Thin-Film Culture Medium for Rapid E. Coli Colony Enumeration
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Solution Overview
Problem
Existing methods for detecting and enumerating coliform and E. coli microorganisms in food and beverage samples are time-consuming, require sophisticated instrumentation, and involve multiple steps, making them costly and inefficient.
Innovation Solution
A culture device with a water-impermeable design and a culture medium containing specific indicators and nutrients that facilitate the growth and differentiation of coliform and E. coli colonies, allowing for faster and more accurate enumeration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional methods are used for detecting and enumerating coliform and E. coli bacteria, then detection accuracy is maintained, but incubation time is long (24-48 hours) and multiple steps are required
Solution Approach 1:
The culture medium is segmented into multiple functional layers: a first water-impermeable sheet with a dry culture medium layer containing coliform-selective agents, a second water-impermeable sheet with a gelling agent layer, and indicator systems distributed throughout. This segmentation allows simultaneous provision of selective growth conditions and rapid detection capabilities, reducing incubation time while maintaining accuracy
Solution Approach 2:
The culture medium is prepared in a dry, rehydratable form with pre-included selective agents (bile salts, sodium dodecyl sulfate) and indicator systems (lactose-fermentation indicator, β-D-glucuronidase indicator, redox indicator). This preliminary preparation enables rapid rehydration and immediate initiation of selective growth and detection processes, eliminating time-consuming preparation steps and reducing overall incubation time
2Productivity
If conventional detection methods are used, then comprehensive microbial analysis is achieved, but device complexity and instrumentation requirements increase
Solution Approach 1:
The culture device performs multiple functions autonomously: the selective agents automatically inhibit non-coliform growth, the lactose-fermentation indicator system self-detects coliform presence through pH changes, the β-D-glucuronidase indicator system specifically identifies E. coli through color changes, and the redox indicator monitors metabolic activity. This self-service capability eliminates the need for complex external instrumentation and highly trained personnel, improving detection efficiency while simplifying the device
Solution Approach 2:
Multiple indicator systems utilize color changes for detection: the lactose-fermentation indicator changes color in response to acid production from lactose fermentation, the β-D-glucuronidase indicator changes color to specifically identify E. coli colonies, and the redox indicator changes color to indicate metabolic activity. These visual color changes provide immediate, instrument-free detection results, enhancing productivity while reducing device complexity
3Measurement precision
If conventional culture methods are used, then accurate colony enumeration is achieved, but the process requires multiple steps and sophisticated procedures
Solution Approach 1:
The culture device merges selective growth, differential identification, and colony enumeration into a single integrated system. The first water-impermeable sheet with dry culture medium containing selective agents combines with the second sheet with gelling agent to create a unified culture environment that simultaneously supports selective coliform growth, provides differential indicators for E. coli identification, and enables direct colony counting on the film surface, eliminating multiple separate steps and simplifying operation while maintaining precision
Solution Approach 2:
The use of water-impermeable sheets as the culture substrate provides a thin-film format that facilitates easy handling, transport, and enumeration. The culture medium is applied as a dry layer on the first sheet, which when rehydrated creates a uniform culture surface on the thin film. This thin-film format simplifies operational steps compared to traditional petri dishes while maintaining accurate colony enumeration capabilities through the transparent or translucent film that allows visual counting
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The device enables rapid detection and enumeration of coliform and E. coli colonies within 24 hours, providing more accurate counts and reducing the need for complex equipment and lengthy incubation periods.
Implementation Method 1
a lactose-fermentation indicator system comprising D-lactose, a first inducer compound that enhances production of β-galactosidase, and a pH indicator
Implementation Method 2
a β-D-glucuronidase indicator system comprising 5-bromo-4-chloro-3-indolyl-β-D-glucuronide and at least one compound that enhance β-glucuronidase activity in E. coli
Implementation Method 3
a redox indicator system and preferably comprises Tetrazolium chloride (TTC)
Implementation Method 4
a first cold-water soluble gelling agent adhered to the first sheet; a second cold-water-soluble gelling agent adhered to the second sheet
Data Source
AI summary
A device for differentially enumerating colonies of coliform and Escherichia coli microorganisms is provided. The device comprises a water-impermeable first sheet; a water-impermeable second sheet attached to the first sheet; a dry, rehydratable culture medium comprising a lactose-fermentation indicator system, a β-D-glucuronidase indicator system, and a first cold-water soluble gelling agent adhered to the first sheet, the culture medium disposed in a microbial growth zone; and a second cold-water-soluble gelling agent adhered to the second sheet. The microbial growth zone is disposed between the first sheet and the second sheet. The first sheet and second sheet are configured to retard passage of carbon dioxide therethrough. Methods of using the device are also provided.