Cell wall components of a Lactobacillus brevis strain inhibit herpes simplex virus type 2 replication

Bacteria-free supernatant of Lactobacillus brevis strain CD2 grown in cell culture medium inhibits herpes simplex virus type 2 (HSV-2) replication in cell culture independently from H2O2 or lactic acid. The mechanisms of action and the bacterial factors responsible for the antiviral effect were studied using bacterial extracts obtained by sonication of L. brevis cells or by lysozyme/antibiotic treatment of the microorganism. The antiviral activity of bacterial cell wall was also studied. Bacterial extract and cell wall were not toxic to cells at the maximal concentration tested (3 mg/ml protein). Both the extract and the cell wall fraction showed a dose-dependent inhibitory activity on HSV2 multiplication when present on Vero cells before virus adsorption and during infection. The inhibition was exerted on the first phases of virus replication cycle. The inhibitory activity was resistant to a 30 minutes treatment at 100°C. DNA and lipids obtained from bacterial extract were devoid of any inhibitory effect. S-layer of bacterial cell-wall containing several heat-resistant molecules (teichoic and lipoteichoic acids, lipoglycans, teichuronic acids and other acidic or neutral polysaccharides) was removed by treatment with LiCl without affecting bacterial viability. Bacterial extract and cell-wall fragments obtained after LiCl treatment showed a dramatic reduction in the antiviral activity suggesting that cell wall components of L. brevis released in bacterial supernatant after sonication or lysozyme/antibiotic treatment are responsible for the inhibiting activity against HSV-2.