Transcriptomic Response of L. monocytogenes to Co-Culture with S. cerevisiae

Spiros Paramithiotis,Alexandra Katidi,Eleftherios H Drosinos

doi:10.3390/beverages7030055

Abstract

The aim of the present study was to assess the transcriptomic response of L. monocytogenes during co-culture with three S. cerevisiae strains. For this purpose, BHI broth was inoculated with 7 log CFU·mL−1 L. monocytogenes serotype 4b strain LQC 15257, isolated from a strawberry sample and 4 log CFU·mL−1 S. cerevisiae strains Y32, Y34 and Y37, isolated from spontaneous olive fermentation. Sampling took place after 24 and 48 h incubation at 5 and 20 °C. RNA was extracted, stabilized and the transcription of virulence associated genes prfA, sigB, hly, plcA, plcB, inlA, inlB, inlC and inlJ, was assessed by RT-qPCR. Co-culture with the yeast strains mostly affected the transcription of sigB and inlJ, the upregulation of which during growth at 5 °C for 24 h, reached 10.13 and 9.76 log2(fold change), respectively. Similarly, the effect that incubation time had on the relative transcription of the genes under study was dependent on the co-cultivating yeast strain. On the other hand, the effect of the yeast strain was less pronounced when the relative transcription of the genes under study was assessed between 20 °C and 5 °C. In that case, incubation temperature seemed to have an important effect since, in the 79.2% of the samples analyzed, upregulation was evident, irrespective of yeast strain presence. These results highlight the complex trophic relationships that take place during co-existence between L. monocytogenes and S. cerevisiae.

Highlights

Listeriosis is a serious infection that is caused by ingestion of food contaminated with the Gram-positive bacterium Listeria monocytogenes; it is characterized by high hospitalization and mortality rates on annual basis in the U.S and the E.U. [1,2]
The aim of the present study was to assess the transcriptomic response of L. monocytogenes during co-culture with three S. cerevisiae strains during growth in Brain Heart Infusion (BHI) broth incubated at 5 ◦ C and 20 ◦ C
The S. cerevisiae strains employed in the present study exhibited no antilisterial activity, assessed through a well diffusion assay performed according to Syrokou et al [39]

Summary

Introduction

Listeriosis is a serious infection that is caused by ingestion of food contaminated with the Gram-positive bacterium Listeria monocytogenes; it is characterized by high hospitalization and mortality rates on annual basis in the U.S and the E.U. [1,2].Control of this pathogen currently relies on implementation of good hygiene practices and, if applicable, the use of antimicrobial compounds and procedures; the effectiveness of which, is verified by frequent microbiological testing. Research is focused in establishing a link between prior exposure to foodrelated abiotic and biotic stimuli and virulence potential through the effect on the transcription of virulence-associated genes. The biotic stimuli that the pathogen may encounter refer to the co-existence with other microorganisms. Such co-existence has been reported in fresh produce, dairy and meat products [13,14,15,16,17]. The outcome of such a co-existence depends on the relative physiological and metabolic attributes

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