RESUMO
<p><b>OBJECTIVE</b>To investigate the aciduric bacteria in different stages of the fissure caries in order to determine potential roles of the microflora in the development of dental caries.</p><p><b>METHODS</b>Plaque samples were taken from 10 incipient carious fissures of the first permanent molars. Plaque samples were also collected from sound fissures of the first permanent molars in 10 other subjects who kept caries free over the past 2 years and from the above 10 subjects. The predominant bacteria were isolated by using both the most probable method in media at pH7.0 and 5.2, and the conventional plating methods. Streptococcus spp. was identified by means of API 20 Strep commercial kit.</p><p><b>RESULTS</b>S. mutans was the predominant aciduric bacteria infissures of caries-free children and more frequently recovered at neutral pH. Whilst, S. sanguis was predominant at pH5.2 in sound and carious of fissures of caries-active children. The proportion of Gram-positive rods at pH5.2 was 82%, significantly greater than that of 61% at pH7.0.</p><p><b>CONCLUSION</b>The ecology of plaque is complex and the composition of microflora at each stage of caries could be different. The composition of bacteria was consistent with the changes of local pH in the plaque.</p>