AUSENCIA DE COMPETENCIA NATURAL EN Lactobacillus casei BL23 BAJO CONDICIONES DE ESTRÉS EN LAS QUE SE SIMULA EL AMBIENTE DEL TRACTO GASTROINTESTINAL

JOAQUINA FINA MARTIN; MARÍA MERCEDES PALOMINO; PABLO WAEHNER; SANDRA M. RUZAL; MARIANA CLAUDIA ALLIEVI

Mar del Plata

Congreso; X CONGRESO ARGENTINO DE MICROBIOLOGÍA GENERAL; 2014

SAMIGE

Most of the probiotic bacteria currently available in the dairy industry belong to the genera Lactobacillus. Probiotics are live microorganisms which when administered in adequate amounts confer a health benefit on the host. Probiotics are used as starter cultures in dairy and non-dairy products. They are considered GRAS (generally recognized as safe) and QPS (Qualified presumption of safety status) for their safe history of usage. Probiotic Lactobacillus strains exceptionally show transferable antibiotic resistance. However, transferability studies have not been assayed systematically. Transferable antibiotic resistance is the only relevant cause for caution since they might potentially serve as hosts of antibiotic-resistance genes, with the risk of transferring these genes to other bacteria. This in fact is the reason why genetically modified microorganisms are not approve to be used in food as they might experience horizontal gene transfer with the autochthonous microbiota, however this fact has never been clearly established. Lactobacilli are able to survive the gastrointestinal transit and transiently colonize our gut. In that environment they encounter multiple stress conditions. To address transferability we decided to evaluated if those gut conditions are able to modify the gene expression of for comX, annotated as alternative sigma factor of the RNA polimerase, YP_001986877.1, Gene ID: 6404650, a putative regulatory element of competence cascade coded in the genome of Lactobacillus casei BL23. For this purpose we checked conditions that resembled those found in the gastrointestinal tract like salt stress or acid pH with bile salts and compared them to those known to promote competence gene expression like starvation, UV and heating. Messenger RNA of comX gene, was analyzed by Dot Blot and qPCR and related to their expression in early stationary phase growth condition and the housekeeping gene 16S rRNA. We also verified the transfer of an antibiotic resistance marker (CmR) evaluating the naturally transformations in any of these conditions by evaluating the most probable number (MPN). The results showed that an increase in the expression of comX was observed in the condition of UV and acid pH with bile salts. However the numbers of naturally transformants obtained in those conditions were not significantly different from non-induced condition as verified by MPN. Although an induction of expression was observed it was not enough to supply competence for plasmid transformation. These results argue in favor of the fact that Lactobacilli might not be able to be naturally transformable, although it is not sufficient to ensure the absence of transfer mechanisms.