Vibrio Testing

The genus Vibrio is a group of gram-negative, non-spore forming, straight or curve shaped rod bacteria. Three species V. cholerae, V. parahaemolyticus and V. vulnificus are considered to be significant human pathogens and have the potential to cause foodborne illness.

Figure 1. Electron micrograph of Vibrio and related contaminated foods

Vibrio naturally presents in coastal water and marine environments and is a natural contaminant of seafood. V. cholerae is usually related to poor hygiene and polluted water supplies. V. parahaemolyticus is the species that most likely to be associated with foodborne illness in humans. The contamination of V. parahaemolyticus is predominantly from foods such as fish, shellfish, and crustaceans particularly oysters. Vibrio can survive during freezing temperature in seafood, thus a significant concern for the seafood industry. V. parahaemolyticus and V. vulnificus are salt-tolerant and lysed almost immediately in freshwater. Foodborne illness caused by V. parahaemolyticus is generally from the consumption of raw or lightly cooked seafood or cooked seafood that has been cross contaminated. Initial levels of Vibrio in seafood is dependent on the environmental factors during harvest. The number of Vibrio naturally in seafood is usually less than 100 CFU/g. The bacteria can grow to the levels that cause illness under poor refrigeration conditions during storage. Inadequate processing and cross contamination can also contribute to the contamination of Vibrio. Vibrio is sensitive to heat and proper cooking to an internal temperature of 65℃ can destroy the bacteria.

Vibrio can cause serious and potentially fatal gastroenteric infections. It is still a major health problem in parts of the developing countries. Symptoms of V. parahaemolyticus infection include nausea, vomiting, abdominal pain, and diarrhea. The symptoms usually occur between 4 hours to a couple of days.

The presence of V. parahaemolyticus in ready-to-eat foods with high numbers (>10⁴ CFU/g) is potentially hazardous as the consumption of the contaminated foods may result in foodborne illness. The level of V. parahaemolyticus between 10² - 10⁴ CFU/g indicates an unacceptable level of contamination and the number below 3 CFU/g is generally regarded as satisfactory. V. cholerae should be absent in 25 g of samples.

Vibrio Testing of Food at Alfa Chemistry

The standard methods (EN/ISO, FDA BAM and AOAC) that have been widely used to enumerate and identify Vibrio spp. are culture-based methods using general microbiological testing supplies. For the detection, saline peptone water (APW) is usually used for enrichment. A second enrichment step using selective medium is typically performed after the initial enrichment. For the quantification, it is conducted by the plate counting technique or the most probable number (MPN) to determine the level of Vibrio in samples. Plating method for Vibrio uses solid medium of thiosulphate citrate bile salts sucrose (TCBS) agar. MPN method is a multi-step assay including presumptive, confirmed, and completed phases based on statistical analysis. The confirmation test is then performed using biochemical identification technique.

Alfa Chemistry offer accurate and validated testing platforms for the identification and enumeration of Vibrio spp. in various food samples to meet customers' needs. We also have experience working on different standards and regulations.

Platform: Plate counting or MPN technique

Limit of detection: <10 CFU/g

Sample type: Food samples mainly seafood

Sample size: 25g