Prevalence and characterization of β-lactamase-producing bacteria in gingivitis among diabetic and non-diabetic patients: a comparative microbiological study

<b>Background.</b> Gingivitis is a reversible gingival inflammation that may progress to periodontitis if untreated. Diabetes mellitus alters the oral microbiota and weakens host defenses, increasing susceptibility to infection. <b>Objectives.</b> To investigate the prevalence and characterization of <i>β</i>-lactamase-producing bacteria isolated from gingival swabs of diabetic and non-diabetic patients with clinically confirmed gingivitis. <b>Methods.</b> Thirty-seven patients were enrolled (17 diabetics and 20 non-diabetics). Gingival swabs were cultured and identified by conventional microbiological and analytical profile index (API). Antimicrobial susceptibility was tested according to the Clinical and Laboratory Standards Institute 2023 guidelines. <i>β</i>-Lactamase activity was assessed using an iodometric colourimetric assay. <b>Results.</b> A total of 65 bacterial isolates were obtained from 37 gingivitis patients. Polymicrobial infections predominated in diabetics (82.4%) vs. non-diabetics (45.0%). Non-diabetics were mainly colonized by <i>Streptococcus mutans</i> (45.9%) and <i>Staphylococcus aureus</i> (40.5%), while diabetics harboured more Gram-negative species, particularly <i>Pseudomonas aeruginosa</i> (21.4%) and <i>Enterobacteriaceae</i> (46.4 % vs. 2.7 %). Overall, 67.7 % of isolates were <i>β</i>-lactamase producers. Resistance was highest to ampicillin (92.3%) and amoxicillin-clavulanate (84.6%), whereas ciprofloxacin (89.2%) and piperacillin-tazobactam (78.5%) retained the greatest activity. <b>Conclusions.</b> Diabetes is associated with increased microbial diversity, Gram-negative colonization, and a frequency of <i>β</i>-lactamase-producing bacteria in gingivitis. These findings highlight diabetes as a risk factor for resistant oral infections and underscore the need for antimicrobial stewardship, resistance surveillance and future molecular studies to clarify resistance mechanisms in high-risk groups.