Inhibitory effects of chitosan in combination with antibiotics on Listeria monocytogenes biofilm

Microorganisms on living or inert surfaces usually form biofilms which makes microbes highly resistant to antibiotics and immune clearance. Herein we investigated the synergistic effect of several antibiotics with chitosan on eradication biofilms built by Listeria monocytogenes, a causative organism of the serious foodborne illness in a wide variety of mammalian species including human and food animals. Our data demonstrated that chitosan combined with the aminoglycoside antibiotic such as amikacin, but not clindamycin, vancomycin and erythromycin was more effective in inhibition or disruption of L. monocytogenes biofilms than the antibiotic alone did. To elicit an optimal anti-biofilm and bactericidal efficiency, chitosan with specialized molecular size (∼13 kDa) and high N-deacetylation degree (∼88%) was required in this combination. Further evidence showed that this strategy was effective in removing biofilms built by multiple L. monocytogenes strains and other Listeria species. Thus, our data highlighted that chitosan/amikacin combination might be useful for the treatment of Listeria biofilms and help prevent the spread of antibiotic resistance through improving antibiotic effectiveness.