jpg|thumb|200px|Gramfarvning af [[E. coli]]-bakterier - en kendt og i langt det meste en gavnlig tyktarmsbakterie.]]
'''Tyktarmsbakterier''' også kendt som '''colibakterier''' eller '''kolibakterier''' er [[bakterie]]r som lever i [[pattedyr]]s og, inkl. [[menneske]]rs, [[tyktarm]]e. Langt de fleste er naturlige og nogle - især [[Escherichia coli]] (undtagen [[VTEC]]-varianter) er gavnlig<ref name="amsoc">[http://www.sciencedaily.com/releases/2008/06/080603085914.htm American Society for Microbiology (2008, June 5). Humans Have Ten Times More Bacteria Than Human Cells: How Do Microbial Communities Affect Human Health?. ScienceDaily] Citat: "...Instead of any one particular organism associated with inflammatory bowel diseases, they observed significant shifts in microbial populations between healthy subjects and those with disease, including a loss of normally protective bacterial populations...."</ref><ref>[http://www.sciencedaily.com/releases/2008/07/080728192701.htm University of Wisconsin-Madison (2008, July 30). Symbiotic Microbes Induce Profound Genetic Changes In Their Hosts. ScienceDaily] Citat: "..."We have thousands of bacteria that live with us, and yet there are only around 100 bacterial pathogens," she says. Given the numbers, "it seems like these pathways and these molecules are likely to be 'symbiosis' pathways more than 'anti-pathogen.'"..."</ref><ref>[http://www.sciencedaily.com/releases/2011/02/110201083928.htm Karolinska Institutet (2011, February 1). Bacteria in the gut may influence brain development. ScienceDaily]</ref><ref>[http://ekstrabladet.dk/kup/sundhed/article1420143.ece 28. sep 2010, ekstrabladet.dk: Lort kan behandle diabetes-patienter]</ref><ref>[http://fpn.dk/liv/krop_valvare/article2240455.ece 09.11.10, fpn.dk: Afføring virker mod diarré]</ref>, da de bl.a. laver livsnødvendig [[K-vitamin]] til os.
De gavnlige tyktarmsbakterier er gavnlige i netop tyktarmen, men kan give infektioner andre steder i kroppen - f.eks. andre [[slimhinde]]r, hvis de utilsigtet kommer her.
