Response of intestinal flora of laboratory-reared leopard frogs (Rana pipiens) to cold and fasting

The bacterial flora of the large intestine was examined in 35 laboratory-reared leopard frogs (Rana pipiens) subjected to one of the following four treatments: (i) normal feeding at 21 degrees C (10 frogs); (ii) fasting for 2 weeks at 21 degrees C (8 frogs); (iii) chilling for 1 week at 4 degrees C (9 frogs); and (iv) simulated hibernation for 3 weeks at 4 degrees C (8 frogs). Bacteria from the intestinal contents and mucosa were counted microscopically and by colony counting after strictly anaerobic culturing. The predominant bacteria were isolated and partially characterized. Fasting for 2 weeks produced no significant changes in total counts or in the types of bacteria cultured. Chilling, whether rapid or in the course of simulated hibernation, was associated with a decrease in the numbers and variety of bacteria. Thus it appears that the lowering of temperature rather than the absence of food is the important factor in the reduction of bacterial flora seen in hibernating frogs. However, the bacteria showed some adaptation to the low temperature, as the longer the host had been at 4 degrees C, the higher the proportion of bacteria which could grow when cultured at that temperature.