Background/objectives Based on the recent identification of E.coli heat shock protein ClpB as a mimetic of the anorexigenic α-melanocyte stimulating hormone (α-MSH), the objective of this study was to preclinically validate Hafnia alvei, a ClpBproducing commensal bacterium as a potential probiotic for appetite and body weight management in overweight and obesity. Methods The involvement of enterobacterial ClpB in the putative anti-obesity effects was studied using ClpB-deficient E.coli. A food-grade H. alvei HA4597 strain synthetizing the ClpB protein with an α-MSH-like motif was selected as a candidate probiotic to be tested in ob/ob and high-fat diet (HFD)-fed obese and overweight mice. The relevance of the enterobacterial ClpB gene to human obesity was studied by in silico analysis of fecal metagenomes of 569 healthy individuals from the "MetaHIT" database. Results Chronic per os administration of native but not ClpB-deficient E.coli strain reduced body weight gain (p < 0.05) and daily meal frequency (p < 0.001) in ob/ob mice. Oral gavage of H.alvei for 18 and 46 days in ob/ob and HFD-fed obese mice, respectively, was well tolerated, reduced body weight gain and fat mass in both obesity models (p < 0.05) and decreased food intake in hyperphagic ob/ob mice (p < 0.001). Elevated fat tissue levels of phosphorylated hormone-sensitive lipase were detected in H.alvei-treated ob/ob mice (p < 0.01). Enterobacterial ClpB gene richness was lower in obese vs. non-obese humans (p < 0.0001) and correlated negatively with BMI in genera of Enterobacter, Klebsiella and Hafnia. Conclusions H.alvei HA4597 strain reduces food intake, body weight and fat mass gain in hyperphagic and obese mice. These data combined with low enterobacterial ClpB gene abundance in the microbiota of obese humans provide the rationale for using H.alvei as a probiotic for appetite and body weight management in overweight and obesity.

Use of new generation probiotics may become an integral part of the prevention and treatment strategies of obesity. The aim of the present study was to test the efficacy of a potential probiotic strain of lactic bacteria Hafnia alvei (H. alvei) HA4597™, in a mouse model of obesity characterized by both hyperphagia and diet-induced adiposity. For this purpose, 10-week-old high-fat-diet (HFD)-fed hyperphagic ob/ob male mice received a daily treatment with 1.4 × 1010 CFU of H. alvei for 38 days. Effects of H. alvei were compared to those of a lipase inhibitor orlistat (80 mg/kg daily) and a vehicle (NaCl 0.9%) in HFD-fed ob/ob mice. A control untreated group of ob/ob mice received the standard diet throughout the experiment. The vehicle-treated HFD group displayed increased food intake, worsening of adiposity, and glycemia. Treatment with H. alvei was accompanied by decreased body weight and fat-mass gain along with reduced food intake to the level of the standard-diet-fed mice. At the end of the experiment, the group treated with H. alvei showed a decrease of glycemia, plasma total cholesterol, and alanine aminotransferase. The orlistat-treated mice showed a lower rate of body weight gain but were hyperphagic and hyperglycemic. These results demonstrate the beneficial anti-obesity and metabolic effects of H. alvei HA4597™ in mice with obesity resulting from hyperphagia and diet-induced adiposity.