Metagenomic study on the composition of culturable and non-culturable bacteria in tap water and biofilms at intensive care units

Abstract

Bacterial community diversity of bulk water and corresponding biofilms of four intensive care units' (ICUs) drinking water systems were studied and compared using 16S rRNA gene amplicons and next generation sequencing. Proteobacteria, mainly Alphaproteobacteria and Betaproteobacteria were dominant in the bulk water and biofilms. Principal component analysis showed different bacterial communities characterizing each of the bulk water and the biofilms in three of the studied ICUs. Taxonomic classification and comparison of different genera between samples highlighted the dominance of Aquabacterium (80%) and Novosphingobium (72%) in bulk water while biofilms harbored different bacteria affiliated to Pelomonas (97%) and Caulobacter (96%), Porphyrobacter (78%) and Staphylococcus (74%). Staphylococcus aureus was the only possible pathogen found with low percentage (2.32%) in three of the ICUs' biofilm and only in one of the ICU's bulk water. This study sheds light on the prevalence of unculturable bacterial flora in the biofilm ignored by the microbiological standard methods. This study was performed on tap and bulk water from ICUs; however, it indicates the need for further studies to investigate the function and activity of the microbial diversity in order to assess the real risk presented by this water microflora on patients' health.

A comparative analysis of drinking water employing metagenomics

“…Artesian BW, the only BW sample in this study to yield a positive HPC, did not contain added disinfectant residual but the sample had been collected post-treatment ( Table 1), and the possibility of introduction during the bottling process cannot be ruled out. No residual disinfectants were present in the artesian BW sample included in this study, and the HPC(1.92 x 10 4 CFU/ml) was similar to heterotrophic bacterial counts obtained in tap water collected from an intensive care unit (2.4 x 10 4 CFU/ml) [22] and is within the HPC magnitude (10 4 CFU/ml) observed in DWDS when the residual chlorine is less than 0.1 mg/L [57].…”

“…Bacterial phyla detected in DW (Figs 2-5) were similar to those commonly detected in municipal DWDS [22,[58][59][60][61] and natural mineral BW [18,62], with Proteobacteria the most abundant. However, Actinobacteria was also detected in all DW samples examined.…”

“…However, Actinobacteria was also detected in all DW samples examined. A culture-independent study focused on the microbiota of DWDS, using 16S rRNA sequencing [22], identified Alpha-and Beta-proteobacteria subclasses as dominant bacterial communities of a water distribution network, but determined the Gammaproteobacteria subclass represented a relative abundance of less than 1%. Other studies of the microbiome of natural mineral water reported Alpha-, Beta-, and Gammaproteobacteria at moderate abundance [22,59,62].…”

“…Culture-dependent methods are used to detect and enumerate indicator organisms and have been remarkably successful in improving DW quality and safety, but do not detect all microorganisms present in that water. Metagenomic analysis employing high-throughput sequencing coupled with bioinformatics has gained attention during the past decade, allowing detection, identification, and characterization of all microorganisms present in DWDS [22][23][24]. Inferences of infectious potential of detected microbial species is determined by detecting genes coding for pathogenic and metabolic properties [24,25].…”

“…Thus, bacteria, viruses, fungi, and protists now can be detected, identified to sub-species level, and characterized. A significant benefit is detection of microorganisms in water that were previously missed or not identified by culture-dependent methods [22,26,27]. Metagenomic surveys carried out by other investigators have provided evidence that ingested dietborne components can have short-and long-term effects on the human microbiota [28][29][30][31].…”