Histamine production by Propionibacterium acnes in batch and continuous culture

Histamine production by Propionibacterium acnes was studied using batch and continuous culture. In batch culture, the culture pH and the production of histamine closely paralleled the pattern of growth, increasing as the growth increased. Continuous culture studies using a chemostat and varying culture pH showed that highest levels of growth of P. acnes occurred at pH 6.0 and that two clear 'peaks' of histamine production were apparent at pH 4.5 and at pH 7.5. The levels measured at pH 7.5 were approximately one third the maximum value measured at pH 4.5. When P. acnes was grown at different dilution rates at pH 5.7, the histamine and biomass production rates increased proportionately as the growth rates were increased, except at the lowest relative dilution rate employed (0.75 microrel) where the production rate of histamine was higher than the value predicted by a proportional relationship.