Investigations on the survival of spores of Bacillus stearothermophilus during moulding of polyethylene with an injection-moulding machine

Spores of Bacillus stearothermophilus were mixed twice (test A and test B) with 700 g of polyethylene-granulate. The results were initial concentrations of about 2 x 10(5) colony-forming-units per g polyethylene. These mixtures passed an injection-moulding machine. The sticks from these mixtures (normed sticks DIN 53453) were moulded with an injection - moulding machine and then collected under sterile conditions and tested for bacteria. Test A: 10 sticks were cut into peaces of granulate size, 10 were powdered by a grinding-machine. 1 g of each material was put into 10 mi of sterile broth for bacteria and incubated for 72 h at 55 degrees C. These tests were made immediately after passing the injection-moulding machine. 10 sticks remained for 11 days at room-temperature and then all were put into sterile broth for bacteria without powdering or cutting and incubated as the others before. Test B: All preparations and handlings were made immediately after passing the injection-moulding machine. 10 sticks were cut into peaces of granulate size, 10 were powdered by a grinding-machine, 10 stayed complete. In addition to that 10 sticks were rasped. The outside 2 mm and the inner 1 mm were collected and analysed separately. The conditions for broth and incubation in test B were identically to those of test A. Results: In test A 5 of 10 media containing parts of sticks of granulate size became cloudy, those containing powder reacted in 8 of 10 cases. The media containing complete sticks remainded clear in all 10 cases. In test B the results for parts of sticks of granulate size, powder and complete sticks were 4 of 10, 8 of 10 and 7 of 10 respectively. There was no reaction from the rasped samples from the outside 2 mm in 10 cases. 6 of 10 media with the inner parts (1 mm) became cloudy. In all cases of cloudy media bacillus was confirmed by microscopy.