Differential Modulation of Listeria monocytogenes Fitness, In Vitro Virulence, and Transcription of Virulence-Associated Genes in Response to the Presence of Different Microorganisms

Abstract

Interactions between Listeria monocytogenes and food-associated or environmental bacteria are critical not only for the growth but also for a number of key biological processes of the microorganism. In this regard, limited information exists on the impact of other microorganisms on the virulence of L. monocytogenes. In this study, the growth of L. monocytogenes was evaluated as single culture or in co-culture with L. innocua, Bacillus subtilis, Lactobacillus plantarum and Pseudomonas aeruginosa in tryptic soy broth (10°C/10 days and 37°C/24 hours). Transcriptional levels of 9 key virulence genes (inlA, inlB, inlC, inlJ, sigB, prfA, hly, plcA, plcB) and invasion efficiency and intracellular growth in Caco-2 cells, were determined for L. monocytogenes following grown in mono- or in co-culture for 3 days at 10°C or 9 hours at 37°C. The growth of L. monocytogenes was negatively affected by the presence of L. innocua and B. subtilis, while the effect of cell-to-cell contact on L. monocytogenes growth was dependent on the competing microorganism. Co-cultivation affected the in vitro virulence properties of L. monocytogenes in a microorganism-specific manner, with L. innocua mainly enhancing and B. subtilis reducing the invasion of the pathogen in Caco-2 cells. Assessment of the mRNA levels of L. monocytogenes virulence genes in the presence of the four tested bacteria revealed a complex pattern in which the observed up- or down-regulation was only partially correlated with growth or in vitro virulence and mainly suggested that L. monocytogenes may display a microorganism-specific transcriptional response. Importance Listeria monocytogenes is the etiological agent of the severe foodborne disease listeriosis. Important insight regarding the physiology and the infection biology of this microorganism has been acquired the past twenty years. However, despite the fact that L. monocytogenes co-exists with various microorganisms throughout its lifecycle and transmission from the environment to foods and then to the host, there is still limited knowledge related to the impact of surrounding microorganisms on L. monocytogenes biological functions. In this study we showed that L. monocytogenes modulates specific biological activities (i.e. growth and virulence potential) as a response to co-existing microorganisms and differentially alters the expression of virulence-associated genes when confronted with different bacterial genus and species. Our work suggests that the interaction with different bacteria plays a key role in the survival strategies by L. monocytogenes and supports the need to incorporate biotic factors in the research conducted for the identification of mechanisms deployed by this organism to be established in different environments.

Lactiplantibacillus plantarum subsp. plantarum and Fructooligosaccharides Combination Inhibits the Growth, Adhesion, Invasion, and Virulence of Listeria monocytogenes

“…The adhesion and invasion abilities of L. monocytogenes to Caco-2 cells are reduced when L. monocytogenes is co-cultured with Lactobacillus spp. [ 68 ], Lactobacillus rhamnoides [ 69 ], and L. plantarum [ 55 ]. Moroni et al observed that the adhesion and invasion ability of L. monocytogenes to colonocytes was reduced by Lactobacillus [ 70 ].…”

“…All assays were independently repeated six times. Most previous reports used 1–2 h to detect the in vitro adhesion and invasion [ 55 ], so we used 1, 1.5, and 2 h for evaluation, and 2 h was the shortest time to detect the difference among different treatment groups.…”

Transcription of Listeria monocytogenes Key Virulence Genes on Tomato, Cucumber and Carrot

“…The pathogenic potential of L. monocytogenes, assessed almost exclusively by invasion to cell lines, such as Caco-2, THP-1 and HT-29, is affected by abiotic and biotic stimuli that include exposure to temperature, acid and osmotic fluctuations as well as the food matrix and co-existing microorganisms [18][19][20][21][22][23][24][25][26][27][28][29][30][31][32]. Correlation between the transcriptomic response of the pathogen to the above stresses with invasiveness, in some cases was successful [13,21]. Several studies have assessed the transcription of virulence associated genes during growth of L. monocytogenes on a food matrix at various storage temperatures and times [8][9][10][11][12][13][15][16][17].…”

“…More accurately, Olesen et al [8], Bae et al [9], Rantsiou et al [10,11] and Mataragas et al [12] studied the transcription of key virulence genes of the pathogen on meat products, Duodu et al [13] and Pilevar et al [14] on fish products, Rantsiou et al [11] and Alessandria et al [15] on dairy products and Hadjilouka et al [16] and Kang et al [17] on fruits and vegetables. The significance of these studies is highlighted by the fact that prior exposure to environmental stimuli affects invasiveness [18][19][20][21][22][23][24][25][26][27][28][29][30][31][32] and that upregulation of virulence associated genes observed during such exposure is correlated with increased invasion efficiency [13,21].…”

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

“…The outcome of such a co-existence depends on the relative physiological and metabolic attributes as well as the environmental conditions, which concomitantly define the relative population dynamics of the members of the microecosystem. The effect that such co-existence may have on the transcription of virulence-associated genes and invasiveness of the pathogen, has been only marginally studied [18][19][20][21][22][23][24][25]; in some cases, a correlation between the transcriptomic response of the pathogen and its invasiveness has been suggested [6,25].…”