Adherence and Persistence of Gram- Non-Oral Bacteria in the Mouth

Objectives: At the Barcelona IADR meeting (2010), we showed that non-oral Streptococcus thermophilus and Saccharomyces cerevisiae adhered in vivo to the salivary pellicle and persisted in the oral cavity for up to 90 min. The aim of the present study was to explore whether this is true also for non-oral Gram-negative bacteria. Methods: 6 volunteers received supragingival debridement. After a 45-min pellicle formation phase, the volunteers rinsed for 2 min with a suspension of E. coli Nissle strain (Ec) or Acetobacter aceti (A.ac), followed by 3x1-min saline rinses to remove non-adherent bacteria. After air-drying, samples were taken repeatedly during 90 min. The maxillary teeth were imprinted in alginate-filled custom trays (Ec) or in a solid, agar medium (A.ac) resulting in a negative template of the maxillary teeth. The alginate imprints were filled with selective MacConkey agar resulting in a positive template of the maxillary teeth. All imprints were incubated aerobically for 24-72 h. Ec colonies were counted directly on the positive templates while A.ac colonies were suspended in saline and cells were identified and counted after FISH. Results: Both Ec and A.ac were found on imprints taken after 5 min. The mean±SD number of Ec-CFUs was 20.5±36.9, range 0-162 (N=18), whereas the numbers of A.ac cells were 8.3E6 and total bacteria 2.5E10. After 30 min, to mention another data point only, the mean±SD number of Ec-CFUs was 6.1±10.3, range 0-35 (N=18), while the numbers of A.ac cells were 3.8E5 and total bacteria 2.5E10. Conclusions: These findings broaden the basis of our concept that specific adherence to the pellicle is not the mechanism by which primary colonizers are selected. Non-oral, Gram-negative microorganisms can adhere to oral structures, albeit with different affinities exhibiting large individual differences. The colonization sequence is determined by the prevailing growth conditions.