Cell counting and bacterial inoculum standardization by spectrophotometric method for Bifidobacterium animalis ssp. Lactis INL1 / Contagem de células e padronização de inóculos bacterianos pelo método espectrofotométrico para Bifidobacterium animalis ssp. Lactis INL1

The genus Bifidobacterium is present in the human intestinal microbiota and in abundance in breast milk, conferring probiotic features to this food. However, a large number of variables affect its growth, hindering possible analysis and its use in organic assays. Different direct and indirect methodologies of bacterial cell counting provide results in some units of measurement, such as colony-forming units (CFU) per gram or mL, or even cell number per mL. Standardizing bacterial inoculum used in long-term daily exposure experiments is sometimes difficult due to the numerous variables involved in plaques cultivation and incubation. Considering that, this study sought to standardize adjusted bacterial inoculum from the indirect method of bacterial counting by spectrophotometry, using calibration curve and plating confirmation to ensure the amount of cells to be inoculated. As a result, we found that colony-forming units grew at a 108 rate at 600 nm, within the 0.010–0.006 absorbance range, and that such rate remains regardless of differences within the CFU/mL count. This method can be used to adjust Bifidobacterium animallis ssp Lactis INL1 inoculum, considering its probiotic effect.