Table 1.

Characteristics of the studies included in the review.

Author/Year /Design	Country	Study Population (Number, M/F Ratio, Mean Age [Years])	Intervention	Follow-Up	Microbiologic Evaluation	Results
Balogh et al., 2020 Follow-up study [28]	Hungary	57 total, M/F 33/24, 39.1 18 obese controls, M/F 5/13, 44.1 17 obese BS patients, M/F 10/7, 39.4 22 healthy controls, M/F 9/13, 33.9	Gastric bypass	12 months	Inoculation of clinical specimens onto selective media (blood agar, chocolate agar, Sabouraud dextrose agar) and identification with MALDI-TOF MS (crevicular fluid)	After surgery and weight loss, the mean germ count increased, but not significantly. Candida albicans and non-albicans Candida species appeared after surgery; Neisseria was either absent throughout or eliminated after surgery.
Džunková et al., 2020 Cohort study [6]	Czech Republic	35, M/F 18/17, 48.0	Sleeve gastrectomy, Roux-en-Y gastric bypass, Omega loop gastric bypass, laparoscopic gastric plication	12 months	16S rRNA gene sequencing (saliva)	Increased proportion of Veillonella species after the decrease of BMI. Streptococcus oralis had a positive correlation with BMI. Megasphaera micronuciformis proportion increased when the BMI decreased.
Hashizume et al., 2015 Cohort study [24]	Brazil	27, M/F 1/26, 45.0	Roux-en-Y gastric bypass	6 months	Inoculation of clinical specimens onto selective media (Mitis salivarius bacitracin Agar, Rogosa SL agar, Sabouraud dextrose agar with chloramphenicol) and identification based on colony morphology and biochemical tests (saliva)	Salivary levels of Streptococcus mutans increased following BS.
Kim et al., 2025 Case-control study [23]	Republic of Korea	55 total, M/F 55/0, 36.0 31 obese BS patients, M/F 31/0, 37.0 24 lean controls, M/F 24/0, 35.0	Sleeve gastrectomy	6 months	16S rRNA gene sequencing (subgingival plaque, saliva, and oral swab)	Distinct species associated with periodontal disease found in the obese, surgically treated group in subgingival plaque (Filifactor alocis, Peptostreptococcaceae spp., Prevotella spp., and Treponema maltophilum). Microbiomes associated with a healthy state increased over time (Streptococcus salivarius and various Veillonella spp.). Clusters containing periodontal pathogens, including Porphyromonas spp., tended to diminish.
Ribeiro et al., 2023 Case-control study [26]	Brazil	40 total, 20 obese BS patients, M/F 5/15, 34.9 20 obese controls, M/F 5/15, 31.7	Roux-en-Y gastric bypass	6 months	16S rRNA gene sequencing (saliva)	Both interventions changed in different degrees the salivary inflammatory biomarkers and microbiota but did not improve the periodontal status after 6 months.
Sales-Peres et al., 2015 Cohort study [25]	Brazil	50, M/F 8/42, 38.9	Roux-en-Y gastric bypass	12 months	RTq-PCR (crevicular fluid)	Porphyromonas gingivalis increased after BS.
Shillitoe et al., 2012 Cohort study [22]	USA	29 M/F 7/22, 41.0	Roux-en-Y gastric bypass	12 weeks	RTq-PCR (saliva)	No changes in the levels of bacteria that exceeded 2-fold, except for the Bifidobacteria species, which showed a 2.4-fold increase in patients without DM type-2 and a 10-fold increase in DM patients. The levels of circulating endotoxin and TNF-α had decreased.
Stefura et al., 2022 Cohort study [27]	Poland	45 M/F 18/27, 43.5	Sleeve gastrectomy, Roux-en-Y gastric bypass	6 months	16S rRNA gene sequencing (oral swab)	Bacteria from phylum Bacteroidetes increased in abundance in the oral cavity 6 months after BS. Patients achieving at least 50% of excess weight loss presented similar results to the entire study group. Patients with less favorable outcomes presented an increase in the phylum Fusobacteria and a decrease in the phylum Firmicutes in the oral cavity.