Chronic periodontitis is a multifactorial infectious disease associated with Gram-negative anaerobes which are part of the subgingival microflora. In recent years, studies have been conducted to assess the presence of Gram-negative facultative anaerobes (Enterobacteriaceae) and their participation in the development and progression of chronic periodontitis. The aim of this study was to determine the presence of Enterobacteriaceae in patients with chronic periodontitis and gingivitis and to assess antimicrobial susceptibility of clinical isolates. A descriptive, observational study was performed including 64 patients with chronic periodontitis and 22 patients with gingivitis. Microbiological samples were taken from the gingival sulcus using paper points, which then were placed in thioglycollate broth. Samples were incubated for 4 hours at 37 degrees C and finally replated on MacConkey agar Bacteria were identified using the API-20E system (Biomerieux, France) and antimicrobial susceptibility was determined using the disk diffusion method. The evaluation of samples showed presence of 29 enterobacterial species distributed as follows: 7 in the group with gingivitis and 22 in the group with chronic periodontitis. In the chronic periodontitis group the most common species were: K. oxytoca n = 5, S. liquefaciens n = 4 and K. pneumoniae and E. coli with n = 3. The gingivitis group had the highest frequency of Erwinia sp. (n = 2). Clinical isolates showed very low sensitivity levels to beta-lactam ampicillin and amoxicillin/ clavulanic acid, 17.2% and 27.6% respectively, and higher sensitivity levels to ciprofloxacin (96.6%), amikacin (79.3%), gentamicin (68.9%) and ceftazidime, ceftriaxone, kanamycin and trimethoprimsulfa (65.5%). In conclusion, the existence of a high frequency of enterobacteria in patients with chronic periodontitis and gingivitis shows that periodontologists should pay greater attention to prevention protocols, and develop mechanical and antimicrobial therapies in which antimicrobial susceptibility profile reports should be considered as part of periodontal treatment.