THE COMBINED EFFECTS OF TEMPERATURE, PH AND NACL ON GROWTH OF DEBARYOMYCES-HANSENII ANALYZED BY FLOW-CYTOMETRY AND PREDICTIVE MICROBIOLOGY

Flow cytometry was applied to determine growth of Debaryomyces hanseni i in a laboratory medium. Viable yeasts were enumerated after staining with the fluorogenic ester fluorescein diacetate (FDA). Initial studi es showed that the flow cytometric determinations correlated well with viable yeast populations determined as colony forming units (CFU) whe reas the relationship between CFU and optical density was only linear over a narrow range of cell concentrations, 10(5.5)-10(7.5) cells/ml. The flow cytometric measurements could reliably detect D. hansenii at concentrations as low as 10(2) cells/ml whereas the lower detection li mit using optical density measurements was 10(5)-10(6) cells/ml. Growt h was determined by flow cytometry at different combinations of temper atures (10-30 degrees C), pH (4.7-6.0) and NaCl concentrations (1-12% w/v). Growth curves were generated by fitting a modified Gompertz equa tion to the growth data using non-linear regression analysis. Lag phas e duration and maximum specific growth rates were derived and quadrati c polynomial models were developed describing the effects of environme ntal conditions on the growth parameters. Model validation based upon repetition of experiments and use of another laboratory medium showed good agreement between observed and predicted maximum specific growth rates whereas predicted lag phases were shorter than the observed lag phases. Copyright (C) 1997 Elsevier Science B.V.