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Updated: Jun 27, 2026
06:34
Identification of Rare Bacterial Pathogens by 16S rRNA Gene Sequencing and MALDI-TOF MS
Published on: July 11, 2016
Modified string test to improve and confirm by molecular characterization for bacterial identification.
Muhammad Dawood Mian1, Saadullah Jan Khan2,3, Rehana Rani1
1Department of Life Sciences, Abasyn University Islamabad Campus, Islamabad, Pakistan.
Access Microbiology
|June 26, 2026
Summary
A modified potassium hydroxide (KOH) string test with methylene blue offers a rapid, cost-effective method for differentiating Gram-positive and Gram-negative bacteria. This simple test shows high concordance with Gram staining, aiding preliminary bacterial identification.
Area of Science:
- Microbiology
- Bacteriology
- Diagnostic methods
Background:
- Accurate bacterial identification is crucial in clinical and environmental settings.
- Gram staining is a standard preliminary method but has limitations in interpretation and complexity.
- There is a need for rapid, simple, and reliable bacterial differentiation techniques.
Purpose of the Study:
- To evaluate a modified potassium hydroxide (KOH) string test using methylene blue for differentiating Gram-positive and Gram-negative bacteria.
- To assess the concordance of the modified KOH test with traditional Gram staining.
- To determine the utility of the modified KOH test as a complementary diagnostic tool.
Main Methods:
- A modified KOH string test was developed using 3% KOH solution and methylene blue.
- 185 bacterial samples from diverse clinical and environmental sources were analyzed.
- Samples were initially characterized by Gram staining and then by the modified KOH test.
- 16S rRNA gene sequencing was used for taxonomic confirmation of selected isolates.
Main Results:
- The modified KOH string test demonstrated complete concordance with Gram staining results.
- Gram-negative bacteria consistently showed visible string formation due to DNA release.
- Gram-positive bacteria did not exhibit string formation.
- The addition of methylene blue enhanced the visualization of DNA release.
Conclusions:
- The modified KOH string test is a rapid, simple, and cost-effective method for preliminary bacterial differentiation.
- This method serves as a valuable complementary tool, especially in resource-limited or high-throughput laboratories.
- The test accurately distinguishes between Gram-positive and Gram-negative bacteria, supporting initial microbiological assessments.
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