Effect of Acid Adaptation on the Environmental Stress Tolerance of Three Strains ofVibrio parahaemolyticus

Effect of Citric Acid on Viability, Membrane Damage, Efflux Pump Activity, and Growth Recovery of Vibrio alginolyticus and Vibrio cholerae Strains

Citric acid, a common food ingredient, can induce cellular stress in foodborne pathogens, potentially affecting their viability and recovery. This study evaluated the physiological responses of Vibrio alginolyticus and Vibrio cholerae cells in logarithmic and stationary growth phases after exposure to citric acid at pH 4.5, 5.0, and 5.5 for 60, 120, and 180 min. After exposure, viability, membrane damage, efflux pump activity, and recovery were evaluated. Culture media type and growth phase had no significant effect on cell viability (p > 0.05). V. cholerae strains were more sensitive to citric acid than V. alginolyticus strains, with a slight reduction (0.5 log CFU/mL) after 180 min of citric acid exposure (p < 0.05). Membrane damage was greater in stationary-phase cells than in logarithmic-phase cells after 60 min, whereas efflux pump activity increased over time and was independent of the growth phase (p < 0.05). Regardless of pH, cells exposed to citric acid for 60 min had longer detection times (7.92 ± 0.7 h) compared to those exposed for 180 min (6.68 ± 1.45 h), and cells grew faster at high pH values and at lower exposure time (p < 0.05). Overall, citric acid induced mild sublethal damage in both V. alginolyticus and V. cholerae, with cell recovery primarily attributed to efflux pump activity. These results provide valuable insights into the risk associated with Vibrio cells under mild citric acid stress, a condition similar to that occurring during the preparation of raw fish dishes marinated in lemon juice.

Machine Learning Potential for Identifying and Forecasting Complex Environmental Drivers of Vibrio vulnificus Infections in the United States

BACKGROUND

Environmental change in coastal areas can drive marine bacteria and resulting infections, such as those caused by Vibrio vulnificus, with both foodborne and nonfoodborne exposure routes and high mortality. Although ecological drivers of V. vulnificus in the environment have been well-characterized, fewer models have been able to apply this to human infection risk due to limited surveillance.

OBJECTIVES

The Cholera and Other Vibrio Illness Surveillance (COVIS) system database has reported V. vulnificus infections in the United States since 1988, offering a unique opportunity to both explore the forecasting capabilities machine learning could provide and to characterize complex environmental drivers of V. vulnificus infections.

METHODS

Machine learning models, in the form of random forest classification models, were trained and refined using the epidemiological data from 2008 to 2018, six environmental variables (sea surface temperature, salinity, chlorophyll a concentration, sea level, land surface temperature, and runoff rate) and categorical encoders to assess our predictive potential to forecast V. vulnificus infections based on environmental data.

RESULTS

The highest-performing model, which used balanced classes, had an Area Under the Curve score of 0.984 and a sensitivity of 0.971, highlighting the potential of machine learning to anticipate areas and periods of V. vulnificus risk. A higher false positive rate was found when the model was applied to real-world imbalanced surveillance data, which is pertinent amid modeled underreporting and misdiagnosis ratios of V. vulnificus infections. Further models were also developed to explore multilevel spatial resolution, finding state-specific models can improve specificity and early warning system potential by exclusively using lagged environmental data.

DISCUSSION

The machine learning approach was able to characterize nonlinear and interacting environmental associations driving V. vulnificus infections. This study accentuates the potential of machine learning and robust surveillance for forecasting environmentally associated marine infections, providing future directions for improvements, further application, and operationalization. https://doi.org/10.1289/EHP15593.

Recent advances in understanding the fitness and survival mechanisms of Vibrio parahaemolyticus

The presence of Vibrio parahaemolyticus (Vp) in different production stages of seafood has generated negative impacts on both public health and the sustainability of the industry. To further better investigate the fitness of Vp at the phenotypical level, a great number of studies have been conducted in recent years using plate counting methods. In the meantime, with the increasing accessibility of the next generation sequencing and the advances in analytical chemistry techniques, omics-oriented biotechnologies have further advanced our knowledge in the survival and virulence mechanisms of Vp at various molecular levels. These observations provide insights to guide the development of novel prevention and control strategies and benefit the monitoring and mitigation of food safety risks associated with Vp contamination. To timely capture these recent advances, this review firstly summarizes the most recent phenotypical level studies and provide insights about the survival of Vp under important in vitro stresses and on aquatic products. After that, molecular survival mechanisms of Vp at transcriptomic and proteomic levels are summarized and discussed. Looking forward, other newer omics-biotechnology such as metabolomics and secretomics show great potential to be used for confirming the cellular responses of Vp. Powerful data mining tools from the field of machine learning and artificial intelligence, that can better utilize the omics data and solve complex problems in the processing, analysis, and interpretation of omics data, will further improve our mechanistic understanding of Vp.

