The cultivated strain L. lactis subsp. lactis IL1403was provided by Dr. Ogier from INRA (French National Institute for Agricultural Research, Jouy-en-Josas, France). Frozen storage cultures of L. lactis IL1403 were thawn and pregrown on Petri dishes with M17 Agar (LAB M, UK) for 24 h at 35 C. One colony from a pregrown Petri dish was used as an inoculum for a 10 mL culture in liquid M17 Broth (FLUKA) at 35 C. 1 mL of bacterial suspension grown overnight (exactly 24 h) was used as inoculum for the next liquid 10 mL M17 broth culture and grown 12e14 h which allowed the L. lactis IL1403 bacteria to reach the middle of the exponential growth phase. The
number of bacteria was determined by plating on M17 Agar and incubating for 3 days at 35 C, and average number of bacteria in the mid-exponential culturewas determined (4.15þ/0.15)*108 cfu/mL. The inoculum needed for the experimentswas prepared by diluting samples of the mid-exponential culture in peptone water. The
calculated inoculum concentrations in calorimetric and in parallel samples were varied from 106 to 100 cfu/mL with the 10-fold increment. It was important to have the correct desired number of colonies in the samples as special attentionwas paid to study growth of individual colonies. From the practical point of view it was the
most difficult to get up to about three colonies, and not more, in a sample (inoculation rate 100 cfu/mL). These colonies are separated from each other sufficiently and grow thus as independent individual colonies. True, in these cases direct visual inspection of samples after the completion of the experiments together with the analysis of poweretime curves enabled to reach an unequivocal verdict on the success of the experiments. However, taking into account that the length of the experiments is typically about one month, the pure trial and error strategy was not the most feasible. Thus dilution procedures were developed and carefully implemented to assure that serial dilutions end with the desired inoculation rates. The exact following of the procedures of preparation of bacterial cultures described above which ensured high reproducibility at lower inoculation rates validated by direct counting of the colonies in the samples after the experiments, allowed to be confident that the number of bacteria in samples was also as assumed at inoculation rates higher than 102 cfu/mL.
thawn and pregrown
The cultivated strain L. lactis subsp. lactis IL1403was provided by Dr. Ogier from INRA (French National Institute for Agricultural Research, Jouy-en-Josas, France). Frozen storage cultures of L. lactis IL1403 were thawn and pregrown on Petri dishes with M17 Agar (LAB M, UK) for 24 h at 35 C. One colony from a pregrown Petri dish was used as an inoculum for a 10 mL culture in liquid M17 Broth (FLUKA) at 35 C. 1 mL of bacterial suspension grown overnight (exactly 24 h) was used as inoculum for the next liquid 10 mL M17 broth culture and grown 12e14 h which allowed the L. lactis IL1403 bacteria to reach the middle of the exponential growth phase. The
number of bacteria was determined by plating on M17 Agar and incubating for 3 days at 35 C, and average number of bacteria in the mid-exponential culturewas determined (4.15þ/0.15)*108 cfu/mL. The inoculum needed for the experimentswas prepared by diluting samples of the mid-exponential culture in peptone water. The
calculated inoculum concentrations in calorimetric and in parallel samples were varied from 106 to 100 cfu/mL with the 10-fold increment. It was important to have the correct desired number of colonies in the samples as special attentionwas paid to study growth of individual colonies. From the practical point of view it was the
most difficult to get up to about three colonies, and not more, in a sample (inoculation rate 100 cfu/mL). These colonies are separated from each other sufficiently and grow thus as independent individual colonies. True, in these cases direct visual inspection of samples after the completion of the experiments together with the analysis of poweretime curves enabled to reach an unequivocal verdict on the success of the experiments. However, taking into account that the length of the experiments is typically about one month, the pure trial and error strategy was not the most feasible. Thus dilution procedures were developed and carefully implemented to assure that serial dilutions end with the desired inoculation rates. The exact following of the procedures of preparation of bacterial cultures described above which ensured high reproducibility at lower inoculation rates validated by direct counting of the colonies in the samples after the experiments, allowed to be confident that the number of bacteria in samples was also as assumed at inoculation rates higher than 102 cfu/mL.
thawn and pregrown
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