Vibrio Gram Negative Bacteria Structure And Classification Biology Essay


Vibrio is a genus of Gram-negative bacteria which has a curve rod shaped structure. On basis of the type of species, the bacteria can be either S-shaped or comma-shaped. They are facultative anaerobes, which mean they can sustain without oxygen. They are highly motile organisms, usually consisting of a single polar flagellum to locomote. This flagellum is surrounded by a sheath continuous to the outer membrane of the cell wall. The bacteria lose their flagella once they become endosymbionts with other organisms (fish, squid. Some Vibrio species, such as the Vibrio cholera, are able to generate three polysaccharides that relate to cell surface - lipopolysaccharide, capsule and rugose exopolysaccharude. The lipopolysaccharide layer and the capsule both assist in the avoidance of detection by the host immune system. The rugose polysaccharide helps the bacterium survive in aquatic environmental when nutrients are deficient.

Vibrios are one of the most common microorganisms found in water across the world. They live in both marine and fresh water habitats and associate themselves in a mutualism with fish and other aquatic life. The idea of mutualism is beneficial for Vibrio species as it lets them to spread their virulent strains. An example is Vibrio cholera. Vibrio cholera is found in coastal areas of algal bloom. Overabundance of algal bloom such as phytoplankton and zooplankton has a huge amount of consequences on food and water safety because Vibrio cholera attaches itself to small crustaceans called Copepods which help spread the Cholera disease. Another example is the relationship between V fisheri and its usual host (a squid). The host expels 90% of the V fisheri each day and this allows the offspring to obtain the endosymbionts that they need. Not only is mutualism involved, some Vibrio species are known to be zoonotic. This means are able to hop from species to species to ensure that they are widely distributed. Shellfish is an example that can host Vibrio species which may make people sick.

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Furthermore, not all Vibrio species are known to be pathogenic. Pathogenic species are usually found in polluted regions that provide poor water purification systems. Moreover, it is also the issue of sewage spillage and untreated sewage that can spread Vibrio species. It is these water systems that create a primary pathway between humans being hosts for these pathogenic strains and displaying Vibrio-induced diseases. The co-existence of both pathogenic and non-pathogenic strains in water enchances genetic diversity for the Vibrio species. This produces an advantage for Vibrio species as the gene transference between different species could lead to new modified virulent strains. Some Vibrio species that are pathogenic could also build a parasitic relationship with the host, typically affecting fish, frogs and eels.

Dormancy is a common phase amongst Vibrio species. Usually, they survive on warm climates and hibernate during cold climates. The ability of the bacteria to be dormant in regions exhibiting colder climate provides an advantage, because it ensures that the organisms will survive in a variety of climate. For microbiologists and public health officials, this trait causes irritation and difficulty for the eradication of Vibrio species as they possess greater ecological tolerance levels.

The Vibrio species exhibit two types of metabolism, they are the respiratory and the fermentative metabolism . Oxygen is the universal electron acceptor in Vibrios. Vibrios reproduce very simply, through asexual reproduction. The optimum temperature for cell function is 37 degrees with an optimum pH of 8.2 which is slightly basic in nature.

The isolation and culturing of Vibrio species has been enhanced by the development of Culture media which are highly selective for Vibrios. In general terms, Vibrio species can be synthesised in either a liquid or solid media. The distinction between these two mediums is the liquid media will enable the synthesis of Vibrio species with polar flagella that are sheathed with the outer membrane of the cell wall, on the other hand the solid media will synthesise flagella that aren't sheathed. Vibrios obtain such simplistic growth factor requirements that they also can be grow in a synthetic media with glucose as a sole source for carbon and energy. Due to the nutritional versatility, every Vibrio species will consume unique amounts of carbon and energy sources producing a vast amount of individualised metabolic diversity. Furthermore, since Vibrios are typically know as marine microorganisms, it is also beneficial to provide a growth media of additional 2-3% NaCl or a sea water base for optimal growth.

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The most commonly used media to synthesise the growth of Vibrios is a selective media called TCBS (Thiosulfate Citrate Bile Salts Sucrose Agar). Also classified under the blood agar culture media, TCBS is highly selective in Vibrio species found in cholera, diarrhoea and food poisoning. This agar was developed by Kobayashi, who modified the original selective medium by Nakanishi. TCBS Agar can provide high selectivity to Vibrios when combined with various constituents and growth media. For example, when combined with a TTGA Agar (Tellurite Taurocholate and Gelatine Agar), it is considered significantly beneficial in growing Vibrio cholera. Characteristic appearances of the colonies help in the identification of V cholera isolates when grown on selective medium such as TCBS agar; however, when the sample contains other indigenous vibrios from marine sources, the identification could be difficult and may require special procedures. Preliminary identification may be achieved by testing for glucose fermentation in Kligler iron agar, nitrate reduction to nitrite, oxidase production, relative growth on nutrient agar with and without salt, and in Moeller's broth containing lysine and ornithine decarboxylases and arginine dihydrolase.

Achievement in isolating and culturing Vibrios is also successful when using enrichment media. Although enrichment media is not particularly useful for the isolation of V.cholera from fresh diarrheal stool, it is useful for isolating Vibrio species from asymptomatic carriers or patients in late convalescence. To isolate Vibrio cholera from food and water samples, it requires the combination of alkaline peptone water for primary enrichment and tellurite-bile salt broth for the secondary enrichment. For isolation of Vibrio cholera from seafood, the material is usually homogenised and inoculated into the enrichment broth. However, such homogenates often contain inhibitory substances and may retard the expected growth of the organisms. It is recommended that the seafood samples should be cut into small pieces, added to 10 times the volume of enrichment broth, shaken vigorously for 1-2 minutes or homogenised, the pieces removed and then the broth incubated at 35 degrees celcius. Vibrio species associated with human infections will only grow in enrichment broths associated with approximately 1% NaCl (excluding Vibrio cholera, Vibrio mimicus and some strains of Vibrio metschnikovii). Sheep blood agar, an enrichment media, is used to determine biotypes of Vibrio cholera. By using this particular agar, it tests for hemolysin production that will separate the strains of Vibrio cholera.

There are various environmental, medical and biotechnological implications in the research of Vibrio species. An application of biotechnology is the usage of non-toxic B-units of Vibrio cholera. When this is attached to a fluorescent protein they can be used to detect neurons. Nerve locations can be detected in vivo (the body). This use of non-toxic Vibrio cholera products can be useful in the operating room when small nerves need to be visualised. A current research of Vibrios is the idea of quorum sensing. This is a communicational system between Vibrio cholera bacterium using molecules called autoinducers. This system enables cells to coordinate a specific function or gene expression as a group.