Assessment and validation of enrichment and target capture approaches to improve Mycobacterium tuberculosis WGS from direct patient samples

Within-host Mycobacterium tuberculosis (Mtb) diversity may detect antibiotic resistance or predict tuberculosis treatment failure and is best captured through sequencing directly from sputum. Here, we compared three sample pre-processing steps for DNA decontamination and studied the yield of a new target enrichment protocol for optimal whole-genome sequencing (WGS) from direct patient samples. Mtb-positive NALC-NaOH-treated patient sputum sediments were pooled, and heat inactivated, split in replicates, and treated by either a wash, DNase I, or benzonase digestion. Levels of contaminating host DNA and target Mtb DNA were assessed by quantitative PCR (qPCR), followed by WGS with and without custom dsDNA target enrichment. The pre-treatment sample has a high host-to-target ratio of DNA (6,168 ± 1,638 host copies/ng to 212.3 ± 59.4 Mtb copies/ng) that significantly decreased with all three treatments. Benzonase treatment resulted in the highest enrichment of Mtb DNA at 100-fold compared with control (3,422 ± 2,162 host copies/ng to 11,721 ± 7,096 Mtb copies/ng). The custom dsDNA probe panel successfully enriched libraries from as little as 0.45 pg of Mtb DNA (100 genome copies). Applied to direct sputum the dsDNA target enrichment panel increased the percent of sequencing reads mapping to the Mtb target for all three pre-processing methods. Comparing the results of the benzonase sample sequenced both with and without enrichment, the percent of sequencing reads mapping to the Mtb increased to 90.95% from 1.18%. We demonstrate a low limit of detection for a new custom dsDNA Mtb target enrichment panel that has a favorable cost profile. The results also demonstrate that pre-processing to remove contaminating extracellular DNA prior to cell lysis and DNA extraction improves the host-to-Mtb DNA ratio but is not adequate to support average coverage WGS without target capture.

MinION 16S datasets of a commercially available microbial community enables the evaluation of DNA extractions and data analyses

New advances in sequencing technology and bioinformatics analysis tools have significantly supported the culture-independent analysis of complex microbial communities associated with environmental, plant, animal and human samples. However, previous work has shown that DNA extraction can have a major influence in the community profile. As such there is a constant need for new methods to efficiently and rapidly prepare and analyze DNA for microbiome research, especially in the case new and emerging technology like the Oxford Nanopore Technologies (ONT) MinION. A commercial standard was used, in triplicate, to evaluate three DNA extraction protocols, including two commercially available and one "in-house" DNA extraction method. All DNA extractions were done as per manufacturer's instructions and prepared with the same commercial ONT 16S sample preparation kit, prior to being analysed using MinION sequencing. Eight MinION 16S datasets of this microbial reference community were obtained. Reads were initially base called and demultiplexed using ONT's Guppy™ sequencing software (version 3.2.4), filtered using NanoFilt and then classified using Usearch. A set of R scripts are presented to process sintax files generated from Usearch and produce an OTU table that can be used for further analyses. All datasets were deposited into the SRA (NCBI) database. These datasets will allow future extraction kit comparisons using MinION sequencing since a standardize laboratory process using commercially available components, such as the MinION 16S sample preparation kit, microbial reference community and extraction kits, were used. The current ONT 16S workflow making use of the Epi2me agent only provides QC metrics and the ID's of the main genera identified and does not provide any tools currently for further downstream community comparison. The analyses scripts provided in the supplementary material will thus further enable the testing of new datasets against these reference sets and provide users the ability to compare their workflows with ours, thus standardizing comparisons and workflows.

Biocide resistant and antibiotic cross-resistant potential pathogens from sewage and river water from a wastewater treatment facility in the North-West, Potchefstroom, South Africa

Exposure to antibiotics, biocides, chemical preservatives, and heavy metals in different settings such as wastewater treatment plants (WWTPs) may apply selective pressure resulting in the enrichment of multiple resistant, co- and cross-resistant strains of bacteria. The purpose of this study was to identify and characterize potentially pathogenic triclosan (TCS) - and/or, chloroxylenol (PCMX) tolerant bacteria from sewage and river water in the North-West, Potchefstroom, South Africa. Several potential pathogens were identified, with Aeromonas isolates being most abundant. Clonal relationships between Aeromonas isolates found at various sampling points were elucidated using ERIC-PCR. Selected isolates were characterized for their minimum inhibitory concentrations against the biocides, as well as antibiotic resistance profiles, followed by an evaluation of synergistic and antagonistic interactions between various antimicrobials. Isolates were also screened for the presence of extracellular enzymes associated with virulence. High-performance liquid chromatography revealed the presence of both biocides in the wastewater, but fingerprinting methods did not reveal whether the WWTP is the source from which these organisms enter the environment. Isolates exhibited various levels of resistance to antimicrobials as well as several occurrences of synergy and antagonisms between the biocides and select antibiotics. Several isolates had a very high potential for virulence but further study is required to identify the specific virulence and resistance genes associated with the isolates in question.