Antibiotic Resistance Genes and Antibiotic Susceptibility of Oral Enterococcus faecalis Isolates Compared to Isolates from Hospitalized Patients and Food

Enterococcus faecalis, a commensal of the intestinal tract of humans and animals is of great significance as leading opportunistic pathogen, and also prevalent in oral diseases, such as endodontic infections, as well as the healthy oral cavity. To investigate the potential of oral E. faecalis to constitute a reservoir of antibiotic resistance, isolates from supragingival plaque/saliva and from endodontic infections were screened regarding their resistance to selected antibiotics in comparison to nosocomial and food isolates. 70 E. faecalis isolates were analyzed with PCR regarding their equipment with the resistance genes tetM, tetO, ermB, ermC, vanA, vanB and blaTEM. Additionally, they were tested for their phenotypic resistance to doxycycline, azithromycin, rifampicin, amoxicillin and streptomycin using the Etest. High percentages of the plaque/saliva, nosocomial and food isolates were resistant to doxycycline and azithromycin, particularly plaque/saliva isolates (81%) and nosocomial isolates (73.3%) showed resistance to doxycycline, significantly more than among the food and endodontic isolates. Rifampicin resistance was widespread among isolates from plaque/saliva (52.4%), endodontic infections (50%) and nosocomial infections (40%); all isolates were susceptible to amoxicillin and all oral isolates to high-level streptomycin. TetM genes were detected in the majority of all isolates and ermB genes were present in many nosocomial and plaque/saliva isolates. Thirty percent of the endodontic isolates and 53% of the nosocomial isolates were equipped with blaTEM genes. The results suggest that the oral cavity can harbor E. faecalis strains with multiple resistances against different antibiotics and thus be regarded as a potential source of resistance traits.