The prevalence of B-lactamase-producing anaerobic oral bacteria and the genes responsible for this enzyme production in patients with chronic periodontitis

Binta, Buhle Ntandokazi
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Introduction: Chronic peridontitis is an inflammatory disease that is caused by the accumulation of bacteria in the form of a biofilm in the periodontal pocket. It can be treated with oral hygiene in conjunction with β-lactam antibiotics. Many oral anaerobic bacteria associated with chronic periodontal diseases have developed resistance to β-lactam antibiotics by virtue of their production of β-lactamase enzymes. This study investigated the prevalence of β-lactamase-producing anaerobic bacteria in the oral cavities of South African patients with periodontitis and the genes responsible for these enzymes production. Methods: Periodontal pocket debri was collected from 48 patients with chronic periodontitis and cultured anaerobically on blood agar plates with and without β-lactam antibiotics. Presumptive β-lactamase-producing isolates were evaluated for definite β-lactamase production using the nitrocefin slide method and identified using the API Rapid 32A system. Antimicrobial sensitivity was performed using a disc diffusion test. Isolates were screened for the presence of the BlaTEM and BlacfxA genes using Polymerase Chain Reaction (PCR). Amplified PCR products were sequenced and the BlacfxA gene was further characterized using Genbank databases. Seventeen isolates containing BlacfxA gene were subjected to broth microdilution technique to determine minimum inhibitory concentrations of Amoxycillin, Augmentin, and Penicillin. Results: Seventy five percent (36 of 48) of patients carried, on average 2 strains of β-lactamase-producing oral anaerobic bacteria, which constituted 10% of the total cultivable oral flora. A total of 85 oral anaerobes were isolated from patients. The predominant isolates were gram negative species such as Prevotella spp (58%), Bacteroides spp (18%) and Porphyromonas spp (7%). The disc diffusion antimicrobial sensitivity test showed that 40% of the strains were resistant to β-lactam antibiotics. PCR results revealed that none of the anaerobes carried BlaTEM. The BlacfxA gene was identified in 51% of the β-lactamase-producing bacteria. Variants of the BlacfxA gene included cfxA2 (77%), cfxA3 (14%) and cfxA6 (9%). Minimum inhibitory concenration antimicrobial susceptibility test results showed that more than 53% of the strains were resistant to β-lactam antibiotics when the BlacfxA gene was present. Conclusions: A high prevalence of β-lactamase-producing oral anaerobic bacteria was found in South African patients with chronic periodontitis. Although, it comprised 10% of their oral flora these anaerobes can protect non-β-lactamase-producers by releasing these enzymes into the environment. The most prevalent β-lactamase gene in this population was BlacfxA subcategory cfxA2 which has epidemiological implications and genetic transfer can occur among these bacteria. On average fifty percent of the isolates that carried this gene were resistant to β-lactam antibiotics therefore alternative antimicrobial agents should be considered in patients that are non-responsive to β-lactam antibiotics. This study indicates that there is a need for education in the dental community regarding antibiotic resistance and regular surveillance with diagnostic testing is needed.