Bacteriophage isolation from human saliva: a pilot study with high school students

INTRODUCTION: The microbiome of the human oral cavity is composed of numerous and diverse bacteria, archaea, eukarya and viruses [1]. Bacteriophages (abbreviated phages) are bacterial viruses that can attack and kill a target bacterium within minutes of infection. Very little is known about the impact of phages on the ecology of the oral microbiome and the aetiology of diseases of the oral cavity [2]. The lytic capacity of some phages suggests, that this may be promising antimicrobial agents that could be used to prevent or treat oral diseases [3]. The study aimed to isolate bacteriophages specific for Streptococcus mutans (causal agent of dental caries) and Enterococcus faecalis (causative agent of persistent apical periodontitis) from human saliva with the engagement of high school students in scientific research. MATERIALS AND METHODS: Saliva samples were collected from 61 healthy donors, undergraduate students from Valsassina College, Lisbon, Portugal. All samples were examined for the presence of phages using the agar overlay method. The study was approved by the Egas Moniz Ethics Committee (approval number 636) and written informed consent was obtained from all subjects. RESULTS: Three to five days after inoculation with E. faecalis, uniform turbid lysis zones were generated by saliva samples collected from 6 of 61 individuals (9.8%). No plaques for S. mutans were evident after direct plating of the material. DISCUSSION AND CONCLUSIONS: It was possible to isolate E. faecalis, but not S. mutans bacteriophages. Our data is similar in prevalence to previous studies who also attempted to isolate lytic bacteriophage from oral E. faecalis [4]. The presence of E. faecalis phages in the saliva of healthy individuals suggests that they may play a role in the control of this bacterium in the oral cavity.