Quorum sensing is a cell-to-cell communication system that exists widely in the microbiome and is related to cell density. The high-density colony population can generate a sufficient number of small molecule signals, activate a variety of downstream cellular processes including virulence and drug resistance mechanisms, tolerate antibiotics, and harm the host. This article gives a general introduction to the current research status of microbial quorum-sensing systems, focuses on the role of quorum-sensing systems in regulating microbial resistance mechanisms, such as drug efflux pump and microbial biofilm formation regulation, and discusses a new strategy for the treatment of drug-resistant bacteria proposed by using quorum quenching to prevent microbial resistance.

Quorum-Sensing Regulation of Antimicrobial Resistance in Bacteria.

Foodborne pathogens are the main factors behind foodborne diseases and food poisoning and thus pose a great threat to food safety. Many outbreaks have been found to be associated with biofilms. It is well documented that biofilms have become an urgent problem in the current food industry as biofilms can renders inhabitants on such films resistant to antimicrobial agents and cleaning. In this paper, recent literature related to the biofilm formation and on the factors that influence foodborne pathogens are reviewed. In addition, the control and removal strategies of foodborne pathogens used to efficiently maintain food safety in the food industry are also discussed.

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Biofilm formation and control strategies of foodborne pathogens: food safety perspectives

Environmental biotechnology offers several promising techniques for the rehabilitation of polluted environments. The modern industrialized world presents novel challenges to the environmental sciences, requiring a constant development and deepening of knowledge to enable the characterization of novel pollutants and a better understanding of the bioremediation strategies as well as their limiting factors. The success of bioremediation depends heavily on the survival and activities of indigenous microbial communities and their interaction with introduced microorganisms. The majority of natural microbiomes remain uncultivated; therefore, further investigations focusing on their intrinsic functions in ecosystems are needed. In this review, we aimed to provide (a) a comprehensive overview of the presence of viable but nonculturable bacteria and yet-to-be-cultivated cells in nature and their diverse awakening strategies in response to, among other factors, signalling extracellular metabolites (autoinducers, resuscitation promoting factors, and siderophores); (b) an outline of the trends in isolating unculturable bacteria; and (c) the potential applications of these hidden players in rehabilitation processes.

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Challenges of unculturable bacteria: environmental perspectives

Bacteria have evolved numerous means of survival in adverse environments with dormancy, as represented by "persistence" and the "viable but nonculturable" (VBNC) state, now recognized to be common modes for such survival. VBNC cells have been defined as cells which, induced by some stress, become nonculturable on media that would normally support their growth but which can be demonstrated by various methods to be alive and capable of returning to a metabolically active and culturable state. Persister cells have been described as a population of cells which, while not being antibiotic resistant, are antibiotic tolerant. This drug-tolerant phenotype is thought to be a result of stress-induced and stochastic physiological changes as opposed to mutational events leading to true resistance. In this review, we describe these two dormancy strategies, characterize the molecular underpinnings of each state, and highlight the similarities and differences between them. We believe these survival modes represent a continuum between actively growing and dead cells, with VBNC cells being in a deeper state of dormancy than persister cells.

Relationship between the Viable but Nonculturable State and Antibiotic Persister Cells.

The viable but nonculturable (VBNC) state has been recognized as a strategy for bacteria to cope with stressful environments; in this state, bacteria fail to grow on routine culture medium but are actually alive and can resuscitate into a culturable state under favorable conditions. The VBNC state may pose a great threat to food safety and public health. To date, more than 100 VBNC microorganism species have been proven to exist in fields of food safety, environmental application, and agricultural diseases. Most harsh conditions can induce these microorganisms into the VBNC state, including food processing and preservation methods, adverse environmental conditions, and plant-disease controlling means. The characteristics of VBNC state cells differ from those of normally growing cells and dead cells, based on which of the various detection methods are developed, and they are of great significance for potential risk assessment. To provide molecular level insights into this state, many studies on induction and resuscitation mechanisms have emerged over the past three decades, including research on omics, specific genes, or proteins involved in VBNC state formation and the roles of promoters in resuscitation from the VBNC state. In this review, microorganism species, induction and resuscitation factors, detection methods, and formation and resuscitation mechanisms of the VBNC state are comprehensively and systematically summarized.

https://onlinelibrary.wiley.com/doi/pdf/10.1111/1541-4337.12513

Induction, detection, formation, and resuscitation of viable but non-culturable state microorganisms.

The viable but non-culturable (VBNC) state, a unique state in which a number of bacteria respond to adverse circumstances, was first discovered in 1982. Unfortunately, it has been reported that many foodborne pathogens can be induced to enter the VBNC state by the limiting environmental conditions during food processing and preservation, such as extreme temperatures, drying, irradiation, pulsed electric field and high pressure stress, as well as the addition of preservatives and disinfectants. After entering the VBNC state, foodborne pathogens will introduce a serious crisis to food safety and public health because they cannot be detected using conventional plate counting techniques. This review provides an overview of the various features of the VBNC state, including the biological characteristics, induction and resuscitation factors, formation and resuscitation mechanisms, detection methods, and relationship to food safety.

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Xihong Zhao

Papers

Current Perspectives on Viable but Non-culturable State in Foodborne Pathogens.