Using a nonlinear mixed model to evaluate multiple effects on bacterial growth curves

BIRGITT WIESE; MARÍA SILVINA JUÁREZ TOMÁS,; MARÍA DEL CARMEN AHUMADA OSTENGO; MARÍA ELENA NADER MACÍAS

Freiburg. Alemania

Conferencia; XXI International Biometric Conference; 2002

International Biometric Society

Using a nonlinear mixed model to evaluate multiple effects on bacterial growth curves. The nonlinear mixed model approach proposed by Lindstrom and Bates (1990) is applied to evaluate the influence of different growth conditions in lactic acid bacteria. In the first example we studied the effects of the factors temperature (3 levels), initial pH (3 levels) and two different culture media on the kinetics of growth of the bacterial strain L.salivarius CRL 1328 isolated from human vagina to compare the conditions of optimal biomass obtention for technological applications. This strain could be used as a probiotic for the prevention of urogenital infections. The growth curves were described by the 4-parameter modified Gompertz model. The temperature showed a significant influence on the parameters lag phase and highest final optical density while the initial pH had only a significant effect on the lag phase. The culture media had a significant influence on the highest final optical density. In a second study we analyzed the effects of different concentrations of NaF (in the range used for therapeutic purposes) on the growth of several lactic acid bacteria isolated from the human oral cavity. The lactic acid bacteria have been related to the progression of dental caries.The bacterial strains were taken from different areas of the mouth from patients with and without caries, the growth curves were also described by the modified Gompertz model. The concentraion of NaF showed a significant influence on the parameters lag phase, maximal growth rate and highest final optical density while the health status had a significant effect only on the highest final optical density.