This study evaluated the ability of the probiotic organism Lactobacillus plantarum to inhibit the pathogenic activity of Pseudomonas aeruginosa, both in vitro and in vivo, and investigated the mechanisms involved in such protection. L. plantarum whole cultures, culture filtrates (acid filtrate and neutralised acid filtrate) and isolated, washed cells were tested in vitro for their effects on the production of the P. aeruginosa quorum-sensing signal molecules, acyl-homoserine-lactones (AHLs), and two virulence factors controlled by these signal molecules, elastase and biofilm. All were inhibited by L. plantarum cultures and filtrates, but not by isolated, washed cells. The acid L. plantarum growth medium itself had some inhibitory activity, but the greatest activity was exerted by the whole culture. To test the in-vivo activity of L. plantarum, a burned-mouse model was used in which burns infected with P. aeruginosa were treated with L. plantarum at 3, 4, 5, 7 and 9 days post-infection. Samples from skin, liver and spleen taken after 5, 10 and 15 days demonstrated inhibition of P. aeruginosa colonisation by L. plantarum. There was also an improvement in tissue repair, enhanced phagocytosis of P. aeruginosa by tissue phagocytes, and a decrease in apoptosis at 10 days. These results indicate that L. plantarum and/or its by-products are potential therapeutic agents for the local treatment of P. aeruginosa burn infections.

Bacterial colonisation and infection remain the major causes of delayed healing and graft rejection following burns. Topical treatment is necessary to reduce the incidence of burn wound infection. Silver sulphadiazine (SDAg) is an often used microbicidal agent. However, this treatment produces adverse reactions and side-effects. On the basis of experimental data and clinical application of lactobacilli as probiotics, we performed this exploratory study to establish the effectiveness of bacteriotherapy with topical application of the innocuous bacteria Lactobacillus plantarum cultured in De Man, Rogosa and Sharpe medium to provide an alternative method for burn treatment using SD-Ag as a reference. These innocuous bacteria would compete with other bacteria that are wound pathogens and would modify the wound environment and promote tissue repair. Eighty burned patients from the Plastic Surgery and Burns Unit were grouped into infected (delayed) second-and third-degree and non infected (early) third-degree burns and treated with L. plantarum or SD-Ag. The proportion of patients with delayed second-degree burns was 0Á71 for L. plantarum and 0Á73 for SD-Ag (relative rate: À2Á72%) with respect to the decrease in bacterial load (,10 5 bacteria/g of tissue), promotion of granulating tissue wound bed and healing. In early third-degree burns, the values were 0Á75 for L. plantarum and 0Á84 for SD-Ag (relative rate: À1Á07%) in preventing wound infection and promotion of granulation tissue, 0Á90 in graft taking for both treatments (relative rate: 0%) and 0Á75 for L. plantarum and 0Á77 for SD-Ag (relative rate: À2Á60%) in healing. In delayed third-degree burns, values were 0Á83 for L. plantarum and 0Á71 for SD-Ag (relative rate: þ16Á90%) with respect to the decrease in the bacterial load (,10 5 bacteria/g of tissue) and providing a granulating tissue wound bed, 0Á90 in graft taking for both treatments (relative rate: 0%) and 0Á75 for L. plantarum and 0Á64 for SD-Ag (relative rate: þ 17Á19%) in healing. Although the number of patients (between 12 and 15 per group) did not enable the application of a power statistical test, these results suggest that the L. plantarum treatment should be studied in greater depth and could be used as a valid alternative for the topical treatment of burns.

Bacterial infection impairs the healing process, promoting the chronicity of inflammation and wounds. Because antibiotics fail to eradicate bacteria, especially in biofilm form, new therapeutic modalities may be required. In the present study, the effectiveness of bacteriotherapy with Lactobacillus plantarum on infected chronic venous ulcers was investigated and its effects on interleukin (IL)-8 production by cells from the ulcer bed and neutrophils isolated from peripheral blood that were previously challenged in vitro with Pseudomonas aeruginosa and L. plantarum were studied. Topical application of L. plantarum culture to lesions (25-60 cm(2)) of 14 diabetic and 20 non-diabetic patients induced debridement, granulation tissue formation and total healing after 30 days in 43% diabetics and in 50% non-diabetics. No significant differences between the groups were observed. The cells from ulcer beds collected after treatment with L. plantarum for 10 days showed a decrease in the percentage of polymorphonuclear, apoptotic and necrotic cells and an enhancement of IL-8 production. IL-8 production by isolated neutrophils from these patients was compared with that in diabetics without ulcers, as well as normal subjects under basal conditions, and after infection of polymorphonuclear cells with P. aeruginosa preincubated either with or without L. plantarum. The basal values in diabetic and ulcer patients were higher than normal (p <0.001) and were increased by P. aeruginosa infection in normal, diabetics (p <0.001) and non-diabetics with ulcers (p <0.01). Preincubation with L. plantarum decreased IL-8 production in patients with ulcers non-diabetic and diabetic (p <0.001). Lactobacillus plantarum treatment reduced wound bacterial load, neutrophils, apoptotic and necrotic cells, modified IL-8 production and induced wound healing.

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