Population dynamics of <i>L</i>. <i>monocytogenes</i> in the host’s hemolymph.

<p>Larvae were injected with live (A,C) or heat-killed (B,D) cells of <i>L</i>. <i>pentosus</i> B281 (white bars), <i>L</i>. <i>plantarum</i> B282 (dotted bars) and <i>L</i>. <i>rhamnosus</i> LGG (grey bars). Infection with the pathogen took place at 6 (A, B) and 24 h (C, D) post LAB administration. Black bars correspond to the control group. Bars with asterisks show groups with significant differences in comparison with the control group with a <i>p</i>-value ≤ 0.05. A total of 30–35 larvae were used for each treatment in order to determine the population of the pathogen in the hemolymph.</p

Significant differences as determined by <i>t</i> test for paired samples in the case of <i>Staphylococcus aureus</i> infection.

<p>Significant differences as determined by <i>t</i> test for paired samples in the case of <i>Staphylococcus aureus</i> infection.</p

Significant differences as determined by <i>t</i> test for paired samples in the case of <i>Listeria monocytogenes</i> infection.

<p>Significant differences as determined by <i>t</i> test for paired samples in the case of <i>Listeria monocytogenes</i> infection.</p

Population dynamics of <i>L</i>. <i>monocytogenes</i> and <i>S</i>. <i>aureus</i> in <i>G</i>. <i>mellonella</i> hemolymph after treatment with LAB CFS.

<p>Larvae were infected with (A) <i>L</i>. <i>monocytogenes</i> and (B) <i>S</i>. <i>aureus</i> and susequently treated with 1/10 CFS of cultures of B281, B282 and LGG LAB strains. Bars with asterisks show groups with significant differences in comparison with the control group with a <i>p</i>-value ≤ 0.05. A total of 30–35 larvae were used for each treatment in order to determine the population of the pathogen in the hemolymph.</p

Investigating the Effect of Different Treatments with Lactic Acid Bacteria on the Fate of <i>Listeria monocytogenes</i> and <i>Staphylococcus aureus</i> Infection in <i>Galleria mellonella</i> Larvae

<div><p>The use of <i>Galleria mellonella</i> as a model host to elucidate microbial pathogenesis and search for novel drugs and therapies has been well appreciated over the past years. However, the effect of microorganisms with functional appeal in the specific host remains scarce. The present study investigates the effect of treatment with selected lactic acid bacteria (LAB) with probiotic potential, as potential protective agents by using live or heat-killed cells at 6 and 24 h prior to infection with <i>Listeria monocytogenes</i> and <i>Staphylococcus aureus</i> or as potential therapeutic agents by using cell-free supernatants (CFS) after infection with the same pathogens. The employed LAB strains were <i>Lactobacillus pentosus</i> B281 and <i>Lactobacillus plantarum</i> B282 (isolated from table olive fermentations) along with <i>Lactobacillus rhamnosus</i> GG (inhabitant of human intestinal tract). Kaplan-Meier survival curves were plotted while the pathogen’s persistence in the larval hemolymph was determined by microbiological analysis. It was observed that the time (6 or 24 h) and type (live or heat-killed cells) of challenge period with LAB prior to infection greatly affected the survival of infected larvae. The highest decrease of <i>L</i>. <i>monocytogenes</i> population in the hemolymph was observed in groups challenged for 6 h with heat-killed cells by an average of 1.8 log units compared to non challenged larvae for strains B281 (<i>p</i> 0.0322), B282 (<i>p</i> 0.0325), and LGG (<i>p</i> 0.0356). In the case of <i>S</i>. <i>aureus</i> infection, the population of the pathogen decreased in the hemolymph by 1 log units at 8 h post infection in the groups challenged for 6 h with heat-killed cells of strains B281 (<i>p</i> 0.0161) and B282 (<i>p</i> 0.0096) and by 1.8 log units in groups challenged with heat-killed cells of LGG strain (<i>p</i> 0.0175). Further use of CFS of each LAB strain did not result in any significant prolonged survival but interestingly it resulted in pronounced decrease of <i>L</i>. <i>monocytogenes</i> in the hemolymph at 24 h and 48 h after infection by more than 1 log unit (<i>p</i> < 0.05) depending on the strain. The results of the present work support the broader use of <i>G</i>. <i>mellonella</i> larvae as a low cost <i>in vivo</i> tool for screening for probiotic properties.</p></div

Kaplan-Meier survival plots of <i>G</i>. <i>mellonella</i> larvae by <i>L</i>. <i>monocytogenes</i> infection.

<p>Larvae were previously administered with 10⁴ live (<b>A, C</b>) and heat-killed (<b>B, D</b>) cells of <i>L</i>. <i>pentosus</i> B281(L_B281), <i>L</i>. <i>plantarum</i> B282 (L_B282) and <i>L</i>. <i>rhamnosus</i> LGG (L_LGG). LAB administration was performed at 6 (<b>A, B</b>) and 24 h (<b>C, D</b>) prior to infection. All groups from each treatment were compared with the control group using the log rank test. The corresponding <i>p</i>-values are given in the parenthesis for each group. Groups of 16 larvae were used for the killing assays.</p

Kaplan-Meier survival plots of <i>G</i>. <i>mellonella</i> larvae by <i>S</i>. <i>aureus</i> infection.

<p>Larvae were previously administered with 10⁴ live (<b>A, C</b>) and heat-killed (<b>B, D</b>) cells of <i>L</i>. <i>pentosus</i> B281(L_B281), <i>L</i>. <i>plantarum</i> B282 (L_B282) and <i>L</i>. <i>rhamnosus</i> LGG (L_LGG). LAB administration was performed at 6 (<b>A, B</b>) and 24 h (<b>C, D</b>) prior to infection. All groups from each treatment were compared with the control group using the log rank test. The corresponding <i>p</i>-values are given in the parenthesis for each group. Groups of 16 larvae were used for the killing assays.</p

Population dynamics of <i>S</i>. <i>aureus</i> in the host’s hemolymph.

<p>Larvae were injected with live (A,C) or heat-killed (B,D) cells of <i>L</i>. <i>pentosus</i> B281 (white bars), <i>L</i>. <i>plantarum</i> B282 (dotted bars) and <i>L</i>. <i>rhamnosus</i> LGG (grey bars). Infection with the pathogen took place at 6 (A, B) and 24 h (C, D) post LAB administration. Black bars correspond to the control group. Bars with asterisks show groups with significant differences in comparison with the control group with a <i>p</i>-value ≤ 0.05. A total of 30–35 larvae were used for each treatment in order to determine the population of the pathogen in the hemolymph.</p