Morphological differentiation between S. mutans and S. sobrinus on modified SB-20 culture medium.
Due to the major role of Streptococcus mutans and Streptococcus sobrinus in the etiology of dental caries, it is important to use culture media that allow for differentiating these bacterial species. The aim of this study was to evaluate the suitability of a modified SB-20 culture medium (SB-20M) for the isolation and morphological differentiation of S. mutans and S. sobrinus, compared to biochemical identification (biotyping). Saliva samples were collected using the spatula method from 145 children, seeded on plates containing the SB-20M, in which sucrose was replaced by coarse granular cane sugar, and incubated in microaerophilia at 37°C during 72 h. Identification of the microorganisms was performed under stereomicroscopy based on colony morphology of 4904 colonies. The morphological identification was examined by biochemical tests of 94 randomly selected colonies with the macroscopic characteristic of S. mutans and S. sobrinus using sugar fermentation, resistance to bacitracin and production of hydrogen peroxide. There was no statistically significant difference (p>0.05) between morphological identification in the SB-20M medium and biochemical identification (biotyping). Biotyping confirmed that S. mutans and S. sobrinus colonies were correctly characterized in the SB-20M in 95.8% and 95.5% of the cases, respectively. Of the mutans streptococci detected in the children 98% were S. mutans and 2% S. sobrinus. The SB-20M medium is reliable for detection and direct morphological identification of S. mutans and S. sobrinus.
Saravia
Marta Estela
ME
Department of Pediatric Clinics, Preventive and Social Dentistry, School of Dentistry of Ribeirão Preto, University of São Paulo, Ribeirão Preto, SP, Brazil.
Nelson-Filho
Paulo
P
Ito
Izabel Yoko
IY
da Silva
Léa Assed Bezerra
LA
da Silva
Raquel Assed Bezerra
RA
Emilson
Claes-Göran
CG
D015373:Bacterial Typing Techniques / Q000379:methods*; D002648:Child; D003470:Culture Media; D003731:Dental Caries / Q000382:microbiology; D006801:Humans; D012463:Saliva / Q000382:microbiology; D013295:Streptococcus mutans / Q000145:classification* / Q000166:cytology / Q000302:isolation & purification; D016986:Streptococcus sobrinus / Q000145:classification* / Q000166:cytology / Q000302:isolation & purification
D003470:Culture Media