Abstract
Quorum sensing (QS), one of the most remarkable microbiological discoveries, is considered a global gene regulatory mechanism for various traits in bacteria, including virulence and spoilage. Hafnia alvei, an opportunistic pathogen and a dominant psychrophile, uses the lux-type QS system to regulate the production of virulence factors and biofilms, which are harmful to the food industry. Based on the QS interference approach, this study aimed to reveal the efficacy of L-carvone at sublethal concentrations on QS-regulated virulence factors and biofilm formation in H. alvei. QS inhibitory activity was demonstrated by the reduction in swinging motility (61.49%), swarming motility (74.94%), biofilm formation (52.41%) and acyl-homoserine lactone (AHL) production (0.5 μL/mL). Additionally, in silico analysis and RT-qPCR studies for AHL synthase HalI and QS transcriptional regulator HalR revealed a plausible molecular mechanism for QS inhibition by L-carvone. These findings suggest that L-carvone (a main component of spearmint essential oils) could be used as a novel quorum sensing inhibitor to control H. alvei in the food industry.
Highlights
Hafnia alvei is a Gram-negative, facultatively anaerobic, rod-shaped, motile bacterium of the family Enterobacteriaceae; it is an opportunistic pathogen and a dominant psychrophile found in putrid food (Vivas et al, 2008)
acyl-homoserine lactone (AHL)-mediated quorum sensing (QS) systems are usually composed of the LuxI-type autoinducer synthetase, and cytoplasmic LuxR-type proteins, which are receptors activated by AHLs (Ng and Bassler, 2009)
It was observed that the Minimum Inhibitory Concentration (MIC) of L-carvone for C. violaceum CV026 was 1.0 μL/mL; L-carvone did not influence the growth of H. alvei at the same concentration
Summary
Hafnia alvei is a Gram-negative, facultatively anaerobic, rod-shaped, motile bacterium of the family Enterobacteriaceae; it is an opportunistic pathogen and a dominant psychrophile found in putrid food (Vivas et al, 2008) It has been widely isolated from different food products, such as raw meat, dairy and aquatic products, and specially from various packed food products stored at low temperatures (Kennedy et al, 2010; Chen et al, 2011; Tan et al, 2014). Quorum sensing is a process that allows single-cell organisms (like bacteria) cooperate, communicate, and act collectively By this process, they can produce, release, detect, and establish connections with small chemical molecules called autoinducers, which in Gram-negative bacteria are acyl-homoserine lactones (AHLs). Compared to antibiotics and antiseptics, QSIs aim to make the bacteria ‘surrender’ instead of killing them, which would weaken them from having resistance (Defoirdt, 2017)
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