Microbial filtration detection is the process of enriching microorganisms in a sample through physical or chemical methods, and then isolating and identifying target bacterial species. This method is widely used in fields such as water quality testing, drug sterility testing, and food microbial contamination analysis. Common detection targets include bacteria (such as Escherichia coli, Staphylococcus aureus), fungi (such as mold, yeast), etc. Accurate separation and identification are key to ensuring reliable detection results.
Microbial filtration and separation methods
2.1 Sample pretreatment and filtration
Microbial filtration typically uses membrane filtration (MF), which is suitable for liquid samples such as water and beverages. Steps are as follows:
1. Sample preparation: Homogenize liquid or solid samples (such as food that requires homogenization and dilution).
2. Filtration: Capture microorganisms through a filter membrane with a pore size of 0.22-0.45 μ m.
3. Transfer: Attach the filter membrane to selective or non selective culture medium for cultivation.
2.2 Selective Separation Technology
Different microorganisms require specific culture media and conditions:
-Bacteria:
-Escherichia coli: Use EMB (Eosin Blue Agar) or MacConkey Agar.
-Staphylococcus aureus: Use mannitol high salt agar (MSA).
-Fungi:
-Mold and yeast: Use Sabouraud glucose agar (SDA) and add antibiotics to inhibit bacterial growth.
Microbial identification technology
3.1 Morphological identification
-Colony characteristics: Observe colony morphology (size, color, edges, surface texture).
-Staphylococcus aureus appears golden in color, smooth and protruding; The fungal colony is fluffy.
-Microscopic observation: Gram staining (distinguishing G ⁺/G ⁻ bacteria), spore staining, etc.
3.2 Biochemical tests
Identification of bacterial strains through metabolic characteristics:
-Oxidase test: Distinguish between Pseudomonas (positive) and Escherichia coli (negative).
-IMViC test: identification of Escherichia coli (result pattern is++--).
-Sugar fermentation test: such as distinguishing between Escherichia coli and Salmonella in terms of lactose fermentation ability.
3.3 Molecular Biology Methods
-16S rRNA sequencing: the "gold standard" for bacterial identification, accurate to the genus or species level.
-PCR technology: amplifies and detects specific genes, such as the uidA gene in Escherichia coli.
-MALDI-TOFMS: Rapid identification of microorganisms through protein fingerprinting.
Applications and Challenges
4.1 Practical Application
-Water quality monitoring: detecting total coliform bacteria and pathogenic bacteria (such as Legionella) in water.
-Aseptic inspection of drugs: Ensure that injections and biological products are free from microbial contamination.
-Food safety: Testing for Salmonella, Listeria, and other bacteria in food.
4.2 Technical Challenges
1. Detection of low abundance microorganisms: Enrichment culture is required when the target bacterial content in the sample is low.
2. Interference from miscellaneous bacteria: Complex samples (such as feces and soil) require optimization of selective culture media.
3. Rapid identification requirements: Traditional methods are time-consuming and require the promotion of molecular biology techniques.