Injury and growth of Serratia marcescens studied in a thermal gradient incubator.

An incubator capable of producing a controlled thermal gradient of 0 to 40 C is described. Serratia marcescens was incubated in small tubes held in the gradient. When turbidity in the tubes was assayed and recorded by a semiautomatic photometer, growth-temperature patterns were obtained. The shape of these patterns was influenced by age of inoculum or by pretreatment of the culture. Cultures incubated for short times at 52 C, treated with hydrogen peroxide, or lyophilized before being incubated tended to grow at higher mean temperatures than untreated cultures. These findings illustrate the general utility of the instrument for studies of microbial growth.