Aggregatibacter-actinomycetemcomitans (A.actinomycetemcomitans) are strongly associated with localized-aggressive-periodontitis (LAgP). The study?s aim was to test for the first time the effect of total sonicated A.actinomycetemcomitans-bacterial-fragments on gingival mesenchymal stem/progenitor cells? (G-MSCs) proliferation and regenerative gene expression in-vitro. G-MSCs were isolated, characterized, expanded and stimulated by total sonicated A.actinomycetemcomitans-bacterial-fragments (0 (negative-control), 15, 60, 120 and 240µg/ml; serovar-b; n=6/group). Cellular proliferation and NF-?? (NFKB1), Alkaline Phosphatase (ALPL), Collagen-I (COL1A1), Collagen-III (COL3A1), Osteonectin (SPARC) and Osteopontin (SPP1) m-RNA expression were assessed via reverse-transcription-polymerase-chain-reaction (RT-PCR) at 24, 48 and 72 hours and CFUs-ability evaluated at twelve days. G-MSCs demonstrated stem/progenitor cells? characteristics. A.actinomycetemcomitans-bacterial-fragments (up to 72 hours) resulted in marked G-MSCs? proliferation over-time (p<0.001) and elevated NFKB1 (p=0.017), COL1A1 (p=0.025), SPARC (p=0.025), decreased ALPL (p=0.017), with no significant differences for COL3A1 and SPP1 expression or stimulation times (p>0.05; Friedman-test). Longer-term stimulation for twelve days reduced G-MSCs? CFUs. Sonicated A.actinomycetemcomitans-bacterial-fragments? exert beneficial short-term effects on G-MSCs? proliferative and non-mineralized tissue forming aptitude. Results shed new light on the importance of periodontal treatment for LAgP patients, using power driven sonic/ultrasonic devices, which, in addition to reducing the subgingival microbial load, produces cell-stimulatory A.actinomycetemcomitans-bacterial-fragments, with positive attributes on tissue reparative/regenerative responses of tissue resident stem/progenitor cells in their niche.