Clostridium botulinum type A growth and toxin production in media and process cheese spread

We found that Clostridium botulinum type A grew well and produced toxin in media with a water activity (a(w)) of 0.972 or 0.965 and a pH of 5.7, but no growth or toxin production was observed at or below an a(w) of 0.949 during incubation at 30 degrees C for 52 to 59 days. a(w) and pH values of media were adjusted to those of cheese spreads commercially produced. Solutes used to adjust a(w) included combinations of NaCl, cheese whey powder, emulsifying salt, sodium tripolyphosphate, and glycerol. In agreement with results obtained for media, toxin was produced in samples of cheese spread (a(w), 0.970; pH, 5.7) at 30 to 70 days of incubation at 30 degrees C.