Lactiplantibacillus plantarum-Nomad and Ideal Probiotic

Probiotics are increasingly recognized as capable of positively modulating several aspects of human health. There are numerous attributes that make an ideal probiotic. Lactiplantibacillus plantarum (Lp) exhibits an ecological and metabolic flexibility that allows it to thrive in a variety of environments. The present review will highlight the genetic and functional characteristics of Lp that make it an ideal probiotic and summarizes the current knowledge about its potential application as a prophylactic or therapeutic intervention.

Vibrio parahaemolyticus CadC regulates acid tolerance response to enhance bacterial motility and cytotoxicity

Pathogens adapted to sub-lethal acidic conditions could increase the virulence and survival ability under lethal conditions. In the aquaculture industry, feed acidifiers have been used to increase the growth of aquatic animals. However, there is limited study on the effects of acidic condition on the virulence and survival of pathogens in aquaculture. In this study, we investigated the survival ability of Vibrio parahaemolyticus at lethal acidic pH (4.0) after adapted the bacteria to sub-lethal acidic pH (5.5) for 1 hr. Our results indicated that the adapted strain increased the survival ability at lethal acidic pH invoked by an inorganic (HCl) or organic (citric) acid. RNA-sequencing (RNA-seq) results revealed that 321 genes were differentially expressed at the sub-lethal acidic pH including cadC, cadBA and groES/groEL relating to acid tolerance response (ATR), as well as genes relating to outer membrane, heat-shock proteins, phosphotransferase system and flagella system. Quantitative real-time polymerase chain reaction (qRT-PCR) confirmed that cadC and cadBA were upregulated under sub-lethal acidic conditions. The CadC protein could directly regulate the expression of cadBA to modulate the ATR in V. parahaemolyticus. RNA-seq data also indicated that 113 genes in the CadC-dependent way and 208 genes in the CadC-independent way were differentially expressed, which were related to the regulation of ATR. Finally, the motility and cytotoxicity of the sub-lethal acidic adapted wild type (WT) were significantly increased compared with the unadapted strain. Our results demonstrated that the dietary acidifiers may increase the virulence and survival of V. parahaemolyticus in aquaculture.

Recent advances in understanding the effect of acid-adaptation on the cross-protection to food-related stress of common foodborne pathogens

Acid stress is one of the most common stresses that foodborne pathogens encounter. It could occur naturally in foods as a by-product of anaerobic respiration (fermentation), or with the addition of acids. However, foodborne pathogens have managed to survive to acid conditions and consequently develop cross-protection to subsequent stresses, challenging the efficacy of hurdle technologies. Here, we cover the studies describing the cross-protection response following acid-adaptation, and the possible molecular mechanisms for cross-protection. The current and future prospective of this research topic with the knowledge gaps in the literature are also discussed. Exposure to acid conditions (pH 3.5 - 5.5) could induce cross-protection for foodborne pathogens against subsequent stress or multiple stresses such as heat, cold, osmosis, antibiotic, disinfectant, and non-thermal technology. So far, the known molecular mechanisms that might be involved in cross-protection include sigma factors, glutamate decarboxylase (GAD) system, protection or repair of molecules, and alteration of cell membrane. Cross-protection could pose a serious threat to food safety, as many hurdle technologies are believed to be effective in controlling foodborne pathogens. Thus, the exact mechanisms underlying cross-protection in a diversity of bacterial species, stress conditions, and food matrixes should be further studied to reduce potential food safety risks. HighlightsFoodborne pathogens have managed to survive to acid stress, which may provide protection to subsequent stresses, known as cross-protection.Acid-stress may induce cross-protection to many stresses such as heat, cold, osmotic, antibiotic, disinfectant, and non-thermal technology stress.At the molecular level, foodborne pathogens use different cross-protection mechanisms, which may correlate with each other.

Unveiling the acid stress response of clinical genotype Vibrio vulnificus isolated from the marine environments of Mangaluru coast, India

Gastric acidity is one of the earliest host defences faced by ingested organisms, and successful pathogens need to overcome this hurdle. The objective of this study was the systematic assessment of acid-stress response of Vibrio vulnificus isolated from coastal regions of Mangaluru. Acid-shock experiments were carried out at pH 4.0 and pH 4.5, with different experimental conditions expected to produce a varied acid response. Exposure to mild acid before the acid shock was favourable to the bacteria but was dependent on cell population and pH of the media and was independent of the strains tested. Lysine-dependent acid response was demonstrated with reference to the previously identified lysine decarboxylase system. Additionally, the results showed that inoculation into oysters provided some level of protection against acid stress. Increased expression of lysine/cadaverine genes was observed upon the addition of ground oyster and was confirmed by quantitative real-time PCR. The potential role of ornithine was analyzed with regard to acid stress, but no change in the survival pattern was observed. These findings highlight the physiology of bacteria in acid stress.