I am going to use MALDI-TOF for identify the E. Coli strains in groundwater and surface water. However,I have read some articles that indicted the microbial samples have to be immediately analyzed after collection within few hours, whereas I expect that field work will take at least two weeks then I have to ship the samples to another country by airplane. Are there any methods or kits for preserving E. coli sample until finishing the field work?
I guess you are not interested in quantification of E. coli in water.
I think you are interested in knowing whether there is contamination of water (fecal contamination from human source or animal source) - by knowing if there is E. coli. Frankly speaking quantification is required for Microbial water analysis.
You can use the ice box for transporting water to your place. Besides culture you can use PCR to detect E. coli.
If you culture E. coli from water. Please do perform antibiotic susceptibility testing to know the trend of resistance to antibiotics.
There are reports of carbapenemase (NDM) producing enteric pathogens isolated from water sources.
If possible use MICROSCAN for identification and susceptibility for suspected E. coli culture. That would be much simpler.
You need to process your water sample within 24 hours with proper trasportation.
See page 19 of attached write up- Regulatory monitoring and testing
Water and wastewater sampling
Please check page 24-25 in the attached write up above.
Refrigeration: Keeping samples between 1°C and 4°C will preserve the majority of physical, chemical and biological characteristics in the short term (< 24 hours) and as such is recommended for all samples between collection and delivery to the laboratory. It is recommended that microbiological samples be refrigerated between 2°C and 10°C (as per AS/NZS 2031:2001). Ice can be used to rapidly cool samples to 4°C before transport. Ice bricks are preferred over loose ice or dry ice.
Transport and storage of water for Microbiological analysis:
During sample transport and storage it is vital that all procedures are followed to ensure that samples are not significantly altered in condition and are in a state fit for analysis at the laboratory. Contamination of samples can easily occur during transport due to container cross contamination, packaging material or chilling products. During sample storage, degradation can occur due to lack of appropriate preservation, inappropriate storage conditions, excessive storage times and sample cross-contamination.
The key aspects of effective transport and storage are to:
• ensure samples are appropriately packed to avoid breakage and cross-contamination
• reduce sample degradation through appropriate preservation
• ensure time between sampling and analysing does not exceed holding time
• sample containers should be sealed, carefully packed with an appropriate packing material, chilled or frozen (as required) and transported in an appropriate cooler (esky) or fridge. It is sometimes necessary to take further action to prevent crosscontamination, either between samples or from ice, during transport. This could include placing sample containers in snap-lock bags or airtight, plastic tubes with screw caps before transport.
If a courier is to be employed, sample security, Chain of Custody and refrigeration issues need to be considered prior to transporting the samples. If a courier is not able to meet all the requirements an alternative form of transport should be found.
A basic list of equipment required for sample transport and storage and includes labels for sample containers (if not already on containers), snap-lock bags or tubes if required, esky or fridge, ice bricks or crushed ice, packing material (eg foam packing), packing tape, consignment note for external courier and Chain of
Custody forms.
You can even follow the manual identification by biochemical characterization by using easily suspectable E. coli colonies on MacConkeys agar.
I am so thankful for your consecutive suggestions.
What I understand that it is difficult to preserve microbial sample for more than 24 hours.
Yes it is true that you have to process your water sample for microbiological analysis within 24 hours.
Only way is to see if there are any diagnostic labs who can refrigerate your water samples for couple of days until you are ready to courier your samples maintaining the cold chain .
It is always better and is the standard to analyze water for microbial load immediately and if impossible immediately then the water must be collected in ice chest and analyzed within 1 day.
You need to get a lab near your sampling site. if there is none, then improvise. Some equipment can be carried along to the site for this purpose.
After incubation, the microbes obtained can be stored for as long as you desire using appropriate storage conditions (there are many of such in literature).
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