Persister cell formation of Listeria monocytogenes in response to natural antimicrobial agent nisin

The aim of this study was to assess the efficacy of four natural antimicrobial compounds (cinnamaldehyde, eugenol, resveratrol and thymoquinone) plus a control chemical disinfectant (sodium hypochlorite) in inhibiting biofilm formation by Listeria monocytogenes CMCC54004 (Lm 54004) at a minimum inhibitory concentration (MIC) and sub-MICs. Crystal violet staining assay and microscopic examination were employed to investigate anti-biofilm effects of the evaluated compounds, and a real-time PCR assay was used to investigate the expression of critical genes by Lm 54004 biofilm. The results showed that five antimicrobial compounds inhibited Lm 54004 biofilm formation in a dose dependent way. Specifically, cinnamaldehyde and resveratrol showed better anti-biofilm effects at 1/4 × MIC, while sodium hypochlorite exhibited the lowest inhibitory rates. A swimming assay confirmed that natural compounds at sub-MICs suppressed Lm 54004 motility to a low degree. Supporting these findings, expression analysis showed that all four natural compounds at 1/4 × MIC significantly down-regulated quorum sensing genes (agrA, agrC, and agrD) rather than suppressing the motility- and flagella-associated genes (degU, motB, and flaA). This study revealed that sub-MICs of natural antimicrobial compounds reduced biofilm formation by suppressing the quorum sensing system rather than by inhibiting flagella formation.

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FROM CHITIN TO CHITOSAN – A POTENTIAL NATURAL ANTIMICROBIAL AGENT

Progress on Chemistry and application of Chitin and its Derivatives ◽

10.15259/pcacd.26.003 ◽

2021 ◽

Vol 26 ◽

pp. 23-40

Author(s):

Zofia Nuc ◽

◽

Aldona Dobrzycka-Krahel

Keyword(s):

Antimicrobial Agent ◽

Wide Spectrum ◽

Antimicrobial Properties ◽

Multidrug Resistant ◽

Modern Medicine ◽

Natural Antimicrobial ◽

Current State ◽

Naturally Occurring ◽

Alternative Sources ◽

Many Sources

Chitin is a naturally occurring polymer. Together with its derivatives such as chitosan, it has a wide spectrum of application possibilities, and many properties not yet exploited. Chitosan possesses many features desirable in an ideal antimicrobial polymer. It shows activity against multidrug-resistant bacterial and fungal strains that pose a challenge to modern medicine. Chitosan also shows activity against certain viruses, such as SARS-CoV-2. It might be used as a drug or a vaccine delivery system, is biodegradable, bioavailable and considered safe for medical use. It is important to continue exploring the potential of chitosan, as well as to investigate its sources. Indeed, many sources of this polymer are still not or have been poorly described. In this paper, we compile the current state of knowledge on the antimicrobial properties of chitosan, list alternative sources of chitin to highlight the potential of these two polymers and encourage further research.

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