Susceptibility testing of Fusobacterium clinical isolates from Taiwanese population with Etest®

Methods: Subgingival samplings were taken with sterile paper points from periodontitis patients recruited from various dental clinics in Taiwan. After anaerobically transportation and plating, Fusobacteria were isolated and identified by their morphology and by fluorescence test. Indirect immunofluorescence assay was performed to make a further confirmation when necessary. Etest® was used to determin their antimicrobial susceptibility for all clinical isolates of Fusobacterium on Brucella blood agar plates. Twelve antibiotics used in this study were: AmoXicillin 500mg / ClavuLanate125mg (XL), AmoxiCillin (AC), AMpicillin (AM), CefaleXin (CX), CefIXime (IX), TetraCycline (TC), DoxyCycline (DC), MinoCycline (MC), Azithromycin (AZ), ClindaMycin (CM), MetronidaZole (MZ), and Ciprofloxacin (CI). Minimal inhibitory concentrations (MIC) of various antibiotics were determined after two days' incubation in anaerobic environments.

Results: There were 16 successful clinical isolates of Fusobacterium, of which 11 isolates (69%) demonstrated moderate to high antimicrobial susceptibilities. MICs of all tested antibiotics were located at between < 0.016 mg/mL (MC and MZ) and 2 mg/mL (AM). The remaining 5 isolates (31%), however, exhibited dangerously high antibiotics resistance, especially to b-lactamase associated antibiotics (XL,AC,AM,CX,and IX). Their MICs were all above 256 mg/mL.

Conclusions: Significant percentage of Fusobacterium clinical isolates was resistant to most antibiotics administration and b-lactamase associated antibiotics exerted virtually no effects on these Taiwanese isolates in this study. The failure of various antibiotics posed a great potential danger to public health in Taiwan.