Comprehensive evaluation of complex polymicrobial specimens using next generation sequencing and standard...

Area of Science:

• Microbiology
• Molecular Biology
• Clinical Diagnostics

Background:

• Accurate identification of all organisms in a sample is crucial for effective clinical decision-making.
• Standard microbiological culture methods can fail to detect fastidious or unusual organisms and may misrepresent microbial abundance.
• Culture-independent methods, such as next-generation sequencing, offer improved capabilities for analyzing complex polymicrobial samples.

Purpose of the Study:

• To compare the detection rates of cultivable organisms between standard culture and next-generation 16S rRNA gene sequencing (NGS16S).
• To assess the completeness of standard culture in identifying microbial constituents in polymicrobial samples.
• To evaluate the concordance and complementarity of NGS16S and culture-based methods for microbial identification.

Main Methods:

• Twenty bronchoalveolar lavage (BAL) samples were analyzed using both standard microbiological culture and NGS16S.
• NGS16S analysis was performed on DNA extracted directly from samples and from organisms recovered on culture plates.
• Bacterial identification was confirmed by comparing results from both molecular and culture-based approaches.

Main Results:

• 96% of identified organisms were cultivable, yet standard culture reported only 21%, highlighting significant underreporting.
• Direct NGS16S identified the predominant organism found by standard culture in 50% of samples; differences often involved anaerobes.
• NGS16S detected more organisms per sample, including fastidious species, while culture excelled in low bacterial load scenarios and non-bacterial pathogen recovery.

Conclusions:

• Standard culture provides an incomplete assessment of microbial communities in polymicrobial samples.
• NGS16S significantly enhances the detection of cultivable and fastidious organisms compared to standard culture alone.
• Combining molecular (NGS16S) and culture-based methods offers a more comprehensive approach to microbial identification in clinical samples.