Varying cecal bacterial loads influences colitis and gastritis in HLA-B27 transgenic rats

Background & Aims: Recent data support an important role of resident lumina l bacteria in experimental colitis. We determined how altered cecal bacteri al loads influence colitis and gastritis. Methods: A cecal self-filling bli nd loop (SFBL) was created or the cecum was excluded from the fecal stream in specific pathogen-free HLA-B27 transgenic (TG) rats with early colitis a nd in nontransgenic (nonTG) littermates; controls underwent sham operation (SHAM). Luminal bacterial concentrations were determined by culture and cou nting chamber. Results: TG rats with SFBL had more severe cecal inflammatio n and leukocytosis than TG SHAM controls. TG excluded rats with low cecal b acterial loads had no cecal inflammation and less colitis and gastritis tha n SHAM controls, despite having normal distal colonic and gastric bacterial concentrations. Metronidazole attenuated cecal inflammation and eliminated Bacteroides in SFBL TG rats. NonTG SFBL rats had mild cecal inflammation a nd no gastritis and colitis. The ratio of total anaerobic to aerobic bacter ia was 1000-fold greater in SFBL than in SHAM rats, with a 10,000-fold incr eased ratio of Bacteroides spp. to aerobes. Conclusions: The luminal bacter ial load and composition determines the activity of cecal inflammation in g enetically susceptible hosts. Lowering cecal bacterial concentrations can d iminish inflammation in remote organs.