Differences exist in the susceptibility profiles of periodontal pathogens isolated from periodontitis patients in Spain and in The Netherlands. This implicates that antibiotic susceptibility testing is necessary to determine efficacy of antimicrobial agents. Also, clinical studies with antibiotics should take these differences into account. The information from the present study indicates that it may not be possible to develop uniform protocols for usage of antibiotics in the treatment of severe periodontitis in the European Union.

Within the limitations of this study, the adjunctive use of systemic azithromycin in the treatment of P. gingivalis periodontitis demonstrated significant clinical and microbiological benefits when compared with SRP plus placebo.

Significant differences among Chile, Colombia and Spain existed regarding the frequency and proportions of specific periodontal pathogens in the subgingival microbiota of periodontitis patients.

Aim To identify loci associated with stages III/IV, grade C periodontitis (PIII/IV‐C) through a genome‐wide association study (GWAS). Materials and Methods 441 Caucasian Spanish PIII/IV‐C cases from the SEPA Network of Research Clinics and 1141 controls from the Banco Nacional de ADN were genotyped with “Axiom Spain Biobank Array,” which contains 757836 markers, including rare and low‐frequency Spanish variants. The analysis of the individual association and subsequently the gene‐level analysis with Sequence Kernel Association Test (SKAT) were carried out adjusting for age, sex and PC1 covariates. Pathway Analysis was additionally performed with Ingenuity Pathway Analysis (IPA) software on the top associated genes. Results In the individual analyses, no genome‐wide significant signals were detected. However, 8 SNPs of 8 loci reached suggestive evidence of association with PIII/IV‐C, including FAT3 rs35709256, CSNK1G2 rs4807188, MYH13 rs2074872, CNTN2 rs116611488, ANTXR1 rs4854545, 8p23.2 rs78672540, ANGPT1 rs13439823 and PLEC rs11993287 (p < 5 × 10−6). SKAT analysis identified other interesting signals at CNTN2, FBXO44, AP1M2, RSPO4, KRI1, BPIFB1 and INMT, although their probability does not exceed the multiple‐test correction. IPA indicated significant enrichment of pathways related to cAMP, IL‐2, CD28, VDR/RXR and PI3K/Akt.  Conclusions GWAS found no SNPs significantly associated with PIII/IV‐C.