Biocide tolerance, phenotypic and molecular response of Lactic Acid Bacteria isolated from naturally-fermented Aloreña table olives throughout fermentation to induction by different physico-chemical stresses

Lactic acid bacteria isolated from Aloreña table olives throughout fermentation process were resistant at least to three antibiotics (Casado Muñoz et al., 2014), however they were very sensitive to all biocides tested in this study (MIC below the epidemiological cut-off values “ECOFF” determined in the present study) except 2-15% of Lc. pseudomesenteroides which were resistant to hexachlorophene and Lb. pentosus to cetrimide and hexadecylpiridinium. To give new insights of how LAB become resistant in a changing environment, the effect of different physico-chemical stresses -including antimicrobials- on phenotypic and genotypic responses of LAB was analyzed in the present study. The results obtained indicated that a similar phenotypic response was obtained under all stress conditions tested (antimicrobials, chemicals and UV light) producing changes in susceptibility patterns of antibiotics (increased MICs for ampicillin, chloramphenicol, ciprofloxacin, teicoplanin and tetracycline, while decreased MICs were shown for clindamycin, erythromycin, streptomycin and trimethoprim in the majority of strains). By means of statistical analysis, cross resistance between different antibiotics was detected in all stress conditions. However, expression profiles of selected genes involved in stress/resistance (rpsL, recA, uvrB and srtA genes) were different depending on the stress parameter, LAB species and strain, and also the target gene. We can conclude that, in spite of the uniform phenotypic responses to several stresses, the repertoire of induced and repressed genes were different upon the stress parameter and the LAB strain. So, a search for a target to improve stress tolerance of LAB especially those of importance as starter/protective cultures or as probiotics may depend on the individual screening of each strain although, we could predict the antibiotic phenotypic response to all stresses.