Genotypic and morphological identification of opportunistic microorganisms in triple-syringe tubing from dental units

In Mexico and around the world, water in dental units, including triple syringes, comes from municipal chlorinated water mains. The microbial contamination of dental unit water systems constitutes a risk factor for opportunistic infections.

The present work aimed to identify the bacteria present in the triple-syringe water lines of dental units at a dental school of a public university in Mexico, with a hypothesis that opportunistic bacteria of importance to human health would be found.

A cross-sectional study was carried-out. A total of 100 samples of triple-syringe tubing from dental units operated by a dental school of a public university in Mexico were analyzed before and after their use in dental practice. Bacterial biofilm was cultured and isolated from the tubing, using standard microbiological methods, and then the species present were identified through 16S rRNA gene sequencing. The characterization of the biofilm was performed by means of scanning electron microscopy (SEM).

Bacterial growth was observed in 20% of the non-disinfected and 10% of the disinfected samples, with 11 strains isolated. Six genera and 11 bacterial species were genetically identified. Coagulasenegative staphylococci (CoNS), considered opportunistic human pathogens, were among the most critical microorganisms. Scanning electron microscopy revealed a thick polymeric matrix with multiple bacterial aggregates.

Opportunistic bacteria from human skin and mucous membranes were detected. Under normal conditions, these bacteria are incapable of causing disease, but are potentially harmful to immunosuppressed patients.