Inactivation of Vibrio sp. in pure cultures and mussel homogenates using high hydrostatic pressure.

The objective of this study was to determine the effect of high hydrostatic pressure (HHP) on the inactivation of Vibrio sp. in pure cultures and mussel homogenates. Four Vibrio strains including V. alginolyticus, V. cholerae, V. parahaemolyticus and V. vulnificus were used. HHP treatments were performed with both pure Vibrio sp. cultures in alkaline peptone water (2% NaCl) and artificially inoculated mussel homogenates at pressure levels of 250, 350 and 450 MPa for 1 and 3 min at 25°C. Counts of Vibrio were determined before and after treatment using drop plating method. The effect of high pressure on the reduction level significantly differed among the respective Vibrio species. Vibrio vulnificus was the most susceptible species to HHP. To achieve a >5 log reduction in mussel homogenates, pressure treatment needs to be (i) 350-450 MPa for ≥1 min at 25°C for both V. alginolyticus and V. cholerae, (ii) 250 MPa for ≥3 min or 350-450 MPa for ≥1 min for V. vulnificus and (iii) 350 MPa for ≥3 min or 450 MPa for ≥1 min for V. parahaemolyticus. SIGNIFICANCE AND IMPACT OF THE STUDY: High hydrostatic pressure (HHP) has been applied to inactivate spoilage and pathogenic micro-organisms in a variety of food products, including seafood. Vibrio sp. are frequently reported as the main cause of foodborne illness associated with consumption of raw or undercooked seafood particularly shellfish worldwide. To date, data on the inactivation of Vibrio sp. via HHP are still limited and most of the trials only investigated HHP application in oysters and clams. This study demonstrates the efficacy of HHP inactivating Vibrio sp. in both pure culture and mussel homogenates.

Gene expression profiles of Vibrio parahaemolyticus in the early stationary phase.

UNLABELLED: Vibrio (V.) parahaemolyticus is an aquatic bacterium capable of causing foodborne gastroenteritis. In the environment or the food chain, V. parahaemolyticus cells are usually forced into the stationary phase, the common phase for bacterial survival in the environment. So far, little is known about whole genomic expression of V. parahaemolyticus in the early stationary phase compared with the exponential growth phase. We performed whole transcriptomic profiling of V. parahaemolyticus cells in both phases (exponential and early stationary phase). Our data showed in total that 172 genes were induced in early stationary phase, while 61 genes were repressed in early stationary phase compared with the exponential phase. Three functional categories showed stable gene expression in the early stationary phase. Eleven functional categories showed that up-regulation of genes was dominant over down-regulation in the early stationary phase. Although genes related to endogenous metabolism were repressed in the early stationary phase, massive regulation of gene expression occurred in the early stationary phase, indicating the expressed gene set of V. parahaemolyticus in the early stationary phase impacts environmental survival. SIGNIFICANCE AND IMPACT OF THE STUDY: Vibrio (V.) parahaemolyticus is one of the main bacterial causes of foodborne intestinal infections. This bacterium usually is forced into stationary phase in the environment, which includes, e.g. seafood. When bacteria are in stationary phase, physiological changes can lead to a resistance to many stresses, including physical and chemical challenges during food processing. To the best of our knowledge, highlighting the whole genome expression changes in the early stationary phase compared with exponential phase, as well as the investigation of physiological changes of V. parahaemolyticus such as the survival mechanism in the stationary phase has been the very first study in this field.

LuxS distribution and AI-2 activity of Campylobacter spp.

AIMS: This study investigates the distribution of LuxS within Campylobacter (Camp.) species and Autoinducer (AI)-2 activity of Camp. jejuni NCTC 11168 in food matrices. METHODS AND RESULTS: LuxS (S-ribosylhomocysteinase) sequences of different Campylobacter spp. were compared, and AI-2 activity was measured with an AI-2 reporter assay. Highest LuxS homologies were shared by Camp. jejuni, Camp. coli and Camp. upsaliensis, and their LuxS sequences had more similarities to the analysed Arcobacter and Vibrio harveyi strains than to all other analysed Campylobacter species. Of 15 analysed species only Camp. lari, Camp. peloridis and Camp. insulaenigrae did not produce AI-2 molecules. Cultivation of Camp. jejuni NCTC 11168 in chicken juice reduced AI-2 activity, and this reduction is not because of lower luxS expression or functionality. CONCLUSION: Not all Campylobacter species encode luxS. Food matrices can reduce AI-2 activity in a LuxS-independent manner. SIGNIFICANCE AND IMPACT OF THE STUDY: Besides, Camp. lari, Camp. peloridis and Camp. insulaenigrae do not show AI-2 activity. Further investigations should clarify the function of AI-2 in Campylobacter spp. and how species lacking luxS could overcome this alteration. Furthermore, the impact of food matrices on these functions needs to be determined as we could show that chicken juice reduced AI-2 activity.

Prevalence and Antimicrobial Resistance of Vibrio spp. in Retail and Farm Shrimps in Ecuador.

The aim of this study was to investigate the prevalence of Vibrio spp. in shrimp at retail and in shrimp farms in Ecuador and to determine the antimicrobial agent resistance patterns of farm isolates. The presence of genes linked to early mortality syndrome (EMS) or acute hepatopancreatic necrosis disease (AHPND) also was evaluated. Vibrio spp. were isolated from retail shrimps in Cuenca, Ecuador, and farm shrimps originating from provinces El Oro and Guayas, Ecuador. A total of 229 shrimp samples were collected, of which 71 originated from retail markets in Cuenca and 158 came from shrimp farms. Overall, 219 (95.6%) samples tested positive for Vibrio spp. Vibrio parahaemolyticus (80.8%) was the most common species detected, followed by Vibrio alginolyticus (50.2%), Vibrio cholerae (11.3%), and Vibrio vulnificus (3.5%). None of the V. parahaemolyticus isolates carried the virulence-associated tdh and trh genes. In V. parahaemolyticus shrimp farm isolates, high resistance was found to ampicillin (92.2%), and intermediate resistance was found to tetracycline (51.3%) and amikacin (22.1%). Of the V. parahaemolyticus strains, 68 were resistant to at least three antimicrobial agents, and 2 were resistant to seven antimicrobial agents simultaneously. Up to 18 resistant isolates were found for V. alginolyticus, whereas V. vulnificus and V. cholerae isolates were more susceptible. None of the V. parahaemolyticus isolates carried the EMS-AHPND plasmid. The results of this study revealed the ubiquitous occurrence of Vibrio spp. in shrimps at retail and on shrimp farms in Ecuador.