Anti-biofilm potential of Lactobacillus casei and Lactobacillus rhamnosus cell-free supernatant extracts against Staphylococcus aureus

Biofilm production is an important virulence factor in Staphylococcus aureus. Most of the infections associated with biofilms of this bacterium are very difficult to treat using antibiotics. The present research studied the effects of the two probiotic Lactobacillus species L. casei and L. rhamnosus on S. aureus biofilm.

Cell‑free supernatant (CFS) extracts of L. casei ATCC 39392 and L. rhamnosus ATCC 7469 culture were prepared. The effects of sub‑minimum inhibitory concentrations of the CFS extracts on cell surface hydrophobicity (CSH), initial attachment, biofilm formation, and their ability in eradicating S. aureus ATCC 33591 biofilms were assessed. In addition, the effects of CFS extracts on expression of the genes involved in formation of S. aureus biofilms (cidA, hld, sarA, icaA, and icaR) were also evaluated through real‑time polymerase chain reaction.

CFSs of both Lactobacillus spp. significantly reduced CSH, initial attachment, and biofilm formation and eradicated the biofilms. The above findings were supported by scanning electron microscopy results. These two Lactobacillus CFSs significantly changed the expression of all studied biofilm‑related genes. Expression levels of cidA, hld, and icaR genes significantly increased by 4.4, 2.3, and 4.76 fold, respectively, but sarA and icaA genes were significantly downregulated by 3.12 and 2.3 fold.

The results indicated that CFS extracts of L. casei and L. rhamnosus had desirable antagonistic and anti‑biofilm effects against S. aureus. Consequently, carrying out further research enables us to prepare pharmaceuticals from these CFSs in order to prevent and treat infections caused by S. aureus biofilms.