CONICET | Buscador de Institutos y Recursos Humanos

Listeria monocytogenes is a relevant foodborne pathogen causing invasive listeriosis in humans, a disease withhigh mortality rates. Its ubiquity and growth characteristics enable this pathogen to survive harsh food processing environments. The addition of bacteriocins, antimicrobial peptides ribosomally synthesized by certainbacteria, appears as a natural alternative to control this pathogen in food. However, the emergence ofL. monocytogenes strains resistant to the inhibitory action of bacteriocins has been detected. In order to analysethe development of this resistance, different properties of L. monocytogenes strains susceptible to bacteriocins(strains 01/155, 99/287 and 99/267) and their respective resistant isolates (strains 01/155B6R, 99/287B6R, 99/286C1R, 99/287 Mo1R, 99/287 M1bR, 99/287 M2dR, 99/267B6R), were compared in this work. Differenceswere analysed in: a) growth of the pathogen strains in direct contact with bacteriocin solution, in co-cultureswith the producing strain, or with different sugars; b) response to antibiotics typically used against listeriosis;c) changes in cell morphology, observed by transmission or scanning electron microscopy; d) expression ofmobility and haemolysin activity, two of L. monocytogenes main virulence factors; and e) biofilm formationability. For all the isolates, the acquired resistance was permanent and crossed between the different bacteriocinsunder study. An inhibitory effect was observed for resistant strains only when they were grown in mixed culturewith any of the bacteriocin-producing strains, with an acidified medium as additional growth stress. In all cases,the decrease in viability was lower for resistant strains and followed a particular profile for each strain. Thevariation of sugar substrate influenced resistant variants growth ability, with a more pronounced difference inthe medium supplemented with glucose. Susceptibility to antibiotics was similar or higher for resistant variants,while neither the mobility nor the haemolytic activity presented differences among resistant or susceptiblestrains. Finally, the resistant variants showed a greater capacity to form biofilms, although this effect wasreversed when grown in the presence of bacteriocins. Each resistant isolate had a particular behaviour pattern,and the acquisition of resistance appeared to be strain and bacteriocin dependent. These results contribute to theknowledge of L. monocytogenes bacteriocin-resistance development, which is essential to favour the use of thesepeptides as biopreservatives.

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