Rachel Mackie 43541005 23/09/2016 
Higher order taxa
Bacteria; Firmicutes; Negativicutes; Selenomonadales; Veillonellaceae; Veillonella
Description and significance
Veillonella parvula is a gram negative, strictly anaerobic, cocci found in the oral cavity, gastrointestinal tract and urinary tract of humans and other animals . Although this species usually grows in pairs, it has also been found in single cells, groups or chains . Colonies are 1-3mm in diameter, entire, smooth and greyish in colour when grown on lactate agar media .
This species was first isolated by Veillon and Zuber in 1898 as Staphylococcus parvula and renamed as Veillonella parvula by Prévot in 1933 . Although V. parvula is generally considered as a commensal organism, it has been found to participate in multispecies infections at various sites in the body as well as rare pure culture infections . Oral V. parvula is of particular interest due to its role in the early development of human dental plaque and associated oral diseases, such as periodontitis .
V. Parvula strain Te3T, isolated from human gastrointestinal tract, was the first complete genome sequence of the family Veillonellaceae . The strain Te3T genome is a single replicon, circular chromosome, which is 2,132,142 bp in length with 38.6% GC content . It is consists of 1920 genes with 1859 genes coding for proteins, 61 genes coding RNA molcules and 15 pseudogenes .
Cell structure and metabolism
V. parvula is characterised by an unusual metabolism surrounding the activity of methylmalonyl-CoA decarboxylase, an enzyme which catalyses the decarboxylase reaction of organic acids to form an electrical gradient of sodium ions . This species is unable to metabolise carbohydrates and instead gain their energy by fermenting short-chain organic acids, principally lactate and pyruvate . Often these organic acids are metabolic end products from carbohydrate fermenting bacteria . As lactic acid is metabolised, weaker acid products of propionic and acetic acids are formed. This metabolic process may provide a lactic acid sink, providing protection for acid producing bacteria, which is an important factor in caries process .
Another characteristic the V. parvula is the ability for form coaggregates with other bacteria. Although cannot adhere to surfaces itself, it can attach to structures on the surface of other cells, which is an important trait in biofilm and dental plaque formation .
Similar to other gram-negative bacteria the cell has an outer membrane and harbours lipopolysaccharide. However, it is more closely related to gram-positive cells due to the presence of cadaverine or putrescine in the peptidoglycan layer . Another feature of the cell wall is the presence of plasmalogens, ester lipids instead of phospholipids, in the cytoplasmic membrane providing finer regulation of membrane fluidity .
The genus Veillonella is one of the most prevalent and most abundant microorganism in the human oral cavity . The main habitats of V. parvula in this niche are the tongue, buccal mucosa, dental plaque and saliva . Although V. parvula has no ability to form plaque on its own, its role as early coloniser in biofilm formation has been found to facilitate the maturation of plaque through symbiotic associations with other organisms . For example, a primary plaque forming bacteria, Eubacterium saburreum, forms filaments from protein and sucrose material, which aid in adherence of V. parvula . During glucose metabolism the conversion of sucrose into dextrose by streptococci species has also been found to provide adherence to teeth . Fructose, another by-product of this glucose conversion, can also be used by V. parvula in lipopolysaccharide formation . In addition, the lactic acid and other organic acids produced by these and other organisms promote colonisation by providing a carbon and energy source for V. parvula. Removal of these acids also allows other organisms, which would normally be unable to withstand low pH, to inhabit the environment .
V. parvula is an important pathogen in oral diseases and has been linked to other local and systemic infections . It plays a major role in dental caries and gum disease, and interradicular infections including abscesses and root canals . Reports of non-oral diseases include tonsillitis , meningitis, osteomyelitis, discitis, sinusitis, endocarditis and prosthetic joint infection .
Comparable to other gram-negative strict anaerobes, the pathogenicity is related to the lipopolysaccharides. However, the biological activity of lipopolysaccharides and the molecular mechanisms of the innate immune response leading to inflammatory infections are still largely unknown . V. parvula is also know to produce hydrogen sulphide in response to proteins found in human blood plasma, which results in toxic effects .
Application to biotechnology
Researchers have developed the first genetic transformation system of Veillonella isolated from saliva using Escherichia coli-Veillonella shuttle vector . These findings provide valuable tools for the further genetic study of this species . The use of genetic manipulation can provide important clinical information on the biology, pathogenesis and antibiotic resistance.
Recent studies investigating the interactions between V. parvula and other bacteria in multispecies biofilm environments aim to determine the development and pathogenesis of human dental plaque. Since caries are highly associated with lactic acid producing bacteria, V. parvula levels may serve as a biological indicators and an early warning sign of acid production . Understanding these interactions during biofilm formation may help in the development of methods for prevention of oral diseases.
V. parvula has been reported to confer general resistance to streptomycin , penicillin , tetracycline, vancomycin, aminoglycosides, ciprofloxacin, and an intermediate resistance to erythromycin , chloramphenicol and lincomycin . It is however, susceptible to penicillin G, cephalotin and clindamycin .
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2. Gronow, S (2009) Complete genome sequence of Veillonella parvula type strain (Te3T ). Standards in Genomic Sciences 1 : 57-65
3. http://www.homd.org Human Oral Microbiome
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6. Mashimo, P.A et al. (1981) Eubacterium saburreum and Veillonella párvula: A Symbiotic Association of Oral Strains*. J Periodontol. 52(7) : 374-9
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8. Rocas, I.N & Siqueira, J.F (2005) Culture-Independent Detection of Eikenella corrodens and Veillonella parvula in Primary Endodontic Infections. J. Endodontics. 32(6) : 509–512
This page is written by Rachel Mackie for the MICR3004 course, Semester 2, 2016