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Rothia dentocariosa
Alexandria Chin, Bench C, 17 November 2024 ^[1]

Classification

Higher order taxa

Bacteria – Terrabacteria group – Actinobacteria – Actinobacteria – Micrococcales – Micrococcaceae – Rothia ^[1]

Species

Rothia dentocariosa
Type strain: strain ATCC 17931= CCUG 35437 = CIP 81.83 = DSM 43762 = DSM 46363 = IFO (now NBRC) 12531 = JCM 3067 = NCTC 10917 = NRRL B-8017. ^[2]

Description and significance

Rothia dentocariosa was first discovered by Onisi in 1949, from dental plaques and caries in humans. ^[4] From his study of the organism he proposed it be named A. dentocariosus because of the morphological similarities with Actinomyces species found in the mouth. His study of the isolate showed that it was a highly pleomorphic, facultative anaerobic organism with both coccoid and branched filament structures. ^[3]

In 1957, while studying carious dentine Roth found a similar group of organisms and believed it to be the same as Onisi’s isolate. However, she found the organism to grow under aerobic conditions and therefore suggested the name N. dentocariosus. ^[3]

Davis and Freer (1960) were unaware of Roth and Onisi’s studies and described a similar group of isolates from the human mouth. They initially suggested the name N. salivae but further studies of the cell wall showed that this organism did not belong in the Nocardia genus as it did not contain diaminopimelic acid, which is a characteristic of Nocardia genus.

Georg and Brown in 1967 created the genus Rothia in the Actinomycetaceae family to accommodate this organism. Rothia was named after Genevieve D. Roth, as a tribute to her work with the organism. ^[3]

In 1997, Stackebrandt et al. moved Rothia to the Micrococcaceae family where it shares signature nucleotides in the 16S rDNA sequence with other genera in the family. ^[10]

R. dentocariosa is a normal inhabitant of the oral cavity, a study showed over 30% of healthy individuals have this organism in their mouth. ^[4] It is present in saliva and is frequently isolated from supragingival plaque and respiratory tract. ^[6] It is not commonly isolated from clinical specimens but it has been isolated from blood, spinal fluids and abscesses. ^[3]

R. dentocariosa is a gram-positive, non-motile, non-spore forming, pleomorphic organism, that can present in coccoid and/or filamentous forms. ^[7] ^[9] It has a highly variable microscopic morphology. ^[3] Morphology differs between young and mature colonies. Young colonies are 1mm in diameter, have entire edges and are smooth to a slight rough with a mucoid consistency. While, mature colonies can be 1-4mm, raised with a rough and cerebriform surface irregular or scalloped edges. ^[3] Laboratory growth of R. dentocariosa requires an enriched medium, such as TSA, ^[3] and organic nitrogen, however carbon dioxide is not necessary. ^[8]

Studying this organism and determining specific identifiers is important as Rothia is often overlooked due to its similarities in morphology with Actinomyces and Nocardia, which have pathogenic members. ^[3] Isolates of R. dentocariosa have been found in periodontal lesions and associated with several cases of infective endocarditis. ^[9]

Genome structure

R. dentocariosa strain ATCC 17931 has a circular genome with 2, 506, 025 bp and is made up of 1 chromosome. It has a total of 2, 126 genes with 2, 040 coding DNA sequences and encodes 2, 213 proteins. ^[5] From a genome annotation, 62 RNA sequences were identified, 10 rRNAs (4, 3 and 3 of 5S, 16S and 23S respectively), 49 tRNAs and 3 ncRNAs. ^[11]

Cell structure and metabolism

As R. dentocariosa is a gram-positive organism, its cell wall has a defined layer of peptidoglycan of the A3-alpha type, which has D-alanine in position 4, L-lysine in position 3 and an inter-peptide bridge of L-alanine. ^[8] Analysis of the cell wall showed that the sugars galactose, fructose, glucose and ribose are involved. ^[7] R. dentocariosa is a non-motile organism and does not have aerial mycelium, making it non-sporogenic. ^[9]

Coaggregation bridging is critically important for the development of microbial plaque and it was observed that Bacteroides intermedius coaggregates with R. dentocariosa in the oral microflora. Bacteroides species is observed several days after on freshly cleaned tooth surface, which recognize microcolonies made by Streptococcus sanguis. R. dentocariosa attaches to the B. intermedius and is prevented from washing out of the oral cavity by it’s adherence to the tooth surface, via S. sanguis. ^[12]

Laboratory testing of the organism’s metabolism showed activity of catalase production, nitrate and nitrite reduction, esculin hydrolysis and acid production from glucose, sucrose, maltose, salicin and glycerol. This can be compared to Nocardia species, which can oxidise sugars but does not ferment them into acid. ^[3] R. dentocariosa’s glucose fermentation also makes it unsuitable for the Actinomyces species as it produces lactic and acetic acid when Actinomyces produce succinate. ^[6]