Response to alkaline stress by root canal bacteria in biofilms.
OBJECTIVE
To determine whether bacteria isolated from infected root canals survive alkaline shifts better in biofilms than in planktonic cultures.


METHODS
Clinical isolates of Enterococcus faecalis, Lactobacillus paracasei, Olsenella uli, Streptococcus anginosus, S. gordonii, S. oralis and Fusobacterium nucleatum in biofilm and planktonic cultures were stressed at pH 10.5 for 4 h, and cell viability determined using the fluorescent staining LIVE/DEAD BacLight bacterial viability kit. In addition, proteins released into extracellular culture fluids were identified by Western blotting.


RESULTS
Enterococcus faecalis, L. paracasei, O. uli and S. gordonii survived in high numbers in both planktonic cultures and in biofilms after alkaline challenge. S. anginosus, S. oralis and F. nucleatum showed increased viability in biofilms compared with planktonic cultures. Alkaline exposure caused all planktonic cultures to aggregate into clusters and resulted in a greater extrusion of cellular proteins compared with cells in biofilms. Increased levels of DnaK, HPr and fructose-1,6-bisphosphate aldolase were observed in culture fluids, especially amongst streptococci.


CONCLUSIONS
In general, bacteria isolated from infected roots canals resisted alkaline stress better in biofilms than in planktonic cultures, however, planktonic cells appeared to use aggregation and the extracellular transport of specific proteins as survival mechanisms.
Chávez de Paz
L E
LE
Department of Oral Biology, Faculty of Odontology, Malmö University, Malmö, Sweden. luis.chavez.de.paz@od.mah.se
Bergenholtz
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G
Dahlén
G
G
Svensäter
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D000818:Animals; D001419:Bacteria / Q000187:drug effects* / Q000235:genetics; D018441:Biofilms / Q000187:drug effects*; D002126:Calcium Hydroxide / Q000494:pharmacology*; D015169:Colony Count, Microbial; D003786:Dental Pulp Cavity / Q000382:microbiology*; D006863:Hydrogen-Ion Concentration; D012388:Root Canal Irrigants / Q000494:pharmacology*
D012388:Root Canal Irrigants; D002126:Calcium Hydroxide